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 Table 1. TPV object
72 ┌─────────┬─────────┬─────────┬──────────────────┐
73 │Name │ Always? │ Type │ Description │
74 ├─────────┼─────────┼─────────┼──────────────────┤
75 │class │ Yes │ string │ Fixed: "TPV" │
76 ├─────────┼─────────┼─────────┼──────────────────┤
77 │device │ No │ string │ Name of │
78 │ │ │ │ originating │
79 │ │ │ │ device. │
80 ├─────────┼─────────┼─────────┼──────────────────┤
81 │status │ No │ numeric │ GPS status: %d, │
82 │ │ │ │ 2=DGPS fix, │
83 │ │ │ │ otherwise not │
84 │ │ │ │ present. │
85 ├─────────┼─────────┼─────────┼──────────────────┤
86 │mode │ Yes │ numeric │ NMEA mode: %d, │
87 │ │ │ │ 0=no mode value │
88 │ │ │ │ yet seen, 1=no │
89 │ │ │ │ fix, 2=2D, 3=3D. │
90 ├─────────┼─────────┼─────────┼──────────────────┤
91 │time │ No │ string │ Time/date stamp │
92 │ │ │ │ in ISO8601 │
93 │ │ │ │ format, UTC. May │
94 │ │ │ │ have a │
95 │ │ │ │ fractional │
96 │ │ │ │ part of up to │
97 │ │ │ │ .001sec │
98 │ │ │ │ precision. May │
99 │ │ │ │ be absent if │
100 │ │ │ │ mode │
101 │ │ │ │ is not 2 │
102 │ │ │ │ or 3. │
103 ├─────────┼─────────┼─────────┼──────────────────┤
104 │ept │ No │ numeric │ Estimated │
105 │ │ │ │ timestamp error │
106 │ │ │ │ (%f, seconds, │
107 │ │ │ │ 95% confidence). │
108 │ │ │ │ Present │
109 │ │ │ │ if time is │
110 │ │ │ │ present. │
111 ├─────────┼─────────┼─────────┼──────────────────┤
112 │lat │ No │ numeric │ Latitude in │
113 │ │ │ │ degrees: +/- │
114 │ │ │ │ signifies │
115 │ │ │ │ North/South. │
116 │ │ │ │ Present │
117 │ │ │ │ when │
118 │ │ │ │ mode is 2 or 3. │
119 ├─────────┼─────────┼─────────┼──────────────────┤
120 │lon │ No │ numeric │ Longitude in │
121 │ │ │ │ degrees: +/- │
122 │ │ │ │ signifies │
123 │ │ │ │ East/West. │
124 │ │ │ │ Present │
125 │ │ │ │ when │
126 │ │ │ │ mode is 2 or 3. │
127 ├─────────┼─────────┼─────────┼──────────────────┤
128 │alt │ No │ numeric │ Altitude in │
129 │ │ │ │ meters. Present │
130 │ │ │ │ if mode is 3. │
131 ├─────────┼─────────┼─────────┼──────────────────┤
132 │epx │ No │ numeric │ Longitude error │
133 │ │ │ │ estimate in │
134 │ │ │ │ meters, 95% │
135 │ │ │ │ confidence. │
136 │ │ │ │ Present │
137 │ │ │ │ if mode │
138 │ │ │ │ is 2 or 3 and │
139 │ │ │ │ DOPs can be │
140 │ │ │ │ calculated from │
141 │ │ │ │ the satellite │
142 │ │ │ │ view. │
143 ├─────────┼─────────┼─────────┼──────────────────┤
144 │epy │ No │ numeric │ Latitude error │
145 │ │ │ │ estimate in │
146 │ │ │ │ meters, 95% │
147 │ │ │ │ confidence. │
148 │ │ │ │ Present │
149 │ │ │ │ if mode │
150 │ │ │ │ is 2 or 3 and │
151 │ │ │ │ DOPs can be │
152 │ │ │ │ calculated from │
153 │ │ │ │ the satellite │
154 │ │ │ │ view. │
155 ├─────────┼─────────┼─────────┼──────────────────┤
156 │epv │ No │ numeric │ Estimated │
157 │ │ │ │ vertical error │
158 │ │ │ │ in meters, 95% │
159 │ │ │ │ confidence. │
160 │ │ │ │ Present │
161 │ │ │ │ if mode │
162 │ │ │ │ is 3 and DOPs │
163 │ │ │ │ can be │
164 │ │ │ │ calculated from │
165 │ │ │ │ the satellite │
166 │ │ │ │ view. │
167 ├─────────┼─────────┼─────────┼──────────────────┤
168 │track │ No │ numeric │ Course over │
169 │ │ │ │ ground, degrees │
170 │ │ │ │ from true north. │
171 ├─────────┼─────────┼─────────┼──────────────────┤
172 │magtrack │ No │ numeric │ Course over │
173 │ │ │ │ ground, degrees │
174 │ │ │ │ magnetic. │
175 ├─────────┼─────────┼─────────┼──────────────────┤
176 │speed │ No │ numeric │ Speed over │
177 │ │ │ │ ground, meters │
178 │ │ │ │ per second. │
179 ├─────────┼─────────┼─────────┼──────────────────┤
180 │climb │ No │ numeric │ Climb (positive) │
181 │ │ │ │ or sink │
182 │ │ │ │ (negative) rate, │
183 │ │ │ │ meters per │
184 │ │ │ │ second. │
185 ├─────────┼─────────┼─────────┼──────────────────┤
186 │epd │ No │ numeric │ Direction error │
187 │ │ │ │ estimate in │
188 │ │ │ │ degrees, 95% │
189 │ │ │ │ confidence. │
190 ├─────────┼─────────┼─────────┼──────────────────┤
191 │eps │ No │ numeric │ Speed error │
192 │ │ │ │ estinmate in │
193 │ │ │ │ meters/sec, 95% │
194 │ │ │ │ confidence. │
195 ├─────────┼─────────┼─────────┼──────────────────┤
196 │epc │ No │ numeric │ Climb/sink error │
197 │ │ │ │ estimate in │
198 │ │ │ │ meters/sec, 95% │
199 │ │ │ │ confidence. │
200 ├─────────┼─────────┼─────────┼──────────────────┤
201 │ecefx │ No │ numeric │ ECEF X position │
202 │ │ │ │ in meters. │
203 ├─────────┼─────────┼─────────┼──────────────────┤
204 │ecefy │ No │ numeric │ ECEF Y position │
205 │ │ │ │ in meters. │
206 ├─────────┼─────────┼─────────┼──────────────────┤
207 │ecefz │ No │ numeric │ ECEF Z position │
208 │ │ │ │ in meters. │
209 ├─────────┼─────────┼─────────┼──────────────────┤
210 │ecefpAcc │ No │ numeric │ ECEF position │
211 │ │ │ │ error in meters. │
212 ├─────────┼─────────┼─────────┼──────────────────┤
213 │ecefvx │ No │ numeric │ ECEF X velocity │
214 │ │ │ │ in │
215 │ │ │ │ meters/second. │
216 ├─────────┼─────────┼─────────┼──────────────────┤
217 │ecefvy │ No │ numeric │ ECEF Y velocity │
218 │ │ │ │ in │
219 │ │ │ │ meters/second. │
220 ├─────────┼─────────┼─────────┼──────────────────┤
221 │ecefvz │ No │ numeric │ ECEF Z velocity │
222 │ │ │ │ in │
223 │ │ │ │ meters/second. │
224 ├─────────┼─────────┼─────────┼──────────────────┤
225 │ecefvAcc │ No │ numeric │ ECEF velocity │
226 │ │ │ │ error in │
227 │ │ │ │ meters/second. │
228 └─────────┴─────────┴─────────┴──────────────────┘
229 When the C client library parses a response of this kind, it will
230 assert validity bits in the top-level set member for each field
231 actually received; see gps.h for bitmask names and values.
232 Here's an example:
234 {"class":"TPV","device":"/dev/pts/1",
236 "time":"2005-06-08T10:34:48.283Z","ept":0.005,
237 "lat":46.498293369,"lon":7.567411672,"alt":1343.127,
238 "eph":36.000,"epv":32.321,
239 "track":10.3788,"speed":0.091,"climb":-0.085,"mode":3}
240 SKY
242 A SKY object reports a sky view of the GPS satellite positions. If
243 there is no GPS device available, or no skyview has been reported
244 yet, only the "class" field will reliably be present.
245 Table 2. SKY object
247 ┌───────────┬─────────┬─────────┬──────────────────┐
248 │Name │ Always? │ Type │ Description │
249 ├───────────┼─────────┼─────────┼──────────────────┤
250 │class │ Yes │ string │ Fixed: "SKY" │
251 ├───────────┼─────────┼─────────┼──────────────────┤
252 │device │ No │ string │ Name of │
253 │ │ │ │ originating │
254 │ │ │ │ device │
255 ├───────────┼─────────┼─────────┼──────────────────┤
256 │time │ No │ string │ Time/date stamp │
257 │ │ │ │ in ISO8601 │
258 │ │ │ │ format, UTC. May │
259 │ │ │ │ have a │
260 │ │ │ │ fractional │
261 │ │ │ │ part of up to │
262 │ │ │ │ .001sec │
263 │ │ │ │ precision. │
264 ├───────────┼─────────┼─────────┼──────────────────┤
265 │xdop │ No │ numeric │ Longitudinal │
266 │ │ │ │ dilution of │
267 │ │ │ │ precision, a │
268 │ │ │ │ dimensionless │
269 │ │ │ │ factor │
270 │ │ │ │ which should be │
271 │ │ │ │ multiplied by a │
272 │ │ │ │ base UERE to get │
273 │ │ │ │ an error │
274 │ │ │ │ estimate. │
275 ├───────────┼─────────┼─────────┼──────────────────┤
276 │ydop │ No │ numeric │ Latitudinal │
277 │ │ │ │ dilution of │
278 │ │ │ │ precision, a │
279 │ │ │ │ dimensionless │
280 │ │ │ │ factor │
281 │ │ │ │ which should be │
282 │ │ │ │ multiplied by a │
283 │ │ │ │ base UERE to get │
284 │ │ │ │ an error │
285 │ │ │ │ estimate. │
286 ├───────────┼─────────┼─────────┼──────────────────┤
287 │vdop │ No │ numeric │ Altitude │
288 │ │ │ │ dilution of │
289 │ │ │ │ precision, a │
290 │ │ │ │ dimensionless │
291 │ │ │ │ factor │
292 │ │ │ │ which should be │
293 │ │ │ │ multiplied by a │
294 │ │ │ │ base UERE to get │
295 │ │ │ │ an error │
296 │ │ │ │ estimate. │
297 ├───────────┼─────────┼─────────┼──────────────────┤
298 │tdop │ No │ numeric │ Time dilution of │
299 │ │ │ │ precision, a │
300 │ │ │ │ dimensionless │
301 │ │ │ │ factor │
302 │ │ │ │ which should be │
303 │ │ │ │ multiplied by a │
304 │ │ │ │ base UERE to get │
305 │ │ │ │ an error │
306 │ │ │ │ estimate. │
307 ├───────────┼─────────┼─────────┼──────────────────┤
308 │hdop │ No │ numeric │ Horizontal │
309 │ │ │ │ dilution of │
310 │ │ │ │ precision, a │
311 │ │ │ │ dimensionless │
312 │ │ │ │ factor │
313 │ │ │ │ which should be │
314 │ │ │ │ multiplied by a │
315 │ │ │ │ base UERE to get │
316 │ │ │ │ a circular │
317 │ │ │ │ error estimate. │
318 ├───────────┼─────────┼─────────┼──────────────────┤
319 │pdop │ No │ numeric │ Spherical │
320 │ │ │ │ dilution of │
321 │ │ │ │ precision, a │
322 │ │ │ │ dimensionless │
323 │ │ │ │ factor │
324 │ │ │ │ which should be │
325 │ │ │ │ multiplied by a │
326 │ │ │ │ base UERE to get │
327 │ │ │ │ an error │
328 │ │ │ │ estimate. │
329 ├───────────┼─────────┼─────────┼──────────────────┤
330 │gdop │ No │ numeric │ Hyperspherical │
331 │ │ │ │ dilution of │
332 │ │ │ │ precision, a │
333 │ │ │ │ dimensionless │
334 │ │ │ │ factor │
335 │ │ │ │ which should be │
336 │ │ │ │ multiplied by a │
337 │ │ │ │ base UERE to get │
338 │ │ │ │ an error │
339 │ │ │ │ estimate. │
340 ├───────────┼─────────┼─────────┼──────────────────┤
341 │satellites │ Yes │ list │ List of │
342 │ │ │ │ satellite │
343 │ │ │ │ objects in │
344 │ │ │ │ skyview │
345 └───────────┴─────────┴─────────┴──────────────────┘
346 Many devices compute dilution of precision factors but do not
347 include them in their reports. Many that do report DOPs report only
348 HDOP, two-dimensional circular error. gpsd always passes through
349 whatever the device actually reports, then attempts to fill in
350 other DOPs by calculating the appropriate determinants in a
351 covariance matrix based on the satellite view. DOPs may be missing
352 if some of these determinants are singular. It can even happen that
353 the device reports an error estimate in meters when the
354 corresponding DOP is unavailable; some devices use more
355 sophisticated error modeling than the covariance calculation.
