1GPSD_JSON(5) GPSD Documentation GPSD_JSON(5)
2
6 gpsd_json - gpsd request/response protocol
7
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 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 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 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 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 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 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 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 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
61 Here are the core-protocol responses:
62 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 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 Table 1. TPV object
80 ┌────────────┬─────────┬──────────────┬─────────────────────┐
81 │Name │ 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 │altHAE │ No │ numeric │ Altitude, height │
113 │ │ │ │ above allipsoid, │
114 │ │ │ │ in meters. │
115 │ │ │ │ Probably WGS84. │
116 │ │ │ │ Present if mode │
117 │ │ │ │ is 3. │
118 ├────────────┼─────────┼──────────────┼─────────────────────┤
119 │altMSL │ No │ numeric │ MSL Altitude in │
120 │ │ │ │ meters. The │
121 │ │ │ │ geoid used is │
122 │ │ │ │ rarely specified │
123 │ │ │ │ and is often │
124 │ │ │ │ inacurate. See │
125 │ │ │ │ the comments │
126 │ │ │ │ below on │
127 │ │ │ │ geoidSep. │
128 │ │ │ │ Present if │
129 │ │ │ │ mode is 3. │
130 │ │ │ │ altMSL is altHAE │
131 │ │ │ │ - geoidSep. │
132 ├────────────┼─────────┼──────────────┼─────────────────────┤
133 │alt │ No │ numeric │ Deprecated. │
134 │ │ │ │ Undefined. Use │
135 │ │ │ │ altHAE or │
136 │ │ │ │ altMSL. │
137 ├────────────┼─────────┼──────────────┼─────────────────────┤
138 │climb │ No │ numeric │ Climb (positive) │
139 │ │ │ │ or sink │
140 │ │ │ │ (negative) rate, │
141 │ │ │ │ meters per │
142 │ │ │ │ second. │
143 ├────────────┼─────────┼──────────────┼─────────────────────┤
144 │datum │ No │ string │ Current datum. │
145 ├────────────┼─────────┼──────────────┼─────────────────────┤
146 │depth │ No │ numeric │ Depth in meters. │
147 │ │ │ │ Probably depth │
148 │ │ │ │ below the keel.. │
149 ├────────────┼─────────┼──────────────┼─────────────────────┤
150 │dgpsAge │ No │ numeric │ Age of DGPS │
151 │ │ │ │ data. In seconds │
152 ├────────────┼─────────┼──────────────┼─────────────────────┤
153 │dgpsSta │ No │ numeric │ Station of DGPS │
154 │ │ │ │ data. │
155 ├────────────┼─────────┼──────────────┼─────────────────────┤
156 │epc │ No │ numeric │ Estimated climb │
157 │ │ │ │ error in meters │
158 │ │ │ │ per second. │
159 │ │ │ │ Present │
160 │ │ │ │ if │
161 │ │ │ │ consecutive 3D │
162 │ │ │ │ fixes. │
163 ├────────────┼─────────┼──────────────┼─────────────────────┤
164 │epd │ No │ numeric │ Estimated track │
165 │ │ │ │ (direction) │
166 │ │ │ │ error in │
167 │ │ │ │ degrees. Present │
168 │ │ │ │ if │
169 │ │ │ │ consecutive │
170 │ │ │ │ 2D fixes. │
171 ├────────────┼─────────┼──────────────┼─────────────────────┤
172 │eph │ No │ numeric │ Estimated │
173 │ │ │ │ horizontal Position │
174 │ │ │ │ (2D) Error in │
175 │ │ │ │ meters. │
176 │ │ │ │ Also known │
177 │ │ │ │ as Estimated │
178 │ │ │ │ Position Error │
179 │ │ │ │ (epe). Present │
180 │ │ │ │ if mode is │
181 │ │ │ │ 2D or 3D and DOPs │
182 │ │ │ │ can be calculated │
183 │ │ │ │ from the satellite │
184 │ │ │ │ view. │
185 ├────────────┼─────────┼──────────────┼─────────────────────┤
186 │eps │ No │ numeric │ Estimated speed │
187 │ │ │ │ error in meters per │
188 │ │ │ │ second. Present │
189 │ │ │ │ for │
190 │ │ │ │ consecutive 2D or │
191 │ │ │ │ 3D fixes. │
192 ├────────────┼─────────┼──────────────┼─────────────────────┤
193 │ept │ No │ numeric │ Estimated timestamp │
194 │ │ │ │ error in seconds. │
195 │ │ │ │ Present if │
196 │ │ │ │ time is present. │
197 ├────────────┼─────────┼──────────────┼─────────────────────┤
198 │epx │ No │ numeric │ Longitude error │
199 │ │ │ │ estimate in meters. │
200 │ │ │ │ Present │
201 │ │ │ │ if mode is │
202 │ │ │ │ 2D or 3D and DOPs │
203 │ │ │ │ can be calculated │
204 │ │ │ │ from the satellite │
205 │ │ │ │ view. │
206 ├────────────┼─────────┼──────────────┼─────────────────────┤
207 │epy │ No │ numeric │ Latitude error │
208 │ │ │ │ estimate in meters. │
209 │ │ │ │ Present │
210 │ │ │ │ if mode is │
211 │ │ │ │ 2 or 3 and DOPs can │
212 │ │ │ │ be calculated from │
213 │ │ │ │ the satellite │
214 │ │ │ │ view. │
215 ├────────────┼─────────┼──────────────┼─────────────────────┤
216 │epv │ No │ numeric │ Estimated vertical │
217 │ │ │ │ error in meters. │
218 │ │ │ │ Present │
219 │ │ │ │ if mode is │
220 │ │ │ │ 3 and DOPs can be │
221 │ │ │ │ calculated from the │
222 │ │ │ │ satellite │
223 │ │ │ │ view. │
224 ├────────────┼─────────┼──────────────┼─────────────────────┤
225 │lat │ No │ numeric │ Latitude in │
226 │ │ │ │ degrees: +/- │
227 │ │ │ │ signifies │
228 │ │ │ │ North/South. │
229 │ │ │ │ Present │
230 │ │ │ │ when mode │
231 │ │ │ │ is 2 or 3. │
232 ├────────────┼─────────┼──────────────┼─────────────────────┤
233 │leapseconds │ integer │ Current leap │ │
234 │ │ │ seconds. │ │
235 ├────────────┼─────────┼──────────────┼─────────────────────┤
236 │lon │ No │ numeric │ Longitude in │
237 │ │ │ │ degrees: +/- │
238 │ │ │ │ signifies │
239 │ │ │ │ East/West. Present │
240 │ │ │ │ when mode │
241 │ │ │ │ is 2 or 3. │
242 ├────────────┼─────────┼──────────────┼─────────────────────┤
243 │track │ No │ numeric │ Course over ground, │
244 │ │ │ │ degrees from true │
245 │ │ │ │ north. │
246 ├────────────┼─────────┼──────────────┼─────────────────────┤
247 │magtrack │ No │ numeric │ Course over ground, │
248 │ │ │ │ degrees magnetic. │
249 ├────────────┼─────────┼──────────────┼─────────────────────┤
250 │magvar │ No │ numeric │ Magnetic variation, │
251 │ │ │ │ degrees. Also │
252 │ │ │ │ known as the │
253 │ │ │ │ magnetic │
254 │ │ │ │ declination (the │
255 │ │ │ │ direction of the │
256 │ │ │ │ horizontal │
257 │ │ │ │ component of the │
258 │ │ │ │ magnetic field │
259 │ │ │ │ measured clockwise │
260 │ │ │ │ from north) in │
261 │ │ │ │ degrees, Positive │
262 │ │ │ │ is West variation. │
263 │ │ │ │ Negative is East │
264 │ │ │ │ variation. │
265 ├────────────┼─────────┼──────────────┼─────────────────────┤
266 │speed │ No │ numeric │ Speed over ground, │
267 │ │ │ │ meters per second. │
268 ├────────────┼─────────┼──────────────┼─────────────────────┤
269 │ecefx │ No │ numeric │ ECEF X position in │
270 │ │ │ │ meters. │
271 ├────────────┼─────────┼──────────────┼─────────────────────┤
272 │ecefy │ No │ numeric │ ECEF Y position in │
273 │ │ │ │ meters. │
274 ├────────────┼─────────┼──────────────┼─────────────────────┤
275 │ecefz │ No │ numeric │ ECEF Z position in │
276 │ │ │ │ meters. │
277 ├────────────┼─────────┼──────────────┼─────────────────────┤
278 │ecefpAcc │ No │ numeric │ ECEF position error │
279 │ │ │ │ in meters. │
280 ├────────────┼─────────┼──────────────┼─────────────────────┤
281 │ecefvx │ No │ numeric │ ECEF X velocity in │
282 │ │ │ │ meters/second. │
283 ├────────────┼─────────┼──────────────┼─────────────────────┤
284 │ecefvy │ No │ numeric │ ECEF Y velocity in │
285 │ │ │ │ meters/second. │
286 ├────────────┼─────────┼──────────────┼─────────────────────┤
287 │ecefvz │ No │ numeric │ ECEF Z velocity in │
288 │ │ │ │ meters/second. │
289 ├────────────┼─────────┼──────────────┼─────────────────────┤
290 │ecefvAcc │ No │ numeric │ ECEF velocity error │
291 │ │ │ │ in meters/second. │
292 ├────────────┼─────────┼──────────────┼─────────────────────┤
293 │sep │ No │ numeric │ Estimated Spherical │
294 │ │ │ │ (3D) Position Error │
295 │ │ │ │ in meters. │
296 │ │ │ │ Present if │
297 │ │ │ │ mode is 3D and DOPs │
298 │ │ │ │ can be calculated │
299 │ │ │ │ from the satellite │
300 │ │ │ │ view. │
301 │ │ │ │ Assumed to be 95% │
302 │ │ │ │ confidence, but │
303 │ │ │ │ many GPS do not │
304 │ │ │ │ specify. │
305 ├────────────┼─────────┼──────────────┼─────────────────────┤
306 │relN │ No │ numeric │ North component of │
307 │ │ │ │ relative position │
308 │ │ │ │ vector in meters. │
309 ├────────────┼─────────┼──────────────┼─────────────────────┤
310 │relE │ No │ numeric │ East component of │
311 │ │ │ │ relative position │
312 │ │ │ │ vector in meters. │
313 ├────────────┼─────────┼──────────────┼─────────────────────┤
314 │relD │ No │ numeric │ Down component of │
315 │ │ │ │ relative position │
316 │ │ │ │ vector in meters. │
317 ├────────────┼─────────┼──────────────┼─────────────────────┤
318 │velN │ No │ numeric │ North velocity │
319 │ │ │ │ component in │
320 │ │ │ │ meters. │
321 ├────────────┼─────────┼──────────────┼─────────────────────┤
322 │velE │ No │ numeric │ wEast velocity │
323 │ │ │ │ component in │
324 │ │ │ │ meters. │
325 ├────────────┼─────────┼──────────────┼─────────────────────┤
326 │velD │ No │ numeric │ Down velocity │
327 │ │ │ │ component in │
328 │ │ │ │ meters. │
329 ├────────────┼─────────┼──────────────┼─────────────────────┤
330 │geoidSep │ No │ numeric │ Geoid separation is │
331 │ │ │ │ the difference │
332 │ │ │ │ between the WGS84 │
333 │ │ │ │ reference elipsoid │
334 │ │ │ │ and the geoid (Mean │
335 │ │ │ │ Sea Level) in │
336 │ │ │ │ meters. Almost no │
337 │ │ │ │ GNSS receiver │
338 │ │ │ │ specifies how they │
339 │ │ │ │ compute their │
340 │ │ │ │ geoid. gpsd │
341 │ │ │ │ interpolates the │
342 │ │ │ │ geoid from a 5x5 │
343 │ │ │ │ degree table of │
344 │ │ │ │ EGM2008 values when │
345 │ │ │ │ the receiver does │
346 │ │ │ │ not supply a geoid │
347 │ │ │ │ separation. The │
348 │ │ │ │ gpsd computed │
349 │ │ │ │ geoidSep is usually │
350 │ │ │ │ within one meter of │
351 │ │ │ │ the "true" value, │
352 │ │ │ │ but can be off as │
353 │ │ │ │ much as 12 meters. │
354 └────────────┴─────────┴──────────────┴─────────────────────┘
355 When the C client library parses a response of this kind, it will
356 assert validity bits in the top-level set member for each field
357 actually received; see gps.h for bitmask names and values.
