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 check in their code for the expected major and minor protocol versions.
18 The GPSD protocol is built on top of JSON, JavaScript Object Notation,
20 as specified in [RFC-7159]: The JavaScript Object Notation (JSON) Data
21 Interchange Format. Similar to ECMA 404.
22 GPSD’s use of JSON is restricted in some ways that make parsing it in
24 fixed-extent languages (such as C) easier.
25 A request line is introduced by "?" and may include multiple commands.
27 Commands begin with a command identifier, followed either by a
28 terminating ';' or by an equal sign "=" and a JSON object treated as an
29 argument. Any ';' or newline indication (either LF or CR-LF) after the
30 end of a command is ignored. All request lines must be composed of
31 US-ASCII characters and may be no more than 80 characters in length,
32 exclusive of the trailing newline.
33 Responses are single JSON objects that have a "class" attribute the
35 value of which is the object type . Object types include, but are not
36 limited to: "TPV", "SKY", "DEVICE", and "ERROR". Objects are sent both
37 in response to commands, and periodically as gpsd sends reports. Each
38 object is terminated by a carriage return and a new line (CR-NL).
39 The order of JSON attributes within a response object is never
41 significant, and you may specify command attributes in any order.
42 Responses never contain the special JSON value null; instead,
43 attributes with empty or undefined values are omitted. The length limit
44 for responses and reports is currently 10240 characters, including the
45 trailing CR-NL. Longer responses will be truncated, so client code must
46 be prepared for the possibility of invalid JSON fragments.
47 The default maximum message length is set by GPS_JSON_RESPONSE_MAX in
49 include/gpsd_json.h. at compile time.
50 In JSON reports, if an attribute is present only if the parent
52 attribute is present or has a particular range, then the parent
53 attribute is emitted first.
54 There is one constraint on the order in which attributes will be
56 omitted. If an optional attribute is present only when a parent
57 attribute has a specified value or range of values, the parent
58 attribute will be emitted first to make parsing easier.
59 The next subsection section documents the core GPSD protocol.
61 Extensions are documented in the following subsections. The extensions
62 may not be supported in your gpsd instance if it has been compiled with
63 a restricted feature set.
64 The protocol was designed and documented by Eric S. Raymond.
66
68 Here are the core-protocol responses.
69 TPV
71 A TPV object is a time-position-velocity report. The "class" and "mode"
72 fields will reliably be present. When "mode" is 0 (Unknown) there is
73 likely no usable data in the sentence. The remaining fields are
74 optional, their presence depends on what data the GNSS receiver has
75 sent, and what gpsd may calculate from that data.
76 A TPV object will usually be sent at least once for every measurement
78 epoch as determined by the "time" field. Unless the receiver has a
79 solid fix, and knows the current leap second, the time may be random.
80 Multiple TPV objects are often sent per epoch. When the receiver
82 dribbles data to gpsd, then gpsd has no choice but to dribble it to the
83 client in multiple TPV messages.
84 The optional "status" field (aka fix type), is a modifier (adjective)
86 to mode. It is not a replacement for, or superset of, the "mode" field.
87 It is almost, but not quite, the same as the NMEA 4.x xxGGA GPS Quality
88 Indicator Values. Many GNSS receivers do not supply it. Those that do
89 interpret the specification in various incompatible ways.
90 All error estimates (epc, epd, epe, eph, ept, epv, epx, epy) are
92 guessed to be 95% confidence, may also be 50%, one sigma, or two sigma
93 confidence. Many GNSS receivers do not specify a confidence level. None
94 specify how the value is calculated. Use error estimates with caution,
95 and only as relative "goodness" indicators. If the GPS reports a value
96 to gpsd, then gpsd will report that value. Otherwise gpsd will try to
97 compute the value from the skyview.
98 See the file include/gps.h, especially struct gps_data_t, for expanded
100 notes on the items and values in the TPV message.
101 Table 1. TPV object
103 ┌────────────┬─────────┬─────────┬──────────────────┐
104 │ │ │ │ │
105 │Name │ Always? │ Type │ Description │
106 ├────────────┼─────────┼─────────┼──────────────────┤
107 │ │ │ │ │
108 │class │ Yes │ string │ Fixed: "TPV" │
109 ├────────────┼─────────┼─────────┼──────────────────┤
110 │ │ │ │ │
111 │device │ No │ string │ Name of the │
112 │ │ │ │ originating │
113 │ │ │ │ device. │
114 ├────────────┼─────────┼─────────┼──────────────────┤
115 │ │ │ │ │
116 │mode │ Yes │ numeric │ NMEA mode: │
117 │ │ │ │ 0=unknown, │
118 │ │ │ │ 1=no fix, │
119 │ │ │ │ 2=2D, │
120 │ │ │ │ 3=3D. │
121 ├────────────┼─────────┼─────────┼──────────────────┤
122 │ │ │ │ │
123 │status │ No │ numeric │ GPS fix status: │
124 │ │ │ │ 0=Unknown, │
125 │ │ │ │ 1=Normal, │
126 │ │ │ │ 2=DGPS, │
127 │ │ │ │ 3=RTK Fixed, │
128 │ │ │ │ 4=RTK Floating, │
129 │ │ │ │ 5=DR, │
130 │ │ │ │ 6=GNSSDR, │
131 │ │ │ │ 7=Time │
132 │ │ │ │ (surveyed), │
133 │ │ │ │ 8=Simulated, │
134 │ │ │ │ 9=P(Y) │
135 ├────────────┼─────────┼─────────┼──────────────────┤
136 │ │ │ │ │
137 │time │ No │ string │ Time/date stamp │
138 │ │ │ │ in ISO8601 │
139 │ │ │ │ format, UTC. May │
140 │ │ │ │ have a │
141 │ │ │ │ fractional part │
142 │ │ │ │ of up to .001sec │
143 │ │ │ │ precision. May │
144 │ │ │ │ be absent if the │
145 │ │ │ │ mode is not 2D │
146 │ │ │ │ or 3D. May be │
147 │ │ │ │ present, but │
148 │ │ │ │ invalid, if │
149 │ │ │ │ there is no fix. │
150 │ │ │ │ Verify 3 │
151 │ │ │ │ consecutive 3D │
152 │ │ │ │ fixes before │
153 │ │ │ │ believing it is │
154 │ │ │ │ UTC. Even then │
155 │ │ │ │ it may be off by │
156 │ │ │ │ several seconds │
157 │ │ │ │ until the │
158 │ │ │ │ current leap │
159 │ │ │ │ seconds is │
160 │ │ │ │ known. │
161 ├────────────┼─────────┼─────────┼──────────────────┤
162 │ │ │ │ │
163 │altHAE │ No │ numeric │ Altitude, height │
164 │ │ │ │ above ellipsoid, │
165 │ │ │ │ in meters. │
166 │ │ │ │ Probably WGS84. │
167 ├────────────┼─────────┼─────────┼──────────────────┤
168 │ │ │ │ │
169 │altMSL │ No │ numeric │ MSL Altitude in │
170 │ │ │ │ meters. The │
171 │ │ │ │ geoid used is │
172 │ │ │ │ rarely specified │
173 │ │ │ │ and is often │
174 │ │ │ │ inaccurate. See │
175 │ │ │ │ the comments │
176 │ │ │ │ below on │
177 │ │ │ │ geoidSep. altMSL │
178 │ │ │ │ is altHAE minus │
179 │ │ │ │ geoidSep. │
180 ├────────────┼─────────┼─────────┼──────────────────┤
181 │ │ │ │ │
182 │alt │ No │ numeric │ Deprecated. │
183 │ │ │ │ Undefined. Use │
184 │ │ │ │ altHAE or │
185 │ │ │ │ altMSL. │
186 ├────────────┼─────────┼─────────┼──────────────────┤
187 │ │ │ │ │
188 │climb │ No │ numeric │ Climb (positive) │
189 │ │ │ │ or sink │
190 │ │ │ │ (negative) rate, │
191 │ │ │ │ meters per │
192 │ │ │ │ second. │
193 ├────────────┼─────────┼─────────┼──────────────────┤
194 │ │ │ │ │
195 │datum │ No │ string │ Current datum. │
196 │ │ │ │ Hopefully WGS84. │
197 ├────────────┼─────────┼─────────┼──────────────────┤
198 │ │ │ │ │
199 │depth │ No │ numeric │ Depth in meters. │
200 │ │ │ │ Probably depth │
201 │ │ │ │ below the │
202 │ │ │ │ keel... │
203 ├────────────┼─────────┼─────────┼──────────────────┤
204 │ │ │ │ │
205 │dgpsAge │ No │ numeric │ Age of DGPS │
206 │ │ │ │ data. In seconds │
207 ├────────────┼─────────┼─────────┼──────────────────┤
208 │ │ │ │ │
209 │dgpsSta │ No │ numeric │ Station of DGPS │
210 │ │ │ │ data. │
211 ├────────────┼─────────┼─────────┼──────────────────┤
212 │ │ │ │ │
213 │epc │ No │ numeric │ Estimated climb │
214 │ │ │ │ error in meters │
215 │ │ │ │ per second. │
216 │ │ │ │ Certainty │
217 │ │ │ │ unknown. │
218 ├────────────┼─────────┼─────────┼──────────────────┤
219 │ │ │ │ │
220 │epd │ No │ numeric │ Estimated track │
221 │ │ │ │ (direction) │
222 │ │ │ │ error in │
223 │ │ │ │ degrees. │
224 │ │ │ │ Certainty │
225 │ │ │ │ unknown. │
226 ├────────────┼─────────┼─────────┼──────────────────┤
227 │ │ │ │ │
228 │eph │ No │ numeric │ Estimated │
229 │ │ │ │ horizontal │
230 │ │ │ │ Position (2D) │
