1GPSD_JSON(5)                  GPSD Documentation                  GPSD_JSON(5)
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3
4

NAME

6       gpsd_json - gpsd request/response protocol
7

OVERVIEW

9       gpsd is a service daemon that can be used to monitor GPSes, DGPS
10       receivers, Marine AIS broadcasts, and various other location-related
11       and kinematic sensors.
12
13       Clients may communicate with gpsd via textual requests and responses
14       over a socket. It is a bad idea for applications to speak the protocol
15       directly: rather, they should use the libgps client library (for C;
16       bindings also exist for other languages) and take appropriate care to
17       conditionalize their code on the major and minor protocol version
18       symbols.
19
20       The GPSD protocol is built on top of JSON, JavaScript Object Notation,
21       as specified in RFC 7159: The JavaScript Object Notation (JSON) Data
22       Interchange Format. GPSD's use of JSON is restricted in some ways that
23       make parsing it in fixed-extent languages (such as C) easier.
24
25       A request line is introduced by "?" and may include multiple commands.
26       Commands begin with a command identifier, followed either by a
27       terminating ';' or by an equal sign "=" and a JSON object treated as an
28       argument. Any ';' or newline indication (either LF or CR-LF) after the
29       end of a command is ignored. All request lines must be composed of
30       US-ASCII characters and may be no more than 80 characters in length,
31       exclusive of the trailing newline.
32
33       Responses are JSON objects all of which have a "class" attribute the
34       value of which is either the name of the invoking command. There are
35       reports (including but not limited to as "TPV", "SKY", "DEVICE", and
36       "ERROR") which are not direct responses to commands.
37
38       The order of JSON attributes within a response object is never
39       significant, and you may specify attributes in commands in any order.
40       Responses never contain the special JSON value null; instead,
41       attributes with empty or undefined values are omitted. The length limit
42       for responses and reports is 1536 characters, including trailing
43       newline; longer responses will be truncated, so client code must be
44       prepared for the possibility of invalid JSON fragments.
45
46       In JSON reports, if an attribute is present only if the parent
47       attribute is present or has a particular range, then the parent
48       attribute is emitted first.
49
50       There is one constraint on the order in which attributes will be
51       omitted. If an optional attribute is present only when a parent
52       attribute has a specified value or range of values, the parent
53       attribute will be emitted first to make parsing easier.
54
55       The next subsection section documents the core GPSD protocol.
56       Extensions are documented in the following subsections. The extensions
57       may not be supported in your gpsd instance if it has been compiled with
58       a restricted feature set.
59