356 The satellite list objects have the following elements:
358 Table 3. Satellite object
360 ┌─────┬─────────┬─────────┬──────────────────┐
361 │Name │ Always? │ Type │ Description │
362 ├─────┼─────────┼─────────┼──────────────────┤
363 │PRN │ Yes │ numeric │ PRN ID of the │
364 │ │ │ │ satellite. 1-63 │
365 │ │ │ │ are GNSS │
366 │ │ │ │ satellites, │
367 │ │ │ │ 64-96 are │
368 │ │ │ │ GLONASS │
369 │ │ │ │ satellites, │
370 │ │ │ │ 100-164 are SBAS │
371 │ │ │ │ satellites │
372 ├─────┼─────────┼─────────┼──────────────────┤
373 │az │ Yes │ numeric │ Azimuth, degrees │
374 │ │ │ │ from true north. │
375 ├─────┼─────────┼─────────┼──────────────────┤
376 │el │ Yes │ numeric │ Elevation in │
377 │ │ │ │ degrees. │
378 ├─────┼─────────┼─────────┼──────────────────┤
379 │ss │ Yes │ numeric │ Signal strength │
380 │ │ │ │ in dB. │
381 ├─────┼─────────┼─────────┼──────────────────┤
382 │used │ Yes │ boolean │ Used in current │
383 │ │ │ │ solution? │
384 │ │ │ │ (SBAS/WAAS/EGNOS │
385 │ │ │ │ satellites │
386 │ │ │ │ may be │
387 │ │ │ │ flagged used if │
388 │ │ │ │ the solution has │
389 │ │ │ │ corrections from │
390 │ │ │ │ them, but │
391 │ │ │ │ not all drivers │
392 │ │ │ │ make this │
393 │ │ │ │ information │
394 │ │ │ │ available.) │
395 └─────┴─────────┴─────────┴──────────────────┘
396 Note that satellite objects do not have a "class" field, as they
397 are never shipped outside of a SKY object.
398 When the C client library parses a SKY response, it will assert the
400 SATELLITE_SET bit in the top-level set member.
401 Here's an example:
403 {"class":"SKY","device":"/dev/pts/1",
405 "time":"2005-07-08T11:28:07.114Z",
406 "xdop":1.55,"hdop":1.24,"pdop":1.99,
407 "satellites":[
408 {"PRN":23,"el":6,"az":84,"ss":0,"used":false},
409 {"PRN":28,"el":7,"az":160,"ss":0,"used":false},
410 {"PRN":8,"el":66,"az":189,"ss":44,"used":true},
411 {"PRN":29,"el":13,"az":273,"ss":0,"used":false},
412 {"PRN":10,"el":51,"az":304,"ss":29,"used":true},
413 {"PRN":4,"el":15,"az":199,"ss":36,"used":true},
414 {"PRN":2,"el":34,"az":241,"ss":43,"used":true},
415 {"PRN":27,"el":71,"az":76,"ss":43,"used":true}]}
416 GST
418 A GST object is a pseudorange noise report.
419 Table 4. GST object
421 ┌───────┬─────────┬─────────┬──────────────────┐
422 │Name │ Always? │ Type │ Description │
423 ├───────┼─────────┼─────────┼──────────────────┤
424 │class │ Yes │ string │ Fixed: "GST" │
425 ├───────┼─────────┼─────────┼──────────────────┤
426 │device │ No │ string │ Name of │
427 │ │ │ │ originating │
428 │ │ │ │ device │
429 ├───────┼─────────┼─────────┼──────────────────┤
430 │time │ No │ string │ Time/date stamp │
431 │ │ │ │ in ISO8601 │
432 │ │ │ │ format, UTC. May │
433 │ │ │ │ have a │
434 │ │ │ │ fractional │
435 │ │ │ │ part of up to │
436 │ │ │ │ .001sec │
437 │ │ │ │ precision. │
438 ├───────┼─────────┼─────────┼──────────────────┤
439 │rms │ No │ numeric │ Value of the │
440 │ │ │ │ standard │
441 │ │ │ │ deviation of the │
442 │ │ │ │ range inputs to │
443 │ │ │ │ the navigation │
444 │ │ │ │ process (range │
445 │ │ │ │ inputs include │
446 │ │ │ │ pseudoranges and │
447 │ │ │ │ DGPS │
448 │ │ │ │ corrections). │
449 ├───────┼─────────┼─────────┼──────────────────┤
450 │major │ No │ numeric │ Standard │
451 │ │ │ │ deviation of │
452 │ │ │ │ semi-major axis │
453 │ │ │ │ of error │
454 │ │ │ │ ellipse, in │
455 │ │ │ │ meters. │
456 ├───────┼─────────┼─────────┼──────────────────┤
457 │minor │ No │ numeric │ Standard │
458 │ │ │ │ deviation of │
459 │ │ │ │ semi-minor axis │
460 │ │ │ │ of error │
461 │ │ │ │ ellipse, in │
462 │ │ │ │ meters. │
463 ├───────┼─────────┼─────────┼──────────────────┤
464 │orient │ No │ numeric │ Orientation of │
465 │ │ │ │ semi-major axis │
466 │ │ │ │ of error │
467 │ │ │ │ ellipse, in │
468 │ │ │ │ degrees from │
469 │ │ │ │ true north. │
470 ├───────┼─────────┼─────────┼──────────────────┤
471 │lat │ No │ numeric │ Standard │
472 │ │ │ │ deviation of │
473 │ │ │ │ latitude error, │
474 │ │ │ │ in meters. │
475 ├───────┼─────────┼─────────┼──────────────────┤
476 │lon │ No │ numeric │ Standard │
477 │ │ │ │ deviation of │
478 │ │ │ │ longitude error, │
479 │ │ │ │ in meters. │
480 ├───────┼─────────┼─────────┼──────────────────┤
481 │alt │ No │ numeric │ Standard │
482 │ │ │ │ deviation of │
483 │ │ │ │ altitude error, │
484 │ │ │ │ in meters. │
485 └───────┴─────────┴─────────┴──────────────────┘
486 Here's an example:
487 {"class":"GST","device":"/dev/ttyUSB0",
489 "time":"2010-12-07T10:23:07.096Z","rms":2.440,
490 "major":1.660,"minor":1.120,"orient":68.989,
491 "lat":1.600,"lon":1.200,"alt":2.520}
492 ATT
494 An ATT object is a vehicle-attitude report. It is returned by
495 digital-compass and gyroscope sensors; depending on device, it may
496 include: heading, pitch, roll, yaw, gyroscope, and magnetic-field
497 readings. Because such sensors are often bundled as part of
498 marine-navigation systems, the ATT response may also include water
499 depth.
500 The "class" and "mode" fields will reliably be present. Others may
502 be reported or not depending on the specific device type.
503 Table 5. ATT object
505 ┌─────────┬─────────┬─────────┬──────────────────┐
506 │Name │ Always? │ Type │ Description │
507 ├─────────┼─────────┼─────────┼──────────────────┤
508 │class │ Yes │ string │ Fixed: "ATT" │
509 ├─────────┼─────────┼─────────┼──────────────────┤
510 │device │ Yes │ string │ Name of │
511 │ │ │ │ originating │
512 │ │ │ │ device │
513 ├─────────┼─────────┼─────────┼──────────────────┤
514 │time │ No │ string │ Time/date stamp │
515 │ │ │ │ in ISO8601 │
516 │ │ │ │ format, UTC. May │
517 │ │ │ │ have a │
518 │ │ │ │ fractional │
519 │ │ │ │ part of up to │
520 │ │ │ │ .001sec │
521 │ │ │ │ precision. │
522 ├─────────┼─────────┼─────────┼──────────────────┤
523 │heading │ No │ numeric │ Heading, degrees │
524 │ │ │ │ from true north. │
525 ├─────────┼─────────┼─────────┼──────────────────┤
526 │mag_st │ No │ string │ Magnetometer │
527 │ │ │ │ status. │
528 ├─────────┼─────────┼─────────┼──────────────────┤
529 │pitch │ No │ numeric │ Pitch in │
530 │ │ │ │ degrees. │
531 ├─────────┼─────────┼─────────┼──────────────────┤
532 │pitch_st │ No │ string │ Pitch sensor │
533 │ │ │ │ status. │
534 ├─────────┼─────────┼─────────┼──────────────────┤
535 │yaw │ No │ numeric │ Yaw in degrees │
536 ├─────────┼─────────┼─────────┼──────────────────┤
537 │yaw_st │ No │ string │ Yaw sensor │
538 │ │ │ │ status. │
539 ├─────────┼─────────┼─────────┼──────────────────┤
540 │roll │ No │ numeric │ Roll in degrees. │
541 ├─────────┼─────────┼─────────┼──────────────────┤
542 │roll_st │ No │ string │ Roll sensor │
543 │ │ │ │ status. │
544 ├─────────┼─────────┼─────────┼──────────────────┤
545 │dip │ No │ numeric │ Local magnetic │
546 │ │ │ │ inclination, │
547 │ │ │ │ degrees, │
548 │ │ │ │ positive when │
549 │ │ │ │ the magnetic │
550 │ │ │ │ field points │
551 │ │ │ │ downward (into │
552 │ │ │ │ the Earth). │
553 ├─────────┼─────────┼─────────┼──────────────────┤
554 │mag_len │ No │ numeric │ Scalar magnetic │
555 │ │ │ │ field strength. │
556 ├─────────┼─────────┼─────────┼──────────────────┤
557 │mag_x │ No │ numeric │ X component of │
558 │ │ │ │ magnetic field │
559 │ │ │ │ strength. │
560 ├─────────┼─────────┼─────────┼──────────────────┤
561 │mag_y │ No │ numeric │ Y component of │
562 │ │ │ │ magnetic field │
563 │ │ │ │ strength. │
564 ├─────────┼─────────┼─────────┼──────────────────┤
565 │mag_z │ No │ numeric │ Z component of │
566 │ │ │ │ magnetic field │
567 │ │ │ │ strength. │
568 ├─────────┼─────────┼─────────┼──────────────────┤
569 │acc_len │ No │ numeric │ Scalar │
570 │ │ │ │ acceleration. │
571 ├─────────┼─────────┼─────────┼──────────────────┤
572 │acc_x │ No │ numeric │ X component of │
573 │ │ │ │ acceleration. │
574 ├─────────┼─────────┼─────────┼──────────────────┤
575 │acc_y │ No │ numeric │ Y component of │
576 │ │ │ │ acceleration. │
577 ├─────────┼─────────┼─────────┼──────────────────┤
578 │acc_z │ No │ numeric │ Z component of │
579 │ │ │ │ acceleration. │
580 ├─────────┼─────────┼─────────┼──────────────────┤
581 │gyro_x │ No │ numeric │ X component of │
582 │ │ │ │ acceleration. │
583 ├─────────┼─────────┼─────────┼──────────────────┤
584 │gyro_y │ No │ numeric │ Y component of │
585 │ │ │ │ acceleration. │
586 ├─────────┼─────────┼─────────┼──────────────────┤
587 │depth │ No │ numeric │ Water depth in │
588 │ │ │ │ meters. │
589 ├─────────┼─────────┼─────────┼──────────────────┤
590 │temp │ No │ numeric │ Temperature at │
591 │ │ │ │ sensor, degrees │
592 │ │ │ │ centigrade. │
593 └─────────┴─────────┴─────────┴──────────────────┘
594 The heading, pitch, and roll status codes (if present) vary by
595 device. For the TNT Revolution digital compasses, they are coded as
596 follows:
597 Table 6. Device flags
599 ┌─────┬────────────────────────────┐
600 │Code │ Description │
601 ├─────┼────────────────────────────┤
602 │C │ magnetometer calibration │
603 │ │ alarm │
604 ├─────┼────────────────────────────┤
605 │L │ low alarm │
606 ├─────┼────────────────────────────┤
607 │M │ low warning │
608 ├─────┼────────────────────────────┤
609 │N │ normal │
610 ├─────┼────────────────────────────┤
611 │O │ high warning │
612 ├─────┼────────────────────────────┤
613 │P │ high alarm │
614 ├─────┼────────────────────────────┤
615 │V │ magnetometer voltage level │
616 │ │ alarm │
617 └─────┴────────────────────────────┘
618 When the C client library parses a response of this kind, it will
619 assert ATT_IS.