231 │ │ │ │ Error in meters. │
232 │ │ │ │ Also known as │
233 │ │ │ │ Estimated │
234 │ │ │ │ Position Error │
235 │ │ │ │ (epe). Certainty │
236 │ │ │ │ unknown. │
237 ├────────────┼─────────┼─────────┼──────────────────┤
238 │ │ │ │ │
239 │eps │ No │ numeric │ Estimated speed │
240 │ │ │ │ error in meters │
241 │ │ │ │ per second. │
242 │ │ │ │ Certainty │
243 │ │ │ │ unknown. │
244 ├────────────┼─────────┼─────────┼──────────────────┤
245 │ │ │ │ │
246 │ept │ No │ numeric │ Estimated time │
247 │ │ │ │ stamp error in │
248 │ │ │ │ seconds. │
249 │ │ │ │ Certainty │
250 │ │ │ │ unknown. │
251 ├────────────┼─────────┼─────────┼──────────────────┤
252 │ │ │ │ │
253 │epx │ No │ numeric │ Longitude error │
254 │ │ │ │ estimate in │
255 │ │ │ │ meters. │
256 │ │ │ │ Certainty │
257 │ │ │ │ unknown. │
258 ├────────────┼─────────┼─────────┼──────────────────┤
259 │ │ │ │ │
260 │epy │ No │ numeric │ Latitude error │
261 │ │ │ │ estimate in │
262 │ │ │ │ meters. │
263 │ │ │ │ Certainty │
264 │ │ │ │ unknown. │
265 ├────────────┼─────────┼─────────┼──────────────────┤
266 │ │ │ │ │
267 │epv │ No │ numeric │ Estimated │
268 │ │ │ │ vertical error │
269 │ │ │ │ in meters. │
270 │ │ │ │ Certainty │
271 │ │ │ │ unknown. │
272 ├────────────┼─────────┼─────────┼──────────────────┤
273 │ │ │ │ │
274 │geoidSep │ No │ numeric │ Geoid separation │
275 │ │ │ │ is the │
276 │ │ │ │ difference │
277 │ │ │ │ between the │
278 │ │ │ │ WGS84 reference │
279 │ │ │ │ ellipsoid and │
280 │ │ │ │ the geoid (Mean │
281 │ │ │ │ Sea Level) in │
282 │ │ │ │ meters. Almost │
283 │ │ │ │ no GNSS receiver │
284 │ │ │ │ specifies how │
285 │ │ │ │ they compute │
286 │ │ │ │ their geoid. │
287 │ │ │ │ gpsd │
288 │ │ │ │ interpolates the │
289 │ │ │ │ geoid from a 5x5 │
290 │ │ │ │ degree table of │
291 │ │ │ │ EGM2008 values │
292 │ │ │ │ when the │
293 │ │ │ │ receiver does │
294 │ │ │ │ not supply a │
295 │ │ │ │ geoid │
296 │ │ │ │ separation. The │
297 │ │ │ │ gpsd computed │
298 │ │ │ │ geoidSep is │
299 │ │ │ │ usually within │
300 │ │ │ │ one meter of the │
301 │ │ │ │ "true" value, │
302 │ │ │ │ but can be off │
303 │ │ │ │ as much as 12 │
304 │ │ │ │ meters. │
305 ├────────────┼─────────┼─────────┼──────────────────┤
306 │ │ │ │ │
307 │lat │ No │ numeric │ Latitude in │
308 │ │ │ │ degrees: +/- │
309 │ │ │ │ signifies │
310 │ │ │ │ North/South. │
311 ├────────────┼─────────┼─────────┼──────────────────┤
312 │ │ │ │ │
313 │leapseconds │ No │ integer │ Current leap │
314 │ │ │ │ seconds. │
315 ├────────────┼─────────┼─────────┼──────────────────┤
316 │ │ │ │ │
317 │lon │ No │ numeric │ Longitude in │
318 │ │ │ │ degrees: +/- │
319 │ │ │ │ signifies │
320 │ │ │ │ East/West. │
321 ├────────────┼─────────┼─────────┼──────────────────┤
322 │ │ │ │ │
323 │track │ No │ numeric │ Course over │
324 │ │ │ │ ground, degrees │
325 │ │ │ │ from true north. │
326 ├────────────┼─────────┼─────────┼──────────────────┤
327 │ │ │ │ │
328 │magtrack │ No │ numeric │ Course over │
329 │ │ │ │ ground, degrees │
330 │ │ │ │ magnetic. │
331 ├────────────┼─────────┼─────────┼──────────────────┤
332 │ │ │ │ │
333 │magvar │ No │ numeric │ Magnetic │
334 │ │ │ │ variation, │
335 │ │ │ │ degrees. Also │
336 │ │ │ │ known as the │
337 │ │ │ │ magnetic │
338 │ │ │ │ declination (the │
339 │ │ │ │ direction of the │
340 │ │ │ │ horizontal │
341 │ │ │ │ component of the │
342 │ │ │ │ magnetic field │
343 │ │ │ │ measured │
344 │ │ │ │ clockwise from │
345 │ │ │ │ north) in │
346 │ │ │ │ degrees, │
347 │ │ │ │ Positive is West │
348 │ │ │ │ variation. │
349 │ │ │ │ Negative is East │
350 │ │ │ │ variation. │
351 ├────────────┼─────────┼─────────┼──────────────────┤
352 │ │ │ │ │
353 │speed │ No │ numeric │ Speed over │
354 │ │ │ │ ground, meters │
355 │ │ │ │ per second. │
356 ├────────────┼─────────┼─────────┼──────────────────┤
357 │ │ │ │ │
358 │ecefx │ No │ numeric │ ECEF X position │
359 │ │ │ │ in meters. │
360 ├────────────┼─────────┼─────────┼──────────────────┤
361 │ │ │ │ │
362 │ecefy │ No │ numeric │ ECEF Y position │
363 │ │ │ │ in meters. │
364 ├────────────┼─────────┼─────────┼──────────────────┤
365 │ │ │ │ │
366 │ecefz │ No │ numeric │ ECEF Z position │
367 │ │ │ │ in meters. │
368 ├────────────┼─────────┼─────────┼──────────────────┤
369 │ │ │ │ │
370 │ecefpAcc │ No │ numeric │ ECEF position │
371 │ │ │ │ error in meters. │
372 │ │ │ │ Certainty │
373 │ │ │ │ unknown. │
374 ├────────────┼─────────┼─────────┼──────────────────┤
375 │ │ │ │ │
376 │ecefvx │ No │ numeric │ ECEF X velocity │
377 │ │ │ │ in meters per │
378 │ │ │ │ second. │
379 ├────────────┼─────────┼─────────┼──────────────────┤
380 │ │ │ │ │
381 │ecefvy │ No │ numeric │ ECEF Y velocity │
382 │ │ │ │ in meters per │
383 │ │ │ │ second. │
384 ├────────────┼─────────┼─────────┼──────────────────┤
385 │ │ │ │ │
386 │ecefvz │ No │ numeric │ ECEF Z velocity │
387 │ │ │ │ in meters per │
388 │ │ │ │ second. │
389 ├────────────┼─────────┼─────────┼──────────────────┤
390 │ │ │ │ │
391 │ecefvAcc │ No │ numeric │ ECEF velocity │
392 │ │ │ │ error in meters │
393 │ │ │ │ per second. │
394 │ │ │ │ Certainty │
395 │ │ │ │ unknown. │
396 ├────────────┼─────────┼─────────┼──────────────────┤
397 │ │ │ │ │
398 │sep │ No │ numeric │ Estimated │
399 │ │ │ │ Spherical (3D) │
400 │ │ │ │ Position Error │
401 │ │ │ │ in meters. │
402 │ │ │ │ Guessed to be │
403 │ │ │ │ 95% confidence, │
404 │ │ │ │ but many GNSS │
405 │ │ │ │ receivers do not │
406 │ │ │ │ specify, so │
407 │ │ │ │ certainty │
408 │ │ │ │ unknown. │
409 ├────────────┼─────────┼─────────┼──────────────────┤
410 │ │ │ │ │
411 │relD │ No │ numeric │ Down component │
412 │ │ │ │ of relative │
413 │ │ │ │ position vector │
414 │ │ │ │ in meters. │
415 ├────────────┼─────────┼─────────┼──────────────────┤
416 │ │ │ │ │
417 │relE │ No │ numeric │ East component │
418 │ │ │ │ of relative │
419 │ │ │ │ position vector │
420 │ │ │ │ in meters. │
421 ├────────────┼─────────┼─────────┼──────────────────┤
422 │ │ │ │ │
423 │relN │ No │ numeric │ North component │
424 │ │ │ │ of relative │
425 │ │ │ │ position vector │
426 │ │ │ │ in meters. │
427 ├────────────┼─────────┼─────────┼──────────────────┤
428 │ │ │ │ │
429 │velD │ No │ numeric │ Down velocity │
430 │ │ │ │ component in │
431 │ │ │ │ meters. │
432 ├────────────┼─────────┼─────────┼──────────────────┤
433 │ │ │ │ │
434 │velE │ No │ numeric │ East velocity │
435 │ │ │ │ component in │
436 │ │ │ │ meters. │
437 ├────────────┼─────────┼─────────┼──────────────────┤
438 │ │ │ │ │
439 │velN │ No │ numeric │ North velocity │
440 │ │ │ │ component in │
441 │ │ │ │ meters. │
442 ├────────────┼─────────┼─────────┼──────────────────┤
443 │ │ │ │ │
444 │wanglem │ No │ numeric │ Wind angle │
445 │ │ │ │ magnetic in │
446 │ │ │ │ degrees. │
447 ├────────────┼─────────┼─────────┼──────────────────┤
448 │ │ │ │ │
449 │wangler │ No │ numeric │ Wind angle │
450 │ │ │ │ relative in │
451 │ │ │ │ degrees. │
452 ├────────────┼─────────┼─────────┼──────────────────┤
453 │ │ │ │ │
454 │wanglet │ No │ numeric │ Wind angle true │
455 │ │ │ │ in degrees. │
456 ├────────────┼─────────┼─────────┼──────────────────┤
457 │ │ │ │ │
458 │wspeedr │ No │ numeric │ Wind speed │
459 │ │ │ │ relative in │
460 │ │ │ │ meters per │
461 │ │ │ │ second. │
462 ├────────────┼─────────┼─────────┼──────────────────┤
463 │ │ │ │ │
464 │wspeedt │ No │ numeric │ Wind speed true │
465 │ │ │ │ in meters per │
466 │ │ │ │ second. │
467 └────────────┴─────────┴─────────┴──────────────────┘
468 When the C client library parses a response of this kind, it will
470 assert validity bits in the top-level set member for each field
471 received; see gps.h for bitmask names and values.
472 Invalid or unknown floating-point values will be set to NAN. Always
474 check floating point values with isfinite() before use. isnan() is not
475 sufficient.
476 Here’s an example TPV sentence:
478 {"class":"TPV","device":"/dev/pts/1",
480 "time":"2005-06-08T10:34:48.283Z","ept":0.005,
481 "lat":46.498293369,"lon":7.567411672,"alt":1343.127,
482 "eph":36.000,"epv":32.321,
483 "track":10.3788,"speed":0.091,"climb":-0.085,"mode":3}
484 SKY
486 A SKY object reports a sky view of the GPS satellite positions. If
487 there is no GPS device available, or no skyview has been reported yet,
488 only the "class" field will reliably be present.