CORE SOCKET PROTOCOL

61       Here are the core-protocol responses:
62
63       TPV
64           A TPV object is a time-position-velocity report. The "class" and
65           "mode" fields will reliably be present. The "mode" field will be
66           emitted before optional fields that may be absent when there is no
67           fix. Error estimates will be emitted after the fix components
68           they're associated with. Others may be reported or not depending on
69           the fix quality.
70
71           All error estimates (epc, epd, epe, eph, ept, epv, epx, epy) are
72           assumed to be 95% confidence, may also be 50%, one sigma, or two
73           sigma confidence. Many GPS do not specify a confidence level. No
74           GPS specifies how the value is calculated. Use error estimates with
75           caution, and only as relative "goodness" indicators. If the GPS
76           reports a value to gpsd, then gpsd will report that value.
77           Otherwise gpsd will try to compute the value from the skyview.
78
79           Table 1. TPV object
80           ┌────────────┬─────────┬──────────────┬─────────────────────┐
81Name        Always? Type         Description         
82           ├────────────┼─────────┼──────────────┼─────────────────────┤
83           │class       │ Yes     │ string       │ Fixed: "TPV"        │
84           ├────────────┼─────────┼──────────────┼─────────────────────┤
85           │device      │ No      │ string       │ Name of             │
86           │            │         │              │ originating         │
87           │            │         │              │ device.             │
88           ├────────────┼─────────┼──────────────┼─────────────────────┤
89           │status      │ No      │ numeric      │ GPS status: %d,     │
90           │            │         │              │ 2=DGPS fix,         │
91           │            │         │              │ otherwise not       │
92           │            │         │              │ present.            │
93           ├────────────┼─────────┼──────────────┼─────────────────────┤
94           │mode        │ Yes     │ numeric      │ NMEA mode: %d,      │
95           │            │         │              │ 0=no mode value     │
96           │            │         │              │ yet seen, 1=no      │
97           │            │         │              │ fix, 2=2D, 3=3D.    │
98           ├────────────┼─────────┼──────────────┼─────────────────────┤
99           │time        │ No      │ string       │ Time/date stamp     │
100           │            │         │              │ in ISO8601          │
101           │            │         │              │ format, UTC. May    │
102           │            │         │              │ have a              │
103           │            │         │              │      fractional     │
104           │            │         │              │ part of up to       │
105           │            │         │              │ .001sec             │
106           │            │         │              │ precision. May      │
107           │            │         │              │ be absent if        │
108           │            │         │              │ mode                │
109           │            │         │              │         is not 2    │
110           │            │         │              │ or 3.               │
111           ├────────────┼─────────┼──────────────┼─────────────────────┤
112           │alt         │ No      │ numeric      │ Altitude in         │
113           │            │         │              │ meters. Present     │
114           │            │         │              │ if mode is 3.       │
115           ├────────────┼─────────┼──────────────┼─────────────────────┤
116           │climb       │ No      │ numeric      │ Climb (positive)    │
117           │            │         │              │ or sink             │
118           │            │         │              │ (negative) rate,    │
119           │            │         │              │ meters per          │
120           │            │         │              │      second.        │
121           ├────────────┼─────────┼──────────────┼─────────────────────┤
122           │datum       │ No      │ string       │ Current datum.      │
123           ├────────────┼─────────┼──────────────┼─────────────────────┤
124           │epc         │ No      │ numeric      │ Estimated climb     │
125           │            │         │              │ error in meters     │
126           │            │         │              │ per second.         │
127           │            │         │              │ Present             │
128           │            │         │              │         if          │
129           │            │         │              │ consecutive 3D      │
130           │            │         │              │ fixes.              │
131           ├────────────┼─────────┼──────────────┼─────────────────────┤
132           │epd         │ No      │ numeric      │ Estimated track     │
133           │            │         │              │ (direction)         │
134           │            │         │              │ error in            │
135           │            │         │              │ degrees. Present    │
136           │            │         │              │ if                  │
137           │            │         │              │         consecutive │
138           │            │         │              │ 2D fixes.           │
139           ├────────────┼─────────┼──────────────┼─────────────────────┤
140           │eph         │ No      │ numeric      │ Estimated           │
141           │            │         │              │ horizontal Position │
142           │            │         │              │ (2D) Error in       │
143           │            │         │              │ meters.             │
144           │            │         │              │         Also known  │
145           │            │         │              │ as Estimated        │
146           │            │         │              │ Position Error      │
147           │            │         │              │ (epe). Present      │
148           │            │         │              │         if mode is  │
149           │            │         │              │ 2D or 3D and DOPs   │
150           │            │         │              │ can be calculated   │
151           │            │         │              │ from the satellite  │
152           │            │         │              │         view.       │
153           ├────────────┼─────────┼──────────────┼─────────────────────┤
154           │eps         │ No      │ numeric      │ Estimated speed     │
155           │            │         │              │ error in meters per │
156           │            │         │              │ second.  Present    │
157           │            │         │              │         for         │
158           │            │         │              │ consecutive 2D or   │
159           │            │         │              │ 3D fixes.           │
160           ├────────────┼─────────┼──────────────┼─────────────────────┤
161           │ept         │ No      │ numeric      │ Estimated timestamp │
162           │            │         │              │ error in seconds.   │
163           │            │         │              │         Present if  │
164           │            │         │              │ time is present.    │
165           ├────────────┼─────────┼──────────────┼─────────────────────┤
166           │epx         │ No      │ numeric      │ Longitude error     │
167           │            │         │              │ estimate in meters. │
168           │            │         │              │ Present             │
169           │            │         │              │         if mode is  │
170           │            │         │              │ 2D or 3D and DOPs   │
171           │            │         │              │ can be calculated   │
172           │            │         │              │ from the satellite  │
173           │            │         │              │         view.       │
174           ├────────────┼─────────┼──────────────┼─────────────────────┤
175           │epy         │ No      │ numeric      │ Latitude error      │
176           │            │         │              │ estimate in meters. │
177           │            │         │              │ Present             │
178           │            │         │              │         if mode is  │
179           │            │         │              │ 2 or 3 and DOPs can │
180           │            │         │              │ be calculated from  │
181           │            │         │              │ the satellite       │
182           │            │         │              │         view.       │
183           ├────────────┼─────────┼──────────────┼─────────────────────┤
184           │epv         │ No      │ numeric      │ Estimated vertical  │
185           │            │         │              │ error in meters.    │
186           │            │         │              │ Present             │
187           │            │         │              │         if mode is  │
188           │            │         │              │ 3 and DOPs can be   │
189           │            │         │              │ calculated from the │
190           │            │         │              │ satellite           │
191           │            │         │              │         view.       │
192           ├────────────┼─────────┼──────────────┼─────────────────────┤
193           │lat         │ No      │ numeric      │ Latitude in         │
194           │            │         │              │ degrees: +/-        │
195           │            │         │              │ signifies           │
196           │            │         │              │ North/South.        │
197           │            │         │              │ Present             │
198           │            │         │              │         when mode   │
199           │            │         │              │ is 2 or 3.          │
200           ├────────────┼─────────┼──────────────┼─────────────────────┤
201           │leapseconds │ integer │ Current leap │                     │
202           │            │         │ seconds.     │                     │
203           ├────────────┼─────────┼──────────────┼─────────────────────┤
204           │lon         │ No      │ numeric      │ Longitude in        │
205           │            │         │              │ degrees: +/-        │
206           │            │         │              │ signifies           │
207           │            │         │              │ East/West. Present  │
208           │            │         │              │         when mode   │
209           │            │         │              │ is 2 or 3.          │
210           ├────────────┼─────────┼──────────────┼─────────────────────┤
211           │track       │ No      │ numeric      │ Course over ground, │
212           │            │         │              │ degrees from true   │
213           │            │         │              │ north.              │
214           ├────────────┼─────────┼──────────────┼─────────────────────┤
215           │magtrack    │ No      │ numeric      │ Course over ground, │
216           │            │         │              │ degrees magnetic.   │
217           ├────────────┼─────────┼──────────────┼─────────────────────┤
218           │speed       │ No      │ numeric      │ Speed over ground,  │
219           │            │         │              │ meters per second.  │
220           ├────────────┼─────────┼──────────────┼─────────────────────┤
221           │ecefx       │ No      │ numeric      │ ECEF X position in  │
222           │            │         │              │ meters.             │
223           ├────────────┼─────────┼──────────────┼─────────────────────┤
224           │ecefy       │ No      │ numeric      │ ECEF Y position in  │
225           │            │         │              │ meters.             │
226           ├────────────┼─────────┼──────────────┼─────────────────────┤
227           │ecefz       │ No      │ numeric      │ ECEF Z position in  │
228           │            │         │              │ meters.             │
229           ├────────────┼─────────┼──────────────┼─────────────────────┤
230           │ecefpAcc    │ No      │ numeric      │ ECEF position error │
231           │            │         │              │ in meters.          │
232           ├────────────┼─────────┼──────────────┼─────────────────────┤
233           │ecefvx      │ No      │ numeric      │ ECEF X velocity in  │
234           │            │         │              │ meters/second.      │
235           ├────────────┼─────────┼──────────────┼─────────────────────┤
236           │ecefvy      │ No      │ numeric      │ ECEF Y velocity in  │
237           │            │         │              │ meters/second.      │
238           ├────────────┼─────────┼──────────────┼─────────────────────┤
239           │ecefvz      │ No      │ numeric      │ ECEF Z velocity in  │
240           │            │         │              │ meters/second.      │
241           ├────────────┼─────────┼──────────────┼─────────────────────┤
242           │ecefvAcc    │ No      │ numeric      │ ECEF velocity error │
243           │            │         │              │ in meters/second.   │
244           ├────────────┼─────────┼──────────────┼─────────────────────┤
245           │sep         │ No      │ numeric      │ Estimated Spherical │
246           │            │         │              │ (3D) Position Error │
247           │            │         │              │ in meters.          │
248           │            │         │              │          Present if │
249           │            │         │              │ mode is 3D and DOPs │
250           │            │         │              │ can be calculated   │
251           │            │         │              │ from the satellite  │
252           │            │         │              │         view.       │
253           │            │         │              │ Assumed to be 95%   │
254           │            │         │              │ confidence, but     │
255           │            │         │              │ many GPS do not     │
256           │            │         │              │ specify.            │
257           └────────────┴─────────┴──────────────┴─────────────────────┘
258           When the C client library parses a response of this kind, it will
259           assert validity bits in the top-level set member for each field
260           actually received; see gps.h for bitmask names and values.
261
262           Here's an example:
263
264               {"class":"TPV","device":"/dev/pts/1",
265                   "time":"2005-06-08T10:34:48.283Z","ept":0.005,
266                   "lat":46.498293369,"lon":7.567411672,"alt":1343.127,
267                   "eph":36.000,"epv":32.321,
268                   "track":10.3788,"speed":0.091,"climb":-0.085,"mode":3}
269
270       SKY
271           A SKY object reports a sky view of the GPS satellite positions. If
272           there is no GPS device available, or no skyview has been reported
273           yet, only the "class" field will reliably be present.
274
275           Table 2. SKY object
276           ┌───────────┬─────────┬─────────┬─────────────────────┐
277Name       Always? Type    Description         
278           ├───────────┼─────────┼─────────┼─────────────────────┤
279           │class      │ Yes     │ string  │ Fixed: "SKY"        │
280           ├───────────┼─────────┼─────────┼─────────────────────┤
281           │device     │ No      │ string  │ Name of             │
282           │           │         │         │ originating         │
283           │           │         │         │ device              │
284           ├───────────┼─────────┼─────────┼─────────────────────┤
285           │time       │ No      │ string  │ Time/date stamp     │
286           │           │         │         │ in ISO8601          │
287           │           │         │         │ format, UTC. May    │
288           │           │         │         │ have a              │
289           │           │         │         │ fractional part     │
290           │           │         │         │ of up to .001sec    │
291           │           │         │         │ precision.          │
292           ├───────────┼─────────┼─────────┼─────────────────────┤
293           │gdop       │ No      │ numeric │ Geometric           │
294           │           │         │         │ (hyperspherical)    │
295           │           │         │         │ dilution of         │
296           │           │         │         │ precision, a        │
297           │           │         │         │         combination │
298           │           │         │         │ of PDOP and         │
299           │           │         │         │ TDOP.  A            │
300           │           │         │         │ dimensionless       │
301           │           │         │         │ factor which        │
302           │           │         │         │         should      │
303           │           │         │         │ be multiplied by    │
304           │           │         │         │ a base UERE         │
305           │           │         │         │         to get      │
306           │           │         │         │ an error            │
307           │           │         │         │ estimate.           │
308           ├───────────┼─────────┼─────────┼─────────────────────┤
309           │hdop       │ No      │ numeric │ Horizontal dilution │
310           │           │         │         │ of precision, a     │
311           │           │         │         │ dimensionless       │
312           │           │         │         │ factor which should │
313           │           │         │         │ be multiplied by a  │
314           │           │         │         │ base UERE to get a  │
315           │           │         │         │ circular error      │
316           │           │         │         │ estimate.           │
317           ├───────────┼─────────┼─────────┼─────────────────────┤
318           │pdop       │ No      │ numeric │ Position            │
319           │           │         │         │ (spherical/3D)      │
320           │           │         │         │ dilution of         │
321           │           │         │         │ precision, a        │
322           │           │         │         │ dimensionless       │
323           │           │         │         │ factor which should │
324           │           │         │         │ be multiplied by a  │
325           │           │         │         │ base UERE to get an │
326           │           │         │         │ error estimate.     │
327           ├───────────┼─────────┼─────────┼─────────────────────┤
328           │tdop       │ No      │ numeric │ Time dilution of    │
329           │           │         │         │ precision, a        │
330           │           │         │         │ dimensionless       │
331           │           │         │         │ factor which should │
332           │           │         │         │ be multiplied by a  │
333           │           │         │         │ base UERE to get an │
334           │           │         │         │ error estimate.     │
335           ├───────────┼─────────┼─────────┼─────────────────────┤
336           │vdop       │ No      │ numeric │ Vertical (altitude) │
337           │           │         │         │ dilution of         │
338           │           │         │         │ precision, a        │
339           │           │         │         │ dimensionless       │
340           │           │         │         │ factor which should │