620 Here's an example:
622 {"class":"ATT","time":1270938096.843,
624 "heading":14223.00,"mag_st":"N",
625 "pitch":169.00,"pitch_st":"N", "roll":-43.00,"roll_st":"N",
626 "dip":13641.000,"mag_x":2454.000}
627 And here are the commands:
629 ?VERSION;
631 Returns an object with the following attributes:
632 Table 7. VERSION object
634 ┌────────────┬─────────┬─────────┬──────────────────┐
635 │Name │ Always? │ Type │ Description │
636 ├────────────┼─────────┼─────────┼──────────────────┤
637 │class │ Yes │ string │ Fixed: "VERSION" │
638 ├────────────┼─────────┼─────────┼──────────────────┤
639 │release │ Yes │ string │ Public release │
640 │ │ │ │ level │
641 ├────────────┼─────────┼─────────┼──────────────────┤
642 │rev │ Yes │ string │ Internal │
643 │ │ │ │ revision-control │
644 │ │ │ │ level. │
645 ├────────────┼─────────┼─────────┼──────────────────┤
646 │proto_major │ Yes │ numeric │ API major │
647 │ │ │ │ revision level. │
648 ├────────────┼─────────┼─────────┼──────────────────┤
649 │proto_minor │ Yes │ numeric │ API minor │
650 │ │ │ │ revision level. │
651 ├────────────┼─────────┼─────────┼──────────────────┤
652 │remote │ No │ string │ URL of the │
653 │ │ │ │ remote daemon │
654 │ │ │ │ reporting this │
655 │ │ │ │ version. If │
656 │ │ │ │ empty, │
657 │ │ │ │ this is the │
658 │ │ │ │ version of the │
659 │ │ │ │ local daemon. │
660 └────────────┴─────────┴─────────┴──────────────────┘
661 The daemon ships a VERSION response to each client when the client
662 first connects to it.
663 When the C client library parses a response of this kind, it will
665 assert the VERSION_SET bit in the top-level set member.
666 Here's an example:
668 {"class":"VERSION","version":"2.40dev",
670 "rev":"06f62e14eae9886cde907dae61c124c53eb1101f",
671 "proto_major":3,"proto_minor":1
672 }
673 ?DEVICES;
675 Returns a device list object with the following elements:
676 Table 8. DEVICES object
678 ┌────────┬─────────┬────────┬──────────────────┐
679 │Name │ Always? │ Type │ Description │
680 ├────────┼─────────┼────────┼──────────────────┤
681 │class │ Yes │ string │ Fixed: "DEVICES" │
682 ├────────┼─────────┼────────┼──────────────────┤
683 │devices │ Yes │ list │ List of device │
684 │ │ │ │ descriptions │
685 ├────────┼─────────┼────────┼──────────────────┤
686 │remote │ No │ string │ URL of the │
687 │ │ │ │ remote daemon │
688 │ │ │ │ reporting the │
689 │ │ │ │ device set. If │
690 │ │ │ │ empty, │
691 │ │ │ │ this is a │
692 │ │ │ │ DEVICES response │
693 │ │ │ │ from the local │
694 │ │ │ │ daemon. │
695 └────────┴─────────┴────────┴──────────────────┘
696 When the C client library parses a response of this kind, it will
697 assert the DEVICELIST_SET bit in the top-level set member.
698 Here's an example:
700 {"class"="DEVICES","devices":[
702 {"class":"DEVICE","path":"/dev/pts/1","flags":1,"driver":"SiRF binary"},
703 {"class":"DEVICE","path":"/dev/pts/3","flags":4,"driver":"AIVDM"}]}
704 The daemon occasionally ships a bare DEVICE object to the client
706 (that is, one not inside a DEVICES wrapper). The data content of
707 these objects will be described later as a response to the ?DEVICE
708 command.
709 ?WATCH;
711 This command sets watcher mode. It also sets or elicits a report of
712 per-subscriber policy and the raw bit. An argument WATCH object
713 changes the subscriber's policy. The response describes the
714 subscriber's policy. The response will also include a DEVICES
715 object.
716 A WATCH object has the following elements:
718 Table 9. WATCH object
720 ┌────────┬─────────┬─────────┬──────────────────┐
721 │Name │ Always? │ Type │ Description │
722 ├────────┼─────────┼─────────┼──────────────────┤
723 │class │ Yes │ string │ Fixed: "WATCH" │
724 ├────────┼─────────┼─────────┼──────────────────┤
725 │enable │ No │ boolean │ Enable (true) or │
726 │ │ │ │ disable (false) │
727 │ │ │ │ watcher mode. │
728 │ │ │ │ Default is │
729 │ │ │ │ true. │
730 ├────────┼─────────┼─────────┼──────────────────┤
731 │json │ No │ boolean │ Enable (true) or │
732 │ │ │ │ disable (false) │
733 │ │ │ │ dumping of JSON │
734 │ │ │ │ reports. │
735 │ │ │ │ Default is │
736 │ │ │ │ false. │
737 ├────────┼─────────┼─────────┼──────────────────┤
738 │nmea │ No │ boolean │ Enable (true) or │
739 │ │ │ │ disable (false) │
740 │ │ │ │ dumping of │
741 │ │ │ │ binary │
742 │ │ │ │ packets as │
743 │ │ │ │ pseudo-NMEA. │
744 │ │ │ │ Default is │
745 │ │ │ │ false. │
746 ├────────┼─────────┼─────────┼──────────────────┤
747 │raw │ No │ integer │ Controls 'raw' │
748 │ │ │ │ mode. When this │
749 │ │ │ │ attribute is set │
750 │ │ │ │ to 1 for a │
751 │ │ │ │ channel, gpsd │
752 │ │ │ │ reports the │
753 │ │ │ │ unprocessed │
754 │ │ │ │ NMEA or AIVDM │
755 │ │ │ │ data stream from │
756 │ │ │ │ whatever device │
757 │ │ │ │ is attached. │
758 │ │ │ │ Binary GPS │
759 │ │ │ │ packets are │
760 │ │ │ │ hex-dumped. │
761 │ │ │ │ RTCM2 and RTCM3 │
762 │ │ │ │ packets │
763 │ │ │ │ are not dumped │
764 │ │ │ │ in raw mode. │
765 │ │ │ │ When this │
766 │ │ │ │ attribute is set │
767 │ │ │ │ to 2 for a │
768 │ │ │ │ channel that │
769 │ │ │ │ processes binary │
770 │ │ │ │ data, gpsd │
771 │ │ │ │ reports the │
772 │ │ │ │ received data │
773 │ │ │ │ verbatim │
774 │ │ │ │ without │
775 │ │ │ │ hex-dumping. │
776 ├────────┼─────────┼─────────┼──────────────────┤
777 │scaled │ No │ boolean │ If true, apply │
778 │ │ │ │ scaling divisors │
779 │ │ │ │ to output before │
780 │ │ │ │ dumping; │
781 │ │ │ │ default is │
782 │ │ │ │ false. │
783 ├────────┼─────────┼─────────┼──────────────────┤
784 │split24 │ No │ boolean │ If true, │
785 │ │ │ │ aggregate AIS │
786 │ │ │ │ type24 sentence │
787 │ │ │ │ parts. If │
788 │ │ │ │ false, │
789 │ │ │ │ report │
790 │ │ │ │ each part as a │
791 │ │ │ │ separate JSON │
792 │ │ │ │ object, leaving │
793 │ │ │ │ the │
794 │ │ │ │ client │
795 │ │ │ │ to match MMSIs │
796 │ │ │ │ and aggregate. │
797 │ │ │ │ Default is │
798 │ │ │ │ false. │
799 │ │ │ │ Applies only to │
800 │ │ │ │ AIS reports. │
801 ├────────┼─────────┼─────────┼──────────────────┤
802 │pps │ No │ boolean │ If true, emit │
803 │ │ │ │ the TOFF JSON │
804 │ │ │ │ message on each │
805 │ │ │ │ cycle and a │
806 │ │ │ │ PPS JSON │
807 │ │ │ │ message when the │
808 │ │ │ │ device issues │
809 │ │ │ │ 1PPS. Default is │
810 │ │ │ │ false. │
811 ├────────┼─────────┼─────────┼──────────────────┤
812 │device │ No │ string │ If present, │
813 │ │ │ │ enable watching │
814 │ │ │ │ only of the │
815 │ │ │ │ specified device │
816 │ │ │ │ rather than │
817 │ │ │ │ all devices. │
818 │ │ │ │ Useful with raw │
819 │ │ │ │ and NMEA modes │
820 │ │ │ │ in which │
821 │ │ │ │ device responses │
822 │ │ │ │ aren't tagged. │
823 │ │ │ │ Has no effect │
824 │ │ │ │ when used │
825 │ │ │ │ with │
826 │ │ │ │ enable:false. │
827 ├────────┼─────────┼─────────┼──────────────────┤
828 │remote │ No │ string │ URL of the │
829 │ │ │ │ remote daemon │
830 │ │ │ │ reporting the │
831 │ │ │ │ watch set. If │
832 │ │ │ │ empty, │
833 │ │ │ │ this is a WATCH │
834 │ │ │ │ response from │
835 │ │ │ │ the local │
836 │ │ │ │ daemon. │
837 └────────┴─────────┴─────────┴──────────────────┘
838 There is an additional boolean "timing" attribute which is
839 undocumented because that portion of the interface is considered
840 unstable and for developer use only.