358 Invalid or known floating point values will be set to NAN.
360 Here's an example:
362 {"class":"TPV","device":"/dev/pts/1",
364 "time":"2005-06-08T10:34:48.283Z","ept":0.005,
365 "lat":46.498293369,"lon":7.567411672,"alt":1343.127,
366 "eph":36.000,"epv":32.321,
367 "track":10.3788,"speed":0.091,"climb":-0.085,"mode":3}
368 SKY
370 A SKY object reports a sky view of the GPS satellite positions. If
371 there is no GPS device available, or no skyview has been reported
372 yet, only the "class" field will reliably be present.
373 Table 2. SKY object
375 ┌───────────┬─────────┬─────────┬─────────────────────┐
376 │Name │ Always? │ Type │ Description │
377 ├───────────┼─────────┼─────────┼─────────────────────┤
378 │class │ Yes │ string │ Fixed: "SKY" │
379 ├───────────┼─────────┼─────────┼─────────────────────┤
380 │device │ No │ string │ Name of │
381 │ │ │ │ originating │
382 │ │ │ │ device │
383 ├───────────┼─────────┼─────────┼─────────────────────┤
384 │time │ No │ string │ Time/date stamp │
385 │ │ │ │ in ISO8601 │
386 │ │ │ │ format, UTC. May │
387 │ │ │ │ have a │
388 │ │ │ │ fractional part │
389 │ │ │ │ of up to .001sec │
390 │ │ │ │ precision. │
391 ├───────────┼─────────┼─────────┼─────────────────────┤
392 │gdop │ No │ numeric │ Geometric │
393 │ │ │ │ (hyperspherical) │
394 │ │ │ │ dilution of │
395 │ │ │ │ precision, a │
396 │ │ │ │ combination │
397 │ │ │ │ of PDOP and │
398 │ │ │ │ TDOP. A │
399 │ │ │ │ dimensionless │
400 │ │ │ │ factor which │
401 │ │ │ │ should │
402 │ │ │ │ be multiplied by │
403 │ │ │ │ a base UERE │
404 │ │ │ │ to get │
405 │ │ │ │ an error │
406 │ │ │ │ estimate. │
407 ├───────────┼─────────┼─────────┼─────────────────────┤
408 │hdop │ No │ numeric │ Horizontal dilution │
409 │ │ │ │ of precision, a │
410 │ │ │ │ dimensionless │
411 │ │ │ │ factor which should │
412 │ │ │ │ be multiplied by a │
413 │ │ │ │ base UERE to get a │
414 │ │ │ │ circular error │
415 │ │ │ │ estimate. │
416 ├───────────┼─────────┼─────────┼─────────────────────┤
417 │pdop │ No │ numeric │ Position │
418 │ │ │ │ (spherical/3D) │
419 │ │ │ │ dilution of │
420 │ │ │ │ precision, a │
421 │ │ │ │ dimensionless │
422 │ │ │ │ factor which should │
423 │ │ │ │ be multiplied by a │
424 │ │ │ │ base UERE to get an │
425 │ │ │ │ error estimate. │
426 ├───────────┼─────────┼─────────┼─────────────────────┤
427 │tdop │ No │ numeric │ Time dilution of │
428 │ │ │ │ precision, a │
429 │ │ │ │ dimensionless │
430 │ │ │ │ factor which should │
431 │ │ │ │ be multiplied by a │
432 │ │ │ │ base UERE to get an │
433 │ │ │ │ error estimate. │
434 ├───────────┼─────────┼─────────┼─────────────────────┤
435 │vdop │ No │ numeric │ Vertical (altitude) │
436 │ │ │ │ dilution of │
437 │ │ │ │ precision, a │
438 │ │ │ │ dimensionless │
439 │ │ │ │ factor which should │
440 │ │ │ │ be multiplied by a │
441 │ │ │ │ base UERE to get an │
442 │ │ │ │ error estimate. │
443 ├───────────┼─────────┼─────────┼─────────────────────┤
444 │xdop │ No │ numeric │ Longitudinal │
445 │ │ │ │ dilution of │
446 │ │ │ │ precision, a │
447 │ │ │ │ dimensionless │
448 │ │ │ │ factor which should │
449 │ │ │ │ be multiplied by a │
450 │ │ │ │ base UERE to get an │
451 │ │ │ │ error estimate. │
452 ├───────────┼─────────┼─────────┼─────────────────────┤
453 │ydop │ No │ numeric │ Latitudinal │
454 │ │ │ │ dilution of │
455 │ │ │ │ precision, a │
456 │ │ │ │ dimensionless │
457 │ │ │ │ factor which should │
458 │ │ │ │ be multiplied by a │
459 │ │ │ │ base UERE to get an │
460 │ │ │ │ error estimate. │
461 ├───────────┼─────────┼─────────┼─────────────────────┤
462 │satellites │ Yes │ list │ List of satellite │
463 │ │ │ │ objects in skyview │
464 └───────────┴─────────┴─────────┴─────────────────────┘
465 Many devices compute dilution of precision factors but do not
466 include them in their reports. Many that do report DOPs report only
467 HDOP, two-dimensional circular error. gpsd always passes through
468 whatever the device actually reports, then attempts to fill in
469 other DOPs by calculating the appropriate determinants in a
470 covariance matrix based on the satellite view. DOPs may be missing
471 if some of these determinants are singular. It can even happen that
472 the device reports an error estimate in meters when the
473 corresponding DOP is unavailable; some devices use more
474 sophisticated error modeling than the covariance calculation.
475 The satellite list objects have the following elements:
477 Table 3. Satellite object
479 ┌───────┬─────────┬─────────┬────────────────────┐
480 │Name │ Always? │ Type │ Description │
481 ├───────┼─────────┼─────────┼────────────────────┤
482 │PRN │ Yes │ numeric │ PRN ID of the │
483 │ │ │ │ satellite. 1-63 │
484 │ │ │ │ are GNSS │
485 │ │ │ │ satellites, │
486 │ │ │ │ 64-96 are │
487 │ │ │ │ GLONASS │
488 │ │ │ │ satellites, │
489 │ │ │ │ 100-164 are SBAS │
490 │ │ │ │ satellites │
491 ├───────┼─────────┼─────────┼────────────────────┤
492 │az │ No │ numeric │ Azimuth, degrees │
493 │ │ │ │ from true north. │
494 ├───────┼─────────┼─────────┼────────────────────┤
495 │el │ No │ numeric │ Elevation in │
496 │ │ │ │ degrees. │
497 ├───────┼─────────┼─────────┼────────────────────┤
498 │ss │ No │ numeric │ Signal to Noise │
499 │ │ │ │ ratio in dBHz. │
500 ├───────┼─────────┼─────────┼────────────────────┤
501 │used │ Yes │ boolean │ Used in current │
502 │ │ │ │ solution? │
503 │ │ │ │ (SBAS/WAAS/EGNOS │
504 │ │ │ │ satellites may │
505 │ │ │ │ be flagged used │
506 │ │ │ │ if the solution │
507 │ │ │ │ has corrections │
508 │ │ │ │ from them, but │
509 │ │ │ │ not all drivers │
510 │ │ │ │ make this │
511 │ │ │ │ information │
512 │ │ │ │ available.) │
513 ├───────┼─────────┼─────────┼────────────────────┤
514 │gnssid │ No │ numeric │ The GNSS ID, as │
515 │ │ │ │ defined by │
516 │ │ │ │ u-blox, not │
517 │ │ │ │ NMEA. 0=GPS, │
518 │ │ │ │ 2=Galileo, │
519 │ │ │ │ 3=Beidou, │
520 │ │ │ │ 5=QZSS, │
521 │ │ │ │ 6-GLONASS. │
522 ├───────┼─────────┼─────────┼────────────────────┤
523 │svid │ no │ numeric │ The satellite ID │
524 │ │ │ │ within its │
525 │ │ │ │ constellation. As │
526 │ │ │ │ defined │
527 │ │ │ │ by u-blox, │
528 │ │ │ │ not NMEA). │
529 ├───────┼─────────┼─────────┼────────────────────┤
530 │sigid │ no │ numeric │ The signal ID of │
531 │ │ │ │ this signal. As │
532 │ │ │ │ defined by u-blox, │
533 │ │ │ │ not │
534 │ │ │ │ NMEA. See │
535 │ │ │ │ u-blox doc for │
536 │ │ │ │ details. │
537 ├───────┼─────────┼─────────┼────────────────────┤
538 │freqid │ no │ numeric │ For GLONASS │
539 │ │ │ │ satellites only: │
540 │ │ │ │ the frequency ID │
541 │ │ │ │ of the signal. As │
542 │ │ │ │ defined by u-blox, │
543 │ │ │ │ range 0 to 13. │
544 │ │ │ │ The freqid is the │
545 │ │ │ │ frequency slot │
546 │ │ │ │ plus 7. │
547 ├───────┼─────────┼─────────┼────────────────────┤
548 │health │ no │ numeric │ The health of this │
549 │ │ │ │ satellite. 0 is │
550 │ │ │ │ unknown, 1 is OK, │
551 │ │ │ │ and 2 is │
552 │ │ │ │ unhealthy. │
553 └───────┴─────────┴─────────┴────────────────────┘
554 Note that satellite objects do not have a "class" field, as they
555 are never shipped outside of a SKY object.
556 When the C client library parses a SKY response, it will assert the
558 SATELLITE_SET bit in the top-level set member.
559 Here's an example:
561 {"class":"SKY","device":"/dev/pts/1",
563 "time":"2005-07-08T11:28:07.114Z",
564 "xdop":1.55,"hdop":1.24,"pdop":1.99,
565 "satellites":[
566 {"PRN":23,"el":6,"az":84,"ss":0,"used":false},
567 {"PRN":28,"el":7,"az":160,"ss":0,"used":false},
568 {"PRN":8,"el":66,"az":189,"ss":44,"used":true},
569 {"PRN":29,"el":13,"az":273,"ss":0,"used":false},
570 {"PRN":10,"el":51,"az":304,"ss":29,"used":true},
571 {"PRN":4,"el":15,"az":199,"ss":36,"used":true},
572 {"PRN":2,"el":34,"az":241,"ss":43,"used":true},
573 {"PRN":27,"el":71,"az":76,"ss":43,"used":true}]}
574 GST
576 A GST object is a pseudorange noise report.
577 Table 4. GST object
579 ┌───────┬─────────┬─────────┬──────────────────┐
580 │Name │ Always? │ Type │ Description │
581 ├───────┼─────────┼─────────┼──────────────────┤
582 │class │ Yes │ string │ Fixed: "GST" │
583 ├───────┼─────────┼─────────┼──────────────────┤
584 │device │ No │ string │ Name of │
585 │ │ │ │ originating │
586 │ │ │ │ device │
587 ├───────┼─────────┼─────────┼──────────────────┤
588 │time │ No │ string │ Time/date stamp │
589 │ │ │ │ in ISO8601 │
590 │ │ │ │ format, UTC. May │
591 │ │ │ │ have a │
592 │ │ │ │ fractional part │
593 │ │ │ │ of up to .001sec │
594 │ │ │ │ precision. │
595 ├───────┼─────────┼─────────┼──────────────────┤
596 │rms │ No │ numeric │ Value of the │
597 │ │ │ │ standard │
598 │ │ │ │ deviation of the │
599 │ │ │ │ range inputs to │
600 │ │ │ │ the navigation │
601 │ │ │ │ process (range │
602 │ │ │ │ inputs include │
603 │ │ │ │ pseudoranges and │
604 │ │ │ │ DGPS │
605 │ │ │ │ corrections). │
606 ├───────┼─────────┼─────────┼──────────────────┤
607 │major │ No │ numeric │ Standard │
608 │ │ │ │ deviation of │
609 │ │ │ │ semi-major axis │
610 │ │ │ │ of error │
611 │ │ │ │ ellipse, in │
612 │ │ │ │ meters. │
613 ├───────┼─────────┼─────────┼──────────────────┤
614 │minor │ No │ numeric │ Standard │
615 │ │ │ │ deviation of │
616 │ │ │ │ semi-minor axis │
617 │ │ │ │ of error │
618 │ │ │ │ ellipse, in │
619 │ │ │ │ meters. │
620 ├───────┼─────────┼─────────┼──────────────────┤
621 │orient │ No │ numeric │ Orientation of │
622 │ │ │ │ semi-major axis │
623 │ │ │ │ of error │
624 │ │ │ │ ellipse, in │
625 │ │ │ │ degrees from │
626 │ │ │ │ true north. │
627 ├───────┼─────────┼─────────┼──────────────────┤
628 │lat │ No │ numeric │ Standard │
629 │ │ │ │ deviation of │
630 │ │ │ │ latitude error, │
631 │ │ │ │ in meters. │
632 ├───────┼─────────┼─────────┼──────────────────┤
633 │lon │ No │ numeric │ Standard │
634 │ │ │ │ deviation of │
635 │ │ │ │ longitude error, │
636 │ │ │ │ in meters. │
637 ├───────┼─────────┼─────────┼──────────────────┤
638 │alt │ No │ numeric │ Standard │
639 │ │ │ │ deviation of │
640 │ │ │ │ altitude error, │
641 │ │ │ │ in meters. │
642 └───────┴─────────┴─────────┴──────────────────┘
643 Here's an example:
644 {"class":"GST","device":"/dev/ttyUSB0",
646 "time":"2010-12-07T10:23:07.096Z","rms":2.440,
647 "major":1.660,"minor":1.120,"orient":68.989,
648 "lat":1.600,"lon":1.200,"alt":2.520}
649 ATT
651 An ATT object is a vehicle-attitude report. It is returned by
652 digital-compass and gyroscope sensors; depending on device, it may
653 include: heading, pitch, roll, yaw, gyroscope, and magnetic-field
654 readings. Because such sensors are often bundled as part of
655 marine-navigation systems, the ATT response may also include water
656 depth.