341           │           │         │         │ be multiplied by a  │
342           │           │         │         │ base UERE to get an │
343           │           │         │         │ error estimate.     │
344           ├───────────┼─────────┼─────────┼─────────────────────┤
345           │xdop       │ No      │ numeric │ Longitudinal        │
346           │           │         │         │ dilution of         │
347           │           │         │         │ precision, a        │
348           │           │         │         │ dimensionless       │
349           │           │         │         │ factor which should │
350           │           │         │         │ be multiplied by a  │
351           │           │         │         │ base UERE to get an │
352           │           │         │         │ error estimate.     │
353           ├───────────┼─────────┼─────────┼─────────────────────┤
354           │ydop       │ No      │ numeric │ Latitudinal         │
355           │           │         │         │ dilution of         │
356           │           │         │         │ precision, a        │
357           │           │         │         │ dimensionless       │
358           │           │         │         │ factor which should │
359           │           │         │         │ be multiplied by a  │
360           │           │         │         │ base UERE to get an │
361           │           │         │         │ error estimate.     │
362           ├───────────┼─────────┼─────────┼─────────────────────┤
363           │satellites │ Yes     │ list    │ List of satellite   │
364           │           │         │         │ objects in skyview  │
365           └───────────┴─────────┴─────────┴─────────────────────┘
366           Many devices compute dilution of precision factors but do not
367           include them in their reports. Many that do report DOPs report only
368           HDOP, two-dimensional circular error.  gpsd always passes through
369           whatever the device actually reports, then attempts to fill in
370           other DOPs by calculating the appropriate determinants in a
371           covariance matrix based on the satellite view. DOPs may be missing
372           if some of these determinants are singular. It can even happen that
373           the device reports an error estimate in meters when the
374           corresponding DOP is unavailable; some devices use more
375           sophisticated error modeling than the covariance calculation.
376
377           The satellite list objects have the following elements:
378
379           Table 3. Satellite object
380           ┌───────┬─────────┬─────────┬────────────────────┐
381Name   Always? Type    Description        
382           ├───────┼─────────┼─────────┼────────────────────┤
383           │PRN    │ Yes     │ numeric │ PRN ID of the      │
384           │       │         │         │ satellite. 1-63    │
385           │       │         │         │ are GNSS           │
386           │       │         │         │ satellites,        │
387           │       │         │         │ 64-96 are          │
388           │       │         │         │ GLONASS            │
389           │       │         │         │ satellites,        │
390           │       │         │         │ 100-164 are SBAS   │
391           │       │         │         │ satellites         │
392           ├───────┼─────────┼─────────┼────────────────────┤
393           │az     │ Yes     │ numeric │ Azimuth, degrees   │
394           │       │         │         │ from true north.   │
395           ├───────┼─────────┼─────────┼────────────────────┤
396           │el     │ Yes     │ numeric │ Elevation in       │
397           │       │         │         │ degrees.           │
398           ├───────┼─────────┼─────────┼────────────────────┤
399           │ss     │ Yes     │ numeric │ Signal strength    │
400           │       │         │         │ in dB.             │
401           ├───────┼─────────┼─────────┼────────────────────┤
402           │used   │ Yes     │ boolean │ Used in current    │
403           │       │         │         │ solution?          │
404           │       │         │         │ (SBAS/WAAS/EGNOS   │
405           │       │         │         │ satellites may     │
406           │       │         │         │ be flagged used    │
407           │       │         │         │ if the solution    │
408           │       │         │         │ has corrections    │
409           │       │         │         │ from them, but     │
410           │       │         │         │ not all drivers    │
411           │       │         │         │ make this          │
412           │       │         │         │ information        │
413           │       │         │         │ available.)        │
414           ├───────┼─────────┼─────────┼────────────────────┤
415           │gnssid │ No      │ numeric │ The GNSS ID, as    │
416           │       │         │         │ defined by         │
417           │       │         │         │ u-blox, not        │
418           │       │         │         │ NMEA.  0=GPS,      │
419           │       │         │         │         2=Galileo, │
420           │       │         │         │ 3=Beidou,          │
421           │       │         │         │ 5=QZSS,            │
422           │       │         │         │ 6-GLONASS.         │
423           ├───────┼─────────┼─────────┼────────────────────┤
424           │svid   │ no      │ numeric │ The satellite ID   │
425           │       │         │         │ within its         │
426           │       │         │         │ constellation.  As │
427           │       │         │         │ defined            │
428           │       │         │         │         by u-blox, │
429           │       │         │         │ not NMEA).         │
430           ├───────┼─────────┼─────────┼────────────────────┤
431           │sigid  │ no      │ numeric │ The signal ID of   │
432           │       │         │         │ this signal.  As   │
433           │       │         │         │ defined by u-blox, │
434           │       │         │         │ not                │
435           │       │         │         │         NMEA. See  │
436           │       │         │         │ u-blox doc for     │
437           │       │         │         │ details.           │
438           └───────┴─────────┴─────────┴────────────────────┘
439           Note that satellite objects do not have a "class" field, as they
440           are never shipped outside of a SKY object.
441
442           When the C client library parses a SKY response, it will assert the
443           SATELLITE_SET bit in the top-level set member.
444
445           Here's an example:
446
447               {"class":"SKY","device":"/dev/pts/1",
448                   "time":"2005-07-08T11:28:07.114Z",
449                   "xdop":1.55,"hdop":1.24,"pdop":1.99,
450                   "satellites":[
451                       {"PRN":23,"el":6,"az":84,"ss":0,"used":false},
452                       {"PRN":28,"el":7,"az":160,"ss":0,"used":false},
453                       {"PRN":8,"el":66,"az":189,"ss":44,"used":true},
454                       {"PRN":29,"el":13,"az":273,"ss":0,"used":false},
455                       {"PRN":10,"el":51,"az":304,"ss":29,"used":true},
456                       {"PRN":4,"el":15,"az":199,"ss":36,"used":true},
457                       {"PRN":2,"el":34,"az":241,"ss":43,"used":true},
458                       {"PRN":27,"el":71,"az":76,"ss":43,"used":true}]}
459
460       GST
461           A GST object is a pseudorange noise report.
462
463           Table 4. GST object
464           ┌───────┬─────────┬─────────┬──────────────────┐
465Name   Always? Type    Description      
466           ├───────┼─────────┼─────────┼──────────────────┤
467           │class  │ Yes     │ string  │ Fixed: "GST"     │
468           ├───────┼─────────┼─────────┼──────────────────┤
469           │device │ No      │ string  │ Name of          │
470           │       │         │         │ originating      │
471           │       │         │         │ device           │
472           ├───────┼─────────┼─────────┼──────────────────┤
473           │time   │ No      │ string  │ Time/date stamp  │
474           │       │         │         │ in ISO8601       │
475           │       │         │         │ format, UTC. May │
476           │       │         │         │ have a           │
477           │       │         │         │ fractional part  │
478           │       │         │         │ of up to .001sec │
479           │       │         │         │ precision.       │
480           ├───────┼─────────┼─────────┼──────────────────┤
481           │rms    │ No      │ numeric │ Value of the     │
482           │       │         │         │ standard         │
483           │       │         │         │ deviation of the │
484           │       │         │         │ range inputs to  │
485           │       │         │         │ the navigation   │
486           │       │         │         │ process (range   │
487           │       │         │         │ inputs include   │
488           │       │         │         │ pseudoranges and │
489           │       │         │         │ DGPS             │
490           │       │         │         │ corrections).    │
491           ├───────┼─────────┼─────────┼──────────────────┤
492           │major  │ No      │ numeric │ Standard         │
493           │       │         │         │ deviation of     │
494           │       │         │         │ semi-major axis  │
495           │       │         │         │ of error         │
496           │       │         │         │ ellipse, in      │
497           │       │         │         │ meters.          │
498           ├───────┼─────────┼─────────┼──────────────────┤
499           │minor  │ No      │ numeric │ Standard         │
500           │       │         │         │ deviation of     │
501           │       │         │         │ semi-minor axis  │
502           │       │         │         │ of error         │
503           │       │         │         │ ellipse, in      │
504           │       │         │         │ meters.          │
505           ├───────┼─────────┼─────────┼──────────────────┤
506           │orient │ No      │ numeric │ Orientation of   │
507           │       │         │         │ semi-major axis  │
508           │       │         │         │ of error         │
509           │       │         │         │ ellipse, in      │
510           │       │         │         │ degrees from     │
511           │       │         │         │ true north.      │
512           ├───────┼─────────┼─────────┼──────────────────┤
513           │lat    │ No      │ numeric │ Standard         │
514           │       │         │         │ deviation of     │
515           │       │         │         │ latitude error,  │
516           │       │         │         │ in meters.       │
517           ├───────┼─────────┼─────────┼──────────────────┤
518           │lon    │ No      │ numeric │ Standard         │
519           │       │         │         │ deviation of     │
520           │       │         │         │ longitude error, │
521           │       │         │         │ in meters.       │
522           ├───────┼─────────┼─────────┼──────────────────┤
523           │alt    │ No      │ numeric │ Standard         │
524           │       │         │         │ deviation of     │
525           │       │         │         │ altitude error,  │
526           │       │         │         │ in meters.       │
527           └───────┴─────────┴─────────┴──────────────────┘
528           Here's an example:
529
530               {"class":"GST","device":"/dev/ttyUSB0",
531                       "time":"2010-12-07T10:23:07.096Z","rms":2.440,
532                       "major":1.660,"minor":1.120,"orient":68.989,
533                       "lat":1.600,"lon":1.200,"alt":2.520}
534
535       ATT
536           An ATT object is a vehicle-attitude report. It is returned by
537           digital-compass and gyroscope sensors; depending on device, it may
538           include: heading, pitch, roll, yaw, gyroscope, and magnetic-field
539           readings. Because such sensors are often bundled as part of
540           marine-navigation systems, the ATT response may also include water
541           depth.
542
543           The "class" and "mode" fields will reliably be present. Others may
544           be reported or not depending on the specific device type.
545
546           Table 5. ATT object
547           ┌─────────┬─────────┬─────────┬──────────────────┐
548Name     Always? Type    Description      
549           ├─────────┼─────────┼─────────┼──────────────────┤
550           │class    │ Yes     │ string  │ Fixed: "ATT"     │
551           ├─────────┼─────────┼─────────┼──────────────────┤
552           │device   │ Yes     │ string  │ Name of          │
553           │         │         │         │ originating      │
554           │         │         │         │ device           │
555           ├─────────┼─────────┼─────────┼──────────────────┤
556           │time     │ No      │ string  │ Time/date stamp  │
557           │         │         │         │ in ISO8601       │
558           │         │         │         │ format, UTC. May │
559           │         │         │         │ have a           │
560           │         │         │         │ fractional part  │
561           │         │         │         │ of up to .001sec │
562           │         │         │         │ precision.       │
563           ├─────────┼─────────┼─────────┼──────────────────┤
564           │heading  │ No      │ numeric │ Heading, degrees │
565           │         │         │         │ from true north. │
566           ├─────────┼─────────┼─────────┼──────────────────┤
567           │mag_st   │ No      │ string  │ Magnetometer     │
568           │         │         │         │ status.          │
569           ├─────────┼─────────┼─────────┼──────────────────┤
570           │pitch    │ No      │ numeric │ Pitch in         │
571           │         │         │         │ degrees.         │
572           ├─────────┼─────────┼─────────┼──────────────────┤
573           │pitch_st │ No      │ string  │ Pitch sensor     │
574           │         │         │         │ status.          │
575           ├─────────┼─────────┼─────────┼──────────────────┤
576           │yaw      │ No      │ numeric │ Yaw in degrees   │
577           ├─────────┼─────────┼─────────┼──────────────────┤
578           │yaw_st   │ No      │ string  │ Yaw sensor       │
579           │         │         │         │ status.          │
580           ├─────────┼─────────┼─────────┼──────────────────┤
581           │roll     │ No      │ numeric │ Roll in degrees. │
582           ├─────────┼─────────┼─────────┼──────────────────┤
583           │roll_st  │ No      │ string  │ Roll sensor      │
584           │         │         │         │ status.          │
585           ├─────────┼─────────┼─────────┼──────────────────┤
586           │dip      │ No      │ numeric │ Local magnetic   │
587           │         │         │         │ inclination,     │
588           │         │         │         │ degrees,         │
589           │         │         │         │ positive when    │
590           │         │         │         │ the magnetic     │
591           │         │         │         │ field points     │
592           │         │         │         │ downward (into   │
593           │         │         │         │ the Earth).      │
594           ├─────────┼─────────┼─────────┼──────────────────┤
595           │mag_len  │ No      │ numeric │ Scalar magnetic  │
596           │         │         │         │ field strength.  │
597           ├─────────┼─────────┼─────────┼──────────────────┤
598           │mag_x    │ No      │ numeric │ X component of   │
599           │         │         │         │ magnetic field   │
600           │         │         │         │ strength.        │
601           ├─────────┼─────────┼─────────┼──────────────────┤
602           │mag_y    │ No      │ numeric │ Y component of   │
603           │         │         │         │ magnetic field   │
604           │         │         │         │ strength.        │
605           ├─────────┼─────────┼─────────┼──────────────────┤
606           │mag_z    │ No      │ numeric │ Z component of   │
607           │         │         │         │ magnetic field   │
608           │         │         │         │ strength.        │
609           ├─────────┼─────────┼─────────┼──────────────────┤
610           │acc_len  │ No      │ numeric │ Scalar           │
611           │         │         │         │ acceleration.    │
612           ├─────────┼─────────┼─────────┼──────────────────┤
613           │acc_x    │ No      │ numeric │ X component of   │
614           │         │         │         │ acceleration.    │
615           ├─────────┼─────────┼─────────┼──────────────────┤
616           │acc_y    │ No      │ numeric │ Y component of   │
617           │         │         │         │ acceleration.    │
618           ├─────────┼─────────┼─────────┼──────────────────┤
619           │acc_z    │ No      │ numeric │ Z component of   │
620           │         │         │         │ acceleration.    │
621           ├─────────┼─────────┼─────────┼──────────────────┤
622           │gyro_x   │ No      │ numeric │ X component of   │
623           │         │         │         │ acceleration.    │
624           ├─────────┼─────────┼─────────┼──────────────────┤
625           │gyro_y   │ No      │ numeric │ Y component of   │
626           │         │         │         │ acceleration.    │
627           ├─────────┼─────────┼─────────┼──────────────────┤
628           │depth    │ No      │ numeric │ Water depth in   │
629           │         │         │         │ meters.          │
630           ├─────────┼─────────┼─────────┼──────────────────┤
631           │temp     │ No      │ numeric │ Temperature at   │
632           │         │         │         │ sensor, degrees  │
633           │         │         │         │ centigrade.      │
634           └─────────┴─────────┴─────────┴──────────────────┘
635           The heading, pitch, and roll status codes (if present) vary by
636           device. For the TNT Revolution digital compasses, they are coded as
637           follows:
638
639           Table 6. Device flags
640           ┌─────┬────────────────────────────┐
641Code Description                
642           ├─────┼────────────────────────────┤
643           │C    │ magnetometer calibration   │
644           │     │ alarm                      │
645           ├─────┼────────────────────────────┤
646           │L    │ low alarm                  │
647           ├─────┼────────────────────────────┤
648           │M    │ low warning                │
649           ├─────┼────────────────────────────┤
650           │N    │ normal                     │
651           ├─────┼────────────────────────────┤
652           │O    │ high warning               │
653           ├─────┼────────────────────────────┤
654           │P    │ high alarm                 │
655           ├─────┼────────────────────────────┤
656           │V    │ magnetometer voltage level │
657           │     │ alarm                      │
658           └─────┴────────────────────────────┘
659           When the C client library parses a response of this kind, it will
660           assert ATT_IS.
661
662           Here's an example:
663
664               {"class":"ATT","time":1270938096.843,
665                   "heading":14223.00,"mag_st":"N",
666                   "pitch":169.00,"pitch_st":"N", "roll":-43.00,"roll_st":"N",
667                   "dip":13641.000,"mag_x":2454.000}
668
669       And here are the commands:
670
671       ?VERSION;