841 In watcher mode, GPS reports are dumped as TPV and SKY responses.
843 AIS, Subframe and RTCM reporting is described in the next section.
844 When the C client library parses a response of this kind, it will
846 assert the POLICY_SET bit in the top-level set member.
847 Here's an example:
849 {"class":"WATCH", "raw":1,"scaled":true}
851 ?POLL;
853 The POLL command requests data from the last-seen fixes on all
854 active GPS devices. Devices must previously have been activated by
855 ?WATCH to be pollable.
856 Polling can lead to possibly surprising results when it is used on
858 a device such as an NMEA GPS for which a complete fix has to be
859 accumulated from several sentences. If you poll while those
860 sentences are being emitted, the response will contain the last
861 complete fix data and may be as much as one cycle time (typically 1
862 second) stale.
863 The POLL response will contain a timestamped list of TPV objects
865 describing cached data, and a timestamped list of SKY objects
866 describing satellite configuration. If a device has not seen fixes,
867 it will be reported with a mode field of zero.
868 Table 10. POLL object
870 ┌───────┬─────────┬────────────┬──────────────────┐
871 │Name │ Always? │ Type │ Description │
872 ├───────┼─────────┼────────────┼──────────────────┤
873 │class │ Yes │ string │ Fixed: "POLL" │
874 ├───────┼─────────┼────────────┼──────────────────┤
875 │time │ Yes │ Numeric │ Timestamp in ISO │
876 │ │ │ │ 8601 format. May │
877 │ │ │ │ have a │
878 │ │ │ │ fractional │
879 │ │ │ │ part of up to │
880 │ │ │ │ .001sec │
881 │ │ │ │ precision. │
882 ├───────┼─────────┼────────────┼──────────────────┤
883 │active │ Yes │ Numeric │ Count of active │
884 │ │ │ │ devices. │
885 ├───────┼─────────┼────────────┼──────────────────┤
886 │tpv │ Yes │ JSON array │ Comma-separated │
887 │ │ │ │ list of TPV │
888 │ │ │ │ objects. │
889 ├───────┼─────────┼────────────┼──────────────────┤
890 │sky │ Yes │ JSON array │ Comma-separated │
891 │ │ │ │ list of SKY │
892 │ │ │ │ objects. │
893 └───────┴─────────┴────────────┴──────────────────┘
894 Here's an example of a POLL response:
895 {"class":"POLL","time":"2010-06-04T10:31:00.289Z","active":1,
897 "tpv":[{"class":"TPV","device":"/dev/ttyUSB0",
898 "time":"2010-09-08T13:33:06.095Z",
899 "ept":0.005,"lat":40.035093060,
900 "lon":-75.519748733,"track":99.4319,"speed":0.123,"mode":2}],
901 "sky":[{"class":"SKY","device":"/dev/ttyUSB0",
902 "time":1270517264.240,"hdop":9.20,
903 "satellites":[{"PRN":16,"el":55,"az":42,"ss":36,"used":true},
904 {"PRN":19,"el":25,"az":177,"ss":0,"used":false},
905 {"PRN":7,"el":13,"az":295,"ss":0,"used":false},
906 {"PRN":6,"el":56,"az":135,"ss":32,"used":true},
907 {"PRN":13,"el":47,"az":304,"ss":0,"used":false},
908 {"PRN":23,"el":66,"az":259,"ss":0,"used":false},
909 {"PRN":20,"el":7,"az":226,"ss":0,"used":false},
910 {"PRN":3,"el":52,"az":163,"ss":32,"used":true},
911 {"PRN":31,"el":16,"az":102,"ss":0,"used":false}
912 ]}]}
913 Note
915 Client software should not assume the field inventory of the
916 POLL response is fixed for all time. As gpsd collects and
917 caches more data from more sensor types, those data are likely
918 to find their way into this response.
919 TOFF
921 This message is emitted on each cycle and reports the offset
922 between the host's clock time and the GPS time at top of second
923 (actually, when the first data for the reporting cycle is
924 received).
925 This message exactly mirrors the PPS message except for two
927 details.
928 TOFF emits no NTP precision, this is assumed to be -2. See the NTP
930 documentation for their definition of precision.
931 The TOFF message reports the GPS time as derived from the GPS
933 serial data stream. The PPS message reports the GPS time as derived
934 from the GPS PPS pulse.
935 A TOFF object has the following elements:
937 Table 11. TOFF object
939 ┌───────────┬─────────┬─────────┬──────────────────┐
940 │Name │ Always? │ Type │ Description │
941 ├───────────┼─────────┼─────────┼──────────────────┤
942 │class │ Yes │ string │ Fixed: "TOFF" │
943 ├───────────┼─────────┼─────────┼──────────────────┤
944 │device │ Yes │ string │ Name of │
945 │ │ │ │ originating │
946 │ │ │ │ device │
947 ├───────────┼─────────┼─────────┼──────────────────┤
948 │real_sec │ Yes │ numeric │ seconds from the │
949 │ │ │ │ GPS clock │
950 ├───────────┼─────────┼─────────┼──────────────────┤
951 │real_nsec │ Yes │ numeric │ nanoseconds from │
952 │ │ │ │ the GPS clock │
953 ├───────────┼─────────┼─────────┼──────────────────┤
954 │clock_sec │ Yes │ numeric │ seconds from the │
955 │ │ │ │ system clock │
956 ├───────────┼─────────┼─────────┼──────────────────┤
957 │clock_nsec │ Yes │ numeric │ nanoseconds from │
958 │ │ │ │ the system clock │
959 └───────────┴─────────┴─────────┴──────────────────┘
960 This message is emitted once per second to watchers of a device and
961 is intended to report the time stamps of the in-band report of the
962 GPS and seconds as reported by the system clock (which may be
963 NTP-corrected) when the first valid timestamp of the reporting
964 cycle was seen.
965 The message contains two second/nanosecond pairs: real_sec and
967 real_nsec contain the time the GPS thinks it was at the start of
968 the current cycle; clock_sec and clock_nsec contain the time the
969 system clock thinks it was on receipt of the first timing message
970 of the cycle. real_nsec is always to nanosecond precision.
971 clock_nsec is nanosecond precision on most systems.
972 Here's an example:
974 {"class":"TOFF","device":"/dev/ttyUSB0",
976 "real_sec":1330212592, "real_nsec":343182,
977 "clock_sec":1330212592,"clock_nsec":343184,
978 "precision":-2}}
979 PPS
981 This message is emitted each time the daemon sees a valid PPS
982 (Pulse Per Second) strobe from a device.
983 This message exactly mirrors the TOFF message except for two
985 details.
986 PPS emits the NTP precision. See the NTP documentation for their
988 definition of precision.
989 The TOFF message reports the GPS time as derived from the GPS
991 serial data stream. The PPS message reports the GPS time as derived
992 from the GPS PPS pulse.
993 There are various sources of error in the reported clock times. The
995 speed of the serial connection between the GPS and the system adds
996 a delay to start of cycle detection. An even bigger error is added
997 by the variable computation time inside the GPS. Taken together the
998 time derived from the start of the GPS cycle can have offsets of 10
999 millisecond to 700 milliseconds and combined jjitter and wander of
1000 100 to 300 millisecond.
1001 A PPS object has the following elements:
1003 Table 12. PPS object
1005 ┌───────────┬─────────┬─────────┬──────────────────┐
1006 │Name │ Always? │ Type │ Description │
1007 ├───────────┼─────────┼─────────┼──────────────────┤
1008 │class │ Yes │ string │ Fixed: "PPS" │
1009 ├───────────┼─────────┼─────────┼──────────────────┤
1010 │device │ Yes │ string │ Name of │
1011 │ │ │ │ originating │
1012 │ │ │ │ device │
1013 ├───────────┼─────────┼─────────┼──────────────────┤
1014 │real_sec │ Yes │ numeric │ seconds from the │
1015 │ │ │ │ PPS source │
1016 ├───────────┼─────────┼─────────┼──────────────────┤
1017 │real_nsec │ Yes │ numeric │ nanoseconds from │
1018 │ │ │ │ the PPS source │
1019 ├───────────┼─────────┼─────────┼──────────────────┤
1020 │clock_sec │ Yes │ numeric │ seconds from the │
1021 │ │ │ │ system clock │
1022 ├───────────┼─────────┼─────────┼──────────────────┤
1023 │clock_nsec │ Yes │ numeric │ nanoseconds from │
1024 │ │ │ │ the system clock │
1025 ├───────────┼─────────┼─────────┼──────────────────┤
1026 │precision │ Yes │ numeric │ NTP style │
1027 │ │ │ │ estimate of PPS │
1028 │ │ │ │ precision │
1029 └───────────┴─────────┴─────────┴──────────────────┘
1030 This message is emitted once per second to watchers of a device
1031 emitting PPS, and reports the time of the start of the GPS second
1032 (when the 1PPS arrives) and seconds as reported by the system clock
1033 (which may be NTP-corrected) at that moment.
1034 The message contains two second/nanosecond pairs: real_sec and
1036 real_nsec contain the time the GPS thinks it was at the PPS edge;
1037 clock_sec and clock_nsec contain the time the system clock thinks
1038 it was at the PPS edge. real_nsec is always to nanosecond
1039 precision. clock_nsec is nanosecond precision on most systems.
1040 There are various sources of error in the reported clock times. For
1042 PPS delivered via a real serial-line strobe, serial-interrupt
1043 latency plus processing time to the timer call should be bounded
1044 above by about 10 microseconds; that can be reduced to less than 1
1045 microsecond if your kernel supports RFC 2783. USB1.1-to-serial
1046 control-line emulation is limited to about 1 millisecond. seconds.
1047 Here's an example:
1049 {"class":"PPS","device":"/dev/ttyUSB0",
1051 "real_sec":1330212592, "real_nsec":343182,
1052 "clock_sec":1330212592,"clock_nsec":343184,
1053 "precision":-3}
1054 OSC
1056 This message reports the status of a GPS-disciplined oscillator
1057 (GPSDO). The GPS PPS output (which has excellent long-term
1058 stability) is typically used to discipline a local oscillator with
1059 much better short-term stability (such as a rubidium atomic clock).