657 The "class" and "mode" fields will reliably be present. Others may
659 be reported or not depending on the specific device type.
660 Table 5. ATT object
662 ┌─────────┬─────────┬─────────┬──────────────────┐
663 │Name │ Always? │ Type │ Description │
664 ├─────────┼─────────┼─────────┼──────────────────┤
665 │class │ Yes │ string │ Fixed: "ATT" │
666 ├─────────┼─────────┼─────────┼──────────────────┤
667 │device │ Yes │ string │ Name of │
668 │ │ │ │ originating │
669 │ │ │ │ device │
670 ├─────────┼─────────┼─────────┼──────────────────┤
671 │time │ No │ string │ Time/date stamp │
672 │ │ │ │ in ISO8601 │
673 │ │ │ │ format, UTC. May │
674 │ │ │ │ have a │
675 │ │ │ │ fractional part │
676 │ │ │ │ of up to .001sec │
677 │ │ │ │ precision. │
678 ├─────────┼─────────┼─────────┼──────────────────┤
679 │heading │ No │ numeric │ Heading, degrees │
680 │ │ │ │ from true north. │
681 ├─────────┼─────────┼─────────┼──────────────────┤
682 │mag_st │ No │ string │ Magnetometer │
683 │ │ │ │ status. │
684 ├─────────┼─────────┼─────────┼──────────────────┤
685 │pitch │ No │ numeric │ Pitch in │
686 │ │ │ │ degrees. │
687 ├─────────┼─────────┼─────────┼──────────────────┤
688 │pitch_st │ No │ string │ Pitch sensor │
689 │ │ │ │ status. │
690 ├─────────┼─────────┼─────────┼──────────────────┤
691 │yaw │ No │ numeric │ Yaw in degrees │
692 ├─────────┼─────────┼─────────┼──────────────────┤
693 │yaw_st │ No │ string │ Yaw sensor │
694 │ │ │ │ status. │
695 ├─────────┼─────────┼─────────┼──────────────────┤
696 │roll │ No │ numeric │ Roll in degrees. │
697 ├─────────┼─────────┼─────────┼──────────────────┤
698 │roll_st │ No │ string │ Roll sensor │
699 │ │ │ │ status. │
700 ├─────────┼─────────┼─────────┼──────────────────┤
701 │dip │ No │ numeric │ Local magnetic │
702 │ │ │ │ inclination, │
703 │ │ │ │ degrees, │
704 │ │ │ │ positive when │
705 │ │ │ │ the magnetic │
706 │ │ │ │ field points │
707 │ │ │ │ downward (into │
708 │ │ │ │ the Earth). │
709 ├─────────┼─────────┼─────────┼──────────────────┤
710 │mag_len │ No │ numeric │ Scalar magnetic │
711 │ │ │ │ field strength. │
712 ├─────────┼─────────┼─────────┼──────────────────┤
713 │mag_x │ No │ numeric │ X component of │
714 │ │ │ │ magnetic field │
715 │ │ │ │ strength. │
716 ├─────────┼─────────┼─────────┼──────────────────┤
717 │mag_y │ No │ numeric │ Y component of │
718 │ │ │ │ magnetic field │
719 │ │ │ │ strength. │
720 ├─────────┼─────────┼─────────┼──────────────────┤
721 │mag_z │ No │ numeric │ Z component of │
722 │ │ │ │ magnetic field │
723 │ │ │ │ strength. │
724 ├─────────┼─────────┼─────────┼──────────────────┤
725 │acc_len │ No │ numeric │ Scalar │
726 │ │ │ │ acceleration. │
727 ├─────────┼─────────┼─────────┼──────────────────┤
728 │acc_x │ No │ numeric │ X component of │
729 │ │ │ │ acceleration. │
730 ├─────────┼─────────┼─────────┼──────────────────┤
731 │acc_y │ No │ numeric │ Y component of │
732 │ │ │ │ acceleration. │
733 ├─────────┼─────────┼─────────┼──────────────────┤
734 │acc_z │ No │ numeric │ Z component of │
735 │ │ │ │ acceleration. │
736 ├─────────┼─────────┼─────────┼──────────────────┤
737 │gyro_x │ No │ numeric │ X component of │
738 │ │ │ │ acceleration. │
739 ├─────────┼─────────┼─────────┼──────────────────┤
740 │gyro_y │ No │ numeric │ Y component of │
741 │ │ │ │ acceleration. │
742 ├─────────┼─────────┼─────────┼──────────────────┤
743 │depth │ No │ numeric │ Water depth in │
744 │ │ │ │ meters. │
745 ├─────────┼─────────┼─────────┼──────────────────┤
746 │temp │ No │ numeric │ Temperature at │
747 │ │ │ │ sensor, degrees │
748 │ │ │ │ centigrade. │
749 └─────────┴─────────┴─────────┴──────────────────┘
750 The heading, pitch, and roll status codes (if present) vary by
751 device. For the TNT Revolution digital compasses, they are coded as
752 follows:
753 Table 6. Device flags
755 ┌─────┬────────────────────────────┐
756 │Code │ Description │
757 ├─────┼────────────────────────────┤
758 │C │ magnetometer calibration │
759 │ │ alarm │
760 ├─────┼────────────────────────────┤
761 │L │ low alarm │
762 ├─────┼────────────────────────────┤
763 │M │ low warning │
764 ├─────┼────────────────────────────┤
765 │N │ normal │
766 ├─────┼────────────────────────────┤
767 │O │ high warning │
768 ├─────┼────────────────────────────┤
769 │P │ high alarm │
770 ├─────┼────────────────────────────┤
771 │V │ magnetometer voltage level │
772 │ │ alarm │
773 └─────┴────────────────────────────┘
774 When the C client library parses a response of this kind, it will
775 assert ATT_IS.
776 Here's an example:
778 {"class":"ATT","time":1270938096.843,
780 "heading":14223.00,"mag_st":"N",
781 "pitch":169.00,"pitch_st":"N", "roll":-43.00,"roll_st":"N",
782 "dip":13641.000,"mag_x":2454.000}
783 And here are the commands:
785 ?VERSION;
787 Returns an object with the following attributes:
788 Table 7. VERSION object
790 ┌────────────┬─────────┬─────────┬──────────────────┐
791 │Name │ Always? │ Type │ Description │
792 ├────────────┼─────────┼─────────┼──────────────────┤
793 │class │ Yes │ string │ Fixed: "VERSION" │
794 ├────────────┼─────────┼─────────┼──────────────────┤
795 │release │ Yes │ string │ Public release │
796 │ │ │ │ level │
797 ├────────────┼─────────┼─────────┼──────────────────┤
798 │rev │ Yes │ string │ Internal │
799 │ │ │ │ revision-control │
800 │ │ │ │ level. │
801 ├────────────┼─────────┼─────────┼──────────────────┤
802 │proto_major │ Yes │ numeric │ API major │
803 │ │ │ │ revision level. │
804 ├────────────┼─────────┼─────────┼──────────────────┤
805 │proto_minor │ Yes │ numeric │ API minor │
806 │ │ │ │ revision level. │
807 ├────────────┼─────────┼─────────┼──────────────────┤
808 │remote │ No │ string │ URL of the │
809 │ │ │ │ remote daemon │
810 │ │ │ │ reporting this │
811 │ │ │ │ version. If │
812 │ │ │ │ empty, │
813 │ │ │ │ this is the │
814 │ │ │ │ version of the │
815 │ │ │ │ local daemon. │
816 └────────────┴─────────┴─────────┴──────────────────┘
817 The daemon ships a VERSION response to each client when the client
818 first connects to it.
819 When the C client library parses a response of this kind, it will
821 assert the VERSION_SET bit in the top-level set member.
822 Here's an example:
824 {"class":"VERSION","version":"2.40dev",
826 "rev":"06f62e14eae9886cde907dae61c124c53eb1101f",
827 "proto_major":3,"proto_minor":1
828 }
829 ?DEVICES;
831 Returns a device list object with the following elements:
832 Table 8. DEVICES object
834 ┌────────┬─────────┬────────┬──────────────────┐
835 │Name │ Always? │ Type │ Description │
836 ├────────┼─────────┼────────┼──────────────────┤
837 │class │ Yes │ string │ Fixed: "DEVICES" │
838 ├────────┼─────────┼────────┼──────────────────┤
839 │devices │ Yes │ list │ List of device │
840 │ │ │ │ descriptions │
841 ├────────┼─────────┼────────┼──────────────────┤
842 │remote │ No │ string │ URL of the │
843 │ │ │ │ remote daemon │
844 │ │ │ │ reporting the │
845 │ │ │ │ device set. If │
846 │ │ │ │ empty, │
847 │ │ │ │ this is a │
848 │ │ │ │ DEVICES response │
849 │ │ │ │ from the local │
850 │ │ │ │ daemon. │
851 └────────┴─────────┴────────┴──────────────────┘
852 When the C client library parses a response of this kind, it will
853 assert the DEVICELIST_SET bit in the top-level set member.
854 Here's an example:
856 {"class"="DEVICES","devices":[
858 {"class":"DEVICE","path":"/dev/pts/1","flags":1,"driver":"SiRF binary"},
859 {"class":"DEVICE","path":"/dev/pts/3","flags":4,"driver":"AIVDM"}]}
860 The daemon occasionally ships a bare DEVICE object to the client
862 (that is, one not inside a DEVICES wrapper). The data content of
863 these objects will be described later as a response to the ?DEVICE
864 command.
865 ?WATCH;
867 This command sets watcher mode. It also sets or elicits a report of
868 per-subscriber policy and the raw bit. An argument WATCH object
869 changes the subscriber's policy. The response describes the
870 subscriber's policy. The response will also include a DEVICES
871 object.