672           Returns an object with the following attributes:
673
674           Table 7. VERSION object
675           ┌────────────┬─────────┬─────────┬──────────────────┐
676Name        Always? Type    Description      
677           ├────────────┼─────────┼─────────┼──────────────────┤
678           │class       │ Yes     │ string  │ Fixed: "VERSION" │
679           ├────────────┼─────────┼─────────┼──────────────────┤
680           │release     │ Yes     │ string  │ Public release   │
681           │            │         │         │ level            │
682           ├────────────┼─────────┼─────────┼──────────────────┤
683           │rev         │ Yes     │ string  │ Internal         │
684           │            │         │         │ revision-control │
685           │            │         │         │ level.           │
686           ├────────────┼─────────┼─────────┼──────────────────┤
687           │proto_major │ Yes     │ numeric │ API major        │
688           │            │         │         │ revision level.  │
689           ├────────────┼─────────┼─────────┼──────────────────┤
690           │proto_minor │ Yes     │ numeric │ API minor        │
691           │            │         │         │ revision level.  │
692           ├────────────┼─────────┼─────────┼──────────────────┤
693           │remote      │ No      │ string  │ URL of the       │
694           │            │         │         │ remote daemon    │
695           │            │         │         │ reporting this   │
696           │            │         │         │ version. If      │
697           │            │         │         │         empty,   │
698           │            │         │         │ this is the      │
699           │            │         │         │ version of the   │
700           │            │         │         │ local daemon.    │
701           └────────────┴─────────┴─────────┴──────────────────┘
702           The daemon ships a VERSION response to each client when the client
703           first connects to it.
704
705           When the C client library parses a response of this kind, it will
706           assert the VERSION_SET bit in the top-level set member.
707
708           Here's an example:
709
710               {"class":"VERSION","version":"2.40dev",
711                   "rev":"06f62e14eae9886cde907dae61c124c53eb1101f",
712                   "proto_major":3,"proto_minor":1
713               }
714
715       ?DEVICES;
716           Returns a device list object with the following elements:
717
718           Table 8. DEVICES object
719           ┌────────┬─────────┬────────┬──────────────────┐
720Name    Always? Type   Description      
721           ├────────┼─────────┼────────┼──────────────────┤
722           │class   │ Yes     │ string │ Fixed: "DEVICES" │
723           ├────────┼─────────┼────────┼──────────────────┤
724           │devices │ Yes     │ list   │ List of device   │
725           │        │         │        │ descriptions     │
726           ├────────┼─────────┼────────┼──────────────────┤
727           │remote  │ No      │ string │ URL of the       │
728           │        │         │        │ remote daemon    │
729           │        │         │        │ reporting the    │
730           │        │         │        │ device set. If   │
731           │        │         │        │         empty,   │
732           │        │         │        │ this is a        │
733           │        │         │        │ DEVICES response │
734           │        │         │        │ from the local   │
735           │        │         │        │ daemon.          │
736           └────────┴─────────┴────────┴──────────────────┘
737           When the C client library parses a response of this kind, it will
738           assert the DEVICELIST_SET bit in the top-level set member.
739
740           Here's an example:
741
742               {"class"="DEVICES","devices":[
743                   {"class":"DEVICE","path":"/dev/pts/1","flags":1,"driver":"SiRF binary"},
744                   {"class":"DEVICE","path":"/dev/pts/3","flags":4,"driver":"AIVDM"}]}
745
746           The daemon occasionally ships a bare DEVICE object to the client
747           (that is, one not inside a DEVICES wrapper). The data content of
748           these objects will be described later as a response to the ?DEVICE
749           command.
750
751       ?WATCH;
752           This command sets watcher mode. It also sets or elicits a report of
753           per-subscriber policy and the raw bit. An argument WATCH object
754           changes the subscriber's policy. The response describes the
755           subscriber's policy. The response will also include a DEVICES
756           object.
757
758           A WATCH object has the following elements:
759
760           Table 9. WATCH object
761           ┌────────┬─────────┬─────────┬──────────────────┐
762Name    Always? Type    Description      
763           ├────────┼─────────┼─────────┼──────────────────┤
764           │class   │ Yes     │ string  │ Fixed: "WATCH"   │
765           ├────────┼─────────┼─────────┼──────────────────┤
766           │enable  │ No      │ boolean │ Enable (true) or │
767           │        │         │         │ disable (false)  │
768           │        │         │         │ watcher mode.    │
769           │        │         │         │ Default is true. │
770           ├────────┼─────────┼─────────┼──────────────────┤
771           │json    │ No      │ boolean │ Enable (true) or │
772           │        │         │         │ disable (false)  │
773           │        │         │         │ dumping of JSON  │
774           │        │         │         │ reports.         │
775           │        │         │         │ Default is       │
776           │        │         │         │ false.           │
777           ├────────┼─────────┼─────────┼──────────────────┤
778           │nmea    │ No      │ boolean │ Enable (true) or │
779           │        │         │         │ disable (false)  │
780           │        │         │         │ dumping of       │
781           │        │         │         │ binary packets   │
782           │        │         │         │ as pseudo-NMEA.  │
783           │        │         │         │ Default is       │
784           │        │         │         │ false.           │
785           ├────────┼─────────┼─────────┼──────────────────┤
786           │raw     │ No      │ integer │ Controls 'raw'   │
787           │        │         │         │ mode. When this  │
788           │        │         │         │ attribute is set │
789           │        │         │         │ to 1 for a       │
790           │        │         │         │ channel, gpsd    │
791           │        │         │         │ reports the      │
792           │        │         │         │ unprocessed NMEA │
793           │        │         │         │ or AIVDM data    │
794           │        │         │         │ stream from      │
795           │        │         │         │ whatever device  │
796           │        │         │         │ is attached.     │
797           │        │         │         │ Binary GPS       │
798           │        │         │         │ packets are      │
799           │        │         │         │ hex-dumped.      │
800           │        │         │         │ RTCM2 and RTCM3  │
801           │        │         │         │         packets  │
802           │        │         │         │ are not dumped   │
803           │        │         │         │ in raw mode.     │
804           │        │         │         │ When this        │
805           │        │         │         │ attribute is set │
806           │        │         │         │ to 2 for a       │
807           │        │         │         │ channel that     │
808           │        │         │         │ processes binary │
809           │        │         │         │ data, gpsd       │
810           │        │         │         │ reports the      │
811           │        │         │         │ received data    │
812           │        │         │         │ verbatim without │
813           │        │         │         │ hex-dumping.     │
814           ├────────┼─────────┼─────────┼──────────────────┤
815           │scaled  │ No      │ boolean │ If true, apply   │
816           │        │         │         │ scaling divisors │
817           │        │         │         │ to output before │
818           │        │         │         │ dumping; default │
819           │        │         │         │ is false.        │
820           ├────────┼─────────┼─────────┼──────────────────┤
821           │split24 │ No      │ boolean │ If true,         │
822           │        │         │         │ aggregate AIS    │
823           │        │         │         │ type24 sentence  │
824           │        │         │         │ parts.  If       │
825           │        │         │         │ false,           │
826           │        │         │         │         report   │
827           │        │         │         │ each part as a   │
828           │        │         │         │ separate JSON    │
829           │        │         │         │ object, leaving  │
830           │        │         │         │ the              │
831           │        │         │         │         client   │
832           │        │         │         │ to match MMSIs   │
833           │        │         │         │ and aggregate.   │
834           │        │         │         │ Default is       │
835           │        │         │         │         false.   │
836           │        │         │         │ Applies only to  │
837           │        │         │         │ AIS reports.     │
838           ├────────┼─────────┼─────────┼──────────────────┤
839           │pps     │ No      │ boolean │ If true, emit    │
840           │        │         │         │ the TOFF JSON    │
841           │        │         │         │ message on each  │
842           │        │         │         │ cycle and a PPS  │
843           │        │         │         │ JSON message     │
844           │        │         │         │ when the device  │
845           │        │         │         │ issues 1PPS.     │
846           │        │         │         │ Default is       │
847           │        │         │         │ false.           │
848           ├────────┼─────────┼─────────┼──────────────────┤
849           │device  │ No      │ string  │ If present,      │
850           │        │         │         │ enable watching  │
851           │        │         │         │ only of the      │
852           │        │         │         │ specified device │
853           │        │         │         │ rather than all  │
854           │        │         │         │ devices.  Useful │
855           │        │         │         │ with raw and     │
856           │        │         │         │ NMEA modes in    │
857           │        │         │         │ which device     │
858           │        │         │         │ responses aren't │
859           │        │         │         │ tagged. Has no   │
860           │        │         │         │ effect when used │
861           │        │         │         │ with             │
862           │        │         │         │ enable:false.    │
863           ├────────┼─────────┼─────────┼──────────────────┤
864           │remote  │ No      │ string  │ URL of the       │
865           │        │         │         │ remote daemon    │
866           │        │         │         │ reporting the    │
867           │        │         │         │ watch set. If    │
868           │        │         │         │         empty,   │
869           │        │         │         │ this is a WATCH  │
870           │        │         │         │ response from    │
871           │        │         │         │ the local        │
872           │        │         │         │ daemon.          │
873           └────────┴─────────┴─────────┴──────────────────┘
874           There is an additional boolean "timing" attribute which is
875           undocumented because that portion of the interface is considered
876           unstable and for developer use only.
877
878           In watcher mode, GPS reports are dumped as TPV and SKY responses.
879           AIS, Subframe and RTCM reporting is described in the next section.
880
881           When the C client library parses a response of this kind, it will
882           assert the POLICY_SET bit in the top-level set member.
883
884           Here's an example:
885
886               {"class":"WATCH", "raw":1,"scaled":true}
887
888       ?POLL;
889           The POLL command requests data from the last-seen fixes on all
890           active GPS devices. Devices must previously have been activated by
891           ?WATCH to be pollable.
892
893           Polling can lead to possibly surprising results when it is used on
894           a device such as an NMEA GPS for which a complete fix has to be
895           accumulated from several sentences. If you poll while those
896           sentences are being emitted, the response will contain the last
897           complete fix data and may be as much as one cycle time (typically 1
898           second) stale.
899
900           The POLL response will contain a timestamped list of TPV objects
901           describing cached data, and a timestamped list of SKY objects
902           describing satellite configuration. If a device has not seen fixes,
903           it will be reported with a mode field of zero.
904
905           Table 10. POLL object
906           ┌───────┬─────────┬────────────┬──────────────────┐
907Name   Always? Type       Description      
908           ├───────┼─────────┼────────────┼──────────────────┤
909           │class  │ Yes     │ string     │ Fixed: "POLL"    │
910           ├───────┼─────────┼────────────┼──────────────────┤
911           │time   │ Yes     │ Numeric    │ Timestamp in ISO │
912           │       │         │            │ 8601 format. May │
913           │       │         │            │ have a           │
914           │       │         │            │ fractional part  │
915           │       │         │            │ of up to .001sec │
916           │       │         │            │ precision.       │
917           ├───────┼─────────┼────────────┼──────────────────┤
918           │active │ Yes     │ Numeric    │ Count of active  │
919           │       │         │            │ devices.         │
920           ├───────┼─────────┼────────────┼──────────────────┤
921           │tpv    │ Yes     │ JSON array │ Comma-separated  │
922           │       │         │            │ list of TPV      │
923           │       │         │            │ objects.         │
924           ├───────┼─────────┼────────────┼──────────────────┤
925           │sky    │ Yes     │ JSON array │ Comma-separated  │
926           │       │         │            │ list of SKY      │
927           │       │         │            │ objects.         │
928           └───────┴─────────┴────────────┴──────────────────┘
929           Here's an example of a POLL response:
930
931               {"class":"POLL","time":"2010-06-04T10:31:00.289Z","active":1,
932                   "tpv":[{"class":"TPV","device":"/dev/ttyUSB0",
933                           "time":"2010-09-08T13:33:06.095Z",
934                   "ept":0.005,"lat":40.035093060,
935                           "lon":-75.519748733,"track":99.4319,"speed":0.123,"mode":2}],
936                   "sky":[{"class":"SKY","device":"/dev/ttyUSB0",
937                           "time":1270517264.240,"hdop":9.20,
938                           "satellites":[{"PRN":16,"el":55,"az":42,"ss":36,"used":true},
939                                         {"PRN":19,"el":25,"az":177,"ss":0,"used":false},
940                                         {"PRN":7,"el":13,"az":295,"ss":0,"used":false},
941                                         {"PRN":6,"el":56,"az":135,"ss":32,"used":true},
942                                         {"PRN":13,"el":47,"az":304,"ss":0,"used":false},
943                                         {"PRN":23,"el":66,"az":259,"ss":0,"used":false},
944                                         {"PRN":20,"el":7,"az":226,"ss":0,"used":false},
945                                         {"PRN":3,"el":52,"az":163,"ss":32,"used":true},
946                                         {"PRN":31,"el":16,"az":102,"ss":0,"used":false}
947               ]}]}
948
949               Note
950               Client software should not assume the field inventory of the
951               POLL response is fixed for all time. As gpsd collects and
952               caches more data from more sensor types, those data are likely
953               to find their way into this response.
954
955       TOFF
956           This message is emitted on each cycle and reports the offset
957           between the host's clock time and the GPS time at top of second
958           (actually, when the first data for the reporting cycle is
959           received).
960
961           This message exactly mirrors the PPS message except for two
962           details.
963
964           TOFF emits no NTP precision, this is assumed to be -2. See the NTP
965           documentation for their definition of precision.
966
967           The TOFF message reports the GPS time as derived from the GPS
968           serial data stream. The PPS message reports the GPS time as derived
969           from the GPS PPS pulse.
970
971           A TOFF object has the following elements:
972
973           Table 11. TOFF object
974           ┌───────────┬─────────┬─────────┬──────────────────┐
975Name       Always? Type    Description      
976           ├───────────┼─────────┼─────────┼──────────────────┤
977           │class      │ Yes     │ string  │ Fixed: "TOFF"    │
978           ├───────────┼─────────┼─────────┼──────────────────┤
979           │device     │ Yes     │ string  │ Name of          │
980           │           │         │         │ originating      │
981           │           │         │         │ device           │
982           ├───────────┼─────────┼─────────┼──────────────────┤
983           │real_sec   │ Yes     │ numeric │ seconds from the │
984           │           │         │         │ GPS clock        │
985           ├───────────┼─────────┼─────────┼──────────────────┤
986           │real_nsec  │ Yes     │ numeric │ nanoseconds from │
987           │           │         │         │ the GPS clock    │
988           ├───────────┼─────────┼─────────┼──────────────────┤
989           │clock_sec  │ Yes     │ numeric │ seconds from the │
990           │           │         │         │ system clock     │
991           ├───────────┼─────────┼─────────┼──────────────────┤
992           │clock_nsec │ Yes     │ numeric │ nanoseconds from │
993           │           │         │         │ the system clock │
994           └───────────┴─────────┴─────────┴──────────────────┘
995           This message is emitted once per second to watchers of a device and
996           is intended to report the time stamps of the in-band report of the
997           GPS and seconds as reported by the system clock (which may be
998           NTP-corrected) when the first valid timestamp of the reporting
999           cycle was seen.
1000
1001           The message contains two second/nanosecond pairs: real_sec and
1002           real_nsec contain the time the GPS thinks it was at the start of
1003           the current cycle; clock_sec and clock_nsec contain the time the
1004           system clock thinks it was on receipt of the first timing message
1005           of the cycle. real_nsec is always to nanosecond precision.
1006           clock_nsec is nanosecond precision on most systems.
1007
1008           Here's an example:
1009
1010               {"class":"TOFF","device":"/dev/ttyUSB0",