1060 An OSC object has the following elements:
1062 Table 13. OSC object
1064 ┌────────────┬─────────┬─────────┬──────────────────┐
1065 │Name │ Always? │ Type │ Description │
1066 ├────────────┼─────────┼─────────┼──────────────────┤
1067 │class │ Yes │ string │ Fixed: "OSC" │
1068 ├────────────┼─────────┼─────────┼──────────────────┤
1069 │device │ Yes │ string │ Name of │
1070 │ │ │ │ originating │
1071 │ │ │ │ device. │
1072 ├────────────┼─────────┼─────────┼──────────────────┤
1073 │running │ Yes │ boolean │ If true, the │
1074 │ │ │ │ oscillator is │
1075 │ │ │ │ currently │
1076 │ │ │ │ running. │
1077 │ │ │ │ Oscillators may │
1078 │ │ │ │ require warm-up │
1079 │ │ │ │ time at start of │
1080 │ │ │ │ day. │
1081 ├────────────┼─────────┼─────────┼──────────────────┤
1082 │reference │ Yes │ boolean │ If true, the │
1083 │ │ │ │ oscillator is │
1084 │ │ │ │ receiving a GPS │
1085 │ │ │ │ PPS signal. │
1086 ├────────────┼─────────┼─────────┼──────────────────┤
1087 │disciplined │ Yes │ boolean │ If true, the GPS │
1088 │ │ │ │ PPS signal is │
1089 │ │ │ │ sufficiently │
1090 │ │ │ │ stable and is │
1091 │ │ │ │ being used to │
1092 │ │ │ │ discipline the │
1093 │ │ │ │ local │
1094 │ │ │ │ oscillator. │
1095 ├────────────┼─────────┼─────────┼──────────────────┤
1096 │delta │ Yes │ numeric │ The time │
1097 │ │ │ │ difference (in │
1098 │ │ │ │ nanoseconds) │
1099 │ │ │ │ between the │
1100 │ │ │ │ GPS-disciplined │
1101 │ │ │ │ oscillator PPS │
1102 │ │ │ │ output pulse and │
1103 │ │ │ │ the most recent │
1104 │ │ │ │ GPS PPS input │
1105 │ │ │ │ pulse. │
1106 └────────────┴─────────┴─────────┴──────────────────┘
1107 Here's an example:
1108 {"class":"OSC","running":true,"device":"/dev/ttyUSB0",
1110 "reference":true,"disciplined":true,"delta":67}
1111 ?DEVICE
1113 This command reports (when followed by ';') the state of a device,
1114 or sets (when followed by '=' and a DEVICE object) device-specific
1115 control bits, notably the device's speed and serial mode and the
1116 native-mode bit. The parameter-setting form will be rejected if
1117 more than one client is attached to the channel.
1118 Pay attention to the response, because it is possible for this
1120 command to fail if the GPS does not support a speed-switching
1121 command or only supports some combinations of serial modes. In case
1122 of failure, the daemon and GPS will continue to communicate at the
1123 old speed.
1124 Use the parameter-setting form with caution. On USB and Bluetooth
1126 GPSes it is also possible for serial mode setting to fail either
1127 because the serial adaptor chip does not support non-8N1 modes or
1128 because the device firmware does not properly synchronize the
1129 serial adaptor chip with the UART on the GPS chipset when the speed
1130 changes. These failures can hang your device, possibly requiring a
1131 GPS power cycle or (in extreme cases) physically disconnecting the
1132 NVRAM backup battery.
1133 A DEVICE object has the following elements:
1135 Table 14. DEVICE object
1137 ┌──────────┬──────────────────┬─────────┬────────────────────┐
1138 │Name │ Always? │ Type │ Description │
1139 ├──────────┼──────────────────┼─────────┼────────────────────┤
1140 │class │ Yes │ string │ Fixed: "DEVICE" │
1141 ├──────────┼──────────────────┼─────────┼────────────────────┤
1142 │path │ No │ string │ Name the device │
1143 │ │ │ │ for which the │
1144 │ │ │ │ control bits are │
1145 │ │ │ │ being │
1146 │ │ │ │ reported, or for │
1147 │ │ │ │ which they are │
1148 │ │ │ │ to be applied. │
1149 │ │ │ │ This │
1150 │ │ │ │ attribute │
1151 │ │ │ │ may be omitted │
1152 │ │ │ │ only when there │
1153 │ │ │ │ is exactly one │
1154 │ │ │ │ subscribed │
1155 │ │ │ │ channel. │
1156 ├──────────┼──────────────────┼─────────┼────────────────────┤
1157 │activated │ No │ string │ Time the device │
1158 │ │ │ │ was activated as │
1159 │ │ │ │ an ISO8601 │
1160 │ │ │ │ timestamp. │
1161 │ │ │ │ If the device is │
1162 │ │ │ │ inactive this │
1163 │ │ │ │ attribute is │
1164 │ │ │ │ absent. │
1165 ├──────────┼──────────────────┼─────────┼────────────────────┤
1166 │flags │ No │ integer │ Bit vector of │
1167 │ │ │ │ property flags. │
1168 │ │ │ │ Currently defined │
1169 │ │ │ │ flags are: │
1170 │ │ │ │ describe │
1171 │ │ │ │ packet types seen │
1172 │ │ │ │ so far (GPS, │
1173 │ │ │ │ RTCM2, RTCM3, │
1174 │ │ │ │ AIS). Won't │
1175 │ │ │ │ be reported if │
1176 │ │ │ │ empty, e.g. before │
1177 │ │ │ │ gpsd has seen │
1178 │ │ │ │ identifiable │
1179 │ │ │ │ packets from │
1180 │ │ │ │ the device. │
1181 ├──────────┼──────────────────┼─────────┼────────────────────┤
1182 │driver │ No │ string │ GPSD's name for │
1183 │ │ │ │ the device driver │
1184 │ │ │ │ type. Won't be │
1185 │ │ │ │ reported before │
1186 │ │ │ │ gpsd has seen │
1187 │ │ │ │ identifiable │
1188 │ │ │ │ packets from │
1189 │ │ │ │ the device. │
1190 ├──────────┼──────────────────┼─────────┼────────────────────┤
1191 │subtype │ When the daemon │ string │ Whatever version │
1192 │ │ sees a delayed │ │ information the │
1193 │ │ response to a │ │ device returned. │
1194 │ │ probe for │ │ │
1195 │ │ subtype or │ │ │
1196 │ │ firmware-version │ │ │
1197 │ │ information. │ │ │
1198 ├──────────┼──────────────────┼─────────┼────────────────────┤
1199 │bps │ No │ integer │ Device speed in │
1200 │ │ │ │ bits per second. │
1201 ├──────────┼──────────────────┼─────────┼────────────────────┤
1202 │parity │ No │ string │ N, O or E for no │
1203 │ │ │ │ parity, odd, or │
1204 │ │ │ │ even. │
1205 ├──────────┼──────────────────┼─────────┼────────────────────┤
1206 │stopbits │ Yes │ string │ Stop bits (1 or │
1207 │ │ │ │ 2). │
1208 ├──────────┼──────────────────┼─────────┼────────────────────┤
1209 │native │ No │ integer │ 0 means NMEA mode │
1210 │ │ │ │ and 1 means │
1211 │ │ │ │ alternate │
1212 │ │ │ │ mode (binary if it │
1213 │ │ │ │ has one, for SiRF │
1214 │ │ │ │ and Evermore │
1215 │ │ │ │ chipsets in │
1216 │ │ │ │ particular). │
1217 │ │ │ │ Attempting to set │
1218 │ │ │ │ this mode on a │
1219 │ │ │ │ non-GPS │
1220 │ │ │ │ device will │
1221 │ │ │ │ yield an error. │
1222 ├──────────┼──────────────────┼─────────┼────────────────────┤
1223 │cycle │ No │ real │ Device cycle time │
1224 │ │ │ │ in seconds. │
1225 ├──────────┼──────────────────┼─────────┼────────────────────┤
1226 │mincycle │ No │ real │ Device minimum │
1227 │ │ │ │ cycle time in │
1228 │ │ │ │ seconds. Reported │
1229 │ │ │ │ from ?DEVICE │
1230 │ │ │ │ when (and only │
1231 │ │ │ │ when) the rate is │
1232 │ │ │ │ switchable. It is │
1233 │ │ │ │ read-only and │
1234 │ │ │ │ not settable. │
1235 └──────────┴──────────────────┴─────────┴────────────────────┘
1236 The serial parameters will (bps, parity, stopbits) be omitted in a
1237 response describing a TCP/IP source such as an Ntrip, DGPSIP, or
1238 AIS feed; on a serial device they will always be present.
1239 The contents of the flags field should be interpreted as follows:
1241 Table 15. Device flags
1243 ┌───────────┬───────┬─────────────────────┐
1244 │C #define │ Value │ Description │
1245 ├───────────┼───────┼─────────────────────┤
1246 │SEEN_GPS │ 0x01 │ GPS data has been │
1247 │ │ │ seen on this device │
1248 ├───────────┼───────┼─────────────────────┤
1249 │SEEN_RTCM2 │ 0x02 │ RTCM2 data has been │
1250 │ │ │ seen on this device │
1251 ├───────────┼───────┼─────────────────────┤
1252 │SEEN_RTCM3 │ 0x04 │ RTCM3 data has been │
1253 │ │ │ seen on this device │
1254 ├───────────┼───────┼─────────────────────┤
1255 │SEEN_AIS │ 0x08 │ AIS data has been │
1256 │ │ │ seen on this device │
1257 └───────────┴───────┴─────────────────────┘
1258 When the C client library parses a response of this kind, it will
1259 assert the DEVICE_SET bit in the top-level set member.
1260 Here's an example:
1262 {"class":"DEVICE","bps":4800,"parity":"N","stopbits":1,"native":0}
1264 When a client is in watcher mode, the daemon will ship it DEVICE
1266 notifications when a device is added to the pool or deactivated.
1267 When the C client library parses a response of this kind, it will
1269 assert the DEVICE_SET bit in the top-level set member.
1270 Here's an example:
1272 {"class":"DEVICE","path":"/dev/pts1","activated":0}
1274 The daemon may ship an error object in response to a syntactically
1276 invalid command line or unknown command. It has the following elements:
1277 Table 16. ERROR notification object
1279 ┌────────┬─────────┬────────┬────────────────┐
1280 │Name │ Always? │ Type │ Description │
1281 ├────────┼─────────┼────────┼────────────────┤
1282 │class │ Yes │ string │ Fixed: "ERROR" │
1283 ├────────┼─────────┼────────┼────────────────┤
1284 │message │ Yes │ string │ Textual error │
1285 │ │ │ │ message │
1286 └────────┴─────────┴────────┴────────────────┘
1287 Here's an example:
1289 {"class":"ERROR","message":"Unrecognized request '?FOO'"}
1291 When the C client library parses a response of this kind, it will
1293 assert the ERR_SET bit in the top-level set member.
1294
1296 RTCM-104 is a family of serial protocols used for broadcasting
1297 pseudorange corrections from differential-GPS reference stations. Many
1298 GPS receivers can accept these corrections to improve their reporting
1299 accuracy.
1300 RTCM-104 comes in two major and incompatible flavors, 2.x and 3.x. Each
1302 major flavor has minor (compatible) revisions.
1303 The applicable standard for RTCM Version 2.x is RTCM Recommended
1305 Standards for Differential NAVSTAR GPS Service RTCM Paper 194-93/SC
1306 104-STD. For RTCM 3.1 it is RTCM Paper 177-2006-SC104-STD. Ordering
1307 instructions for both standards are accessible from the website of the
1308 Radio Technical Commission for Maritime Services[1] under
1309 "Publications".
1310 RTCM WIRE TRANSMISSIONS
1312 Differential-GPS correction stations consist of a GPS reference
1313 receiver coupled to a low frequency (LF) transmitter. The GPS reference
1314 receiver is a survey-grade GPS that does GPS carrier tracking and can
1315 work out its own position to a few millimeters. It generates range and
1316 range-rate corrections and encodes them into RTCM104. It ships the
1317 RTCM104 to the LF transmitter over serial rs-232 signal at 100 baud or
1318 200 baud depending on the requirements of the transmitter.
1319 The LF transmitter broadcasts the approximately 300khz radio signal
1321 that differential-GPS radio receivers pick up. Transmitters that are
1322 meant to have a higher range will need to transmit at the slower rate.