489 Table 2. SKY object
491 ┌───────────┬─────────┬─────────┬──────────────────┐
492 │ │ │ │ │
493 │Name │ Always? │ Type │ Description │
494 ├───────────┼─────────┼─────────┼──────────────────┤
495 │ │ │ │ │
496 │class │ Yes │ string │ Fixed: "SKY" │
497 ├───────────┼─────────┼─────────┼──────────────────┤
498 │ │ │ │ │
499 │device │ No │ string │ Name of │
500 │ │ │ │ originating │
501 │ │ │ │ device │
502 ├───────────┼─────────┼─────────┼──────────────────┤
503 │ │ │ │ │
504 │time │ No │ string │ Time/date stamp │
505 │ │ │ │ in ISO8601 │
506 │ │ │ │ format, UTC. May │
507 │ │ │ │ have a │
508 │ │ │ │ fractional part │
509 │ │ │ │ of up to .001sec │
510 │ │ │ │ precision. │
511 ├───────────┼─────────┼─────────┼──────────────────┤
512 │ │ │ │ │
513 │gdop │ No │ numeric │ Geometric │
514 │ │ │ │ (hyperspherical) │
515 │ │ │ │ dilution of │
516 │ │ │ │ precision, a │
517 │ │ │ │ combination of │
518 │ │ │ │ PDOP and TDOP. A │
519 │ │ │ │ dimensionless │
520 │ │ │ │ factor which │
521 │ │ │ │ should be │
522 │ │ │ │ multiplied by a │
523 │ │ │ │ base UERE to get │
524 │ │ │ │ an error │
525 │ │ │ │ estimate. │
526 ├───────────┼─────────┼─────────┼──────────────────┤
527 │ │ │ │ │
528 │hdop │ No │ numeric │ Horizontal │
529 │ │ │ │ dilution of │
530 │ │ │ │ precision, a │
531 │ │ │ │ dimensionless │
532 │ │ │ │ factor which │
533 │ │ │ │ should be │
534 │ │ │ │ multiplied by a │
535 │ │ │ │ base UERE to get │
536 │ │ │ │ a circular error │
537 │ │ │ │ estimate. │
538 ├───────────┼─────────┼─────────┼──────────────────┤
539 │ │ │ │ │
540 │pdop │ No │ numeric │ Position │
541 │ │ │ │ (spherical/3D) │
542 │ │ │ │ dilution of │
543 │ │ │ │ precision, a │
544 │ │ │ │ dimensionless │
545 │ │ │ │ factor which │
546 │ │ │ │ should be │
547 │ │ │ │ multiplied by a │
548 │ │ │ │ base UERE to get │
549 │ │ │ │ an error │
550 │ │ │ │ estimate. │
551 ├───────────┼─────────┼─────────┼──────────────────┤
552 │ │ │ │ │
553 │tdop │ No │ numeric │ Time dilution of │
554 │ │ │ │ precision, a │
555 │ │ │ │ dimensionless │
556 │ │ │ │ factor which │
557 │ │ │ │ should be │
558 │ │ │ │ multiplied by a │
559 │ │ │ │ base UERE to get │
560 │ │ │ │ an error │
561 │ │ │ │ estimate. │
562 ├───────────┼─────────┼─────────┼──────────────────┤
563 │ │ │ │ │
564 │vdop │ No │ numeric │ Vertical │
565 │ │ │ │ (altitude) │
566 │ │ │ │ dilution of │
567 │ │ │ │ precision, a │
568 │ │ │ │ dimensionless │
569 │ │ │ │ factor which │
570 │ │ │ │ should be │
571 │ │ │ │ multiplied by a │
572 │ │ │ │ base UERE to get │
573 │ │ │ │ an error │
574 │ │ │ │ estimate. │
575 ├───────────┼─────────┼─────────┼──────────────────┤
576 │ │ │ │ │
577 │xdop │ No │ numeric │ Longitudinal │
578 │ │ │ │ dilution of │
579 │ │ │ │ precision, a │
580 │ │ │ │ dimensionless │
581 │ │ │ │ factor which │
582 │ │ │ │ should be │
583 │ │ │ │ multiplied by a │
584 │ │ │ │ base UERE to get │
585 │ │ │ │ an error │
586 │ │ │ │ estimate. │
587 ├───────────┼─────────┼─────────┼──────────────────┤
588 │ │ │ │ │
589 │ydop │ No │ numeric │ Latitudinal │
590 │ │ │ │ dilution of │
591 │ │ │ │ precision, a │
592 │ │ │ │ dimensionless │
593 │ │ │ │ factor which │
594 │ │ │ │ should be │
595 │ │ │ │ multiplied by a │
596 │ │ │ │ base UERE to get │
597 │ │ │ │ an error │
598 │ │ │ │ estimate. │
599 ├───────────┼─────────┼─────────┼──────────────────┤
600 │ │ │ │ │
601 │nSat │ No │ numeric │ Number of │
602 │ │ │ │ satellite │
603 │ │ │ │ objects in │
604 │ │ │ │ "satellites" │
605 │ │ │ │ array. │
606 ├───────────┼─────────┼─────────┼──────────────────┤
607 │ │ │ │ │
608 │uSat │ No │ numeric │ Number of │
609 │ │ │ │ satellites used │
610 │ │ │ │ in navigation │
611 │ │ │ │ solution. │
612 ├───────────┼─────────┼─────────┼──────────────────┤
613 │ │ │ │ │
614 │satellites │ Yes │ list │ List of │
615 │ │ │ │ satellite │
616 │ │ │ │ objects in │
617 │ │ │ │ skyview │
618 └───────────┴─────────┴─────────┴──────────────────┘
619 Many devices compute dilution of precision factors but do not include
621 them in their reports. Many that do report DOPs report only HDOP,
622 two-dimensional circular error. gpsd always passes through whatever the
623 device reports, then attempts to fill in other DOPs by calculating the
624 appropriate determinants in a covariance matrix based on the satellite
625 view. DOPs may be missing if some of these determinants are singular.
626 It can even happen that the device reports an error estimate in meters
627 when the corresponding DOP is unavailable; some devices use more
628 sophisticated error modeling than the covariance calculation.
629 The satellite list objects have the following elements:
631 Table 3. Satellite object
633 ┌───────┬─────────┬─────────┬──────────────────┐
634 │ │ │ │ │
635 │Name │ Always? │ Type │ Description │
636 ├───────┼─────────┼─────────┼──────────────────┤
637 │ │ │ │ │
638 │PRN │ Yes │ numeric │ PRN ID of the │
639 │ │ │ │ satellite. 1-63 │
640 │ │ │ │ are GNSS │
641 │ │ │ │ satellites, │
642 │ │ │ │ 64-96 are │
643 │ │ │ │ GLONASS │
644 │ │ │ │ satellites, │
645 │ │ │ │ 100-164 are SBAS │
646 │ │ │ │ satellites │
647 ├───────┼─────────┼─────────┼──────────────────┤
648 │ │ │ │ │
649 │az │ No │ numeric │ Azimuth, degrees │
650 │ │ │ │ from true north. │
651 ├───────┼─────────┼─────────┼──────────────────┤
652 │ │ │ │ │
653 │el │ No │ numeric │ Elevation in │
654 │ │ │ │ degrees. │
655 ├───────┼─────────┼─────────┼──────────────────┤
656 │ │ │ │ │
657 │ss │ No │ numeric │ Signal to Noise │
658 │ │ │ │ ratio in dBHz. │
659 ├───────┼─────────┼─────────┼──────────────────┤
660 │ │ │ │ │
661 │used │ Yes │ boolean │ Used in current │
662 │ │ │ │ solution? │
663 │ │ │ │ (SBAS/WAAS/EGNOS │
664 │ │ │ │ satellites may │
665 │ │ │ │ be flagged used │
666 │ │ │ │ if the solution │
667 │ │ │ │ has corrections │
668 │ │ │ │ from them, but │
669 │ │ │ │ not all drivers │
670 │ │ │ │ make this │
671 │ │ │ │ information │
672 │ │ │ │ available.) │
673 ├───────┼─────────┼─────────┼──────────────────┤
674 │ │ │ │ │
675 │gnssid │ No │ numeric │ The GNSS ID, as │
676 │ │ │ │ defined by │
677 │ │ │ │ u-blox, not │
678 │ │ │ │ NMEA. 0=GPS, │
679 │ │ │ │ 2=Galileo, │
680 │ │ │ │ 3=Beidou, │
681 │ │ │ │ 5=QZSS, │
682 │ │ │ │ 6-GLONASS. │
683 ├───────┼─────────┼─────────┼──────────────────┤
684 │ │ │ │ │
685 │svid │ No │ numeric │ The satellite ID │
686 │ │ │ │ within its │
687 │ │ │ │ constellation. │
688 │ │ │ │ As defined by │
689 │ │ │ │ u-blox, not │
690 │ │ │ │ NMEA). │
691 ├───────┼─────────┼─────────┼──────────────────┤
692 │ │ │ │ │
693 │sigid │ No │ numeric │ The signal ID of │
694 │ │ │ │ this signal. As │
695 │ │ │ │ defined by │
696 │ │ │ │ u-blox, not │
697 │ │ │ │ NMEA. See u-blox │
698 │ │ │ │ doc for details. │
699 ├───────┼─────────┼─────────┼──────────────────┤
700 │ │ │ │ │
701 │freqid │ No │ numeric │ For GLONASS │
702 │ │ │ │ satellites only: │
703 │ │ │ │ the frequency ID │
704 │ │ │ │ of the signal. │
705 │ │ │ │ As defined by │
706 │ │ │ │ u-blox, range 0 │
707 │ │ │ │ to 13. The │
708 │ │ │ │ freqid is the │
709 │ │ │ │ frequency slot │
710 │ │ │ │ plus 7. │
711 ├───────┼─────────┼─────────┼──────────────────┤
712 │ │ │ │ │
713 │health │ No │ numeric │ The health of │
714 │ │ │ │ this satellite. │
715 │ │ │ │ 0 is unknown, 1 │
716 │ │ │ │ is OK, and 2 is │
717 │ │ │ │ unhealthy. │
718 └───────┴─────────┴─────────┴──────────────────┘
719 Note that satellite objects do not have a "class" field, as they are
721 never shipped outside of a SKY object.