1011                    "real_sec":1330212592, "real_nsec":343182,
1012                    "clock_sec":1330212592,"clock_nsec":343184,
1013                    "precision":-2}}
1014
1015       PPS
1016           This message is emitted each time the daemon sees a valid PPS
1017           (Pulse Per Second) strobe from a device.
1018
1019           This message exactly mirrors the TOFF message except for two
1020           details.
1021
1022           PPS emits the NTP precision. See the NTP documentation for their
1023           definition of precision.
1024
1025           The TOFF message reports the GPS time as derived from the GPS
1026           serial data stream. The PPS message reports the GPS time as derived
1027           from the GPS PPS pulse.
1028
1029           There are various sources of error in the reported clock times. The
1030           speed of the serial connection between the GPS and the system adds
1031           a delay to start of cycle detection. An even bigger error is added
1032           by the variable computation time inside the GPS. Taken together the
1033           time derived from the start of the GPS cycle can have offsets of 10
1034           millisecond to 700 milliseconds and combined jjitter and wander of
1035           100 to 300 millisecond.
1036
1037           A PPS object has the following elements:
1038
1039           Table 12. PPS object
1040           ┌───────────┬─────────┬─────────┬──────────────────┐
1041Name       Always? Type    Description      
1042           ├───────────┼─────────┼─────────┼──────────────────┤
1043           │class      │ Yes     │ string  │ Fixed: "PPS"     │
1044           ├───────────┼─────────┼─────────┼──────────────────┤
1045           │device     │ Yes     │ string  │ Name of          │
1046           │           │         │         │ originating      │
1047           │           │         │         │ device           │
1048           ├───────────┼─────────┼─────────┼──────────────────┤
1049           │real_sec   │ Yes     │ numeric │ seconds from the │
1050           │           │         │         │ PPS source       │
1051           ├───────────┼─────────┼─────────┼──────────────────┤
1052           │real_nsec  │ Yes     │ numeric │ nanoseconds from │
1053           │           │         │         │ the PPS source   │
1054           ├───────────┼─────────┼─────────┼──────────────────┤
1055           │clock_sec  │ Yes     │ numeric │ seconds from the │
1056           │           │         │         │ system clock     │
1057           ├───────────┼─────────┼─────────┼──────────────────┤
1058           │clock_nsec │ Yes     │ numeric │ nanoseconds from │
1059           │           │         │         │ the system clock │
1060           ├───────────┼─────────┼─────────┼──────────────────┤
1061           │precision  │ Yes     │ numeric │ NTP style        │
1062           │           │         │         │ estimate of PPS  │
1063           │           │         │         │ precision        │
1064           └───────────┴─────────┴─────────┴──────────────────┘
1065           This message is emitted once per second to watchers of a device
1066           emitting PPS, and reports the time of the start of the GPS second
1067           (when the 1PPS arrives) and seconds as reported by the system clock
1068           (which may be NTP-corrected) at that moment.
1069
1070           The message contains two second/nanosecond pairs: real_sec and
1071           real_nsec contain the time the GPS thinks it was at the PPS edge;
1072           clock_sec and clock_nsec contain the time the system clock thinks
1073           it was at the PPS edge. real_nsec is always to nanosecond
1074           precision. clock_nsec is nanosecond precision on most systems.
1075
1076           There are various sources of error in the reported clock times. For
1077           PPS delivered via a real serial-line strobe, serial-interrupt
1078           latency plus processing time to the timer call should be bounded
1079           above by about 10 microseconds; that can be reduced to less than 1
1080           microsecond if your kernel supports RFC 2783. USB1.1-to-serial
1081           control-line emulation is limited to about 1 millisecond. seconds.
1082
1083           Here's an example:
1084
1085               {"class":"PPS","device":"/dev/ttyUSB0",
1086                    "real_sec":1330212592, "real_nsec":343182,
1087                    "clock_sec":1330212592,"clock_nsec":343184,
1088                    "precision":-3}
1089
1090       OSC
1091           This message reports the status of a GPS-disciplined oscillator
1092           (GPSDO). The GPS PPS output (which has excellent long-term
1093           stability) is typically used to discipline a local oscillator with
1094           much better short-term stability (such as a rubidium atomic clock).
1095
1096           An OSC object has the following elements:
1097
1098           Table 13. OSC object
1099           ┌────────────┬─────────┬─────────┬──────────────────┐
1100Name        Always? Type    Description      
1101           ├────────────┼─────────┼─────────┼──────────────────┤
1102           │class       │ Yes     │ string  │ Fixed: "OSC"     │
1103           ├────────────┼─────────┼─────────┼──────────────────┤
1104           │device      │ Yes     │ string  │ Name of          │
1105           │            │         │         │ originating      │
1106           │            │         │         │ device.          │
1107           ├────────────┼─────────┼─────────┼──────────────────┤
1108           │running     │ Yes     │ boolean │ If true, the     │
1109           │            │         │         │ oscillator is    │
1110           │            │         │         │ currently        │
1111           │            │         │         │ running.         │
1112           │            │         │         │ Oscillators may  │
1113           │            │         │         │ require warm-up  │
1114           │            │         │         │ time at start of │
1115           │            │         │         │ day.             │
1116           ├────────────┼─────────┼─────────┼──────────────────┤
1117           │reference   │ Yes     │ boolean │ If true, the     │
1118           │            │         │         │ oscillator is    │
1119           │            │         │         │ receiving a GPS  │
1120           │            │         │         │ PPS signal.      │
1121           ├────────────┼─────────┼─────────┼──────────────────┤
1122           │disciplined │ Yes     │ boolean │ If true, the GPS │
1123           │            │         │         │ PPS signal is    │
1124           │            │         │         │ sufficiently     │
1125           │            │         │         │ stable and is    │
1126           │            │         │         │ being used to    │
1127           │            │         │         │ discipline the   │
1128           │            │         │         │ local            │
1129           │            │         │         │ oscillator.      │
1130           ├────────────┼─────────┼─────────┼──────────────────┤
1131           │delta       │ Yes     │ numeric │ The time         │
1132           │            │         │         │ difference (in   │
1133           │            │         │         │ nanoseconds)     │
1134           │            │         │         │ between the      │
1135           │            │         │         │ GPS-disciplined  │
1136           │            │         │         │ oscillator PPS   │
1137           │            │         │         │ output pulse and │
1138           │            │         │         │ the most recent  │
1139           │            │         │         │ GPS PPS input    │
1140           │            │         │         │ pulse.           │
1141           └────────────┴─────────┴─────────┴──────────────────┘
1142           Here's an example:
1143
1144               {"class":"OSC","running":true,"device":"/dev/ttyUSB0",
1145                   "reference":true,"disciplined":true,"delta":67}
1146
1147       ?DEVICE
1148           This command reports (when followed by ';') the state of a device,
1149           or sets (when followed by '=' and a DEVICE object) device-specific
1150           control bits, notably the device's speed and serial mode and the
1151           native-mode bit. The parameter-setting form will be rejected if
1152           more than one client is attached to the channel.
1153
1154           Pay attention to the response, because it is possible for this
1155           command to fail if the GPS does not support a speed-switching
1156           command or only supports some combinations of serial modes. In case
1157           of failure, the daemon and GPS will continue to communicate at the
1158           old speed.
1159
1160           Use the parameter-setting form with caution. On USB and Bluetooth
1161           GPSes it is also possible for serial mode setting to fail either
1162           because the serial adaptor chip does not support non-8N1 modes or
1163           because the device firmware does not properly synchronize the
1164           serial adaptor chip with the UART on the GPS chipset when the speed
1165           changes. These failures can hang your device, possibly requiring a
1166           GPS power cycle or (in extreme cases) physically disconnecting the
1167           NVRAM backup battery.
1168
1169           A DEVICE object has the following elements:
1170
1171           Table 14. DEVICE object
1172           ┌──────────┬──────────────────┬─────────┬────────────────────┐
1173Name      Always?          Type    Description        
1174           ├──────────┼──────────────────┼─────────┼────────────────────┤
1175           │class     │ Yes              │ string  │ Fixed: "DEVICE"    │
1176           ├──────────┼──────────────────┼─────────┼────────────────────┤
1177           │path      │ No               │ string  │ Name the device    │
1178           │          │                  │         │ for which the      │
1179           │          │                  │         │ control bits are   │
1180           │          │                  │         │ being reported,    │
1181           │          │                  │         │ or for which       │
1182           │          │                  │         │ they are to be     │
1183           │          │                  │         │ applied. This      │
1184           │          │                  │         │         attribute  │
1185           │          │                  │         │ may be omitted     │
1186           │          │                  │         │ only when there    │
1187           │          │                  │         │ is exactly one     │
1188           │          │                  │         │         subscribed │
1189           │          │                  │         │ channel.           │
1190           ├──────────┼──────────────────┼─────────┼────────────────────┤
1191           │activated │ No               │ string  │ Time the device    │
1192           │          │                  │         │ was activated as   │
1193           │          │                  │         │ an ISO8601         │
1194           │          │                  │         │         timestamp. │
1195           │          │                  │         │ If the device is   │
1196           │          │                  │         │ inactive this      │
1197           │          │                  │         │ attribute is       │
1198           │          │                  │         │         absent.    │
1199           ├──────────┼──────────────────┼─────────┼────────────────────┤
1200           │flags     │ No               │ integer │ Bit vector of      │
1201           │          │                  │         │ property flags.    │
1202           │          │                  │         │ Currently defined  │
1203           │          │                  │         │ flags are:         │
1204           │          │                  │         │         describe   │
1205           │          │                  │         │ packet types seen  │
1206           │          │                  │         │ so far (GPS,       │
1207           │          │                  │         │ RTCM2, RTCM3,      │
1208           │          │                  │         │ AIS). Won't be     │
1209           │          │                  │         │ reported if empty, │
1210           │          │                  │         │ e.g. before gpsd   │
1211           │          │                  │         │ has seen           │
1212           │          │                  │         │ identifiable       │
1213           │          │                  │         │ packets from the   │
1214           │          │                  │         │ device.            │
1215           ├──────────┼──────────────────┼─────────┼────────────────────┤
1216           │driver    │ No               │ string  │ GPSD's name for    │
1217           │          │                  │         │ the device driver  │
1218           │          │                  │         │ type. Won't be     │
1219           │          │                  │         │ reported before    │
1220           │          │                  │         │ gpsd has seen      │
1221           │          │                  │         │ identifiable       │
1222           │          │                  │         │ packets from the   │
1223           │          │                  │         │ device.            │
1224           ├──────────┼──────────────────┼─────────┼────────────────────┤
1225           │subtype   │ When the daemon  │ string  │ Whatever version   │
1226           │          │ sees a delayed   │         │ information the    │
1227           │          │ response to a    │         │ device returned.   │
1228           │          │ probe for        │         │                    │
1229           │          │ subtype or       │         │                    │
1230           │          │ firmware-version │         │                    │
1231           │          │ information.     │         │                    │
1232           ├──────────┼──────────────────┼─────────┼────────────────────┤
1233           │bps       │ No               │ integer │ Device speed in    │
1234           │          │                  │         │ bits per second.   │
1235           ├──────────┼──────────────────┼─────────┼────────────────────┤
1236           │parity    │ No               │ string  │ N, O or E for no   │
1237           │          │                  │         │ parity, odd, or    │
1238           │          │                  │         │ even.              │
1239           ├──────────┼──────────────────┼─────────┼────────────────────┤
1240           │stopbits  │ Yes              │ string  │ Stop bits (1 or    │
1241           │          │                  │         │ 2).                │
1242           ├──────────┼──────────────────┼─────────┼────────────────────┤
1243           │native    │ No               │ integer │ 0 means NMEA mode  │
1244           │          │                  │         │ and 1 means        │
1245           │          │                  │         │ alternate mode     │
1246           │          │                  │         │ (binary if it has  │
1247           │          │                  │         │ one, for SiRF and  │
1248           │          │                  │         │ Evermore chipsets  │
1249           │          │                  │         │ in particular).    │
1250           │          │                  │         │ Attempting to set  │
1251           │          │                  │         │ this mode on a     │
1252           │          │                  │         │ non-GPS device     │
1253           │          │                  │         │ will yield an      │
1254           │          │                  │         │ error.             │
1255           ├──────────┼──────────────────┼─────────┼────────────────────┤
1256           │cycle     │ No               │ real    │ Device cycle time  │
1257           │          │                  │         │ in seconds.        │
1258           ├──────────┼──────────────────┼─────────┼────────────────────┤
1259           │mincycle  │ No               │ real    │ Device minimum     │
1260           │          │                  │         │ cycle time in      │
1261           │          │                  │         │ seconds. Reported  │
1262           │          │                  │         │ from ?DEVICE when  │
1263           │          │                  │         │ (and only when)    │
1264           │          │                  │         │ the rate is        │
1265           │          │                  │         │ switchable. It is  │
1266           │          │                  │         │ read-only and not  │
1267           │          │                  │         │ settable.          │
1268           └──────────┴──────────────────┴─────────┴────────────────────┘
1269           The serial parameters will (bps, parity, stopbits) be omitted in a
1270           response describing a TCP/IP source such as an Ntrip, DGPSIP, or
1271           AIS feed; on a serial device they will always be present.
1272
1273           The contents of the flags field should be interpreted as follows:
1274
1275           Table 15. Device flags
1276           ┌───────────┬───────┬─────────────────────┐
1277C #define  Value Description         
1278           ├───────────┼───────┼─────────────────────┤
1279           │SEEN_GPS   │ 0x01  │ GPS data has been   │
1280           │           │       │ seen on this device │
1281           ├───────────┼───────┼─────────────────────┤
1282           │SEEN_RTCM2 │ 0x02  │ RTCM2 data has been │
1283           │           │       │ seen on this device │
1284           ├───────────┼───────┼─────────────────────┤
1285           │SEEN_RTCM3 │ 0x04  │ RTCM3 data has been │
1286           │           │       │ seen on this device │
1287           ├───────────┼───────┼─────────────────────┤
1288           │SEEN_AIS   │ 0x08  │ AIS data has been   │
1289           │           │       │ seen on this device │
1290           └───────────┴───────┴─────────────────────┘
1291           When the C client library parses a response of this kind, it will
1292           assert the DEVICE_SET bit in the top-level set member.
1293
1294           Here's an example:
1295
1296               {"class":"DEVICE","bps":4800,"parity":"N","stopbits":1,"native":0}
1297
1298       When a client is in watcher mode, the daemon will ship it DEVICE
1299       notifications when a device is added to the pool or deactivated.
1300
1301       When the C client library parses a response of this kind, it will
1302       assert the DEVICE_SET bit in the top-level set member.
1303
1304       Here's an example:
1305
1306           {"class":"DEVICE","path":"/dev/pts1","activated":0}
1307
1308       The daemon may ship an error object in response to a syntactically
1309       invalid command line or unknown command. It has the following elements:
1310
1311       Table 16. ERROR notification object
1312       ┌────────┬─────────┬────────┬────────────────┐
1313Name    Always? Type   Description    
1314       ├────────┼─────────┼────────┼────────────────┤
1315       │class   │ Yes     │ string │ Fixed: "ERROR" │
1316       ├────────┼─────────┼────────┼────────────────┤
1317       │message │ Yes     │ string │ Textual error  │
1318       │        │         │        │ message        │
1319       └────────┴─────────┴────────┴────────────────┘
1320
1321       Here's an example:
1322
1323           {"class":"ERROR","message":"Unrecognized request '?FOO'"}
1324
1325       When the C client library parses a response of this kind, it will
1326       assert the ERR_SET bit in the top-level set member.
1327