1323 The higher the data rate the harder it will be for the remote radio
1324 receiver to receive with a good signal-to-noise ration. (Higher data
1325 rate signals can't be averaged over as long a time frame, hence they
1326 appear noisier.)
1327 RTCM WIRE FORMATS
1329 An RTCM 2.x message consists of a sequence of up to 33 30-bit words.
1330 The 24 most significant bits of each word are data and the six least
1331 significant bits are parity. The parity algorithm used is the same
1332 ISGPS-2000 as that used on GPS satellite downlinks. Each RTCM 2.x
1333 message consists of two header words followed by zero or more data
1334 words, depending upon message type.
1335 An RTCM 3.x message begins with a fixed leader byte 0xD3. That is
1337 followed by six bits of version information and 10 bits of payload
1338 length information. Following that is the payload; following the
1339 payload is a 3-byte checksum of the payload using the Qualcomm CRC-24Q
1340 algorithm.
1341 RTCM2 JSON FORMAT
1343 Each RTCM2 message is dumped as a single JSON object per message, with
1344 the message fields as attributes of that object. Arrays of satellite,
1345 station, and constellation statistics become arrays of JSON
1346 sub-objects. Each sentence will normally also have a "device" field
1347 containing the pathname of the originating device.
1348 All attributes other than the device field are mandatory. Header
1350 attributes are emitted before others.
1351 Header portion
1353 Table 17. SKY object
1354 ┌───────────────┬─────────┬─────────────────────────────┐
1355 │Name │ Type │ │
1356 │ │ │ Description │
1357 ├───────────────┼─────────┼─────────────────────────────┤
1358 │class │ string │ │
1359 │ │ │ Fixed: │
1360 │ │ │ "RTCM2". │
1361 ├───────────────┼─────────┼─────────────────────────────┤
1362 │type │ integer │ │
1363 │ │ │ Message │
1364 │ │ │ type (1-9). │
1365 ├───────────────┼─────────┼─────────────────────────────┤
1366 │station_id │ integer │ │
1367 │ │ │ The id of │
1368 │ │ │ the GPS │
1369 │ │ │ reference │
1370 │ │ │ receiver. │
1371 │ │ │ The LF │
1372 │ │ │ transmitters │
1373 │ │ │ also have │
1374 │ │ │ (different) │
1375 │ │ │ id numbers. │
1376 ├───────────────┼─────────┼─────────────────────────────┤
1377 │zcount │ real │ │
1378 │ │ │ The │
1379 │ │ │ reference │
1380 │ │ │ time of the │
1381 │ │ │ corrections │
1382 │ │ │ in the │
1383 │ │ │ message in │
1384 │ │ │ seconds │
1385 │ │ │ within the │
1386 │ │ │ current │
1387 │ │ │ hour. Note │
1388 │ │ │ that it is │
1389 │ │ │ in GPS time, │
1390 │ │ │ which is │
1391 │ │ │ some seconds │
1392 │ │ │ ahead of UTC │
1393 │ │ │ (see the │
1394 │ │ │ U.S. Naval │
1395 │ │ │ Observatory's │
1396 │ │ │ table of │
1397 │ │ │ leap second │
1398 │ │ │ corrections[2]). │
1399 ├───────────────┼─────────┼─────────────────────────────┤
1400 │seqnum │ integer │ │
1401 │ │ │ Sequence number. │
1402 │ │ │ Only 3 bits │
1403 │ │ │ wide, wraps │
1404 │ │ │ after 7. │
1405 ├───────────────┼─────────┼─────────────────────────────┤
1406 │length │ integer │ │
1407 │ │ │ The number of │
1408 │ │ │ words after the │
1409 │ │ │ header that │
1410 │ │ │ comprise the │
1411 │ │ │ message. │
1412 ├───────────────┼─────────┼─────────────────────────────┤
1413 │station_health │ integer │ │
1414 │ │ │ Station │
1415 │ │ │ transmission │
1416 │ │ │ status. │
1417 │ │ │ Indicates the │
1418 │ │ │ health of the │
1419 │ │ │ beacon as a │
1420 │ │ │ reference │
1421 │ │ │ source. Any │
1422 │ │ │ nonzero value │
1423 │ │ │ means the │
1424 │ │ │ satellite is │
1425 │ │ │ probably │
1426 │ │ │ transmitting bad │
1427 │ │ │ data and should │
1428 │ │ │ not be used in a │
1429 │ │ │ fix. 6 means the │
1430 │ │ │ transmission is │
1431 │ │ │ unmonitored. 7 │
1432 │ │ │ means the │
1433 │ │ │ station is not │
1434 │ │ │ working │
1435 │ │ │ properly. Other │
1436 │ │ │ values are │
1437 │ │ │ defined by the │
1438 │ │ │ beacon operator. │
1439 └───────────────┴─────────┴─────────────────────────────┘
1440 <message type> is one of
1442 1
1444 full corrections - one message containing corrections for all
1445 GPS satellites in view. This is not common.
1446 3
1448 reference station parameters - the position of the reference
1449 station GPS antenna.
1450 4
1452 datum — the datum to which the DGPS data is referred.
1453 5
1455 constellation health — information about the satellites the
1456 beacon can see.
1457 6
1459 null message — just a filler.
1460 7
1462 radio beacon almanac — information about this or other beacons.
1463 9
1465 subset corrections — a message containing corrections for only
1466 a subset of the GPS satellites in view.
1467 16
1469 special message — a text message from the beacon operator.
1470 31
1472 GLONASS subset corrections — a message containing corrections
1473 for a set of the GLONASS satellites in view.
1474 Type 1 and 9: Correction data
1476 One or more satellite objects follow the header for type 1 or type
1477 9 messages. Here is the format:
1478 Table 18. Satellite object
1480 ┌──────┬─────────┬─────────────────────────┐
1481 │Name │ Type │ │
1482 │ │ │ Description │
1483 ├──────┼─────────┼─────────────────────────┤
1484 │ident │ integer │ │
1485 │ │ │ The PRN │
1486 │ │ │ number of │
1487 │ │ │ the │
1488 │ │ │ satellite │
1489 │ │ │ for which │
1490 │ │ │ this is │
1491 │ │ │ correction │
1492 │ │ │ data. │
1493 ├──────┼─────────┼─────────────────────────┤
1494 │udre │ integer │ │
1495 │ │ │ User │
1496 │ │ │ Differential │
1497 │ │ │ Range Error │
1498 │ │ │ (0-3). See │
1499 │ │ │ the table │
1500 │ │ │ following │
1501 │ │ │ for values. │
1502 ├──────┼─────────┼─────────────────────────┤
1503 │iod │ integer │ │
1504 │ │ │ Issue Of │
1505 │ │ │ Data, │
1506 │ │ │ matching the │
1507 │ │ │ IOD for the │
1508 │ │ │ current │
1509 │ │ │ ephemeris of │
1510 │ │ │ this │
1511 │ │ │ satellite, │
1512 │ │ │ as │
1513 │ │ │ transmitted │
1514 │ │ │ by the │
1515 │ │ │ satellite. │
1516 │ │ │ The IOD is a │
1517 │ │ │ unique tag │
1518 │ │ │ that │
1519 │ │ │ identifies │
1520 │ │ │ the │
1521 │ │ │ ephemeris; │
1522 │ │ │ the GPS │
1523 │ │ │ using the │
1524 │ │ │ DGPS │
1525 │ │ │ correction │
1526 │ │ │ and the DGPS │
1527 │ │ │ generating │
1528 │ │ │ the data │
1529 │ │ │ must use the │
1530 │ │ │ same orbital │
1531 │ │ │ positions │
1532 │ │ │ for the │
1533 │ │ │ satellite. │
1534 ├──────┼─────────┼─────────────────────────┤
1535 │prc │ real │ │
1536 │ │ │ The │
1537 │ │ │ pseudorange │
1538 │ │ │ error in │
1539 │ │ │ meters for │
1540 │ │ │ this │
1541 │ │ │ satellite as │
1542 │ │ │ measured by │
1543 │ │ │ the beacon │
1544 │ │ │ reference │
1545 │ │ │ receiver at │
1546 │ │ │ the epoch │
1547 │ │ │ indicated by │
1548 │ │ │ the z_count │
1549 │ │ │ in the │
1550 │ │ │ parent │
1551 │ │ │ record. │
1552 ├──────┼─────────┼─────────────────────────┤
1553 │rrc │ real │ │
1554 │ │ │ The rate of │
1555 │ │ │ change of │
1556 │ │ │ pseudorange │
1557 │ │ │ error in │
1558 │ │ │ meters/sec │
1559 │ │ │ for this │
1560 │ │ │ satellite as │
1561 │ │ │ measured by │
1562 │ │ │ the beacon │
1563 │ │ │ reference │
1564 │ │ │ receiver at │
1565 │ │ │ the epoch │
1566 │ │ │ indicated by │
1567 │ │ │ the z_count │
1568 │ │ │ field in the │
1569 │ │ │ parent │
1570 │ │ │ record. This │
1571 │ │ │ is used to │
1572 │ │ │ calculate │
1573 │ │ │ pseudorange │
1574 │ │ │ errors at │
1575 │ │ │ other │
1576 │ │ │ epochs, if │
1577 │ │ │ required by │
1578 │ │ │ the GPS │
1579 │ │ │ receiver. │
1580 └──────┴─────────┴─────────────────────────┘
1581 User Differential Range Error values are as follows:
1583 Table 19. UDRE values
1585 ┌──┬──────────────────────┐
1586 │0 │ 1-sigma error <= 1m │
1587 ├──┼──────────────────────┤
1588 │1 │ 1-sigma error <= 4m │
1589 ├──┼──────────────────────┤
1590 │2 │ 1-sigma error <= 8m │
1591 ├──┼──────────────────────┤
1592 │3 │ 1-sigma error > 8m │
1593 └──┴──────────────────────┘
1594 Here's an example:
1596 {"class":"RTCM2","type":1,
1598 "station_id":688,"zcount":843.0,"seqnum":5,"length":19,"station_health":6,
1599 "satellites":[
1600 {"ident":10,"udre":0,"iod":46,"prc":-2.400,"rrc":0.000},
1601 {"ident":13,"udre":0,"iod":94,"prc":-4.420,"rrc":0.000},
1602 {"ident":7,"udre":0,"iod":22,"prc":-5.160,"rrc":0.002},
1603 {"ident":2,"udre":0,"iod":34,"prc":-6.480,"rrc":0.000},
1604 {"ident":4,"udre":0,"iod":47,"prc":-8.860,"rrc":0.000},
1605 {"ident":8,"udre":0,"iod":76,"prc":-7.980,"rrc":0.002},
1606 {"ident":5,"udre":0,"iod":99,"prc":-8.260,"rrc":0.002},
1607 {"ident":23,"udre":0,"iod":81,"prc":-8.060,"rrc":0.000},
1608 {"ident":16,"udre":0,"iod":70,"prc":-11.740,"rrc":0.000},
1609 {"ident":30,"udre":0,"iod":4,"prc":-18.960,"rrc":-0.006},
1610 {"ident":29,"udre":0,"iod":101,"prc":-24.960,"rrc":-0.002}
1611 ]}
1612 Type 3: Reference Station Parameters
1614 Here are the payload members of a type 3 (Reference Station
1615 Parameters) message:
1616 Table 20. Reference Station Parameters
1618 ┌─────┬──────┬────────────────────────┐
1619 │Name │ Type │ │
1620 │ │ │ Description │
1621 ├─────┼──────┼────────────────────────┤
1622 │x │ real │ │
1623 │ │ │ ECEF X │
1624 │ │ │ coordinate. │
1625 ├─────┼──────┼────────────────────────┤
1626 │y │ real │ │
1627 │ │ │ ECEF Y │
1628 │ │ │ coordinate. │
1629 ├─────┼──────┼────────────────────────┤
1630 │z │ real │ │
1631 │ │ │ ECEF Z │
1632 │ │ │ coordinate. │
1633 └─────┴──────┴────────────────────────┘
1634 The coordinates are the position of the station, in meters to two
1636 decimal places, in Earth Centred Earth Fixed coordinates. These are
1637 usually referred to the WGS84 reference frame, but may be referred
1638 to NAD83 in the US (essentially identical to WGS84 for all except
1639 geodesists), or to some other reference frame in other parts of the
1640 world.