872 A WATCH object has the following elements:
874 Table 9. WATCH object
876 ┌────────┬─────────┬─────────┬──────────────────┐
877 │Name │ Always? │ Type │ Description │
878 ├────────┼─────────┼─────────┼──────────────────┤
879 │class │ Yes │ string │ Fixed: "WATCH" │
880 ├────────┼─────────┼─────────┼──────────────────┤
881 │enable │ No │ boolean │ Enable (true) or │
882 │ │ │ │ disable (false) │
883 │ │ │ │ watcher mode. │
884 │ │ │ │ Default is true. │
885 ├────────┼─────────┼─────────┼──────────────────┤
886 │json │ No │ boolean │ Enable (true) or │
887 │ │ │ │ disable (false) │
888 │ │ │ │ dumping of JSON │
889 │ │ │ │ reports. │
890 │ │ │ │ Default is │
891 │ │ │ │ false. │
892 ├────────┼─────────┼─────────┼──────────────────┤
893 │nmea │ No │ boolean │ Enable (true) or │
894 │ │ │ │ disable (false) │
895 │ │ │ │ dumping of │
896 │ │ │ │ binary packets │
897 │ │ │ │ as pseudo-NMEA. │
898 │ │ │ │ Default is │
899 │ │ │ │ false. │
900 ├────────┼─────────┼─────────┼──────────────────┤
901 │raw │ No │ integer │ Controls 'raw' │
902 │ │ │ │ mode. When this │
903 │ │ │ │ attribute is set │
904 │ │ │ │ to 1 for a │
905 │ │ │ │ channel, gpsd │
906 │ │ │ │ reports the │
907 │ │ │ │ unprocessed NMEA │
908 │ │ │ │ or AIVDM data │
909 │ │ │ │ stream from │
910 │ │ │ │ whatever device │
911 │ │ │ │ is attached. │
912 │ │ │ │ Binary GPS │
913 │ │ │ │ packets are │
914 │ │ │ │ hex-dumped. │
915 │ │ │ │ RTCM2 and RTCM3 │
916 │ │ │ │ packets │
917 │ │ │ │ are not dumped │
918 │ │ │ │ in raw mode. │
919 │ │ │ │ When this │
920 │ │ │ │ attribute is set │
921 │ │ │ │ to 2 for a │
922 │ │ │ │ channel that │
923 │ │ │ │ processes binary │
924 │ │ │ │ data, gpsd │
925 │ │ │ │ reports the │
926 │ │ │ │ received data │
927 │ │ │ │ verbatim without │
928 │ │ │ │ hex-dumping. │
929 ├────────┼─────────┼─────────┼──────────────────┤
930 │scaled │ No │ boolean │ If true, apply │
931 │ │ │ │ scaling divisors │
932 │ │ │ │ to output before │
933 │ │ │ │ dumping; default │
934 │ │ │ │ is false. │
935 ├────────┼─────────┼─────────┼──────────────────┤
936 │split24 │ No │ boolean │ If true, │
937 │ │ │ │ aggregate AIS │
938 │ │ │ │ type24 sentence │
939 │ │ │ │ parts. If │
940 │ │ │ │ false, │
941 │ │ │ │ report │
942 │ │ │ │ each part as a │
943 │ │ │ │ separate JSON │
944 │ │ │ │ object, leaving │
945 │ │ │ │ the │
946 │ │ │ │ client │
947 │ │ │ │ to match MMSIs │
948 │ │ │ │ and aggregate. │
949 │ │ │ │ Default is │
950 │ │ │ │ false. │
951 │ │ │ │ Applies only to │
952 │ │ │ │ AIS reports. │
953 ├────────┼─────────┼─────────┼──────────────────┤
954 │pps │ No │ boolean │ If true, emit │
955 │ │ │ │ the TOFF JSON │
956 │ │ │ │ message on each │
957 │ │ │ │ cycle and a PPS │
958 │ │ │ │ JSON message │
959 │ │ │ │ when the device │
960 │ │ │ │ issues 1PPS. │
961 │ │ │ │ Default is │
962 │ │ │ │ false. │
963 ├────────┼─────────┼─────────┼──────────────────┤
964 │device │ No │ string │ If present, │
965 │ │ │ │ enable watching │
966 │ │ │ │ only of the │
967 │ │ │ │ specified device │
968 │ │ │ │ rather than all │
969 │ │ │ │ devices. Useful │
970 │ │ │ │ with raw and │
971 │ │ │ │ NMEA modes in │
972 │ │ │ │ which device │
973 │ │ │ │ responses aren't │
974 │ │ │ │ tagged. Has no │
975 │ │ │ │ effect when used │
976 │ │ │ │ with │
977 │ │ │ │ enable:false. │
978 ├────────┼─────────┼─────────┼──────────────────┤
979 │remote │ No │ string │ URL of the │
980 │ │ │ │ remote daemon │
981 │ │ │ │ reporting the │
982 │ │ │ │ watch set. If │
983 │ │ │ │ empty, │
984 │ │ │ │ this is a WATCH │
985 │ │ │ │ response from │
986 │ │ │ │ the local │
987 │ │ │ │ daemon. │
988 └────────┴─────────┴─────────┴──────────────────┘
989 There is an additional boolean "timing" attribute which is
990 undocumented because that portion of the interface is considered
991 unstable and for developer use only.
992 In watcher mode, GPS reports are dumped as TPV and SKY responses.
994 AIS, Subframe and RTCM reporting is described in the next section.
995 When the C client library parses a response of this kind, it will
997 assert the POLICY_SET bit in the top-level set member.
998 Here's an example:
1000 {"class":"WATCH", "raw":1,"scaled":true}
1002 ?POLL;
1004 The POLL command requests data from the last-seen fixes on all
1005 active GPS devices. Devices must previously have been activated by
1006 ?WATCH to be pollable.
1007 Polling can lead to possibly surprising results when it is used on
1009 a device such as an NMEA GPS for which a complete fix has to be
1010 accumulated from several sentences. If you poll while those
1011 sentences are being emitted, the response will contain the last
1012 complete fix data and may be as much as one cycle time (typically 1
1013 second) stale.
1014 The POLL response will contain a timestamped list of TPV objects
1016 describing cached data, and a timestamped list of SKY objects
1017 describing satellite configuration. If a device has not seen fixes,
1018 it will be reported with a mode field of zero.
1019 Table 10. POLL object
1021 ┌───────┬─────────┬────────────┬──────────────────┐
1022 │Name │ Always? │ Type │ Description │
1023 ├───────┼─────────┼────────────┼──────────────────┤
1024 │class │ Yes │ string │ Fixed: "POLL" │
1025 ├───────┼─────────┼────────────┼──────────────────┤
1026 │time │ Yes │ Numeric │ Timestamp in ISO │
1027 │ │ │ │ 8601 format. May │
1028 │ │ │ │ have a │
1029 │ │ │ │ fractional part │
1030 │ │ │ │ of up to .001sec │
1031 │ │ │ │ precision. │
1032 ├───────┼─────────┼────────────┼──────────────────┤
1033 │active │ Yes │ Numeric │ Count of active │
1034 │ │ │ │ devices. │
1035 ├───────┼─────────┼────────────┼──────────────────┤
1036 │tpv │ Yes │ JSON array │ Comma-separated │
1037 │ │ │ │ list of TPV │
1038 │ │ │ │ objects. │
1039 ├───────┼─────────┼────────────┼──────────────────┤
1040 │sky │ Yes │ JSON array │ Comma-separated │
1041 │ │ │ │ list of SKY │
1042 │ │ │ │ objects. │
1043 └───────┴─────────┴────────────┴──────────────────┘
1044 Here's an example of a POLL response:
1045 {"class":"POLL","time":"2010-06-04T10:31:00.289Z","active":1,
1047 "tpv":[{"class":"TPV","device":"/dev/ttyUSB0",
1048 "time":"2010-09-08T13:33:06.095Z",
1049 "ept":0.005,"lat":40.035093060,
1050 "lon":-75.519748733,"track":99.4319,"speed":0.123,"mode":2}],
1051 "sky":[{"class":"SKY","device":"/dev/ttyUSB0",
1052 "time":1270517264.240,"hdop":9.20,
1053 "satellites":[{"PRN":16,"el":55,"az":42,"ss":36,"used":true},
1054 {"PRN":19,"el":25,"az":177,"ss":0,"used":false},
1055 {"PRN":7,"el":13,"az":295,"ss":0,"used":false},
1056 {"PRN":6,"el":56,"az":135,"ss":32,"used":true},
1057 {"PRN":13,"el":47,"az":304,"ss":0,"used":false},
1058 {"PRN":23,"el":66,"az":259,"ss":0,"used":false},
1059 {"PRN":20,"el":7,"az":226,"ss":0,"used":false},
1060 {"PRN":3,"el":52,"az":163,"ss":32,"used":true},
1061 {"PRN":31,"el":16,"az":102,"ss":0,"used":false}
1062 ]}]}
1063 Note
1065 Client software should not assume the field inventory of the
1066 POLL response is fixed for all time. As gpsd collects and
1067 caches more data from more sensor types, those data are likely
1068 to find their way into this response.
1069 TOFF
1071 This message is emitted on each cycle and reports the offset
1072 between the host's clock time and the GPS time at top of second
1073 (actually, when the first data for the reporting cycle is
1074 received).
1075 This message exactly mirrors the PPS message except for two
1077 details.
1078 TOFF emits no NTP precision, this is assumed to be -2. See the NTP
1080 documentation for their definition of precision.
1081 The TOFF message reports the GPS time as derived from the GPS
1083 serial data stream. The PPS message reports the GPS time as derived
1084 from the GPS PPS pulse.
1085 A TOFF object has the following elements:
1087 Table 11. TOFF object
1089 ┌───────────┬─────────┬─────────┬──────────────────┐
1090 │Name │ Always? │ Type │ Description │
1091 ├───────────┼─────────┼─────────┼──────────────────┤
1092 │class │ Yes │ string │ Fixed: "TOFF" │
1093 ├───────────┼─────────┼─────────┼──────────────────┤
1094 │device │ Yes │ string │ Name of │
1095 │ │ │ │ originating │
1096 │ │ │ │ device │
1097 ├───────────┼─────────┼─────────┼──────────────────┤
1098 │real_sec │ Yes │ numeric │ seconds from the │
1099 │ │ │ │ GPS clock │
1100 ├───────────┼─────────┼─────────┼──────────────────┤
1101 │real_nsec │ Yes │ numeric │ nanoseconds from │
1102 │ │ │ │ the GPS clock │
1103 ├───────────┼─────────┼─────────┼──────────────────┤
1104 │clock_sec │ Yes │ numeric │ seconds from the │
1105 │ │ │ │ system clock │
1106 ├───────────┼─────────┼─────────┼──────────────────┤
1107 │clock_nsec │ Yes │ numeric │ nanoseconds from │
1108 │ │ │ │ the system clock │
1109 └───────────┴─────────┴─────────┴──────────────────┘
1110 This message is emitted once per second to watchers of a device and
1111 is intended to report the time stamps of the in-band report of the
1112 GPS and seconds as reported by the system clock (which may be
1113 NTP-corrected) when the first valid timestamp of the reporting
1114 cycle was seen.
1115 The message contains two second/nanosecond pairs: real_sec and
1117 real_nsec contain the time the GPS thinks it was at the start of
1118 the current cycle; clock_sec and clock_nsec contain the time the
1119 system clock thinks it was on receipt of the first timing message
1120 of the cycle. real_nsec is always to nanosecond precision.
1121 clock_nsec is nanosecond precision on most systems.
1122 Here's an example:
1124 {"class":"TOFF","device":"/dev/ttyUSB0",
1126 "real_sec":1330212592, "real_nsec":343182,
1127 "clock_sec":1330212592,"clock_nsec":343184,
1128 "precision":-2}}
1129 PPS
1131 This message is emitted each time the daemon sees a valid PPS
1132 (Pulse Per Second) strobe from a device.
1133 This message exactly mirrors the TOFF message except for two
1135 details.
1136 PPS emits the NTP precision. See the NTP documentation for their
1138 definition of precision.
1139 The TOFF message reports the GPS time as derived from the GPS
1141 serial data stream. The PPS message reports the GPS time as derived
1142 from the GPS PPS pulse.
1143 There are various sources of error in the reported clock times. The
1145 speed of the serial connection between the GPS and the system adds
1146 a delay to start of cycle detection. An even bigger error is added
1147 by the variable computation time inside the GPS. Taken together the
1148 time derived from the start of the GPS cycle can have offsets of 10
1149 millisecond to 700 milliseconds and combined jjitter and wander of
1150 100 to 300 millisecond.