722 When the C client library parses a SKY response, it will assert the
724 SATELLITE_SET bit in the top-level set member.
725 Here’s an example:
727 {"class":"SKY","device":"/dev/pts/1",
729 "time":"2005-07-08T11:28:07.114Z",
730 "xdop":1.55,"hdop":1.24,"pdop":1.99,
731 "satellites":[
732 {"PRN":23,"el":6,"az":84,"ss":0,"used":false},
733 {"PRN":28,"el":7,"az":160,"ss":0,"used":false},
734 {"PRN":8,"el":66,"az":189,"ss":44,"used":true},
735 {"PRN":29,"el":13,"az":273,"ss":0,"used":false},
736 {"PRN":10,"el":51,"az":304,"ss":29,"used":true},
737 {"PRN":4,"el":15,"az":199,"ss":36,"used":true},
738 {"PRN":2,"el":34,"az":241,"ss":43,"used":true},
739 {"PRN":27,"el":71,"az":76,"ss":43,"used":true}]}
740 GST
742 A GST object is a pseudorange noise report.
743 Table 4. GST object
745 ┌───────┬─────────┬─────────┬──────────────────┐
746 │ │ │ │ │
747 │Name │ Always? │ Type │ Description │
748 ├───────┼─────────┼─────────┼──────────────────┤
749 │ │ │ │ │
750 │class │ Yes │ string │ Fixed: "GST" │
751 ├───────┼─────────┼─────────┼──────────────────┤
752 │ │ │ │ │
753 │device │ No │ string │ Name of │
754 │ │ │ │ originating │
755 │ │ │ │ device │
756 ├───────┼─────────┼─────────┼──────────────────┤
757 │ │ │ │ │
758 │time │ No │ string │ Time/date stamp │
759 │ │ │ │ in ISO8601 │
760 │ │ │ │ format, UTC. May │
761 │ │ │ │ have a │
762 │ │ │ │ fractional part │
763 │ │ │ │ of up to .001sec │
764 │ │ │ │ precision. │
765 ├───────┼─────────┼─────────┼──────────────────┤
766 │ │ │ │ │
767 │rms │ No │ numeric │ Value of the │
768 │ │ │ │ standard │
769 │ │ │ │ deviation of the │
770 │ │ │ │ range inputs to │
771 │ │ │ │ the navigation │
772 │ │ │ │ process (range │
773 │ │ │ │ inputs include │
774 │ │ │ │ pseudoranges and │
775 │ │ │ │ DGPS │
776 │ │ │ │ corrections). │
777 ├───────┼─────────┼─────────┼──────────────────┤
778 │ │ │ │ │
779 │major │ No │ numeric │ Standard │
780 │ │ │ │ deviation of │
781 │ │ │ │ semi-major axis │
782 │ │ │ │ of error │
783 │ │ │ │ ellipse, in │
784 │ │ │ │ meters. │
785 ├───────┼─────────┼─────────┼──────────────────┤
786 │ │ │ │ │
787 │minor │ No │ numeric │ Standard │
788 │ │ │ │ deviation of │
789 │ │ │ │ semi-minor axis │
790 │ │ │ │ of error │
791 │ │ │ │ ellipse, in │
792 │ │ │ │ meters. │
793 ├───────┼─────────┼─────────┼──────────────────┤
794 │ │ │ │ │
795 │orient │ No │ numeric │ Orientation of │
796 │ │ │ │ semi-major axis │
797 │ │ │ │ of error │
798 │ │ │ │ ellipse, in │
799 │ │ │ │ degrees from │
800 │ │ │ │ true north. │
801 ├───────┼─────────┼─────────┼──────────────────┤
802 │ │ │ │ │
803 │lat │ No │ numeric │ Standard │
804 │ │ │ │ deviation of │
805 │ │ │ │ latitude error, │
806 │ │ │ │ in meters. │
807 ├───────┼─────────┼─────────┼──────────────────┤
808 │ │ │ │ │
809 │lon │ No │ numeric │ Standard │
810 │ │ │ │ deviation of │
811 │ │ │ │ longitude error, │
812 │ │ │ │ in meters. │
813 ├───────┼─────────┼─────────┼──────────────────┤
814 │ │ │ │ │
815 │alt │ No │ numeric │ Standard │
816 │ │ │ │ deviation of │
817 │ │ │ │ altitude error, │
818 │ │ │ │ in meters. │
819 └───────┴─────────┴─────────┴──────────────────┘
820 Here’s an example:
822 {"class":"GST","device":"/dev/ttyUSB0",
824 "time":"2010-12-07T10:23:07.096Z","rms":2.440,
825 "major":1.660,"minor":1.120,"orient":68.989,
826 "lat":1.600,"lon":1.200,"alt":2.520}
827 ATT
829 An ATT object is a vehicle-attitude report. It is returned by
830 digital-compass and gyroscope sensors; depending on device, it may
831 include: heading, pitch, roll, yaw, gyroscope, and magnetic-field
832 readings. Because such sensors are often bundled as part of
833 marine-navigation systems, the ATT response may also include water
834 depth.
835 The "class" and "mode" fields will reliably be present. Others may be
837 reported or not depending on the specific device type.
838 The ATT object is synchronous to the GNSS epoch. Some devices report
840 attitude information with arbitrary, even out of order, time scales.
841 gpsd reports those in an IMU object. The ATT and IMU objects have the
842 same fields, but IMU objects are output as soon as possible. Some
843 devices output both types with arbitrary interleaving.
844 Table 5. ATT object
846 ┌─────────┬─────────┬─────────┬──────────────────┐
847 │ │ │ │ │
848 │Name │ Always? │ Type │ Description │
849 ├─────────┼─────────┼─────────┼──────────────────┤
850 │ │ │ │ │
851 │class │ Yes │ string │ Fixed: "ATT" │
852 ├─────────┼─────────┼─────────┼──────────────────┤
853 │ │ │ │ │
854 │device │ Yes │ string │ Name of │
855 │ │ │ │ originating │
856 │ │ │ │ device │
857 ├─────────┼─────────┼─────────┼──────────────────┤
858 │ │ │ │ │
859 │time │ No │ string │ Time/date stamp │
860 │ │ │ │ in ISO8601 │
861 │ │ │ │ format, UTC. May │
862 │ │ │ │ have a │
863 │ │ │ │ fractional part │
864 │ │ │ │ of up to .001sec │
865 │ │ │ │ precision. │
866 ├─────────┼─────────┼─────────┼──────────────────┤
867 │ │ │ │ │
868 │timeTag │ No │ string │ Arbitrary time │
869 │ │ │ │ tag of │
870 │ │ │ │ measurement. │
871 ├─────────┼─────────┼─────────┼──────────────────┤
872 │ │ │ │ │
873 │heading │ No │ numeric │ Heading, degrees │
874 │ │ │ │ from true north. │
875 ├─────────┼─────────┼─────────┼──────────────────┤
876 │ │ │ │ │
877 │mag_st │ No │ string │ Magnetometer │
878 │ │ │ │ status. │
879 ├─────────┼─────────┼─────────┼──────────────────┤
880 │ │ │ │ │
881 │pitch │ No │ numeric │ Pitch in │
882 │ │ │ │ degrees. │
883 ├─────────┼─────────┼─────────┼──────────────────┤
884 │ │ │ │ │
885 │pitch_st │ No │ string │ Pitch sensor │
886 │ │ │ │ status. │
887 ├─────────┼─────────┼─────────┼──────────────────┤
888 │ │ │ │ │
889 │yaw │ No │ numeric │ Yaw in degrees │
890 ├─────────┼─────────┼─────────┼──────────────────┤
891 │ │ │ │ │
892 │yaw_st │ No │ string │ Yaw sensor │
893 │ │ │ │ status. │
894 ├─────────┼─────────┼─────────┼──────────────────┤
895 │ │ │ │ │
896 │roll │ No │ numeric │ Roll in degrees. │
897 ├─────────┼─────────┼─────────┼──────────────────┤
898 │ │ │ │ │
899 │roll_st │ No │ string │ Roll sensor │
900 │ │ │ │ status. │
901 ├─────────┼─────────┼─────────┼──────────────────┤
902 │ │ │ │ │
903 │dip │ No │ numeric │ Local magnetic │
904 │ │ │ │ inclination, │
905 │ │ │ │ degrees, │
906 │ │ │ │ positive when │
907 │ │ │ │ the magnetic │
908 │ │ │ │ field points │
909 │ │ │ │ downward (into │
910 │ │ │ │ the Earth). │
911 ├─────────┼─────────┼─────────┼──────────────────┤
912 │ │ │ │ │
913 │mag_len │ No │ numeric │ Scalar magnetic │
914 │ │ │ │ field strength. │
915 ├─────────┼─────────┼─────────┼──────────────────┤
916 │ │ │ │ │
917 │mag_x │ No │ numeric │ X component of │
918 │ │ │ │ magnetic field │
919 │ │ │ │ strength. │
920 ├─────────┼─────────┼─────────┼──────────────────┤
921 │ │ │ │ │
922 │mag_y │ No │ numeric │ Y component of │
923 │ │ │ │ magnetic field │
924 │ │ │ │ strength. │
925 ├─────────┼─────────┼─────────┼──────────────────┤
926 │ │ │ │ │
927 │mag_z │ No │ numeric │ Z component of │
928 │ │ │ │ magnetic field │
929 │ │ │ │ strength. │
930 ├─────────┼─────────┼─────────┼──────────────────┤
931 │ │ │ │ │
932 │acc_len │ No │ numeric │ Scalar │
933 │ │ │ │ acceleration. │
934 ├─────────┼─────────┼─────────┼──────────────────┤
935 │ │ │ │ │
936 │acc_x │ No │ numeric │ X component of │
937 │ │ │ │ acceleration │
938 │ │ │ │ (m/s^2). │
939 ├─────────┼─────────┼─────────┼──────────────────┤
940 │ │ │ │ │
941 │acc_y │ No │ numeric │ Y component of │
942 │ │ │ │ acceleration │
943 │ │ │ │ (m/s^2). │
944 ├─────────┼─────────┼─────────┼──────────────────┤
945 │ │ │ │ │
946 │acc_z │ No │ numeric │ Z component of │
947 │ │ │ │ acceleration │
948 │ │ │ │ (m/s^2). │
949 ├─────────┼─────────┼─────────┼──────────────────┤
950 │ │ │ │ │
951 │gyro_x │ No │ numeric │ X component of │
952 │ │ │ │ angular rate │
953 │ │ │ │ (deg/s) │
954 ├─────────┼─────────┼─────────┼──────────────────┤
955 │ │ │ │ │
956 │gyro_y │ No │ numeric │ Y component of │
957 │ │ │ │ angular rate │
958 │ │ │ │ (deg/s) │
959 ├─────────┼─────────┼─────────┼──────────────────┤
960 │ │ │ │ │
961 │gyro_z │ No │ numeric │ Z component of │
962 │ │ │ │ angular rate │
963 │ │ │ │ (deg/s) │
964 ├─────────┼─────────┼─────────┼──────────────────┤
965 │ │ │ │ │
966 │depth │ No │ numeric │ Water depth in │
967 │ │ │ │ meters. │
968 ├─────────┼─────────┼─────────┼──────────────────┤
969 │ │ │ │ │
970 │temp │ No │ numeric │ Temperature at │
971 │ │ │ │ the sensor, │
972 │ │ │ │ degrees │
973 │ │ │ │ centigrade. │
974 └─────────┴─────────┴─────────┴──────────────────┘
975 The heading, pitch, and roll status codes (if present) vary by device.
977 For the TNT Revolution digital compasses, they are coded as follows:
978 Table 6. Device flags
980 ┌─────┬────────────────────────────┐
981 │ │ │
982 │Code │ Description │
983 ├─────┼────────────────────────────┤
984 │ │ │
985 │C │ magnetometer calibration │
986 │ │ alarm │
987 ├─────┼────────────────────────────┤
988 │ │ │
989 │L │ low alarm │
990 ├─────┼────────────────────────────┤
991 │ │ │
992 │M │ low warning │
993 ├─────┼────────────────────────────┤
994 │ │ │
995 │N │ normal │
996 ├─────┼────────────────────────────┤
997 │ │ │
998 │O │ high warning │
999 ├─────┼────────────────────────────┤
1000 │ │ │
1001 │P │ high alarm │
1002 ├─────┼────────────────────────────┤
1003 │ │ │
1004 │V │ magnetometer voltage level │
1005 │ │ alarm │
1006 └─────┴────────────────────────────┘
1007 When the C client library parses a response of this kind, it will
1009 assert ATT_IS.