1641 An invalid reference message is represented by a type 3 header
1643 without payload fields.
1644 Here's an example:
1646 {"class":"RTCM2","type":3,
1648 "station_id":652,"zcount":1657.2,"seqnum":2,"length":4,"station_health":6,
1649 "x":3878620.92,"y":670281.40,"z":5002093.59
1650 }
1651 Type 4: Datum
1653 Here are the payload members of a type 4 (Datum) message:
1654 Table 21. Datum
1656 ┌───────────┬─────────┬────────────────────────┐
1657 │Name │ Type │ │
1658 │ │ │ Description │
1659 ├───────────┼─────────┼────────────────────────┤
1660 │dgnss_type │ string │ │
1661 │ │ │ Either │
1662 │ │ │ "GPS", │
1663 │ │ │ "GLONASS", │
1664 │ │ │ "GALILEO", │
1665 │ │ │ or │
1666 │ │ │ "UNKNOWN". │
1667 ├───────────┼─────────┼────────────────────────┤
1668 │dat │ integer │ │
1669 │ │ │ 0 or 1 and │
1670 │ │ │ indicates │
1671 │ │ │ the sense │
1672 │ │ │ of the │
1673 │ │ │ offset │
1674 │ │ │ shift given │
1675 │ │ │ by dx, dy, │
1676 │ │ │ dz. dat = 0 │
1677 │ │ │ means that │
1678 │ │ │ the station │
1679 │ │ │ coordinates │
1680 │ │ │ (in the │
1681 │ │ │ reference │
1682 │ │ │ message) │
1683 │ │ │ are │
1684 │ │ │ referred to │
1685 │ │ │ a local │
1686 │ │ │ datum and │
1687 │ │ │ that adding │
1688 │ │ │ dx, dy, dz │
1689 │ │ │ to that │
1690 │ │ │ position │
1691 │ │ │ will render │
1692 │ │ │ it in GNSS │
1693 │ │ │ coordinates │
1694 │ │ │ (WGS84 for │
1695 │ │ │ GPS). If │
1696 │ │ │ dat = 1 │
1697 │ │ │ then the │
1698 │ │ │ ref station │
1699 │ │ │ position is │
1700 │ │ │ in GNSS │
1701 │ │ │ coordinates │
1702 │ │ │ and adding │
1703 │ │ │ dx, dy, dz │
1704 │ │ │ will give │
1705 │ │ │ it referred │
1706 │ │ │ to the │
1707 │ │ │ local │
1708 │ │ │ datum. │
1709 ├───────────┼─────────┼────────────────────────┤
1710 │datum_name │ string │ │
1711 │ │ │ A standard │
1712 │ │ │ name for │
1713 │ │ │ the datum. │
1714 ├───────────┼─────────┼────────────────────────┤
1715 │dx │ real │ │
1716 │ │ │ X offset. │
1717 ├───────────┼─────────┼────────────────────────┤
1718 │dy │ real │ │
1719 │ │ │ Y offset. │
1720 ├───────────┼─────────┼────────────────────────┤
1721 │dz │ real │ │
1722 │ │ │ Z offset. │
1723 └───────────┴─────────┴────────────────────────┘
1724 <dx> <dy> <dz> are offsets to convert from local datum to GNSS
1726 datum or vice versa. These fields are optional.
1727 An invalid datum message is represented by a type 4 header without
1729 payload fields.
1730 Type 5: Constellation Health
1732 One or more of these follow the header for type 5 messages — one
1733 for each satellite.
1734 Here is the format:
1736 Table 22. Constellation health
1738 ┌────────────┬─────────┬──────────────────────────┐
1739 │Name │ Type │ │
1740 │ │ │ Description │
1741 ├────────────┼─────────┼──────────────────────────┤
1742 │ident │ integer │ │
1743 │ │ │ The PRN │
1744 │ │ │ number of │
1745 │ │ │ the │
1746 │ │ │ satellite. │
1747 ├────────────┼─────────┼──────────────────────────┤
1748 │iodl │ bool │ │
1749 │ │ │ True │
1750 │ │ │ indicates │
1751 │ │ │ that this │
1752 │ │ │ information │
1753 │ │ │ relates to │
1754 │ │ │ the │
1755 │ │ │ satellite │
1756 │ │ │ information │
1757 │ │ │ in an │
1758 │ │ │ accompanying │
1759 │ │ │ type 1 or │
1760 │ │ │ type 9 │
1761 │ │ │ message. │
1762 ├────────────┼─────────┼──────────────────────────┤
1763 │health │ integer │ 0 indicates that the │
1764 │ │ │ satellite is healthy. │
1765 │ │ │ Any other value │
1766 │ │ │ indicates a │
1767 │ │ │ problem (coding is not │
1768 │ │ │ known)..PP │
1769 ├────────────┼─────────┼──────────────────────────┤
1770 │snr │ integer │ │
1771 │ │ │ The │
1772 │ │ │ carrier/noise │
1773 │ │ │ ratio of the │
1774 │ │ │ received │
1775 │ │ │ signal in │
1776 │ │ │ the range 25 │
1777 │ │ │ to 55 │
1778 │ │ │ dB(Hz). │
1779 ├────────────┼─────────┼──────────────────────────┤
1780 │health_en │ bool │ │
1781 │ │ │ If set to │
1782 │ │ │ True it │
1783 │ │ │ indicates │
1784 │ │ │ that the │
1785 │ │ │ satellite is │
1786 │ │ │ healthy even │
1787 │ │ │ if the │
1788 │ │ │ satellite │
1789 │ │ │ navigation │
1790 │ │ │ data says it │
1791 │ │ │ is unhealthy. │
1792 ├────────────┼─────────┼──────────────────────────┤
1793 │new_data │ bool │ True indicates that the │
1794 │ │ │ IOD for this satellite │
1795 │ │ │ will │
1796 │ │ │ soon be updated │
1797 │ │ │ in type 1 or 9 │
1798 │ │ │ messages..PP │
1799 ├────────────┼─────────┼──────────────────────────┤
1800 │los_warning │ bool │ │
1801 │ │ │ Line-of-sight │
1802 │ │ │ warning. True │
1803 │ │ │ indicates │
1804 │ │ │ that the │
1805 │ │ │ satellite │
1806 │ │ │ will shortly │
1807 │ │ │ go unhealthy. │
1808 ├────────────┼─────────┼──────────────────────────┤
1809 │tou │ integer │ │
1810 │ │ │ Healthy time │
1811 │ │ │ remaining in │
1812 │ │ │ seconds. │
1813 └────────────┴─────────┴──────────────────────────┘
1814 Type 6: Null
1816 This just indicates a null message. There are no payload fields.
1817 Unknown message
1819 This format is used to dump message words in hexadecimal when the
1820 message type field doesn't match any of the known ones.
1821 Here is the format:
1823 Table 23. Unknown Message
1825 ┌─────┬──────┬────────────────────────┐
1826 │Name │ Type │ │
1827 │ │ │ Description │
1828 ├─────┼──────┼────────────────────────┤
1829 │data │ list │ │
1830 │ │ │ A list of │
1831 │ │ │ strings. │
1832 └─────┴──────┴────────────────────────┘
1833 Each string in the array is a hex literal representing 30 bits of
1835 information, after parity checks and inversion. The high two bits
1836 should be ignored.