1151 A PPS object has the following elements:
1153 Table 12. PPS object
1155 ┌───────────┬─────────┬─────────┬──────────────────┐
1156 │Name │ Always? │ Type │ Description │
1157 ├───────────┼─────────┼─────────┼──────────────────┤
1158 │class │ Yes │ string │ Fixed: "PPS" │
1159 ├───────────┼─────────┼─────────┼──────────────────┤
1160 │device │ Yes │ string │ Name of │
1161 │ │ │ │ originating │
1162 │ │ │ │ device │
1163 ├───────────┼─────────┼─────────┼──────────────────┤
1164 │real_sec │ Yes │ numeric │ seconds from the │
1165 │ │ │ │ PPS source │
1166 ├───────────┼─────────┼─────────┼──────────────────┤
1167 │real_nsec │ Yes │ numeric │ nanoseconds from │
1168 │ │ │ │ the PPS source │
1169 ├───────────┼─────────┼─────────┼──────────────────┤
1170 │clock_sec │ Yes │ numeric │ seconds from the │
1171 │ │ │ │ system clock │
1172 ├───────────┼─────────┼─────────┼──────────────────┤
1173 │clock_nsec │ Yes │ numeric │ nanoseconds from │
1174 │ │ │ │ the system clock │
1175 ├───────────┼─────────┼─────────┼──────────────────┤
1176 │precision │ Yes │ numeric │ NTP style │
1177 │ │ │ │ estimate of PPS │
1178 │ │ │ │ precision │
1179 ├───────────┼─────────┼─────────┼──────────────────┤
1180 │qErr │ No │ numeric │ Quantization │
1181 │ │ │ │ error of the │
1182 │ │ │ │ PPS, in pico │
1183 │ │ │ │ seconds. │
1184 │ │ │ │ Sometimes called │
1185 │ │ │ │ the "sawtooth" │
1186 │ │ │ │ error. │
1187 └───────────┴─────────┴─────────┴──────────────────┘
1188 This message is emitted once per second to watchers of a device
1189 emitting PPS, and reports the time of the start of the GPS second
1190 (when the 1PPS arrives) and seconds as reported by the system clock
1191 (which may be NTP-corrected) at that moment.
1192 The message contains two second/nanosecond pairs: real_sec and
1194 real_nsec contain the time the GPS thinks it was at the PPS edge;
1195 clock_sec and clock_nsec contain the time the system clock thinks
1196 it was at the PPS edge. real_nsec is always to nanosecond
1197 precision. clock_nsec is nanosecond precision on most systems.
1198 There are various sources of error in the reported clock times. For
1200 PPS delivered via a real serial-line strobe, serial-interrupt
1201 latency plus processing time to the timer call should be bounded
1202 above by about 10 microseconds; that can be reduced to less than 1
1203 microsecond if your kernel supports RFC 2783. USB1.1-to-serial
1204 control-line emulation is limited to about 1 millisecond. seconds.
1205 Here's an example:
1207 {"class":"PPS","device":"/dev/ttyUSB0",
1209 "real_sec":1330212592, "real_nsec":343182,
1210 "clock_sec":1330212592,"clock_nsec":343184,
1211 "precision":-3}
1212 OSC
1214 This message reports the status of a GPS-disciplined oscillator
1215 (GPSDO). The GPS PPS output (which has excellent long-term
1216 stability) is typically used to discipline a local oscillator with
1217 much better short-term stability (such as a rubidium atomic clock).
1218 An OSC object has the following elements:
1220 Table 13. OSC object
1222 ┌────────────┬─────────┬─────────┬──────────────────┐
1223 │Name │ Always? │ Type │ Description │
1224 ├────────────┼─────────┼─────────┼──────────────────┤
1225 │class │ Yes │ string │ Fixed: "OSC" │
1226 ├────────────┼─────────┼─────────┼──────────────────┤
1227 │device │ Yes │ string │ Name of │
1228 │ │ │ │ originating │
1229 │ │ │ │ device. │
1230 ├────────────┼─────────┼─────────┼──────────────────┤
1231 │running │ Yes │ boolean │ If true, the │
1232 │ │ │ │ oscillator is │
1233 │ │ │ │ currently │
1234 │ │ │ │ running. │
1235 │ │ │ │ Oscillators may │
1236 │ │ │ │ require warm-up │
1237 │ │ │ │ time at start of │
1238 │ │ │ │ day. │
1239 ├────────────┼─────────┼─────────┼──────────────────┤
1240 │reference │ Yes │ boolean │ If true, the │
1241 │ │ │ │ oscillator is │
1242 │ │ │ │ receiving a GPS │
1243 │ │ │ │ PPS signal. │
1244 ├────────────┼─────────┼─────────┼──────────────────┤
1245 │disciplined │ Yes │ boolean │ If true, the GPS │
1246 │ │ │ │ PPS signal is │
1247 │ │ │ │ sufficiently │
1248 │ │ │ │ stable and is │
1249 │ │ │ │ being used to │
1250 │ │ │ │ discipline the │
1251 │ │ │ │ local │
1252 │ │ │ │ oscillator. │
1253 ├────────────┼─────────┼─────────┼──────────────────┤
1254 │delta │ Yes │ numeric │ The time │
1255 │ │ │ │ difference (in │
1256 │ │ │ │ nanoseconds) │
1257 │ │ │ │ between the │
1258 │ │ │ │ GPS-disciplined │
1259 │ │ │ │ oscillator PPS │
1260 │ │ │ │ output pulse and │
1261 │ │ │ │ the most recent │
1262 │ │ │ │ GPS PPS input │
1263 │ │ │ │ pulse. │
1264 └────────────┴─────────┴─────────┴──────────────────┘
1265 Here's an example:
1266 {"class":"OSC","running":true,"device":"/dev/ttyUSB0",
1268 "reference":true,"disciplined":true,"delta":67}
1269 ?DEVICE
1271 This command reports (when followed by ';') the state of a device,
1272 or sets (when followed by '=' and a DEVICE object) device-specific
1273 control bits, notably the device's speed and serial mode and the
1274 native-mode bit. The parameter-setting form will be rejected if
1275 more than one client is attached to the channel.
1276 Pay attention to the response, because it is possible for this
1278 command to fail if the GPS does not support a speed-switching
1279 command or only supports some combinations of serial modes. In case
1280 of failure, the daemon and GPS will continue to communicate at the
1281 old speed.
1282 Use the parameter-setting form with caution. On USB and Bluetooth
1284 GPSes it is also possible for serial mode setting to fail either
1285 because the serial adaptor chip does not support non-8N1 modes or
1286 because the device firmware does not properly synchronize the
1287 serial adaptor chip with the UART on the GPS chipset when the speed
1288 changes. These failures can hang your device, possibly requiring a
1289 GPS power cycle or (in extreme cases) physically disconnecting the
1290 NVRAM backup battery.
1291 A DEVICE object has the following elements:
1293 Table 14. DEVICE object
1295 ┌──────────┬─────────┬─────────┬────────────────────┐
1296 │Name │ Always? │ Type │ Description │
1297 ├──────────┼─────────┼─────────┼────────────────────┤
1298 │class │ Yes │ string │ Fixed: "DEVICE" │
1299 ├──────────┼─────────┼─────────┼────────────────────┤
1300 │path │ No │ string │ Name the device │
1301 │ │ │ │ for which the │
1302 │ │ │ │ control bits are │
1303 │ │ │ │ being reported, │
1304 │ │ │ │ or for which │
1305 │ │ │ │ they are to be │
1306 │ │ │ │ applied. This │
1307 │ │ │ │ attribute │
1308 │ │ │ │ may be omitted │
1309 │ │ │ │ only when there │
1310 │ │ │ │ is exactly one │
1311 │ │ │ │ subscribed │
1312 │ │ │ │ channel. │
1313 ├──────────┼─────────┼─────────┼────────────────────┤
1314 │activated │ No │ string │ Time the device │
1315 │ │ │ │ was activated as │
1316 │ │ │ │ an ISO8601 │
1317 │ │ │ │ timestamp. │
1318 │ │ │ │ If the device is │
1319 │ │ │ │ inactive this │
1320 │ │ │ │ attribute is │
1321 │ │ │ │ absent. │
1322 ├──────────┼─────────┼─────────┼────────────────────┤
1323 │flags │ No │ integer │ Bit vector of │
1324 │ │ │ │ property flags. │
1325 │ │ │ │ Currently defined │
1326 │ │ │ │ flags are: │
1327 │ │ │ │ describe │
1328 │ │ │ │ packet types seen │
1329 │ │ │ │ so far (GPS, │
1330 │ │ │ │ RTCM2, RTCM3, │
1331 │ │ │ │ AIS). Won't be │
1332 │ │ │ │ reported if empty, │
1333 │ │ │ │ e.g. before gpsd │
1334 │ │ │ │ has seen │
1335 │ │ │ │ identifiable │
1336 │ │ │ │ packets from the │
1337 │ │ │ │ device. │
1338 ├──────────┼─────────┼─────────┼────────────────────┤
1339 │driver │ No │ string │ GPSD's name for │
1340 │ │ │ │ the device driver │
1341 │ │ │ │ type. Won't be │
1342 │ │ │ │ reported before │
1343 │ │ │ │ gpsd has seen │
1344 │ │ │ │ identifiable │
1345 │ │ │ │ packets from the │
1346 │ │ │ │ device. │
1347 ├──────────┼─────────┼─────────┼────────────────────┤
1348 │subtype │ No │ string │ Whatever version │
1349 │ │ │ │ information the │
1350 │ │ │ │ device driver │
1351 │ │ │ │ returned. │
1352 ├──────────┼─────────┼─────────┼────────────────────┤
1353 │subtype1 │ No │ string │ More version │
1354 │ │ │ │ information the │
1355 │ │ │ │ device driver │
1356 │ │ │ │ returned. │
1357 ├──────────┼─────────┼─────────┼────────────────────┤
1358 │bps │ No │ integer │ Device speed in │
1359 │ │ │ │ bits per second. │
1360 ├──────────┼─────────┼─────────┼────────────────────┤
1361 │parity │ No │ string │ N, O or E for no │
1362 │ │ │ │ parity, odd, or │
1363 │ │ │ │ even. │
1364 ├──────────┼─────────┼─────────┼────────────────────┤
1365 │stopbits │ Yes │ string │ Stop bits (1 or │
1366 │ │ │ │ 2). │
1367 ├──────────┼─────────┼─────────┼────────────────────┤
1368 │native │ No │ integer │ 0 means NMEA mode │
1369 │ │ │ │ and 1 means │
1370 │ │ │ │ alternate mode │
1371 │ │ │ │ (binary if it has │
1372 │ │ │ │ one, for SiRF and │
1373 │ │ │ │ Evermore chipsets │
1374 │ │ │ │ in particular). │
1375 │ │ │ │ Attempting to set │
1376 │ │ │ │ this mode on a │
1377 │ │ │ │ non-GPS device │
1378 │ │ │ │ will yield an │
1379 │ │ │ │ error. │
1380 ├──────────┼─────────┼─────────┼────────────────────┤
1381 │cycle │ No │ real │ Device cycle time │
1382 │ │ │ │ in seconds. │
1383 ├──────────┼─────────┼─────────┼────────────────────┤
1384 │mincycle │ No │ real │ Device minimum │
1385 │ │ │ │ cycle time in │
1386 │ │ │ │ seconds. Reported │
1387 │ │ │ │ from ?DEVICE when │
1388 │ │ │ │ (and only when) │
1389 │ │ │ │ the rate is │
1390 │ │ │ │ switchable. It is │
1391 │ │ │ │ read-only and not │
1392 │ │ │ │ settable. │
1393 └──────────┴─────────┴─────────┴────────────────────┘
1394 The serial parameters will (bps, parity, stopbits) be omitted in a
1395 response describing a TCP/IP source such as an Ntrip, DGPSIP, or
1396 AIS feed; on a serial device they will always be present.
1397 The contents of the flags field should be interpreted as follows:
1399 Table 15. Device flags
1401 ┌───────────┬───────┬─────────────────────┐
1402 │C #define │ Value │ Description │
1403 ├───────────┼───────┼─────────────────────┤
1404 │SEEN_GPS │ 0x01 │ GPS data has been │
1405 │ │ │ seen on this device │
1406 ├───────────┼───────┼─────────────────────┤
1407 │SEEN_RTCM2 │ 0x02 │ RTCM2 data has been │
1408 │ │ │ seen on this device │
1409 ├───────────┼───────┼─────────────────────┤
1410 │SEEN_RTCM3 │ 0x04 │ RTCM3 data has been │
1411 │ │ │ seen on this device │
1412 ├───────────┼───────┼─────────────────────┤
1413 │SEEN_AIS │ 0x08 │ AIS data has been │
1414 │ │ │ seen on this device │
1415 └───────────┴───────┴─────────────────────┘
1416 When the C client library parses a response of this kind, it will
1417 assert the DEVICE_SET bit in the top-level set member.
1418 Here's an example:
1420 {"class":"DEVICE","bps":4800,"parity":"N","stopbits":1,"native":0}
1422 When a client is in watcher mode, the daemon will ship it DEVICE
1424 notifications when a device is added to the pool or deactivated.