1010 Here’s an example:
1012 {"class":"ATT","time":1270938096.843,
1014 "heading":14223.00,"mag_st":"N",
1015 "pitch":169.00,"pitch_st":"N", "roll":-43.00,"roll_st":"N",
1016 "dip":13641.000,"mag_x":2454.000}
1017 IMU
1019 The IMU object is asynchronous to the GNSS epoch. It is reported with
1020 arbitrary, even out of order, time scales.
1021 The ATT and IMU objects have the same fields, but IMU objects are
1023 output as soon as possible.
1024 Seee the ATT onject description for field details.
1026 TOFF
1028 This message is emitted on each cycle and reports the offset between
1029 the host’s clock time and the GPS time at top of the second (actually,
1030 when the first data for the reporting cycle is received).
1031 This message exactly mirrors the PPS message.
1033 The TOFF message reports the GPS time as derived from the GPS serial
1035 data stream. The PPS message reports the GPS time as derived from the
1036 GPS PPS pulse.
1037 A TOFF object has the following elements:
1039 Table 7. TOFF object
1041 ┌───────────┬─────────┬─────────┬──────────────────┐
1042 │ │ │ │ │
1043 │Name │ Always? │ Type │ Description │
1044 ├───────────┼─────────┼─────────┼──────────────────┤
1045 │ │ │ │ │
1046 │class │ Yes │ string │ Fixed: "TOFF" │
1047 ├───────────┼─────────┼─────────┼──────────────────┤
1048 │ │ │ │ │
1049 │device │ Yes │ string │ Name of the │
1050 │ │ │ │ originating │
1051 │ │ │ │ device │
1052 ├───────────┼─────────┼─────────┼──────────────────┤
1053 │ │ │ │ │
1054 │real_sec │ Yes │ numeric │ seconds from the │
1055 │ │ │ │ GPS clock │
1056 ├───────────┼─────────┼─────────┼──────────────────┤
1057 │ │ │ │ │
1058 │real_nsec │ Yes │ numeric │ nanoseconds from │
1059 │ │ │ │ the GPS clock │
1060 ├───────────┼─────────┼─────────┼──────────────────┤
1061 │ │ │ │ │
1062 │clock_sec │ Yes │ numeric │ seconds from the │
1063 │ │ │ │ system clock │
1064 ├───────────┼─────────┼─────────┼──────────────────┤
1065 │ │ │ │ │
1066 │clock_nsec │ Yes │ numeric │ nanoseconds from │
1067 │ │ │ │ the system clock │
1068 └───────────┴─────────┴─────────┴──────────────────┘
1069 This message is emitted once per second to watchers of a device and is
1071 intended to report the timestamps of the in-band report of the GPS and
1072 seconds as reported by the system clock (which may be NTP-corrected)
1073 when the first valid time stamp of the reporting cycle was seen.
1074 The message contains two second/nanosecond pairs: real_sec and
1076 real_nsec contain the time the GPS thinks it was at the start of the
1077 current cycle; clock_sec and clock_nsec contain the time the system
1078 clock thinks it was on receipt of the first timing message of the
1079 cycle. real_nsec is always to nanosecond precision. clock_nsec is
1080 nanosecond precision on most systems.
1081 Here’s an example:
1083 {"class":"TOFF","device":"/dev/ttyUSB0",
1085 "real_sec":1330212592, "real_nsec":343182,
1086 "clock_sec":1330212592,"clock_nsec":343184,
1087 "precision":-2}
1088 PPS
1090 This message is emitted each time the daemon sees a valid PPS (Pulse
1091 Per Second) strobe from a device.
1092 This message exactly mirrors the TOFF message.
1094 The TOFF message reports the GPS time as derived from the GPS serial
1096 data stream. The PPS message reports the GPS time as derived from the
1097 GPS PPS pulse.
1098 There are various sources of error in the reported clock times. The
1100 speed of the serial connection between the GPS and the system adds a
1101 delay to the start of cycle detection. An even bigger error is added by
1102 the variable computation time inside the GPS. Taken together the time
1103 derived from the start of the GPS cycle can have offsets of 10
1104 milliseconds to 700 milliseconds and combined jitter and wander of 100
1105 to 300 milliseconds.
1106 See the NTP documentation for their definition of precision.
1108 A PPS object has the following elements:
1110 Table 8. PPS object
1112 ┌───────────┬─────────┬─────────┬──────────────────┐
1113 │ │ │ │ │
1114 │Name │ Always? │ Type │ Description │
1115 ├───────────┼─────────┼─────────┼──────────────────┤
1116 │ │ │ │ │
1117 │class │ Yes │ string │ Fixed: "PPS" │
1118 ├───────────┼─────────┼─────────┼──────────────────┤
1119 │ │ │ │ │
1120 │device │ Yes │ string │ Name of the │
1121 │ │ │ │ originating │
1122 │ │ │ │ device │
1123 ├───────────┼─────────┼─────────┼──────────────────┤
1124 │ │ │ │ │
1125 │real_sec │ Yes │ numeric │ seconds from the │
1126 │ │ │ │ PPS source │
1127 ├───────────┼─────────┼─────────┼──────────────────┤
1128 │ │ │ │ │
1129 │real_nsec │ Yes │ numeric │ nanoseconds from │
1130 │ │ │ │ the PPS source │
1131 ├───────────┼─────────┼─────────┼──────────────────┤
1132 │ │ │ │ │
1133 │clock_sec │ Yes │ numeric │ seconds from the │
1134 │ │ │ │ system clock │
1135 ├───────────┼─────────┼─────────┼──────────────────┤
1136 │ │ │ │ │
1137 │clock_nsec │ Yes │ numeric │ nanoseconds from │
1138 │ │ │ │ the system clock │
1139 ├───────────┼─────────┼─────────┼──────────────────┤
1140 │ │ │ │ │
1141 │precision │ Yes │ numeric │ NTP style │
1142 │ │ │ │ estimate of PPS │
1143 │ │ │ │ precision │
1144 ├───────────┼─────────┼─────────┼──────────────────┤
1145 │ │ │ │ │
1146 │shm │ Yes │ string │ shm key of this │
1147 │ │ │ │ PPS │
1148 ├───────────┼─────────┼─────────┼──────────────────┤
1149 │ │ │ │ │
1150 │qErr │ No │ numeric │ Quantization │
1151 │ │ │ │ error of the │
1152 │ │ │ │ PPS, in │
1153 │ │ │ │ picoseconds. │
1154 │ │ │ │ Sometimes called │
1155 │ │ │ │ the "sawtooth" │
1156 │ │ │ │ error. │
1157 └───────────┴─────────┴─────────┴──────────────────┘
1158 This message is emitted once per second to watchers of a device
1160 emitting PPS, and reports the time of the start of the GPS second (when
1161 the 1PPS arrives) and seconds as reported by the system clock (which
1162 may be NTP-corrected) at that moment.
1163 The message contains two second/nanosecond pairs: real_sec and
1165 real_nsec contain the time the GPS thinks it was at the PPS edge;
1166 clock_sec and clock_nsec contain the time the system clock thinks it
1167 was at the PPS edge. real_nsec is always to nanosecond precision.
1168 clock_nsec is nanosecond precision on most systems.
1169 There are various sources of error in the reported clock times. For PPS
1171 delivered via a real serial-line strobe, serial-interrupt latency plus
1172 processing time to the timer call should be bounded above by about 10
1173 microseconds; that can be reduced to less than 1 microsecond if your
1174 kernel supports [RFC-2783]. USB1.1-to-serial control-line emulation is
1175 limited to about 1 millisecond. seconds.
1176 Here’s an example:
1178 {"class":"PPS","device":"/dev/ttyUSB0",
1180 "real_sec":1330212592, "real_nsec":343182,
1181 "clock_sec":1330212592,"clock_nsec":343184,
1182 "precision":-3}
1183 OSC
1185 This message reports the status of a GPS-disciplined oscillator
1186 (GPSDO). The GPS PPS output (which has excellent long-term stability)
1187 is typically used to discipline a local oscillator with much better
1188 short-term stability (such as a rubidium atomic clock).