RTCM2

1329       RTCM-104 is a family of serial protocols used for broadcasting
1330       pseudorange corrections from differential-GPS reference stations. Many
1331       GPS receivers can accept these corrections to improve their reporting
1332       accuracy.
1333
1334       RTCM-104 comes in two major and incompatible flavors, 2.x and 3.x. Each
1335       major flavor has minor (compatible) revisions.
1336
1337       The applicable standard for RTCM Version 2.x is RTCM Recommended
1338       Standards for Differential NAVSTAR GPS Service RTCM Paper 194-93/SC
1339       104-STD. For RTCM 3.1 it is RTCM Paper 177-2006-SC104-STD. Ordering
1340       instructions for both standards are accessible from the website of the
1341       Radio Technical Commission for Maritime Services[1] under
1342       "Publications".
1343
1344   RTCM WIRE TRANSMISSIONS
1345       Differential-GPS correction stations consist of a GPS reference
1346       receiver coupled to a low frequency (LF) transmitter. The GPS reference
1347       receiver is a survey-grade GPS that does GPS carrier tracking and can
1348       work out its own position to a few millimeters. It generates range and
1349       range-rate corrections and encodes them into RTCM104. It ships the
1350       RTCM104 to the LF transmitter over serial rs-232 signal at 100 baud or
1351       200 baud depending on the requirements of the transmitter.
1352
1353       The LF transmitter broadcasts the approximately 300khz radio signal
1354       that differential-GPS radio receivers pick up. Transmitters that are
1355       meant to have a higher range will need to transmit at the slower rate.
1356       The higher the data rate the harder it will be for the remote radio
1357       receiver to receive with a good signal-to-noise ration. (Higher data
1358       rate signals can't be averaged over as long a time frame, hence they
1359       appear noisier.)
1360
1361   RTCM WIRE FORMATS
1362       An RTCM 2.x message consists of a sequence of up to 33 30-bit words.
1363       The 24 most significant bits of each word are data and the six least
1364       significant bits are parity. The parity algorithm used is the same
1365       ISGPS-2000 as that used on GPS satellite downlinks. Each RTCM 2.x
1366       message consists of two header words followed by zero or more data
1367       words, depending upon message type.
1368
1369       An RTCM 3.x message begins with a fixed leader byte 0xD3. That is
1370       followed by six bits of version information and 10 bits of payload
1371       length information. Following that is the payload; following the
1372       payload is a 3-byte checksum of the payload using the Qualcomm CRC-24Q
1373       algorithm.
1374
1375   RTCM2 JSON FORMAT
1376       Each RTCM2 message is dumped as a single JSON object per message, with
1377       the message fields as attributes of that object. Arrays of satellite,
1378       station, and constellation statistics become arrays of JSON
1379       sub-objects. Each sentence will normally also have a "device" field
1380       containing the pathname of the originating device.
1381
1382       All attributes other than the device field are mandatory. Header
1383       attributes are emitted before others.
1384
1385       Header portion
1386           Table 17. SKY object
1387           ┌───────────────┬─────────┬─────────────────────────────┐
1388Name           Type    │                             │
1389           │               │         │            Description      │
1390           ├───────────────┼─────────┼─────────────────────────────┤
1391           │class          │ string  │                             │
1392           │               │         │            Fixed:           │
1393           │               │         │            "RTCM2".         │
1394           ├───────────────┼─────────┼─────────────────────────────┤
1395           │type           │ integer │                             │
1396           │               │         │            Message          │
1397           │               │         │            type (1-9).      │
1398           ├───────────────┼─────────┼─────────────────────────────┤
1399           │station_id     │ integer │                             │
1400           │               │         │            The id of        │
1401           │               │         │            the GPS          │
1402           │               │         │            reference        │
1403           │               │         │            receiver.        │
1404           │               │         │            The LF           │
1405           │               │         │            transmitters     │
1406           │               │         │            also have        │
1407           │               │         │            (different)      │
1408           │               │         │            id numbers.      │
1409           ├───────────────┼─────────┼─────────────────────────────┤
1410           │zcount         │ real    │                             │
1411           │               │         │            The              │
1412           │               │         │            reference        │
1413           │               │         │            time of the      │
1414           │               │         │            corrections      │
1415           │               │         │            in the           │
1416           │               │         │            message in       │
1417           │               │         │            seconds          │
1418           │               │         │            within the       │
1419           │               │         │            current          │
1420           │               │         │            hour. Note       │
1421           │               │         │            that it is       │
1422           │               │         │            in GPS time,     │
1423           │               │         │            which is         │
1424           │               │         │            some seconds     │
1425           │               │         │            ahead of UTC     │
1426           │               │         │            (see the         │
1427           │               │         │            U.S. Naval       │
1428           │               │         │            Observatory's    │
1429           │               │         │            table of         
1430           │               │         │            leap second      │
1431           │               │         │            corrections[2]). │
1432           ├───────────────┼─────────┼─────────────────────────────┤
1433           │seqnum         │ integer │                             │
1434           │               │         │            Sequence number. │
1435           │               │         │            Only 3 bits      │
1436           │               │         │            wide, wraps      │
1437           │               │         │            after 7.         │
1438           ├───────────────┼─────────┼─────────────────────────────┤
1439           │length         │ integer │                             │
1440           │               │         │            The number of    │
1441           │               │         │            words after the  │
1442           │               │         │            header that      │
1443           │               │         │            comprise the     │
1444           │               │         │            message.         │
1445           ├───────────────┼─────────┼─────────────────────────────┤
1446           │station_health │ integer │                             │
1447           │               │         │            Station          │
1448           │               │         │            transmission     │
1449           │               │         │            status.          │
1450           │               │         │            Indicates the    │
1451           │               │         │            health of the    │
1452           │               │         │            beacon as a      │
1453           │               │         │            reference        │
1454           │               │         │            source. Any      │
1455           │               │         │            nonzero value    │
1456           │               │         │            means the        │
1457           │               │         │            satellite is     │
1458           │               │         │            probably         │
1459           │               │         │            transmitting bad │
1460           │               │         │            data and should  │
1461           │               │         │            not be used in a │
1462           │               │         │            fix. 6 means the │
1463           │               │         │            transmission is  │
1464           │               │         │            unmonitored. 7   │
1465           │               │         │            means the        │
1466           │               │         │            station is not   │
1467           │               │         │            working          │
1468           │               │         │            properly. Other  │
1469           │               │         │            values are       │
1470           │               │         │            defined by the   │
1471           │               │         │            beacon operator. │
1472           └───────────────┴─────────┴─────────────────────────────┘
1473
1474           <message type> is one of
1475
1476           1
1477               full corrections - one message containing corrections for all
1478               GPS satellites in view. This is not common.
1479
1480           3
1481               reference station parameters - the position of the reference
1482               station GPS antenna.
1483
1484           4
1485               datum — the datum to which the DGPS data is referred.
1486
1487           5
1488               constellation health — information about the satellites the
1489               beacon can see.
1490
1491           6
1492               null message — just a filler.
1493
1494           7
1495               radio beacon almanac — information about this or other beacons.
1496
1497           9
1498               subset corrections — a message containing corrections for only
1499               a subset of the GPS satellites in view.
1500
1501           16
1502               special message — a text message from the beacon operator.
1503
1504           31
1505               GLONASS subset corrections — a message containing corrections
1506               for a set of the GLONASS satellites in view.
1507
1508       Type 1 and 9: Correction data
1509           One or more satellite objects follow the header for type 1 or type
1510           9 messages. Here is the format:
1511
1512           Table 18. Satellite object
1513           ┌──────┬─────────┬─────────────────────────┐
1514Name  Type    │                         │
1515           │      │         │            Description  │
1516           ├──────┼─────────┼─────────────────────────┤
1517           │ident │ integer │                         │
1518           │      │         │            The PRN      │
1519           │      │         │            number of    │
1520           │      │         │            the          │
1521           │      │         │            satellite    │
1522           │      │         │            for which    │
1523           │      │         │            this is      │
1524           │      │         │            correction   │
1525           │      │         │            data.        │
1526           ├──────┼─────────┼─────────────────────────┤
1527           │udre  │ integer │                         │
1528           │      │         │            User         │
1529           │      │         │            Differential │
1530           │      │         │            Range Error  │
1531           │      │         │            (0-3). See   │
1532           │      │         │            the table    │
1533           │      │         │            following    │
1534           │      │         │            for values.  │
1535           ├──────┼─────────┼─────────────────────────┤
1536           │iod   │ integer │                         │
1537           │      │         │            Issue Of     │
1538           │      │         │            Data,        │
1539           │      │         │            matching the │
1540           │      │         │            IOD for the  │
1541           │      │         │            current      │
1542           │      │         │            ephemeris of │
1543           │      │         │            this         │
1544           │      │         │            satellite,   │
1545           │      │         │            as           │
1546           │      │         │            transmitted  │
1547           │      │         │            by the       │
1548           │      │         │            satellite.   │
1549           │      │         │            The IOD is a │
1550           │      │         │            unique tag   │
1551           │      │         │            that         │
1552           │      │         │            identifies   │
1553           │      │         │            the          │
1554           │      │         │            ephemeris;   │
1555           │      │         │            the GPS      │
1556           │      │         │            using the    │
1557           │      │         │            DGPS         │
1558           │      │         │            correction   │
1559           │      │         │            and the DGPS │
1560           │      │         │            generating   │
1561           │      │         │            the data     │
1562           │      │         │            must use the │
1563           │      │         │            same orbital │
1564           │      │         │            positions    │
1565           │      │         │            for the      │
1566           │      │         │            satellite.   │
1567           ├──────┼─────────┼─────────────────────────┤
1568           │prc   │ real    │                         │
1569           │      │         │            The          │
1570           │      │         │            pseudorange  │
1571           │      │         │            error in     │
1572           │      │         │            meters for   │
1573           │      │         │            this         │
1574           │      │         │            satellite as │
1575           │      │         │            measured by  │
1576           │      │         │            the beacon   │
1577           │      │         │            reference    │
1578           │      │         │            receiver at  │
1579           │      │         │            the epoch    │
1580           │      │         │            indicated by │
1581           │      │         │            the z_count  │
1582           │      │         │            in the       │
1583           │      │         │            parent       │
1584           │      │         │            record.      │
1585           ├──────┼─────────┼─────────────────────────┤
1586           │rrc   │ real    │                         │
1587           │      │         │            The rate of  │
1588           │      │         │            change of    │
1589           │      │         │            pseudorange  │
1590           │      │         │            error in     │
1591           │      │         │            meters/sec   │
1592           │      │         │            for this     │
1593           │      │         │            satellite as │
1594           │      │         │            measured by  │
1595           │      │         │            the beacon   │
1596           │      │         │            reference    │
1597           │      │         │            receiver at  │
1598           │      │         │            the epoch    │
1599           │      │         │            indicated by │
1600           │      │         │            the z_count  │
1601           │      │         │            field in the │
1602           │      │         │            parent       │
1603           │      │         │            record. This │
1604           │      │         │            is used to   │
1605           │      │         │            calculate    │
1606           │      │         │            pseudorange  │
1607           │      │         │            errors at    │
1608           │      │         │            other        │
1609           │      │         │            epochs, if   │
1610           │      │         │            required by  │
1611           │      │         │            the GPS      │
1612           │      │         │            receiver.    │
1613           └──────┴─────────┴─────────────────────────┘
1614
1615           User Differential Range Error values are as follows:
1616
1617           Table 19. UDRE values
1618           ┌──┬────────────────────┐
1619           │0 │ 1-sigma error<= 1m │
1620           ├──┼────────────────────┤
1621           │1 │ 1-sigma error<= 4m │
1622           ├──┼────────────────────┤
1623           │2 │ 1-sigma error<= 8m │
1624           ├──┼────────────────────┤
1625           │3 │ 1-sigma error>  8m │
1626           └──┴────────────────────┘
1627
1628           Here's an example:
1629
1630               {"class":"RTCM2","type":1,
1631                   "station_id":688,"zcount":843.0,"seqnum":5,"length":19,"station_health":6,
1632                   "satellites":[
1633               {"ident":10,"udre":0,"iod":46,"prc":-2.400,"rrc":0.000},
1634               {"ident":13,"udre":0,"iod":94,"prc":-4.420,"rrc":0.000},
1635               {"ident":7,"udre":0,"iod":22,"prc":-5.160,"rrc":0.002},
1636               {"ident":2,"udre":0,"iod":34,"prc":-6.480,"rrc":0.000},
1637               {"ident":4,"udre":0,"iod":47,"prc":-8.860,"rrc":0.000},
1638               {"ident":8,"udre":0,"iod":76,"prc":-7.980,"rrc":0.002},
1639               {"ident":5,"udre":0,"iod":99,"prc":-8.260,"rrc":0.002},
1640               {"ident":23,"udre":0,"iod":81,"prc":-8.060,"rrc":0.000},
1641               {"ident":16,"udre":0,"iod":70,"prc":-11.740,"rrc":0.000},
1642               {"ident":30,"udre":0,"iod":4,"prc":-18.960,"rrc":-0.006},
1643               {"ident":29,"udre":0,"iod":101,"prc":-24.960,"rrc":-0.002}
1644               ]}
1645
1646       Type 3: Reference Station Parameters
1647           Here are the payload members of a type 3 (Reference Station
1648           Parameters) message:
1649
1650           Table 20. Reference Station Parameters
1651           ┌─────┬──────┬────────────────────────┐
1652Name Type │                        │
1653           │     │      │            Description │
1654           ├─────┼──────┼────────────────────────┤
1655           │x    │ real │                        │
1656           │     │      │            ECEF X      │
1657           │     │      │            coordinate. │
1658           ├─────┼──────┼────────────────────────┤
1659           │y    │ real │                        │
1660           │     │      │            ECEF Y      │
1661           │     │      │            coordinate. │
1662           ├─────┼──────┼────────────────────────┤
1663           │z    │ real │                        │
1664           │     │      │            ECEF Z      │
1665           │     │      │            coordinate. │
1666           └─────┴──────┴────────────────────────┘
1667
1668           The coordinates are the position of the station, in meters to two
1669           decimal places, in Earth Centred Earth Fixed coordinates. These are
1670           usually referred to the WGS84 reference frame, but may be referred
1671           to NAD83 in the US (essentially identical to WGS84 for all except
1672           geodesists), or to some other reference frame in other parts of the
1673           world.
1674
1675           An invalid reference message is represented by a type 3 header
1676           without payload fields.
1677
1678           Here's an example:
1679
1680               {"class":"RTCM2","type":3,
1681                   "station_id":652,"zcount":1657.2,"seqnum":2,"length":4,"station_health":6,
1682                   "x":3878620.92,"y":670281.40,"z":5002093.59
1683               }
1684
1685       Type 4: Datum
1686           Here are the payload members of a type 4 (Datum) message:
1687
1688           Table 21. Datum
1689           ┌───────────┬─────────┬────────────────────────┐
1690Name       Type    │                        │
1691           │           │         │            Description │
1692           ├───────────┼─────────┼────────────────────────┤
1693           │dgnss_type │ string  │                        │
1694           │           │         │            Either      │
1695           │           │         │            "GPS",      │
1696           │           │         │            "GLONASS",  │
1697           │           │         │            "GALILEO",  │
1698           │           │         │            or          │
1699           │           │         │            "UNKNOWN".  │
1700           ├───────────┼─────────┼────────────────────────┤
1701           │dat        │ integer │                        │
1702           │           │         │            0 or 1 and  │
1703           │           │         │            indicates   │
1704           │           │         │            the sense   │
1705           │           │         │            of the      │
1706           │           │         │            offset      │
1707           │           │         │            shift given │
1708           │           │         │            by dx, dy,  │
1709           │           │         │            dz. dat = 0 │
1710           │           │         │            means that  │
1711           │           │         │            the station │
1712           │           │         │            coordinates │
1713           │           │         │            (in the     │
1714           │           │         │            reference   │
1715           │           │         │            message)    │
1716           │           │         │            are         │
1717           │           │         │            referred to │
1718           │           │         │            a local     │
1719           │           │         │            datum and   │
1720           │           │         │            that adding │
1721           │           │         │            dx, dy, dz  │
1722           │           │         │            to that     │
1723           │           │         │            position    │
1724           │           │         │            will render │
1725           │           │         │            it in GNSS  │
1726           │           │         │            coordinates │
1727           │           │         │            (WGS84 for  │
1728           │           │         │            GPS). If    │
1729           │           │         │            dat = 1     │
1730           │           │         │            then the    │
1731           │           │         │            ref station │
1732           │           │         │            position is │
1733           │           │         │            in GNSS     │
1734           │           │         │            coordinates │
1735           │           │         │            and adding  │
1736           │           │         │            dx, dy, dz  │
1737           │           │         │            will give   │
1738           │           │         │            it referred │
1739           │           │         │            to the      │
1740           │           │         │            local       │
1741           │           │         │            datum.      │
1742           ├───────────┼─────────┼────────────────────────┤
1743           │datum_name │ string  │                        │
1744           │           │         │            A standard  │
1745           │           │         │            name for    │
1746           │           │         │            the datum.  │
1747           ├───────────┼─────────┼────────────────────────┤
1748           │dx         │ real    │                        │
1749           │           │         │            X offset.   │
1750           ├───────────┼─────────┼────────────────────────┤
1751           │dy         │ real    │                        │
1752           │           │         │            Y offset.   │
1753           ├───────────┼─────────┼────────────────────────┤
1754           │dz         │ real    │                        │
1755           │           │         │            Z offset.   │
1756           └───────────┴─────────┴────────────────────────┘
1757
1758           <dx> <dy> <dz> are offsets to convert from local datum to GNSS
1759           datum or vice versa. These fields are optional.
1760
1761           An invalid datum message is represented by a type 4 header without
1762           payload fields.
1763
1764       Type 5: Constellation Health
1765           One or more of these follow the header for type 5 messages — one
1766           for each satellite.