1425 When the C client library parses a response of this kind, it will
1427 assert the DEVICE_SET bit in the top-level set member.
1428 Here's an example:
1430 {"class":"DEVICE","path":"/dev/pts1","activated":0}
1432 The daemon may ship an error object in response to a syntactically
1434 invalid command line or unknown command. It has the following elements:
1435 Table 16. ERROR notification object
1437 ┌────────┬─────────┬────────┬────────────────┐
1438 │Name │ Always? │ Type │ Description │
1439 ├────────┼─────────┼────────┼────────────────┤
1440 │class │ Yes │ string │ Fixed: "ERROR" │
1441 ├────────┼─────────┼────────┼────────────────┤
1442 │message │ Yes │ string │ Textual error │
1443 │ │ │ │ message │
1444 └────────┴─────────┴────────┴────────────────┘
1445 Here's an example:
1447 {"class":"ERROR","message":"Unrecognized request '?FOO'"}
1449 When the C client library parses a response of this kind, it will
1451 assert the ERR_SET bit in the top-level set member.
1452
1454 RTCM-104 is a family of serial protocols used for broadcasting
1455 pseudorange corrections from differential-GPS reference stations. Many
1456 GPS receivers can accept these corrections to improve their reporting
1457 accuracy.
1458 RTCM-104 comes in two major and incompatible flavors, 2.x and 3.x. Each
1460 major flavor has minor (compatible) revisions.
1461 The applicable standard for RTCM Version 2.x is RTCM Recommended
1463 Standards for Differential NAVSTAR GPS Service RTCM Paper 194-93/SC
1464 104-STD. For RTCM 3.1 it is RTCM Paper 177-2006-SC104-STD. Ordering
1465 instructions for both standards are accessible from the website of the
1466 Radio Technical Commission for Maritime Services[1] under
1467 "Publications".
1468 RTCM WIRE TRANSMISSIONS
1470 Differential-GPS correction stations consist of a GPS reference
1471 receiver coupled to a low frequency (LF) transmitter. The GPS reference
1472 receiver is a survey-grade GPS that does GPS carrier tracking and can
1473 work out its own position to a few millimeters. It generates range and
1474 range-rate corrections and encodes them into RTCM104. It ships the
1475 RTCM104 to the LF transmitter over serial rs-232 signal at 100 baud or
1476 200 baud depending on the requirements of the transmitter.
1477 The LF transmitter broadcasts the approximately 300khz radio signal
1479 that differential-GPS radio receivers pick up. Transmitters that are
1480 meant to have a higher range will need to transmit at the slower rate.
1481 The higher the data rate the harder it will be for the remote radio
1482 receiver to receive with a good signal-to-noise ration. (Higher data
1483 rate signals can't be averaged over as long a time frame, hence they
1484 appear noisier.)
1485 RTCM WIRE FORMATS
1487 An RTCM 2.x message consists of a sequence of up to 33 30-bit words.
1488 The 24 most significant bits of each word are data and the six least
1489 significant bits are parity. The parity algorithm used is the same
1490 ISGPS-2000 as that used on GPS satellite downlinks. Each RTCM 2.x
1491 message consists of two header words followed by zero or more data
1492 words, depending upon message type.
1493 An RTCM 3.x message begins with a fixed leader byte 0xD3. That is
1495 followed by six bits of version information and 10 bits of payload
1496 length information. Following that is the payload; following the
1497 payload is a 3-byte checksum of the payload using the Qualcomm CRC-24Q
1498 algorithm.
1499 RTCM2 JSON FORMAT
1501 Each RTCM2 message is dumped as a single JSON object per message, with
1502 the message fields as attributes of that object. Arrays of satellite,
1503 station, and constellation statistics become arrays of JSON
1504 sub-objects. Each sentence will normally also have a "device" field
1505 containing the pathname of the originating device.
1506 All attributes other than the device field are mandatory. Header
1508 attributes are emitted before others.
1509 Header portion
1511 Table 17. SKY object
1512 ┌───────────────┬─────────┬─────────────────────────────┐
1513 │Name │ Type │ │
1514 │ │ │ Description │
1515 ├───────────────┼─────────┼─────────────────────────────┤
1516 │class │ string │ │
1517 │ │ │ Fixed: │
1518 │ │ │ "RTCM2". │
1519 ├───────────────┼─────────┼─────────────────────────────┤
1520 │type │ integer │ │
1521 │ │ │ Message │
1522 │ │ │ type (1-9). │
1523 ├───────────────┼─────────┼─────────────────────────────┤
1524 │station_id │ integer │ │
1525 │ │ │ The id of │
1526 │ │ │ the GPS │
1527 │ │ │ reference │
1528 │ │ │ receiver. │
1529 │ │ │ The LF │
1530 │ │ │ transmitters │
1531 │ │ │ also have │
1532 │ │ │ (different) │
1533 │ │ │ id numbers. │
1534 ├───────────────┼─────────┼─────────────────────────────┤
1535 │zcount │ real │ │
1536 │ │ │ The │
1537 │ │ │ reference │
1538 │ │ │ time of the │
1539 │ │ │ corrections │
1540 │ │ │ in the │
1541 │ │ │ message in │
1542 │ │ │ seconds │
1543 │ │ │ within the │
1544 │ │ │ current │
1545 │ │ │ hour. Note │
1546 │ │ │ that it is │
1547 │ │ │ in GPS time, │
1548 │ │ │ which is │
1549 │ │ │ some seconds │
1550 │ │ │ ahead of UTC │
1551 │ │ │ (see the │
1552 │ │ │ U.S. Naval │
1553 │ │ │ Observatory's │
1554 │ │ │ table of │
1555 │ │ │ leap second │
1556 │ │ │ corrections[2]). │
1557 ├───────────────┼─────────┼─────────────────────────────┤
1558 │seqnum │ integer │ │
1559 │ │ │ Sequence number. │
1560 │ │ │ Only 3 bits │
1561 │ │ │ wide, wraps │
1562 │ │ │ after 7. │
1563 ├───────────────┼─────────┼─────────────────────────────┤
1564 │length │ integer │ │
1565 │ │ │ The number of │
1566 │ │ │ words after the │
1567 │ │ │ header that │
1568 │ │ │ comprise the │
1569 │ │ │ message. │
1570 ├───────────────┼─────────┼─────────────────────────────┤
1571 │station_health │ integer │ │
1572 │ │ │ Station │
1573 │ │ │ transmission │
1574 │ │ │ status. │
1575 │ │ │ Indicates the │
1576 │ │ │ health of the │
1577 │ │ │ beacon as a │
1578 │ │ │ reference │
1579 │ │ │ source. Any │
1580 │ │ │ nonzero value │
1581 │ │ │ means the │
1582 │ │ │ satellite is │
1583 │ │ │ probably │
1584 │ │ │ transmitting bad │
1585 │ │ │ data and should │
1586 │ │ │ not be used in a │
1587 │ │ │ fix. 6 means the │
1588 │ │ │ transmission is │
1589 │ │ │ unmonitored. 7 │
1590 │ │ │ means the │
1591 │ │ │ station is not │
1592 │ │ │ working │
1593 │ │ │ properly. Other │
1594 │ │ │ values are │
1595 │ │ │ defined by the │
1596 │ │ │ beacon operator. │
1597 └───────────────┴─────────┴─────────────────────────────┘
1598 <message type> is one of
1600 1
1602 full corrections - one message containing corrections for all
1603 GPS satellites in view. This is not common.
1604 3
1606 reference station parameters - the position of the reference
1607 station GPS antenna.
1608 4
1610 datum — the datum to which the DGPS data is referred.
1611 5
1613 constellation health — information about the satellites the
1614 beacon can see.
1615 6
1617 null message — just a filler.
1618 7
1620 radio beacon almanac — information about this or other beacons.
1621 9
1623 subset corrections — a message containing corrections for only
1624 a subset of the GPS satellites in view.
1625 16
1627 special message — a text message from the beacon operator.
1628 31
1630 GLONASS subset corrections — a message containing corrections
1631 for a set of the GLONASS satellites in view.
1632 Type 1 and 9: Correction data
1634 One or more satellite objects follow the header for type 1 or type
1635 9 messages. Here is the format:
1636 Table 18. Satellite object
1638 ┌──────┬─────────┬─────────────────────────┐
1639 │Name │ Type │ │
1640 │ │ │ Description │
1641 ├──────┼─────────┼─────────────────────────┤
1642 │ident │ integer │ │
1643 │ │ │ The PRN │
1644 │ │ │ number of │
1645 │ │ │ the │
1646 │ │ │ satellite │
1647 │ │ │ for which │
1648 │ │ │ this is │
1649 │ │ │ correction │
1650 │ │ │ data. │
1651 ├──────┼─────────┼─────────────────────────┤
1652 │udre │ integer │ │
1653 │ │ │ User │
1654 │ │ │ Differential │
1655 │ │ │ Range Error │
1656 │ │ │ (0-3). See │
1657 │ │ │ the table │
1658 │ │ │ following │
1659 │ │ │ for values. │
1660 ├──────┼─────────┼─────────────────────────┤
1661 │iod │ integer │ │
1662 │ │ │ Issue Of │
1663 │ │ │ Data, │
1664 │ │ │ matching the │
1665 │ │ │ IOD for the │
1666 │ │ │ current │
1667 │ │ │ ephemeris of │
1668 │ │ │ this │
1669 │ │ │ satellite, │
1670 │ │ │ as │
1671 │ │ │ transmitted │
1672 │ │ │ by the │
1673 │ │ │ satellite. │
1674 │ │ │ The IOD is a │
1675 │ │ │ unique tag │
1676 │ │ │ that │
1677 │ │ │ identifies │
1678 │ │ │ the │
1679 │ │ │ ephemeris; │
1680 │ │ │ the GPS │
1681 │ │ │ using the │
1682 │ │ │ DGPS │
1683 │ │ │ correction │
1684 │ │ │ and the DGPS │
1685 │ │ │ generating │
1686 │ │ │ the data │
1687 │ │ │ must use the │
1688 │ │ │ same orbital │
1689 │ │ │ positions │
1690 │ │ │ for the │
1691 │ │ │ satellite. │
1692 ├──────┼─────────┼─────────────────────────┤
1693 │prc │ real │ │
1694 │ │ │ The │
1695 │ │ │ pseudorange │
1696 │ │ │ error in │
1697 │ │ │ meters for │
1698 │ │ │ this │
1699 │ │ │ satellite as │
1700 │ │ │ measured by │
1701 │ │ │ the beacon │
1702 │ │ │ reference │
1703 │ │ │ receiver at │
1704 │ │ │ the epoch │
1705 │ │ │ indicated by │
1706 │ │ │ the z_count │
1707 │ │ │ in the │
1708 │ │ │ parent │
1709 │ │ │ record. │
1710 ├──────┼─────────┼─────────────────────────┤
1711 │rrc │ real │ │
1712 │ │ │ The rate of │
1713 │ │ │ change of │
1714 │ │ │ pseudorange │
1715 │ │ │ error in │
1716 │ │ │ meters/sec │
1717 │ │ │ for this │
1718 │ │ │ satellite as │
1719 │ │ │ measured by │
1720 │ │ │ the beacon │
1721 │ │ │ reference │
1722 │ │ │ receiver at │
1723 │ │ │ the epoch │
1724 │ │ │ indicated by │
1725 │ │ │ the z_count │
1726 │ │ │ field in the │
1727 │ │ │ parent │
1728 │ │ │ record. This │
1729 │ │ │ is used to │
1730 │ │ │ calculate │
1731 │ │ │ pseudorange │
1732 │ │ │ errors at │
1733 │ │ │ other │
1734 │ │ │ epochs, if │
1735 │ │ │ required by │
1736 │ │ │ the GPS │
1737 │ │ │ receiver. │
1738 └──────┴─────────┴─────────────────────────┘
1739 User Differential Range Error values are as follows:
1741 Table 19. UDRE values
1743 ┌──┬────────────────────┐
1744 │0 │ 1-sigma error<= 1m │
1745 ├──┼────────────────────┤
1746 │1 │ 1-sigma error<= 4m │
1747 ├──┼────────────────────┤
1748 │2 │ 1-sigma error<= 8m │
1749 ├──┼────────────────────┤
1750 │3 │ 1-sigma error> 8m │
1751 └──┴────────────────────┘
1752 Here's an example:
1754 {"class":"RTCM2","type":1,
1756 "station_id":688,"zcount":843.0,"seqnum":5,"length":19,"station_health":6,
1757 "satellites":[
1758 {"ident":10,"udre":0,"iod":46,"prc":-2.400,"rrc":0.000},
1759 {"ident":13,"udre":0,"iod":94,"prc":-4.420,"rrc":0.000},
1760 {"ident":7,"udre":0,"iod":22,"prc":-5.160,"rrc":0.002},
1761 {"ident":2,"udre":0,"iod":34,"prc":-6.480,"rrc":0.000},
1762 {"ident":4,"udre":0,"iod":47,"prc":-8.860,"rrc":0.000},
1763 {"ident":8,"udre":0,"iod":76,"prc":-7.980,"rrc":0.002},
1764 {"ident":5,"udre":0,"iod":99,"prc":-8.260,"rrc":0.002},
1765 {"ident":23,"udre":0,"iod":81,"prc":-8.060,"rrc":0.000},
1766 {"ident":16,"udre":0,"iod":70,"prc":-11.740,"rrc":0.000},
1767 {"ident":30,"udre":0,"iod":4,"prc":-18.960,"rrc":-0.006},
1768 {"ident":29,"udre":0,"iod":101,"prc":-24.960,"rrc":-0.002}
1769 ]}
1770 Type 3: Reference Station Parameters
1772 Here are the payload members of a type 3 (Reference Station
1773 Parameters) message:
1774 Table 20. Reference Station Parameters
1776 ┌─────┬──────┬────────────────────────┐
1777 │Name │ Type │ │
1778 │ │ │ Description │
1779 ├─────┼──────┼────────────────────────┤
1780 │x │ real │ │
1781 │ │ │ ECEF X │
1782 │ │ │ coordinate. │
1783 ├─────┼──────┼────────────────────────┤
1784 │y │ real │ │
1785 │ │ │ ECEF Y │
1786 │ │ │ coordinate. │
1787 ├─────┼──────┼────────────────────────┤
1788 │z │ real │ │
1789 │ │ │ ECEF Z │
1790 │ │ │ coordinate. │
1791 └─────┴──────┴────────────────────────┘
1792 The coordinates are the position of the station, in meters to two
1794 decimal places, in Earth Centred Earth Fixed coordinates. These are
1795 usually referred to the WGS84 reference frame, but may be referred
1796 to NAD83 in the US (essentially identical to WGS84 for all except
1797 geodesists), or to some other reference frame in other parts of the
1798 world.