1189 An OSC object has the following elements:
1191 Table 9. OSC object
1193 ┌────────────┬─────────┬─────────┬──────────────────┐
1194 │ │ │ │ │
1195 │Name │ Always? │ Type │ Description │
1196 ├────────────┼─────────┼─────────┼──────────────────┤
1197 │ │ │ │ │
1198 │class │ Yes │ string │ Fixed: "OSC" │
1199 ├────────────┼─────────┼─────────┼──────────────────┤
1200 │ │ │ │ │
1201 │device │ Yes │ string │ Name of the │
1202 │ │ │ │ originating │
1203 │ │ │ │ device. │
1204 ├────────────┼─────────┼─────────┼──────────────────┤
1205 │ │ │ │ │
1206 │running │ Yes │ boolean │ If true, the │
1207 │ │ │ │ oscillator is │
1208 │ │ │ │ currently │
1209 │ │ │ │ running. │
1210 │ │ │ │ Oscillators may │
1211 │ │ │ │ require warm-up │
1212 │ │ │ │ time at the │
1213 │ │ │ │ start of the │
1214 │ │ │ │ day. │
1215 ├────────────┼─────────┼─────────┼──────────────────┤
1216 │ │ │ │ │
1217 │reference │ Yes │ boolean │ If true, the │
1218 │ │ │ │ oscillator is │
1219 │ │ │ │ receiving a GPS │
1220 │ │ │ │ PPS signal. │
1221 ├────────────┼─────────┼─────────┼──────────────────┤
1222 │ │ │ │ │
1223 │disciplined │ Yes │ boolean │ If true, the GPS │
1224 │ │ │ │ PPS signal is │
1225 │ │ │ │ sufficiently │
1226 │ │ │ │ stable and is │
1227 │ │ │ │ being used to │
1228 │ │ │ │ discipline the │
1229 │ │ │ │ local │
1230 │ │ │ │ oscillator. │
1231 ├────────────┼─────────┼─────────┼──────────────────┤
1232 │ │ │ │ │
1233 │delta │ Yes │ numeric │ The time │
1234 │ │ │ │ difference (in │
1235 │ │ │ │ nanoseconds) │
1236 │ │ │ │ between the │
1237 │ │ │ │ GPS-disciplined │
1238 │ │ │ │ oscillator PPS │
1239 │ │ │ │ output pulse and │
1240 │ │ │ │ the most recent │
1241 │ │ │ │ GPS PPS input │
1242 │ │ │ │ pulse. │
1243 └────────────┴─────────┴─────────┴──────────────────┘
1244 Here’s an example:
1246 {"class":"OSC","running":true,"device":"/dev/ttyUSB0",
1248 "reference":true,"disciplined":true,"delta":67}
1249
1251 And here are the commands you can send to gpsd.
1252 ?VERSION;
1254 Returns an object with the following attributes:
1255 Table 10. VERSION object
1257 ┌────────────┬─────────┬─────────┬──────────────────┐
1258 │ │ │ │ │
1259 │Name │ Always? │ Type │ Description │
1260 ├────────────┼─────────┼─────────┼──────────────────┤
1261 │ │ │ │ │
1262 │class │ Yes │ string │ Fixed: "VERSION" │
1263 ├────────────┼─────────┼─────────┼──────────────────┤
1264 │ │ │ │ │
1265 │release │ Yes │ string │ Public release │
1266 │ │ │ │ level │
1267 ├────────────┼─────────┼─────────┼──────────────────┤
1268 │ │ │ │ │
1269 │rev │ Yes │ string │ Internal │
1270 │ │ │ │ revision-control │
1271 │ │ │ │ level. │
1272 ├────────────┼─────────┼─────────┼──────────────────┤
1273 │ │ │ │ │
1274 │proto_major │ Yes │ numeric │ API major │
1275 │ │ │ │ revision level. │
1276 ├────────────┼─────────┼─────────┼──────────────────┤
1277 │ │ │ │ │
1278 │proto_minor │ Yes │ numeric │ API minor │
1279 │ │ │ │ revision level. │
1280 ├────────────┼─────────┼─────────┼──────────────────┤
1281 │ │ │ │ │
1282 │remote │ No │ string │ URL of the │
1283 │ │ │ │ remote daemon │
1284 │ │ │ │ reporting this │
1285 │ │ │ │ version. If │
1286 │ │ │ │ empty, this is │
1287 │ │ │ │ the version of │
1288 │ │ │ │ the local │
1289 │ │ │ │ daemon. │
1290 └────────────┴─────────┴─────────┴──────────────────┘
1291 The daemon ships a VERSION response to each client when the client
1293 first connects to it.
1294 When the C client library parses a response of this kind, it will
1296 assert the VERSION_SET bit in the top-level set member.
1297 Here’s an example:
1299 {"class":"VERSION","version":"2.40dev",
1301 "rev":"06f62e14eae9886cde907dae61c124c53eb1101f",
1302 "proto_major":3,"proto_minor":1
1303 }
1304 ?DEVICES;
1306 Returns a device list object with the following elements:
1307 Table 11. DEVICES object
1309 ┌────────┬─────────┬────────┬──────────────────┐
1310 │ │ │ │ │
1311 │Name │ Always? │ Type │ Description │
1312 ├────────┼─────────┼────────┼──────────────────┤
1313 │ │ │ │ │
1314 │class │ Yes │ string │ Fixed: "DEVICES" │
1315 ├────────┼─────────┼────────┼──────────────────┤
1316 │ │ │ │ │
1317 │devices │ Yes │ list │ List of device │
1318 │ │ │ │ descriptions │
1319 ├────────┼─────────┼────────┼──────────────────┤
1320 │ │ │ │ │
1321 │remote │ No │ string │ URL of the │
1322 │ │ │ │ remote daemon │
1323 │ │ │ │ reporting the │
1324 │ │ │ │ device set. If │
1325 │ │ │ │ empty, this is a │
1326 │ │ │ │ DEVICES response │
1327 │ │ │ │ from the local │
1328 │ │ │ │ daemon. │
1329 └────────┴─────────┴────────┴──────────────────┘
1330 When the C client library parses a response of this kind, it will
1332 assert the DEVICELIST_SET bit in the top-level set member.
1333 Here’s an example:
1335 {"class"="DEVICES","devices":[
1337 {"class":"DEVICE","path":"/dev/pts/1","flags":1,"driver":"SiRF binary"},
1338 {"class":"DEVICE","path":"/dev/pts/3","flags":4,"driver":"AIVDM"}]}
1339 The daemon occasionally ships a bare DEVICE object to the client (that
1341 is, one not inside a DEVICES wrapper). The data content of these
1342 objects will be described later as a response to the ?DEVICE command.
1343 ?WATCH;
1345 This command sets watcher mode. It also sets or elicits a report of
1346 per-subscriber policy and the raw bit. An argument WATCH object changes
1347 the subscriber’s policy. The response describes the subscriber’s
1348 policy. The response will also include a DEVICES object.
1349 A WATCH object has the following elements:
1351 Table 12. WATCH object
1353 ┌────────┬─────────┬─────────┬──────────────────┐
1354 │ │ │ │ │
1355 │Name │ Always? │ Type │ Description │
1356 ├────────┼─────────┼─────────┼──────────────────┤
1357 │ │ │ │ │
1358 │class │ Yes │ string │ Fixed: "WATCH" │
1359 ├────────┼─────────┼─────────┼──────────────────┤
1360 │ │ │ │ │
1361 │enable │ No │ boolean │ Enable (true) or │
1362 │ │ │ │ disable (false) │
1363 │ │ │ │ watcher mode. │
1364 │ │ │ │ Default is true. │
1365 ├────────┼─────────┼─────────┼──────────────────┤
1366 │ │ │ │ │
1367 │json │ No │ boolean │ Enable (true) or │
1368 │ │ │ │ disable (false) │
1369 │ │ │ │ dumping of JSON │
1370 │ │ │ │ reports. Default │
1371 │ │ │ │ is false. │
1372 ├────────┼─────────┼─────────┼──────────────────┤
1373 │ │ │ │ │
1374 │nmea │ No │ boolean │ Enable (true) or │
1375 │ │ │ │ disable (false) │
1376 │ │ │ │ dumping of │
1377 │ │ │ │ binary packets │
1378 │ │ │ │ as pseudo-NMEA. │
1379 │ │ │ │ Default is │
1380 │ │ │ │ false. │
1381 ├────────┼─────────┼─────────┼──────────────────┤
1382 │ │ │ │ │
1383 │raw │ No │ integer │ Controls 'raw' │
1384 │ │ │ │ mode. When this │
1385 │ │ │ │ attribute is set │
1386 │ │ │ │ to 1 for a │
1387 │ │ │ │ channel, gpsd │
1388 │ │ │ │ reports the │
1389 │ │ │ │ unprocessed NMEA │
1390 │ │ │ │ or AIVDM data │
1391 │ │ │ │ stream from │
1392 │ │ │ │ whatever device │
1393 │ │ │ │ is attached. │
1394 │ │ │ │ Binary GPS │
1395 │ │ │ │ packets are │
1396 │ │ │ │ hex-dumped. │
1397 │ │ │ │ RTCM2 and RTCM3 │
1398 │ │ │ │ packets are not │
1399 │ │ │ │ dumped in raw │
1400 │ │ │ │ mode. When this │
1401 │ │ │ │ attribute is set │
1402 │ │ │ │ to 2 for a │
1403 │ │ │ │ channel that │
1404 │ │ │ │ processes binary │
1405 │ │ │ │ data, gpsd │
1406 │ │ │ │ reports the │
1407 │ │ │ │ received data │
1408 │ │ │ │ verbatim without │
1409 │ │ │ │ hex-dumping. │
1410 ├────────┼─────────┼─────────┼──────────────────┤
1411 │ │ │ │ │
1412 │scaled │ No │ boolean │ If true, apply │
1413 │ │ │ │ scaling divisors │
1414 │ │ │ │ to output before │
1415 │ │ │ │ dumping; default │
1416 │ │ │ │ is false. │
1417 ├────────┼─────────┼─────────┼──────────────────┤
1418 │ │ │ │ │
1419 │split24 │ No │ boolean │ If true, │
1420 │ │ │ │ aggregate AIS │
1421 │ │ │ │ type24 sentence │
1422 │ │ │ │ parts. If false, │
1423 │ │ │ │ report each part │
1424 │ │ │ │ as a separate │
1425 │ │ │ │ JSON object, │
1426 │ │ │ │ leaving the │
1427 │ │ │ │ client to match │
1428 │ │ │ │ MMSIs and │
1429 │ │ │ │ aggregate. │
1430 │ │ │ │ Default is │
1431 │ │ │ │ false. Applies │
1432 │ │ │ │ only to AIS │
1433 │ │ │ │ reports. │
1434 ├────────┼─────────┼─────────┼──────────────────┤
1435 │ │ │ │ │
1436 │pps │ No │ boolean │ If true, emit │
1437 │ │ │ │ the TOFF JSON │
1438 │ │ │ │ message on each │
1439 │ │ │ │ cycle and a PPS │
1440 │ │ │ │ JSON message │
1441 │ │ │ │ when the device │
1442 │ │ │ │ issues 1PPS. │
1443 │ │ │ │ Default is │
1444 │ │ │ │ false. │
1445 ├────────┼─────────┼─────────┼──────────────────┤
1446 │ │ │ │ │
1447 │device │ No │ string │ If present, │
1448 │ │ │ │ enable watching │
1449 │ │ │ │ only of the │
1450 │ │ │ │ specified device │
1451 │ │ │ │ rather than all │
1452 │ │ │ │ devices. Useful │
1453 │ │ │ │ with raw and │
1454 │ │ │ │ NMEA modes in │
1455 │ │ │ │ which device │
1456 │ │ │ │ responses aren’t │
1457 │ │ │ │ tagged. Has no │
1458 │ │ │ │ effect when used │
1459 │ │ │ │ with │
1460 │ │ │ │ enable:false. │
1461 ├────────┼─────────┼─────────┼──────────────────┤
1462 │ │ │ │ │
1463 │remote │ No │ string │ URL of the │
1464 │ │ │ │ remote daemon │
1465 │ │ │ │ reporting the │
1466 │ │ │ │ watch set. If │
1467 │ │ │ │ empty, this is a │
1468 │ │ │ │ WATCH response │
1469 │ │ │ │ from the local │
1470 │ │ │ │ daemon. │
1471 └────────┴─────────┴─────────┴──────────────────┘
1472 There is an additional boolean "timing" attribute which is undocumented
1474 because that portion of the interface is considered unstable and for
1475 developer use only.
1476 In watcher mode, GPS reports are dumped as TPV and SKY responses. AIS,
1478 Subframe and RTCM reporting is described in the next section.
1479 When the C client library parses a response of this kind, it will
1481 assert the POLICY_SET bit in the top-level set member.
1482 Here’s an example:
1484 {"class":"WATCH", "raw":1,"scaled":true}
1486 ?POLL;
1488 The POLL command requests data from the last-seen fixes on all active
1489 GPS devices. Devices must previously have been activated by ?WATCH to
1490 be pollable.
1491 Polling can lead to possibly surprising results when it is used on a
1493 device such as an NMEA GPS for which a complete fix has to be
1494 accumulated from several sentences. If you poll while those sentences
1495 are being emitted, the response will contain only the fix data
1496 collected so far in the current epoch. It may be as much as one cycle
1497 time (typically 1 second) stale.
1498 The POLL response will contain a timestamped list of TPV objects
1500 describing cached data, and a timestamped list of SKY objects
1501 describing satellite configuration. If a device has not seen fixes, it
1502 will be reported with a mode field of zero.