1767
1768           Here is the format:
1769
1770           Table 22. Constellation health
1771           ┌────────────┬─────────┬──────────────────────────┐
1772Name        Type    │                          │
1773           │            │         │            Description   │
1774           ├────────────┼─────────┼──────────────────────────┤
1775           │ident       │ integer │                          │
1776           │            │         │            The PRN       │
1777           │            │         │            number of     │
1778           │            │         │            the           │
1779           │            │         │            satellite.    │
1780           ├────────────┼─────────┼──────────────────────────┤
1781           │iodl        │ bool    │                          │
1782           │            │         │            True          │
1783           │            │         │            indicates     │
1784           │            │         │            that this     │
1785           │            │         │            information   │
1786           │            │         │            relates to    │
1787           │            │         │            the           │
1788           │            │         │            satellite     │
1789           │            │         │            information   │
1790           │            │         │            in an         │
1791           │            │         │            accompanying  │
1792           │            │         │            type 1 or     │
1793           │            │         │            type 9        │
1794           │            │         │            message.      │
1795           ├────────────┼─────────┼──────────────────────────┤
1796           │health      │ integer │ 0 indicates that the     │
1797           │            │         │ satellite is healthy.    │
1798           │            │         │ Any other value          │
1799           │            │         │ indicates a problem      │
1800           │            │         │ (coding is not           │
1801           │            │         │ known)..PP               │
1802           ├────────────┼─────────┼──────────────────────────┤
1803           │snr         │ integer │                          │
1804           │            │         │            The           │
1805           │            │         │            carrier/noise │
1806           │            │         │            ratio of the  │
1807           │            │         │            received      │
1808           │            │         │            signal in     │
1809           │            │         │            the range 25  │
1810           │            │         │            to 55         │
1811           │            │         │            dB(Hz).       │
1812           ├────────────┼─────────┼──────────────────────────┤
1813           │health_en   │ bool    │                          │
1814           │            │         │            If set to     │
1815           │            │         │            True it       │
1816           │            │         │            indicates     │
1817           │            │         │            that the      │
1818           │            │         │            satellite is  │
1819           │            │         │            healthy even  │
1820           │            │         │            if the        │
1821           │            │         │            satellite     │
1822           │            │         │            navigation    │
1823           │            │         │            data says it  │
1824           │            │         │            is unhealthy. │
1825           ├────────────┼─────────┼──────────────────────────┤
1826           │new_data    │ bool    │ True indicates that the  │
1827           │            │         │ IOD for this satellite   │
1828           │            │         │ will                     │
1829           │            │         │         soon be updated  │
1830           │            │         │ in type 1 or 9           │
1831           │            │         │ messages..PP             │
1832           ├────────────┼─────────┼──────────────────────────┤
1833           │los_warning │ bool    │                          │
1834           │            │         │            Line-of-sight │
1835           │            │         │            warning. True │
1836           │            │         │            indicates     │
1837           │            │         │            that the      │
1838           │            │         │            satellite     │
1839           │            │         │            will shortly  │
1840           │            │         │            go unhealthy. │
1841           ├────────────┼─────────┼──────────────────────────┤
1842           │tou         │ integer │                          │
1843           │            │         │            Healthy time  │
1844           │            │         │            remaining in  │
1845           │            │         │            seconds.      │
1846           └────────────┴─────────┴──────────────────────────┘
1847
1848       Type 6: Null
1849           This just indicates a null message. There are no payload fields.
1850
1851       Unknown message
1852           This format is used to dump message words in hexadecimal when the
1853           message type field doesn't match any of the known ones.
1854
1855           Here is the format:
1856
1857           Table 23. Unknown Message
1858           ┌─────┬──────┬────────────────────────┐
1859Name Type │                        │
1860           │     │      │            Description │
1861           ├─────┼──────┼────────────────────────┤
1862           │data │ list │                        │
1863           │     │      │            A list of   │
1864           │     │      │            strings.    │
1865           └─────┴──────┴────────────────────────┘
1866
1867           Each string in the array is a hex literal representing 30 bits of
1868           information, after parity checks and inversion. The high two bits
1869           should be ignored.
1870
1871       Type 7: Radio Beacon Almanac
1872           Here is the format:
1873
1874           Table 24. Contellation health
1875           ┌───────────┬─────────┬───────────────────────────┐
1876Name       Type    │                           │
1877           │           │         │            Description    │
1878           ├───────────┼─────────┼───────────────────────────┤
1879           │lat        │ real    │                           │
1880           │           │         │            Latitude in    │
1881           │           │         │            degrees, of    │
1882           │           │         │            the LF         │
1883           │           │         │            transmitter    │
1884           │           │         │            antenna for    │
1885           │           │         │            the station    │
1886           │           │         │            for which      │
1887           │           │         │            this is an     │
1888           │           │         │            almanac.       │
1889           │           │         │            North is       │
1890           │           │         │            positive.      │
1891           ├───────────┼─────────┼───────────────────────────┤
1892           │lon        │ real    │                           │
1893           │           │         │            Longitude      │
1894           │           │         │            in degrees,    │
1895           │           │         │            of the LF      │
1896           │           │         │            transmitter    │
1897           │           │         │            antenna for    │
1898           │           │         │            the station    │
1899           │           │         │            for which      │
1900           │           │         │            this is an     │
1901           │           │         │            almanac.       │
1902           │           │         │            East is        │
1903           │           │         │            positive.      │
1904           ├───────────┼─────────┼───────────────────────────┤
1905           │range      │ integer │ Published range of the    │
1906           │           │         │ station in km..PP         │
1907           ├───────────┼─────────┼───────────────────────────┤
1908           │frequency  │ real    │                           │
1909           │           │         │            Station        │
1910           │           │         │            broadcast      │
1911           │           │         │            frequency      │
1912           │           │         │            in kHz.        │
1913           ├───────────┼─────────┼───────────────────────────┤
1914           │health     │ integer │                           │
1915           │           │         │            <health> is    │
1916           │           │         │            the health     │
1917           │           │         │            of the         │
1918           │           │         │            station for    │
1919           │           │         │            which this     │
1920           │           │         │            is an          │
1921           │           │         │            almanac. If    │
1922           │           │         │            it is          │
1923           │           │         │            non-zero,      │
1924           │           │         │            the station    │
1925           │           │         │            is issuing     │
1926           │           │         │            suspect        │
1927           │           │         │            data and       │
1928           │           │         │            should not     │
1929           │           │         │            be used for    │
1930           │           │         │            fixes. The     │
1931           │           │         │            ITU and        │
1932           │           │         │            RTCM104        │
1933           │           │         │            standards      │
1934           │           │         │            differ         │
1935           │           │         │            about the      │
1936           │           │         │            mode           │
1937           │           │         │            detailed       │
1938           │           │         │            interpretation │
1939           │           │         │            of the         │
1940           │           │         │            <health>       │
1941           │           │         │            field and      │
1942           │           │         │            even about     │
1943           │           │         │            its bit        │
1944           │           │         │            width.         │
1945           ├───────────┼─────────┼───────────────────────────┤
1946           │station_id │ integer │                           │
1947           │           │         │            The id of the  │
1948           │           │         │            transmitter.   │
1949           │           │         │            This is not    │
1950           │           │         │            the same as    │
1951           │           │         │            the reference  │
1952           │           │         │            id in the      │
1953           │           │         │            header, the    │
1954           │           │         │            latter being   │
1955           │           │         │            the id of the  │
1956           │           │         │            reference      │
1957           │           │         │            receiver.      │
1958           ├───────────┼─────────┼───────────────────────────┤
1959           │bitrate    │ integer │                           │
1960           │           │         │            The            │
1961           │           │         │            transmitted    │
1962           │           │         │            bitrate.       │
1963           └───────────┴─────────┴───────────────────────────┘
1964
1965           Here's an example:
1966
1967               {"class":"RTCM2","type":9,"station_id":268,"zcount":252.6,
1968                       "seqnum":4,"length":5,"station_health":0,
1969                       "satellites":[
1970                           {"ident":13,"udre":0,"iod":3,"prc":-25.940,"rrc":0.066},
1971                           {"ident":2,"udre":0,"iod":73,"prc":0.920,"rrc":-0.080},
1972                           {"ident":8,"udre":0,"iod":22,"prc":23.820,"rrc":0.014}
1973               ]}
1974
1975       Type 13: GPS Time of Week
1976           Here are the payload members of a type 13 (Groumf Tramitter
1977           Parameters) message:
1978
1979           Table 25. Grund Transmitter Parameters
1980           ┌──────────┬─────────┬─────────────────────────┐
1981Name      Type    │                         │
1982           │          │         │            Description  │
1983           ├──────────┼─────────┼─────────────────────────┤
1984           │status    │ bool    │                         │
1985           │          │         │            If True,     │
1986           │          │         │            signals      │
1987           │          │         │            user to      │
1988           │          │         │            expect a     │
1989           │          │         │            type 16      │
1990           │          │         │            explanatory  │
1991           │          │         │            message      │
1992           │          │         │            associated   │
1993           │          │         │            with this    │
1994           │          │         │            station.     │
1995           │          │         │            Probably     │
1996           │          │         │            indicates    │
1997           │          │         │            some sort    │
1998           │          │         │            of unusual   │
1999           │          │         │            event.       │
2000           ├──────────┼─────────┼─────────────────────────┤
2001           │rangeflag │ bool    │                         │
2002           │          │         │            If True,     │
2003           │          │         │            indicates    │
2004           │          │         │            that the     │
2005           │          │         │            estimated    │
2006           │          │         │            range is     │
2007           │          │         │            different    │
2008           │          │         │            from that    │
2009           │          │         │            found in     │
2010           │          │         │            the Type 7   │
2011           │          │         │            message      │
2012           │          │         │            (which       │
2013           │          │         │            contains     │
2014           │          │         │            the          │
2015           │          │         │            beacon's     │
2016           │          │         │            listed       │
2017           │          │         │            range).      │
2018           │          │         │            Generally    │
2019           │          │         │            indicates a  │
2020           │          │         │            range        │
2021           │          │         │            reduction    │
2022           │          │         │            due to       │
2023           │          │         │            causes such  │
2024           │          │         │            as poor      │
2025           │          │         │            ionospheric  │
2026           │          │         │            conditions   │
2027           │          │         │            or reduced   │
2028           │          │         │            transmission │
2029           │          │         │            power.       │
2030           ├──────────┼─────────┼─────────────────────────┤
2031           │lat       │ real    │                         │
2032           │          │         │            Degrees      │
2033           │          │         │            latitude,    │
2034           │          │         │            signed.      │
2035           │          │         │            Positive is  │
2036           │          │         │            N, negative  │
2037           │          │         │            is S.        │
2038           ├──────────┼─────────┼─────────────────────────┤
2039           │lon       │ real    │                         │
2040           │          │         │            Degrees      │
2041           │          │         │            longitude,   │
2042           │          │         │            signed.      │
2043           │          │         │            Positive is  │
2044           │          │         │            E, negative  │
2045           │          │         │            is W.        │
2046           ├──────────┼─────────┼─────────────────────────┤
2047           │range     │ integer │                         │
2048           │          │         │            Transmission │
2049           │          │         │            range in km  │
2050           │          │         │            (1-1024).    │
2051           └──────────┴─────────┴─────────────────────────┘
2052
2053           This message type replaces message type 3 (Reference Station
2054           Parameters) in RTCM 2.3.
2055
2056       Type 14: GPS Time of Week
2057           Here are the payload members of a type 14 (GPS Time of Week)
2058           message:
2059
2060           Table 26. Reference Station Parameters
2061           ┌─────────┬─────────┬────────────────────────┐
2062Name     Type    │                        │
2063           │         │         │            Description │
2064           ├─────────┼─────────┼────────────────────────┤
2065           │week     │ integer │                        │
2066           │         │         │            GPS week    │
2067           │         │         │            (0-123).    │
2068           ├─────────┼─────────┼────────────────────────┤
2069           │hour     │ integer │                        │
2070           │         │         │            Hour of     │
2071           │         │         │            week        │
2072           │         │         │            (0-167).    │
2073           ├─────────┼─────────┼────────────────────────┤
2074           │leapsecs │ integer │                        │
2075           │         │         │            Leap        │
2076           │         │         │            Seconds     │
2077           │         │         │            (0-63).     │
2078           └─────────┴─────────┴────────────────────────┘
2079
2080           Here's an example:
2081
2082               {"class":"RTCM2","type":14,"station_id":652,"zcount":1657.2,
2083                       "seqnum":3,"length":1,"station_health":6,"week":601,"hour":109,
2084                       "leapsecs":15}
2085
2086       Type 16: Special Message
2087           Table 27. Special Message
2088           ┌────────┬────────┬────────────────────────┐
2089Name    Type   │                        │
2090           │        │        │            Description │
2091           ├────────┼────────┼────────────────────────┤
2092           │message │ string │                        │
2093           │        │        │            A text      │
2094           │        │        │            message     │
2095           │        │        │            sent by the │
2096           │        │        │            beacon      │
2097           │        │        │            operator.   │
2098           └────────┴────────┴────────────────────────┘
2099
2100       Type 31: Correction data
2101           One or more GLONASS satellite objects follow the header for type 1
2102           or type 9 messages. Here is the format:
2103
2104           Table 28. Satellite object
2105           ┌───────┬──────────┬────────────────────────────────┐
2106Name   Type     │                                │
2107           │       │          │            Description         │
2108           ├───────┼──────────┼────────────────────────────────┤
2109           │ident  │ integer  │                                │
2110           │       │          │            The PRN             │
2111           │       │          │            number of           │
2112           │       │          │            the                 │
2113           │       │          │            satellite           │
2114           │       │          │            for which           │
2115           │       │          │            this is             │
2116           │       │          │            correction          │
2117           │       │          │            data.               │
2118           ├───────┼──────────┼────────────────────────────────┤
2119           │udre   │ integer  │                                │
2120           │       │          │            User                │
2121           │       │          │            Differential        │
2122           │       │          │            Range Error         │
2123           │       │          │            (0-3). See          │
2124           │       │          │            the table           │
2125           │       │          │            following           │
2126           │       │          │            for values.         │
2127           ├───────┼──────────┼────────────────────────────────┤
2128           │change │ boolean  │                                │
2129           │       │          │            Change-of-ephemeris │
2130           │       │          │            bit.                │
2131           ├───────┼──────────┼────────────────────────────────┤
2132           │tod    │ uinteger │                                │
2133           │       │          │            Count of 30-second  │
2134           │       │          │            periods since the   │
2135           │       │          │            top of the hour.    │
2136           ├───────┼──────────┼────────────────────────────────┤
2137           │prc    │ real     │                                │
2138           │       │          │            The pseudorange     │
2139           │       │          │            error in meters for │
2140           │       │          │            this satellite as   │
2141           │       │          │            measured by the     │
2142           │       │          │            beacon reference    │
2143           │       │          │            receiver at the     │
2144           │       │          │            epoch indicated by  │
2145           │       │          │            the z_count in the  │
2146           │       │          │            parent record.      │
2147           ├───────┼──────────┼────────────────────────────────┤
2148           │rrc    │ real     │                                │
2149           │       │          │            The rate of change  │
2150           │       │          │            of pseudorange      │
2151           │       │          │            error in meters/sec │
2152           │       │          │            for this satellite  │
2153           │       │          │            as measured by the  │
2154           │       │          │            beacon reference    │
2155           │       │          │            receiver at the     │
2156           │       │          │            epoch indicated by  │
2157           │       │          │            the z_count field   │
2158           │       │          │            in the parent       │
2159           │       │          │            record. This is     │
2160           │       │          │            used to calculate   │
2161           │       │          │            pseudorange errors  │
2162           │       │          │            at other epochs, if │
2163           │       │          │            required by the GPS │
2164           │       │          │            receiver.           │
2165           └───────┴──────────┴────────────────────────────────┘
2166
2167           Here's an example:
2168
2169               {"class":"RTCM2","type":31,"station_id":652,"zcount":1642.2,
2170                   "seqnum":0,"length":14,"station_health":6,
2171                   "satellites":[
2172                       {"ident":5,"udre":0,"change":false,"tod":0,"prc":132.360,"rrc":0.000},
2173                       {"ident":15,"udre":0,"change":false,"tod":0,"prc":134.840,"rrc":0.002},
2174                       {"ident":14,"udre":0,"change":false,"tod":0,"prc":141.520,"rrc":0.000},
2175                       {"ident":6,"udre":0,"change":false,"tod":0,"prc":127.000,"rrc":0.000},
2176                       {"ident":21,"udre":0,"change":false,"tod":0,"prc":128.780,"rrc":0.000},
2177                       {"ident":22,"udre":0,"change":false,"tod":0,"prc":125.260,"rrc":0.002},
2178                       {"ident":20,"udre":0,"change":false,"tod":0,"prc":117.280,"rrc":-0.004},
2179                       {"ident":16,"udre":0,"change":false,"tod":17,"prc":113.460,"rrc":0.018}
2180               ]}
2181