1799 An invalid reference message is represented by a type 3 header
1801 without payload fields.
1802 Here's an example:
1804 {"class":"RTCM2","type":3,
1806 "station_id":652,"zcount":1657.2,"seqnum":2,"length":4,"station_health":6,
1807 "x":3878620.92,"y":670281.40,"z":5002093.59
1808 }
1809 Type 4: Datum
1811 Here are the payload members of a type 4 (Datum) message:
1812 Table 21. Datum
1814 ┌───────────┬─────────┬────────────────────────┐
1815 │Name │ Type │ │
1816 │ │ │ Description │
1817 ├───────────┼─────────┼────────────────────────┤
1818 │dgnss_type │ string │ │
1819 │ │ │ Either │
1820 │ │ │ "GPS", │
1821 │ │ │ "GLONASS", │
1822 │ │ │ "GALILEO", │
1823 │ │ │ or │
1824 │ │ │ "UNKNOWN". │
1825 ├───────────┼─────────┼────────────────────────┤
1826 │dat │ integer │ │
1827 │ │ │ 0 or 1 and │
1828 │ │ │ indicates │
1829 │ │ │ the sense │
1830 │ │ │ of the │
1831 │ │ │ offset │
1832 │ │ │ shift given │
1833 │ │ │ by dx, dy, │
1834 │ │ │ dz. dat = 0 │
1835 │ │ │ means that │
1836 │ │ │ the station │
1837 │ │ │ coordinates │
1838 │ │ │ (in the │
1839 │ │ │ reference │
1840 │ │ │ message) │
1841 │ │ │ are │
1842 │ │ │ referred to │
1843 │ │ │ a local │
1844 │ │ │ datum and │
1845 │ │ │ that adding │
1846 │ │ │ dx, dy, dz │
1847 │ │ │ to that │
1848 │ │ │ position │
1849 │ │ │ will render │
1850 │ │ │ it in GNSS │
1851 │ │ │ coordinates │
1852 │ │ │ (WGS84 for │
1853 │ │ │ GPS). If │
1854 │ │ │ dat = 1 │
1855 │ │ │ then the │
1856 │ │ │ ref station │
1857 │ │ │ position is │
1858 │ │ │ in GNSS │
1859 │ │ │ coordinates │
1860 │ │ │ and adding │
1861 │ │ │ dx, dy, dz │
1862 │ │ │ will give │
1863 │ │ │ it referred │
1864 │ │ │ to the │
1865 │ │ │ local │
1866 │ │ │ datum. │
1867 ├───────────┼─────────┼────────────────────────┤
1868 │datum_name │ string │ │
1869 │ │ │ A standard │
1870 │ │ │ name for │
1871 │ │ │ the datum. │
1872 ├───────────┼─────────┼────────────────────────┤
1873 │dx │ real │ │
1874 │ │ │ X offset. │
1875 ├───────────┼─────────┼────────────────────────┤
1876 │dy │ real │ │
1877 │ │ │ Y offset. │
1878 ├───────────┼─────────┼────────────────────────┤
1879 │dz │ real │ │
1880 │ │ │ Z offset. │
1881 └───────────┴─────────┴────────────────────────┘
1882 <dx> <dy> <dz> are offsets to convert from local datum to GNSS
1884 datum or vice versa. These fields are optional.
1885 An invalid datum message is represented by a type 4 header without
1887 payload fields.
1888 Type 5: Constellation Health
1890 One or more of these follow the header for type 5 messages — one
1891 for each satellite.
1892 Here is the format:
1894 Table 22. Constellation health
1896 ┌────────────┬─────────┬──────────────────────────┐
1897 │Name │ Type │ │
1898 │ │ │ Description │
1899 ├────────────┼─────────┼──────────────────────────┤
1900 │ident │ integer │ │
1901 │ │ │ The PRN │
1902 │ │ │ number of │
1903 │ │ │ the │
1904 │ │ │ satellite. │
1905 ├────────────┼─────────┼──────────────────────────┤
1906 │iodl │ bool │ │
1907 │ │ │ True │
1908 │ │ │ indicates │
1909 │ │ │ that this │
1910 │ │ │ information │
1911 │ │ │ relates to │
1912 │ │ │ the │
1913 │ │ │ satellite │
1914 │ │ │ information │
1915 │ │ │ in an │
1916 │ │ │ accompanying │
1917 │ │ │ type 1 or │
1918 │ │ │ type 9 │
1919 │ │ │ message. │
1920 ├────────────┼─────────┼──────────────────────────┤
1921 │health │ integer │ 0 indicates that the │
1922 │ │ │ satellite is healthy. │
1923 │ │ │ Any other value │
1924 │ │ │ indicates a problem │
1925 │ │ │ (coding is not │
1926 │ │ │ known)..PP │
1927 ├────────────┼─────────┼──────────────────────────┤
1928 │snr │ integer │ │
1929 │ │ │ The │
1930 │ │ │ carrier/noise │
1931 │ │ │ ratio of the │
1932 │ │ │ received │
1933 │ │ │ signal in │
1934 │ │ │ the range 25 │
1935 │ │ │ to 55 │
1936 │ │ │ dB(Hz). │
1937 ├────────────┼─────────┼──────────────────────────┤
1938 │health_en │ bool │ │
1939 │ │ │ If set to │
1940 │ │ │ True it │
1941 │ │ │ indicates │
1942 │ │ │ that the │
1943 │ │ │ satellite is │
1944 │ │ │ healthy even │
1945 │ │ │ if the │
1946 │ │ │ satellite │
1947 │ │ │ navigation │
1948 │ │ │ data says it │
1949 │ │ │ is unhealthy. │
1950 ├────────────┼─────────┼──────────────────────────┤
1951 │new_data │ bool │ True indicates that the │
1952 │ │ │ IOD for this satellite │
1953 │ │ │ will │
1954 │ │ │ soon be updated │
1955 │ │ │ in type 1 or 9 │
1956 │ │ │ messages..PP │
1957 ├────────────┼─────────┼──────────────────────────┤
1958 │los_warning │ bool │ │
1959 │ │ │ Line-of-sight │
1960 │ │ │ warning. True │
1961 │ │ │ indicates │
1962 │ │ │ that the │
1963 │ │ │ satellite │
1964 │ │ │ will shortly │
1965 │ │ │ go unhealthy. │
1966 ├────────────┼─────────┼──────────────────────────┤
1967 │tou │ integer │ │
1968 │ │ │ Healthy time │
1969 │ │ │ remaining in │
1970 │ │ │ seconds. │
1971 └────────────┴─────────┴──────────────────────────┘
1972 Type 6: Null
1974 This just indicates a null message. There are no payload fields.
1975 Unknown message
1977 This format is used to dump message words in hexadecimal when the
1978 message type field doesn't match any of the known ones.
1979 Here is the format:
1981 Table 23. Unknown Message
1983 ┌─────┬──────┬────────────────────────┐
1984 │Name │ Type │ │
1985 │ │ │ Description │
1986 ├─────┼──────┼────────────────────────┤
1987 │data │ list │ │
1988 │ │ │ A list of │
1989 │ │ │ strings. │
1990 └─────┴──────┴────────────────────────┘
1991 Each string in the array is a hex literal representing 30 bits of
1993 information, after parity checks and inversion. The high two bits
1994 should be ignored.