1503 Table 13. POLL object
1505 ┌───────┬─────────┬────────────┬──────────────────┐
1506 │ │ │ │ │
1507 │Name │ Always? │ Type │ Description │
1508 ├───────┼─────────┼────────────┼──────────────────┤
1509 │ │ │ │ │
1510 │class │ Yes │ string │ Fixed: "POLL" │
1511 ├───────┼─────────┼────────────┼──────────────────┤
1512 │ │ │ │ │
1513 │time │ Yes │ Numeric │ Timestamp in ISO │
1514 │ │ │ │ 8601 format. May │
1515 │ │ │ │ have a │
1516 │ │ │ │ fractional part │
1517 │ │ │ │ of up to .001sec │
1518 │ │ │ │ precision. │
1519 ├───────┼─────────┼────────────┼──────────────────┤
1520 │ │ │ │ │
1521 │active │ Yes │ Numeric │ Count of active │
1522 │ │ │ │ devices. │
1523 ├───────┼─────────┼────────────┼──────────────────┤
1524 │ │ │ │ │
1525 │tpv │ Yes │ JSON array │ Comma-separated │
1526 │ │ │ │ list of TPV │
1527 │ │ │ │ objects. │
1528 ├───────┼─────────┼────────────┼──────────────────┤
1529 │ │ │ │ │
1530 │sky │ Yes │ JSON array │ Comma-separated │
1531 │ │ │ │ list of SKY │
1532 │ │ │ │ objects. │
1533 └───────┴─────────┴────────────┴──────────────────┘
1534 Here’s an example of a POLL response:
1536 {"class":"POLL","time":"2010-06-04T10:31:00.289Z","active":1,
1538 "tpv":[{"class":"TPV","device":"/dev/ttyUSB0",
1539 "time":"2010-09-08T13:33:06.095Z",
1540 "ept":0.005,"lat":40.035093060,
1541 "lon":-75.519748733,"track":99.4319,"speed":0.123,"mode":2}],
1542 "sky":[{"class":"SKY","device":"/dev/ttyUSB0",
1543 "time":1270517264.240,"hdop":9.20,
1544 "satellites":[{"PRN":16,"el":55,"az":42,"ss":36,"used":true},
1545 {"PRN":19,"el":25,"az":177,"ss":0,"used":false},
1546 {"PRN":7,"el":13,"az":295,"ss":0,"used":false},
1547 {"PRN":6,"el":56,"az":135,"ss":32,"used":true},
1548 {"PRN":13,"el":47,"az":304,"ss":0,"used":false},
1549 {"PRN":23,"el":66,"az":259,"ss":0,"used":false},
1550 {"PRN":20,"el":7,"az":226,"ss":0,"used":false},
1551 {"PRN":3,"el":52,"az":163,"ss":32,"used":true},
1552 {"PRN":31,"el":16,"az":102,"ss":0,"used":false}
1553 ]}]}
1554 Note
1556 Client software should not assume the field inventory of the POLL
1557 response is fixed for all time. As gpsd collects and caches more
1558 data from more sensor types, those data are likely to find their
1559 way into this response.
1560 ?DEVICE; ?DEVICE=
1562 This command reports (when followed by ';') the state of a device, or
1563 sets (when followed by '=' and a DEVICE object) device-specific control
1564 bits, notably the device’s speed and serial mode and the native-mode
1565 bit. The parameter-setting form will be rejected if more than one
1566 client is attached to the channel.
1567 Pay attention to the response, because it is possible for this command
1569 to fail if the GPS does not support a speed-switching command or only
1570 supports some combinations of serial modes. In case of failure, the
1571 daemon and GPS will continue to communicate at the old speed.
1572 Use the parameter-setting form with caution. On USB and Bluetooth GPSes
1574 it is also possible for serial mode setting to fail either because the
1575 serial adaptor chip does not support non-8N1 modes or because the
1576 device firmware does not properly synchronize the serial adaptor chip
1577 with the UART on the GPS chipset when the speed changes. These failures
1578 can hang your device, possibly requiring a GPS power cycle or (in
1579 extreme cases) physically disconnecting the NVRAM backup battery.
1580 A DEVICE object has the following elements:
1582 Table 14. DEVICE object
1584 ┌──────────┬─────────┬─────────┬──────────────────┐
1585 │ │ │ │ │
1586 │Name │ Always? │ Type │ Description │
1587 ├──────────┼─────────┼─────────┼──────────────────┤
1588 │ │ │ │ │
1589 │class │ Yes │ string │ Fixed: "DEVICE" │
1590 ├──────────┼─────────┼─────────┼──────────────────┤
1591 │ │ │ │ │
1592 │path │ No │ string │ Name the device │
1593 │ │ │ │ for which the │
1594 │ │ │ │ control bits are │
1595 │ │ │ │ being reported, │
1596 │ │ │ │ or for which │
1597 │ │ │ │ they are to be │
1598 │ │ │ │ applied. This │
1599 │ │ │ │ attribute may be │
1600 │ │ │ │ omitted only │
1601 │ │ │ │ when there is │
1602 │ │ │ │ exactly one │
1603 │ │ │ │ subscribed │
1604 │ │ │ │ channel. │
1605 ├──────────┼─────────┼─────────┼──────────────────┤
1606 │ │ │ │ │
1607 │activated │ No │ string │ Time the device │
1608 │ │ │ │ was activated as │
1609 │ │ │ │ an ISO8601 time │
1610 │ │ │ │ stamp. If the │
1611 │ │ │ │ device is │
1612 │ │ │ │ inactive this │
1613 │ │ │ │ attribute is │
1614 │ │ │ │ absent. │
1615 ├──────────┼─────────┼─────────┼──────────────────┤
1616 │ │ │ │ │
1617 │flags │ No │ integer │ Bit vector of │
1618 │ │ │ │ property flags. │
1619 │ │ │ │ Currently │
1620 │ │ │ │ defined flags │
1621 │ │ │ │ are: describe │
1622 │ │ │ │ packet types │
1623 │ │ │ │ seen so far │
1624 │ │ │ │ (GPS, RTCM2, │
1625 │ │ │ │ RTCM3, AIS). │
1626 │ │ │ │ Won’t be │
1627 │ │ │ │ reported if │
1628 │ │ │ │ empty, e.g. │
1629 │ │ │ │ before gpsd has │
1630 │ │ │ │ seen │
1631 │ │ │ │ identifiable │
1632 │ │ │ │ packets from the │
1633 │ │ │ │ device. │
1634 ├──────────┼─────────┼─────────┼──────────────────┤
1635 │ │ │ │ │
1636 │driver │ No │ string │ GPSD’s name for │
1637 │ │ │ │ the device │
1638 │ │ │ │ driver type. │
1639 │ │ │ │ Won’t be │
1640 │ │ │ │ reported before │
1641 │ │ │ │ gpsd has seen │
1642 │ │ │ │ identifiable │
1643 │ │ │ │ packets from the │
1644 │ │ │ │ device. │
1645 ├──────────┼─────────┼─────────┼──────────────────┤
1646 │ │ │ │ │
1647 │subtype │ No │ string │ Whatever version │
1648 │ │ │ │ information the │
1649 │ │ │ │ device driver │
1650 │ │ │ │ returned. │
1651 ├──────────┼─────────┼─────────┼──────────────────┤
1652 │ │ │ │ │
1653 │subtype1 │ No │ string │ More version │
1654 │ │ │ │ information the │
1655 │ │ │ │ device driver │
1656 │ │ │ │ returned. │
1657 ├──────────┼─────────┼─────────┼──────────────────┤
1658 │ │ │ │ │
1659 │readonly │ No │ boolean │ True if device │
1660 │ │ │ │ is read-only. │
1661 ├──────────┼─────────┼─────────┼──────────────────┤
1662 │ │ │ │ │
1663 │bps │ No │ integer │ Device speed in │
1664 │ │ │ │ bits per second. │
1665 ├──────────┼─────────┼─────────┼──────────────────┤
1666 │ │ │ │ │
1667 │parity │ No │ string │ N, O or E for no │
1668 │ │ │ │ parity, odd, or │
1669 │ │ │ │ even. │
1670 ├──────────┼─────────┼─────────┼──────────────────┤
1671 │ │ │ │ │
1672 │stopbits │ Yes │ string │ Stop bits (1 or │
1673 │ │ │ │ 2). │
1674 ├──────────┼─────────┼─────────┼──────────────────┤
1675 │ │ │ │ │
1676 │native │ No │ integer │ 0 means NMEA │
1677 │ │ │ │ mode and 1 means │
1678 │ │ │ │ alternate mode │
1679 │ │ │ │ (binary if it │
1680 │ │ │ │ has one, for │
1681 │ │ │ │ SiRF and │
1682 │ │ │ │ Evermore │
1683 │ │ │ │ chipsets in │
1684 │ │ │ │ particular). │
1685 │ │ │ │ Attempting to │
1686 │ │ │ │ set this mode on │
1687 │ │ │ │ a non-GPS device │
1688 │ │ │ │ will yield an │
1689 │ │ │ │ error. │
1690 ├──────────┼─────────┼─────────┼──────────────────┤
1691 │ │ │ │ │
1692 │cycle │ No │ real │ Device cycle │
1693 │ │ │ │ time in seconds. │
1694 ├──────────┼─────────┼─────────┼──────────────────┤
1695 │ │ │ │ │
1696 │mincycle │ No │ real │ Device minimum │
1697 │ │ │ │ cycle time in │
1698 │ │ │ │ seconds. │
1699 │ │ │ │ Reported from │
1700 │ │ │ │ ?DEVICE when │
1701 │ │ │ │ (and only when) │
1702 │ │ │ │ the rate is │
1703 │ │ │ │ switchable. It │
1704 │ │ │ │ is read-only and │
1705 │ │ │ │ not settable. │
1706 └──────────┴─────────┴─────────┴──────────────────┘
1707 The serial parameters will (bps, parity, stopbits) be omitted in a
1709 response describing a TCP/IP source such as an Ntrip, DGPSIP, or AIS
1710 feed; on a serial device they will always be present.
1711 The contents of the flags field should be interpreted as follows:
1713 Table 15. Device flags
1715 ┌───────────┬───────┬─────────────────────┐
1716 │ │ │ │
1717 │C #define │ Value │ Description │
1718 ├───────────┼───────┼─────────────────────┤
1719 │ │ │ │
1720 │SEEN_GPS │ 0x01 │ GPS data has been │
1721 │ │ │ seen on this device │
1722 ├───────────┼───────┼─────────────────────┤
1723 │ │ │ │
1724 │SEEN_RTCM2 │ 0x02 │ RTCM2 data has been │
1725 │ │ │ seen on this device │
1726 ├───────────┼───────┼─────────────────────┤
1727 │ │ │ │
1728 │SEEN_RTCM3 │ 0x04 │ RTCM3 data has been │
1729 │ │ │ seen on this device │
1730 ├───────────┼───────┼─────────────────────┤
1731 │ │ │ │
1732 │SEEN_AIS │ 0x08 │ AIS data has been │
1733 │ │ │ seen on this device │
1734 └───────────┴───────┴─────────────────────┘
1735 When the C client library parses a response of this kind, it will
1737 assert the DEVICE_SET bit in the top-level set member.