RTCM3 DUMP FORMAT

2183       The support for RTCM104v3 dumping is incomplete and buggy. Do not
2184       attempt to use it for production! Anyone interested in it should read
2185       the source code.
2186

AIS DUMP FORMATS

2188       AIS support is an extension. It may not be present if your instance of
2189       gpsd has been built with a restricted feature set.
2190
2191       AIS packets are dumped as JSON objects with class "AIS". Each AIS
2192       report object contains a "type" field giving the AIS message type and a
2193       "scaled" field telling whether the remainder of the fields are dumped
2194       in scaled or unscaled form. (These will be emitted before any
2195       type-specific fields.) It will also contain a "device" field naming the
2196       data source. Other fields have names and types as specified in the
2197       AIVDM/AIVDO Protocol Decoding document on the GPSD project website;
2198       each message field table may be directly interpreted as a specification
2199       for the members of the corresponding JSON object type.
2200
2201       By default, certain scaling and conversion operations are performed for
2202       JSON output. Latitudes and longitudes are scaled to decimal degrees
2203       rather than the native AIS unit of 1/10000th of a minute of arc. Ship
2204       (but not air) speeds are scaled to knots rather than tenth-of-knot
2205       units. Rate of turn may appear as "nan" if is unavailable, or as one of
2206       the strings "fastright" or "fastleft" if it is out of the AIS encoding
2207       range; otherwise it is quadratically mapped back to the turn sensor
2208       number in degrees per minute. Vessel draughts are converted to decimal
2209       meters rather than native AIS decimeters. Various other scaling
2210       conversions are described in "AIVDM/AIVDO Protocol Decoding".
2211

SUBFRAME DUMP FORMATS

2213       Subframe support is always compiled into gpsd but many GPSes do not
2214       output subframe data or the gpsd driver may not support subframes.
2215
2216       Subframe packets are dumped as JSON objects with class "SUBFRAME". Each
2217       subframe report object contains a "frame" field giving the subframe
2218       number, a "tSV" field for the transmitting satellite number, a "TOW17"
2219       field containing the 17 MSBs of the start of the next 12-second message
2220       and a "scaled" field telling whether the remainder of the fields are
2221       dumped in scaled or unscaled form. It will also contain a "device"
2222       field naming the data source. Each SUBFRAME object will have a
2223       sub-object specific to that subframe page type. Those sub-object fields
2224       have names and types similar to those specified in the IS-GPS-200E
2225       document; each message field table may be directly interpreted as a
2226       specification for the members of the corresponding JSON object type.
2227

SEE ALSO

2229       gpsd(8), libgps(3),
2230

AUTHOR

2232       The protocol was designed and documented by Eric S. Raymond.
2233

NOTES

2235        1. Radio Technical Commission for Maritime Services
2236           http://www.rtcm.org/
2237
2238        2. table of leap second corrections
2239           ftp://maia.usno.navy.mil/ser7/tai-utc.dat
2240
2241
2242
2243The GPSD Project                 23 June 2019                     GPSD_JSON(5)
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