1995 Type 7: Radio Beacon Almanac
1997 Here is the format:
1998 Table 24. Contellation health
2000 ┌───────────┬─────────┬───────────────────────────┐
2001 │Name │ Type │ │
2002 │ │ │ Description │
2003 ├───────────┼─────────┼───────────────────────────┤
2004 │lat │ real │ │
2005 │ │ │ Latitude in │
2006 │ │ │ degrees, of │
2007 │ │ │ the LF │
2008 │ │ │ transmitter │
2009 │ │ │ antenna for │
2010 │ │ │ the station │
2011 │ │ │ for which │
2012 │ │ │ this is an │
2013 │ │ │ almanac. │
2014 │ │ │ North is │
2015 │ │ │ positive. │
2016 ├───────────┼─────────┼───────────────────────────┤
2017 │lon │ real │ │
2018 │ │ │ Longitude │
2019 │ │ │ in degrees, │
2020 │ │ │ of the LF │
2021 │ │ │ transmitter │
2022 │ │ │ antenna for │
2023 │ │ │ the station │
2024 │ │ │ for which │
2025 │ │ │ this is an │
2026 │ │ │ almanac. │
2027 │ │ │ East is │
2028 │ │ │ positive. │
2029 ├───────────┼─────────┼───────────────────────────┤
2030 │range │ integer │ Published range of the │
2031 │ │ │ station in km..PP │
2032 ├───────────┼─────────┼───────────────────────────┤
2033 │frequency │ real │ │
2034 │ │ │ Station │
2035 │ │ │ broadcast │
2036 │ │ │ frequency │
2037 │ │ │ in kHz. │
2038 ├───────────┼─────────┼───────────────────────────┤
2039 │health │ integer │ │
2040 │ │ │ <health> is │
2041 │ │ │ the health │
2042 │ │ │ of the │
2043 │ │ │ station for │
2044 │ │ │ which this │
2045 │ │ │ is an │
2046 │ │ │ almanac. If │
2047 │ │ │ it is │
2048 │ │ │ non-zero, │
2049 │ │ │ the station │
2050 │ │ │ is issuing │
2051 │ │ │ suspect │
2052 │ │ │ data and │
2053 │ │ │ should not │
2054 │ │ │ be used for │
2055 │ │ │ fixes. The │
2056 │ │ │ ITU and │
2057 │ │ │ RTCM104 │
2058 │ │ │ standards │
2059 │ │ │ differ │
2060 │ │ │ about the │
2061 │ │ │ mode │
2062 │ │ │ detailed │
2063 │ │ │ interpretation │
2064 │ │ │ of the │
2065 │ │ │ <health> │
2066 │ │ │ field and │
2067 │ │ │ even about │
2068 │ │ │ its bit │
2069 │ │ │ width. │
2070 ├───────────┼─────────┼───────────────────────────┤
2071 │station_id │ integer │ │
2072 │ │ │ The id of the │
2073 │ │ │ transmitter. │
2074 │ │ │ This is not │
2075 │ │ │ the same as │
2076 │ │ │ the reference │
2077 │ │ │ id in the │
2078 │ │ │ header, the │
2079 │ │ │ latter being │
2080 │ │ │ the id of the │
2081 │ │ │ reference │
2082 │ │ │ receiver. │
2083 ├───────────┼─────────┼───────────────────────────┤
2084 │bitrate │ integer │ │
2085 │ │ │ The │
2086 │ │ │ transmitted │
2087 │ │ │ bitrate. │
2088 └───────────┴─────────┴───────────────────────────┘
2089 Here's an example:
2091 {"class":"RTCM2","type":9,"station_id":268,"zcount":252.6,
2093 "seqnum":4,"length":5,"station_health":0,
2094 "satellites":[
2095 {"ident":13,"udre":0,"iod":3,"prc":-25.940,"rrc":0.066},
2096 {"ident":2,"udre":0,"iod":73,"prc":0.920,"rrc":-0.080},
2097 {"ident":8,"udre":0,"iod":22,"prc":23.820,"rrc":0.014}
2098 ]}
2099 Type 13: GPS Time of Week
2101 Here are the payload members of a type 13 (Groumf Tramitter
2102 Parameters) message:
2103 Table 25. Grund Transmitter Parameters
2105 ┌──────────┬─────────┬─────────────────────────┐
2106 │Name │ Type │ │
2107 │ │ │ Description │
2108 ├──────────┼─────────┼─────────────────────────┤
2109 │status │ bool │ │
2110 │ │ │ If True, │
2111 │ │ │ signals │
2112 │ │ │ user to │
2113 │ │ │ expect a │
2114 │ │ │ type 16 │
2115 │ │ │ explanatory │
2116 │ │ │ message │
2117 │ │ │ associated │
2118 │ │ │ with this │
2119 │ │ │ station. │
2120 │ │ │ Probably │
2121 │ │ │ indicates │
2122 │ │ │ some sort │
2123 │ │ │ of unusual │
2124 │ │ │ event. │
2125 ├──────────┼─────────┼─────────────────────────┤
2126 │rangeflag │ bool │ │
2127 │ │ │ If True, │
2128 │ │ │ indicates │
2129 │ │ │ that the │
2130 │ │ │ estimated │
2131 │ │ │ range is │
2132 │ │ │ different │
2133 │ │ │ from that │
2134 │ │ │ found in │
2135 │ │ │ the Type 7 │
2136 │ │ │ message │
2137 │ │ │ (which │
2138 │ │ │ contains │
2139 │ │ │ the │
2140 │ │ │ beacon's │
2141 │ │ │ listed │
2142 │ │ │ range). │
2143 │ │ │ Generally │
2144 │ │ │ indicates a │
2145 │ │ │ range │
2146 │ │ │ reduction │
2147 │ │ │ due to │
2148 │ │ │ causes such │
2149 │ │ │ as poor │
2150 │ │ │ ionospheric │
2151 │ │ │ conditions │
2152 │ │ │ or reduced │
2153 │ │ │ transmission │
2154 │ │ │ power. │
2155 ├──────────┼─────────┼─────────────────────────┤
2156 │lat │ real │ │
2157 │ │ │ Degrees │
2158 │ │ │ latitude, │
2159 │ │ │ signed. │
2160 │ │ │ Positive is │
2161 │ │ │ N, negative │
2162 │ │ │ is S. │
2163 ├──────────┼─────────┼─────────────────────────┤
2164 │lon │ real │ │
2165 │ │ │ Degrees │
2166 │ │ │ longitude, │
2167 │ │ │ signed. │
2168 │ │ │ Positive is │
2169 │ │ │ E, negative │
2170 │ │ │ is W. │
2171 ├──────────┼─────────┼─────────────────────────┤
2172 │range │ integer │ │
2173 │ │ │ Transmission │
2174 │ │ │ range in km │
2175 │ │ │ (1-1024). │
2176 └──────────┴─────────┴─────────────────────────┘
2177 This message type replaces message type 3 (Reference Station
2179 Parameters) in RTCM 2.3.
2180 Type 14: GPS Time of Week
2182 Here are the payload members of a type 14 (GPS Time of Week)
2183 message:
2184 Table 26. Reference Station Parameters
2186 ┌─────────┬─────────┬────────────────────────┐
2187 │Name │ Type │ │
2188 │ │ │ Description │
2189 ├─────────┼─────────┼────────────────────────┤
2190 │week │ integer │ │
2191 │ │ │ GPS week │
2192 │ │ │ (0-123). │
2193 ├─────────┼─────────┼────────────────────────┤
2194 │hour │ integer │ │
2195 │ │ │ Hour of │
2196 │ │ │ week │
2197 │ │ │ (0-167). │
2198 ├─────────┼─────────┼────────────────────────┤
2199 │leapsecs │ integer │ │
2200 │ │ │ Leap │
2201 │ │ │ Seconds │
2202 │ │ │ (0-63). │
2203 └─────────┴─────────┴────────────────────────┘
2204 Here's an example:
2206 {"class":"RTCM2","type":14,"station_id":652,"zcount":1657.2,
2208 "seqnum":3,"length":1,"station_health":6,"week":601,"hour":109,
2209 "leapsecs":15}
2210 Type 16: Special Message
2212 Table 27. Special Message
2213 ┌────────┬────────┬────────────────────────┐
2214 │Name │ Type │ │
2215 │ │ │ Description │
2216 ├────────┼────────┼────────────────────────┤
2217 │message │ string │ │
2218 │ │ │ A text │
2219 │ │ │ message │
2220 │ │ │ sent by the │
2221 │ │ │ beacon │
2222 │ │ │ operator. │
2223 └────────┴────────┴────────────────────────┘
2224 Type 31: Correction data
2226 One or more GLONASS satellite objects follow the header for type 1
2227 or type 9 messages. Here is the format:
2228 Table 28. Satellite object
2230 ┌───────┬──────────┬────────────────────────────────┐
2231 │Name │ Type │ │
2232 │ │ │ Description │
2233 ├───────┼──────────┼────────────────────────────────┤
2234 │ident │ integer │ │
2235 │ │ │ The PRN │
2236 │ │ │ number of │
2237 │ │ │ the │
2238 │ │ │ satellite │
2239 │ │ │ for which │
2240 │ │ │ this is │
2241 │ │ │ correction │
2242 │ │ │ data. │
2243 ├───────┼──────────┼────────────────────────────────┤
2244 │udre │ integer │ │
2245 │ │ │ User │
2246 │ │ │ Differential │
2247 │ │ │ Range Error │
2248 │ │ │ (0-3). See │
2249 │ │ │ the table │
2250 │ │ │ following │
2251 │ │ │ for values. │
2252 ├───────┼──────────┼────────────────────────────────┤
2253 │change │ boolean │ │
2254 │ │ │ Change-of-ephemeris │
2255 │ │ │ bit. │
2256 ├───────┼──────────┼────────────────────────────────┤
2257 │tod │ uinteger │ │
2258 │ │ │ Count of 30-second │
2259 │ │ │ periods since the │
2260 │ │ │ top of the hour. │
2261 ├───────┼──────────┼────────────────────────────────┤
2262 │prc │ real │ │
2263 │ │ │ The pseudorange │
2264 │ │ │ error in meters for │
2265 │ │ │ this satellite as │
2266 │ │ │ measured by the │
2267 │ │ │ beacon reference │
2268 │ │ │ receiver at the │
2269 │ │ │ epoch indicated by │
2270 │ │ │ the z_count in the │
2271 │ │ │ parent record. │
2272 ├───────┼──────────┼────────────────────────────────┤
2273 │rrc │ real │ │
2274 │ │ │ The rate of change │
2275 │ │ │ of pseudorange │
2276 │ │ │ error in meters/sec │
2277 │ │ │ for this satellite │
2278 │ │ │ as measured by the │
2279 │ │ │ beacon reference │
2280 │ │ │ receiver at the │
2281 │ │ │ epoch indicated by │
2282 │ │ │ the z_count field │
2283 │ │ │ in the parent │
2284 │ │ │ record. This is │
2285 │ │ │ used to calculate │
2286 │ │ │ pseudorange errors │
2287 │ │ │ at other epochs, if │
2288 │ │ │ required by the GPS │
2289 │ │ │ receiver. │
2290 └───────┴──────────┴────────────────────────────────┘
2291 Here's an example:
2293 {"class":"RTCM2","type":31,"station_id":652,"zcount":1642.2,
2295 "seqnum":0,"length":14,"station_health":6,
2296 "satellites":[
2297 {"ident":5,"udre":0,"change":false,"tod":0,"prc":132.360,"rrc":0.000},
2298 {"ident":15,"udre":0,"change":false,"tod":0,"prc":134.840,"rrc":0.002},
2299 {"ident":14,"udre":0,"change":false,"tod":0,"prc":141.520,"rrc":0.000},
2300 {"ident":6,"udre":0,"change":false,"tod":0,"prc":127.000,"rrc":0.000},
2301 {"ident":21,"udre":0,"change":false,"tod":0,"prc":128.780,"rrc":0.000},
2302 {"ident":22,"udre":0,"change":false,"tod":0,"prc":125.260,"rrc":0.002},
2303 {"ident":20,"udre":0,"change":false,"tod":0,"prc":117.280,"rrc":-0.004},
2304 {"ident":16,"udre":0,"change":false,"tod":17,"prc":113.460,"rrc":0.018}
2305 ]}
2306
2308 The support for RTCM104v3 dumping is incomplete and buggy. Do not
2309 attempt to use it for production! Anyone interested in it should read
2310 the source code.
2311
2313 AIS support is an extension. It may not be present if your instance of
2314 gpsd has been built with a restricted feature set.
2315 AIS packets are dumped as JSON objects with class "AIS". Each AIS
2317 report object contains a "type" field giving the AIS message type and a
2318 "scaled" field telling whether the remainder of the fields are dumped
2319 in scaled or unscaled form. (These will be emitted before any
2320 type-specific fields.) It will also contain a "device" field naming the
2321 data source. Other fields have names and types as specified in the
2322 AIVDM/AIVDO Protocol Decoding document on the GPSD project website;
2323 each message field table may be directly interpreted as a specification
2324 for the members of the corresponding JSON object type.
2325 By default, certain scaling and conversion operations are performed for
2327 JSON output. Latitudes and longitudes are scaled to decimal degrees
2328 rather than the native AIS unit of 1/10000th of a minute of arc. Ship
2329 (but not air) speeds are scaled to knots rather than tenth-of-knot
2330 units. Rate of turn may appear as "nan" if is unavailable, or as one of
2331 the strings "fastright" or "fastleft" if it is out of the AIS encoding
2332 range; otherwise it is quadratically mapped back to the turn sensor
2333 number in degrees per minute. Vessel draughts are converted to decimal
2334 meters rather than native AIS decimeters. Various other scaling
2335 conversions are described in "AIVDM/AIVDO Protocol Decoding".
2336
2338 Subframe support is always compiled into gpsd but many GPSes do not
2339 output subframe data or the gpsd driver may not support subframes.
2340 Subframe packets are dumped as JSON objects with class "SUBFRAME". Each
2342 subframe report object contains a "frame" field giving the subframe
2343 number, a "tSV" field for the transmitting satellite number, a "TOW17"
2344 field containing the 17 MSBs of the start of the next 12-second message
2345 and a "scaled" field telling whether the remainder of the fields are
2346 dumped in scaled or unscaled form. It will also contain a "device"
2347 field naming the data source. Each SUBFRAME object will have a
2348 sub-object specific to that subframe page type. Those sub-object fields
2349 have names and types similar to those specified in the IS-GPS-200E
2350 document; each message field table may be directly interpreted as a
2351 specification for the members of the corresponding JSON object type.
2352
2354 gpsd(8), libgps(3),
2355
2357 The protocol was designed and documented by Eric S. Raymond.
2358
2360 1. Radio Technical Commission for Maritime Services
2361 http://www.rtcm.org/
2362 2. table of leap second corrections
2364 ftp://maia.usno.navy.mil/ser7/tai-utc.dat
2365The GPSD Project 23 June 2019 GPSD_JSON(5)