1837 Type 7: Radio Beacon Almanac
1839 Here is the format:
1840 Table 24. Contellation health
1842 ┌───────────┬─────────┬───────────────────────────┐
1843 │Name │ Type │ │
1844 │ │ │ Description │
1845 ├───────────┼─────────┼───────────────────────────┤
1846 │lat │ real │ │
1847 │ │ │ Latitude in │
1848 │ │ │ degrees, of │
1849 │ │ │ the LF │
1850 │ │ │ transmitter │
1851 │ │ │ antenna for │
1852 │ │ │ the station │
1853 │ │ │ for which │
1854 │ │ │ this is an │
1855 │ │ │ almanac. │
1856 │ │ │ North is │
1857 │ │ │ positive. │
1858 ├───────────┼─────────┼───────────────────────────┤
1859 │lon │ real │ │
1860 │ │ │ Longitude │
1861 │ │ │ in degrees, │
1862 │ │ │ of the LF │
1863 │ │ │ transmitter │
1864 │ │ │ antenna for │
1865 │ │ │ the station │
1866 │ │ │ for which │
1867 │ │ │ this is an │
1868 │ │ │ almanac. │
1869 │ │ │ East is │
1870 │ │ │ positive. │
1871 ├───────────┼─────────┼───────────────────────────┤
1872 │range │ integer │ Published range of the │
1873 │ │ │ station in km..PP │
1874 ├───────────┼─────────┼───────────────────────────┤
1875 │frequency │ real │ │
1876 │ │ │ Station │
1877 │ │ │ broadcast │
1878 │ │ │ frequency │
1879 │ │ │ in kHz. │
1880 ├───────────┼─────────┼───────────────────────────┤
1881 │health │ integer │ │
1882 │ │ │ <health> is │
1883 │ │ │ the health │
1884 │ │ │ of the │
1885 │ │ │ station for │
1886 │ │ │ which this │
1887 │ │ │ is an │
1888 │ │ │ almanac. If │
1889 │ │ │ it is │
1890 │ │ │ non-zero, │
1891 │ │ │ the station │
1892 │ │ │ is issuing │
1893 │ │ │ suspect │
1894 │ │ │ data and │
1895 │ │ │ should not │
1896 │ │ │ be used for │
1897 │ │ │ fixes. The │
1898 │ │ │ ITU and │
1899 │ │ │ RTCM104 │
1900 │ │ │ standards │
1901 │ │ │ differ │
1902 │ │ │ about the │
1903 │ │ │ mode │
1904 │ │ │ detailed │
1905 │ │ │ interpretation │
1906 │ │ │ of the │
1907 │ │ │ <health> │
1908 │ │ │ field and │
1909 │ │ │ even about │
1910 │ │ │ its bit │
1911 │ │ │ width. │
1912 ├───────────┼─────────┼───────────────────────────┤
1913 │station_id │ integer │ │
1914 │ │ │ The id of the │
1915 │ │ │ transmitter. │
1916 │ │ │ This is not │
1917 │ │ │ the same as │
1918 │ │ │ the reference │
1919 │ │ │ id in the │
1920 │ │ │ header, the │
1921 │ │ │ latter being │
1922 │ │ │ the id of the │
1923 │ │ │ reference │
1924 │ │ │ receiver. │
1925 ├───────────┼─────────┼───────────────────────────┤
1926 │bitrate │ integer │ │
1927 │ │ │ The │
1928 │ │ │ transmitted │
1929 │ │ │ bitrate. │
1930 └───────────┴─────────┴───────────────────────────┘
1931 Here's an example:
1933 {"class":"RTCM2","type":9,"station_id":268,"zcount":252.6,
1935 "seqnum":4,"length":5,"station_health":0,
1936 "satellites":[
1937 {"ident":13,"udre":0,"iod":3,"prc":-25.940,"rrc":0.066},
1938 {"ident":2,"udre":0,"iod":73,"prc":0.920,"rrc":-0.080},
1939 {"ident":8,"udre":0,"iod":22,"prc":23.820,"rrc":0.014}
1940 ]}
1941 Type 13: GPS Time of Week
1943 Here are the payload members of a type 13 (Groumf Tramitter
1944 Parameters) message:
1945 Table 25. Grund Transmitter Parameters
1947 ┌──────────┬─────────┬─────────────────────────┐
1948 │Name │ Type │ │
1949 │ │ │ Description │
1950 ├──────────┼─────────┼─────────────────────────┤
1951 │status │ bool │ │
1952 │ │ │ If True, │
1953 │ │ │ signals │
1954 │ │ │ user to │
1955 │ │ │ expect a │
1956 │ │ │ type 16 │
1957 │ │ │ explanatory │
1958 │ │ │ message │
1959 │ │ │ associated │
1960 │ │ │ with this │
1961 │ │ │ station. │
1962 │ │ │ Probably │
1963 │ │ │ indicates │
1964 │ │ │ some sort │
1965 │ │ │ of unusual │
1966 │ │ │ event. │
1967 ├──────────┼─────────┼─────────────────────────┤
1968 │rangeflag │ bool │ │
1969 │ │ │ If True, │
1970 │ │ │ indicates │
1971 │ │ │ that the │
1972 │ │ │ estimated │
1973 │ │ │ range is │
1974 │ │ │ different │
1975 │ │ │ from that │
1976 │ │ │ found in │
1977 │ │ │ the Type 7 │
1978 │ │ │ message │
1979 │ │ │ (which │
1980 │ │ │ contains │
1981 │ │ │ the │
1982 │ │ │ beacon's │
1983 │ │ │ listed │
1984 │ │ │ range). │
1985 │ │ │ Generally │
1986 │ │ │ indicates a │
1987 │ │ │ range │
1988 │ │ │ reduction │
1989 │ │ │ due to │
1990 │ │ │ causes such │
1991 │ │ │ as poor │
1992 │ │ │ ionospheric │
1993 │ │ │ conditions │
1994 │ │ │ or reduced │
1995 │ │ │ transmission │
1996 │ │ │ power. │
1997 ├──────────┼─────────┼─────────────────────────┤
1998 │lat │ real │ │
1999 │ │ │ Degrees │
2000 │ │ │ latitude, │
2001 │ │ │ signed. │
2002 │ │ │ Positive is │
2003 │ │ │ N, negative │
2004 │ │ │ is S. │
2005 ├──────────┼─────────┼─────────────────────────┤
2006 │lon │ real │ │
2007 │ │ │ Degrees │
2008 │ │ │ longitude, │
2009 │ │ │ signed. │
2010 │ │ │ Positive is │
2011 │ │ │ E, negative │
2012 │ │ │ is W. │
2013 ├──────────┼─────────┼─────────────────────────┤
2014 │range │ integer │ │
2015 │ │ │ Transmission │
2016 │ │ │ range in km │
2017 │ │ │ (1-1024). │
2018 └──────────┴─────────┴─────────────────────────┘
2019 This message type replaces message type 3 (Reference Station
2021 Parameters) in RTCM 2.3.
2022 Type 14: GPS Time of Week
2024 Here are the payload members of a type 14 (GPS Time of Week)
2025 message:
2026 Table 26. Reference Station Parameters
2028 ┌─────────┬─────────┬────────────────────────┐
2029 │Name │ Type │ │
2030 │ │ │ Description │
2031 ├─────────┼─────────┼────────────────────────┤
2032 │week │ integer │ │
2033 │ │ │ GPS week │
2034 │ │ │ (0-123). │
2035 ├─────────┼─────────┼────────────────────────┤
2036 │hour │ integer │ │
2037 │ │ │ Hour of │
2038 │ │ │ week │
2039 │ │ │ (0-167). │
2040 ├─────────┼─────────┼────────────────────────┤
2041 │leapsecs │ integer │ │
2042 │ │ │ Leap │
2043 │ │ │ Seconds │
2044 │ │ │ (0-63). │
2045 └─────────┴─────────┴────────────────────────┘
2046 Here's an example:
2048 {"class":"RTCM2","type":14,"station_id":652,"zcount":1657.2,
2050 "seqnum":3,"length":1,"station_health":6,"week":601,"hour":109,
2051 "leapsecs":15}
2052 Type 16: Special Message
2054 Table 27. Special Message
2055 ┌────────┬────────┬────────────────────────┐
2056 │Name │ Type │ │
2057 │ │ │ Description │
2058 ├────────┼────────┼────────────────────────┤
2059 │message │ string │ │
2060 │ │ │ A text │
2061 │ │ │ message │
2062 │ │ │ sent by the │
2063 │ │ │ beacon │
2064 │ │ │ operator. │
2065 └────────┴────────┴────────────────────────┘
2066 Type 31: Correction data
2068 One or more GLONASS satellite objects follow the header for type 1
2069 or type 9 messages. Here is the format:
2070 Table 28. Satellite object
2072 ┌───────┬──────────┬────────────────────────────────┐
2073 │Name │ Type │ │
2074 │ │ │ Description │
2075 ├───────┼──────────┼────────────────────────────────┤
2076 │ident │ integer │ │
2077 │ │ │ The PRN │
2078 │ │ │ number of │
2079 │ │ │ the │
2080 │ │ │ satellite │
2081 │ │ │ for which │
2082 │ │ │ this is │
2083 │ │ │ correction │
2084 │ │ │ data. │
2085 ├───────┼──────────┼────────────────────────────────┤
2086 │udre │ integer │ │
2087 │ │ │ User │
2088 │ │ │ Differential │
2089 │ │ │ Range Error │
2090 │ │ │ (0-3). See │
2091 │ │ │ the table │
2092 │ │ │ following │
2093 │ │ │ for values. │
2094 ├───────┼──────────┼────────────────────────────────┤
2095 │change │ boolean │ │
2096 │ │ │ Change-of-ephemeris │
2097 │ │ │ bit. │
2098 ├───────┼──────────┼────────────────────────────────┤
2099 │tod │ uinteger │ │
2100 │ │ │ Count of 30-second │
2101 │ │ │ periods since the │
2102 │ │ │ top of the hour. │
2103 ├───────┼──────────┼────────────────────────────────┤
2104 │prc │ real │ │
2105 │ │ │ The pseudorange │
2106 │ │ │ error in meters for │
2107 │ │ │ this satellite as │
2108 │ │ │ measured by the │
2109 │ │ │ beacon reference │
2110 │ │ │ receiver at the │
2111 │ │ │ epoch indicated by │
2112 │ │ │ the z_count in the │
2113 │ │ │ parent record. │
2114 ├───────┼──────────┼────────────────────────────────┤
2115 │rrc │ real │ │
2116 │ │ │ The rate of change │
2117 │ │ │ of pseudorange │
2118 │ │ │ error in meters/sec │
2119 │ │ │ for this satellite │
2120 │ │ │ as measured by the │
2121 │ │ │ beacon reference │
2122 │ │ │ receiver at the │
2123 │ │ │ epoch indicated by │
2124 │ │ │ the z_count field │
2125 │ │ │ in the parent │
2126 │ │ │ record. This is │
2127 │ │ │ used to calculate │
2128 │ │ │ pseudorange errors │
2129 │ │ │ at other epochs, if │
2130 │ │ │ required by the GPS │
2131 │ │ │ receiver. │
2132 └───────┴──────────┴────────────────────────────────┘
2133 Here's an example:
2135 {"class":"RTCM2","type":31,"station_id":652,"zcount":1642.2,
2137 "seqnum":0,"length":14,"station_health":6,
2138 "satellites":[
2139 {"ident":5,"udre":0,"change":false,"tod":0,"prc":132.360,"rrc":0.000},
2140 {"ident":15,"udre":0,"change":false,"tod":0,"prc":134.840,"rrc":0.002},
2141 {"ident":14,"udre":0,"change":false,"tod":0,"prc":141.520,"rrc":0.000},
2142 {"ident":6,"udre":0,"change":false,"tod":0,"prc":127.000,"rrc":0.000},
2143 {"ident":21,"udre":0,"change":false,"tod":0,"prc":128.780,"rrc":0.000},
2144 {"ident":22,"udre":0,"change":false,"tod":0,"prc":125.260,"rrc":0.002},
2145 {"ident":20,"udre":0,"change":false,"tod":0,"prc":117.280,"rrc":-0.004},
2146 {"ident":16,"udre":0,"change":false,"tod":17,"prc":113.460,"rrc":0.018}
2147 ]}
2148
2150 The support for RTCM104v3 dumping is incomplete and buggy. Do not
2151 attempt to use it for production! Anyone interested in it should read
2152 the source code.
2153
2155 AIS support is an extension. It may not be present if your instance of
2156 gpsd has been built with a restricted feature set.
2157 AIS packets are dumped as JSON objects with class "AIS". Each AIS
2159 report object contains a "type" field giving the AIS message type and a
2160 "scaled" field telling whether the remainder of the fields are dumped
2161 in scaled or unscaled form. (These will be emitted before any
2162 type-specific fields.) It will also contain a "device" field naming the
2163 data source. Other fields have names and types as specified in the
2164 AIVDM/AIVDO Protocol Decoding document on the GPSD project website;
2165 each message field table may be directly interpreted as a specification
2166 for the members of the corresponding JSON object type.
2167 By default, certain scaling and conversion operations are performed for
2169 JSON output. Latitudes and longitudes are scaled to decimal degrees
2170 rather than the native AIS unit of 1/10000th of a minute of arc. Ship
2171 (but not air) speeds are scaled to knots rather than tenth-of-knot
2172 units. Rate of turn may appear as "nan" if is unavailable, or as one of
2173 the strings "fastright" or "fastleft" if it is out of the AIS encoding
2174 range; otherwise it is quadratically mapped back to the turn sensor
2175 number in degrees per minute. Vessel draughts are converted to decimal
2176 meters rather than native AIS decimeters. Various other scaling
2177 conversions are described in "AIVDM/AIVDO Protocol Decoding".
2178
2180 Subframe support is always compiled into gpsd but many GPSes do not
2181 output subframe data or the gpsd driver may not support subframes.
2182 Subframe packets are dumped as JSON objects with class "SUBFRAME". Each
2184 subframe report object contains a "frame" field giving the subframe
2185 number, a "tSV" field for the transmitting satellite number, a "TOW17"
2186 field containing the 17 MSBs of the start of the next 12-second message
2187 and a "scaled" field telling whether the remainder of the fields are
2188 dumped in scaled or unscaled form. It will also contain a "device"
2189 field naming the data source. Each SUBFRAME object will have a
2190 sub-object specific to that subframe page type. Those sub-object fields
2191 have names and types similar to those specified in the IS-GPS-200E
2192 document; each message field table may be directly interpreted as a
2193 specification for the members of the corresponding JSON object type.
2194
2196 gpsd(8), libgps(3),
2197
2199 The protocol was designed and documented by Eric S. Raymond.
2200
2202 1. Radio Technical Commission for Maritime Services
2203 http://www.rtcm.org/
2204 2. table of leap second corrections
2206 ftp://maia.usno.navy.mil/ser7/tai-utc.dat
2207The GPSD Project 17 Jun 2018 GPSD_JSON(5)