1738 Here’s an example:
1740 {"class":"DEVICE","bps":4800,"parity":"N","stopbits":1,"native":0}
1742 When a client is in watcher mode, the daemon will ship it DEVICE
1744 notifications when a device is added to the pool or deactivated.
1745 When the C client library parses a response of this kind, it will
1747 assert the DEVICE_SET bit in the top-level set member.
1748 Here’s an example:
1750 {"class":"DEVICE","path":"/dev/pts1","activated":0}
1752 ERROR
1754 The daemon may ship an error object in response to a syntactically
1755 invalid command line or unknown command. It has the following elements:
1756 Table 16. ERROR notification object
1758 ┌────────┬─────────┬────────┬────────────────┐
1759 │ │ │ │ │
1760 │Name │ Always? │ Type │ Description │
1761 ├────────┼─────────┼────────┼────────────────┤
1762 │ │ │ │ │
1763 │class │ Yes │ string │ Fixed: "ERROR" │
1764 ├────────┼─────────┼────────┼────────────────┤
1765 │ │ │ │ │
1766 │message │ Yes │ string │ Textual error │
1767 │ │ │ │ message │
1768 └────────┴─────────┴────────┴────────────────┘
1769 Here’s an example:
1771 {"class":"ERROR","message":"Unrecognized request '?FOO'"}
1773 When the C client library parses a response of this kind, it will
1775 assert the ERR_SET bit in the top-level set member.
1776
1778 RTCM-104 is a family of serial protocols used for broadcasting
1779 pseudorange corrections from differential-GPS reference stations. Many
1780 GPS receivers can accept these corrections to improve their reporting
1781 accuracy.
1782 RTCM-104 comes in two major and incompatible flavors, 2.x and 3.x. Each
1784 major flavor has minor (compatible) revisions.
1785 The applicable standard for RTCM Version 2.x is RTCM Recommended
1787 Standards for Differential NAVSTAR GPS Service RTCM Paper 194-93/SC
1788 104-STD. For RTCM 3.1 it is RTCM Paper 177-2006-SC104-STD. Ordering
1789 instructions for both standards are accessible from the website of the
1790 Radio Technical Commission for Maritime Services
1791 <https://www.rtcm.org/> under "Publications".
1792 RTCM WIRE TRANSMISSIONS
1794 Differential-GPS correction stations consist of a GPS reference
1795 receiver coupled to a low frequency (LF) transmitter. The GPS reference
1796 receiver is a survey-grade GPS that does GPS carrier tracking and can
1797 work out its position to a few millimeters. It generates range and
1798 range-rate corrections and encodes them into RTCM104. It ships the
1799 RTCM104 to the LF transmitter over serial rs-232 signal at 100 baud or
1800 200 baud depending on the requirements of the transmitter.
1801 The LF transmitter broadcasts the approximately 300khz radio signal
1803 that differential-GPS radio receivers pick up. Transmitters that are
1804 meant to have a higher range will need to transmit at a slower rate.
1805 The higher the data rate the harder it will be for the remote radio
1806 receiver to receive with a good signal-to-noise ration. (Higher data
1807 rate signals can’t be averaged over as long a time frame, hence they
1808 appear noisier.)
1809 RTCM WIRE FORMATS
1811 An RTCM 2.x message consists of a sequence of up to 33 30-bit words.
1812 The 24 most significant bits of each word are data and the six least
1813 significant bits are parity. The parity algorithm used is the same
1814 ISGPS-2000 as that used on GPS satellite downlinks. Each RTCM 2.x
1815 message consists of two header words followed by zero or more data
1816 words, depending upon the message type.
1817 An RTCM 3.x message begins with a fixed leader byte 0xD3. That is
1819 followed by six bits of version information and 10 bits of payload
1820 length information. Following that is the payload; following the
1821 payload is a 3-byte checksum of the payload using the Qualcomm CRC-24Q
1822 algorithm.
1823 RTCM2 JSON FORMAT
1825 Each RTCM2 message is dumped as a single JSON object per message, with
1826 the message fields as attributes of that object. Arrays of satellite,
1827 station, and constellation statistics become arrays of JSON
1828 sub-objects. Each sentence will normally also have a "device" field
1829 containing the pathname of the originating device.
1830 All attributes other than the device field are mandatory. Header
1832 attributes are emitted before others.
1833 Header portion
1835 Table 17. SKY object
1836 ┌───────────────┬─────────┬─────────────────────────────────────────────┐
1837 │ │ │ │
1838 │Name │ Type │ Description │
1839 ├───────────────┼─────────┼─────────────────────────────────────────────┤
1840 │ │ │ │
1841 │class │ string │ Fixed: "RTCM2". │
1842 ├───────────────┼─────────┼─────────────────────────────────────────────┤
1843 │ │ │ │
1844 │type │ integer │ Message type (1-9). │
1845 ├───────────────┼─────────┼─────────────────────────────────────────────┤
1846 │ │ │ │
1847 │station_id │ integer │ The id of the GPS │
1848 │ │ │ reference receiver. │
1849 │ │ │ The LF transmitters │
1850 │ │ │ also have │
1851 │ │ │ (different) id │
1852 │ │ │ numbers. │
1853 ├───────────────┼─────────┼─────────────────────────────────────────────┤
1854 │ │ │ │
1855 │zcount │ real │ The reference time │
1856 │ │ │ of the corrections │
1857 │ │ │ in the message in │
1858 │ │ │ seconds within the │
1859 │ │ │ current hour. Note │
1860 │ │ │ that it is in GPS │
1861 │ │ │ time, which is some │
1862 │ │ │ seconds ahead of │
1863 │ │ │ UTC (see the U.S. │
1864 │ │ │ Naval Observatory’s │
1865 │ │ │ table of leap │
1866 │ │ │ second │
1867 │ │ │ <ftp://maia.usno.navy.mil/ser7/tai-utc.dat> │
1868 │ │ │ corrections" ). │
1869 ├───────────────┼─────────┼─────────────────────────────────────────────┤
1870 │ │ │ │
1871 │seqnum │ integer │ Sequence number. Only 3 bits wide, wraps │
1872 │ │ │ after 7. │
1873 ├───────────────┼─────────┼─────────────────────────────────────────────┤
1874 │ │ │ │
1875 │length │ integer │ The number of words after the header that │
1876 │ │ │ comprise the message. │
1877 ├───────────────┼─────────┼─────────────────────────────────────────────┤
1878 │ │ │ │
1879 │station_health │ integer │ Station transmission status. Indicates the │
1880 │ │ │ health of the beacon as a reference source. │
1881 │ │ │ Any nonzero value means the satellite is │
1882 │ │ │ probably transmitting bad data and should │
1883 │ │ │ not be used in a fix. 6 means the │
1884 │ │ │ transmission is unmonitored. 7 means the │
1885 │ │ │ station is not working properly. Other │
1886 │ │ │ values are defined by the beacon operator. │
1887 └───────────────┴─────────┴─────────────────────────────────────────────┘
1888 <message type> is one of
1890 1
1892 full corrections — one message containing corrections for all GPS
1893 satellites in view. This is not common.
1894 3
1896 reference station parameters — the position of the reference
1897 station GPS antenna.
1898 4
1900 datum — the datum to which the DGPS data is referred.
1901 5
1903 constellation health — information about the satellites the beacon
1904 can see.
1905 6
1907 null message — just a filler.
1908 7
1910 radio beacon almanac — information about this or other beacons.
1911 9
1913 subset corrections — a message containing corrections for only a
1914 subset of the GPS satellites in view.
1915 16
1917 special message — a text message from the beacon operator.
1918 31
1920 GLONASS subset corrections — a message containing corrections for a
1921 set of the GLONASS satellites in view.
1922 Type 1 and 9: Correction data
1924 One or more satellite objects follow the header for type 1 or type 9
1925 messages. Here is the format:
1926 Table 18. Satellite object
1928 ┌──────┬─────────┬─────────────────────┐
1929 │ │ │ │
1930 │Name │ Type │ Description │
1931 ├──────┼─────────┼─────────────────────┤
1932 │ │ │ │
1933 │ident │ integer │ The PRN number of │
1934 │ │ │ the satellite for │
1935 │ │ │ which this is │
1936 │ │ │ correction data. │
1937 ├──────┼─────────┼─────────────────────┤
1938 │ │ │ │
1939 │udre │ integer │ User Differential │
1940 │ │ │ Range Error (0-3). │
1941 │ │ │ See the table │
1942 │ │ │ following for │
1943 │ │ │ values. │
1944 ├──────┼─────────┼─────────────────────┤
1945 │ │ │ │
1946 │iod │ integer │ Issue Of Data, │
1947 │ │ │ matching the IOD │
1948 │ │ │ for the current │
1949 │ │ │ ephemeris of this │
1950 │ │ │ satellite, as │
1951 │ │ │ transmitted by the │
1952 │ │ │ satellite. The IOD │
1953 │ │ │ is a unique tag │
1954 │ │ │ that identifies the │
1955 │ │ │ ephemeris; the GPS │
1956 │ │ │ using the DGPS │
1957 │ │ │ correction and the │
1958 │ │ │ DGPS generating the │
1959 │ │ │ data must use the │
1960 │ │ │ same orbital │
1961 │ │ │ positions for the │
1962 │ │ │ satellite. │
1963 ├──────┼─────────┼─────────────────────┤
1964 │ │ │ │
1965 │prc │ real │ The pseudorange │
1966 │ │ │ error in meters for │
1967 │ │ │ this satellite as │
1968 │ │ │ measured by the │
1969 │ │ │ beacon reference │
1970 │ │ │ receiver at the │
1971 │ │ │ epoch indicated by │
1972 │ │ │ the z_count in the │
1973 │ │ │ parent record. │
1974 ├──────┼─────────┼─────────────────────┤
1975 │ │ │ │
1976 │rrc │ real │ The rate of change │
1977 │ │ │ of pseudorange │
1978 │ │ │ error in meters/sec │
1979 │ │ │ for this satellite │
1980 │ │ │ as measured by the │
1981 │ │ │ beacon reference │
1982 │ │ │ receiver at the │
1983 │ │ │ epoch indicated by │
1984 │ │ │ the z_count field │
1985 │ │ │ in the parent │
1986 │ │ │ record. This is │
1987 │ │ │ used to calculate │
1988 │ │ │ pseudorange errors │
1989 │ │ │ at other epochs, if │
1990 │ │ │ required by the GPS │
1991 │ │ │ receiver. │
1992 └──────┴─────────┴─────────────────────┘
1993 User Differential Range Error values are as follows:
1995 Table 19. UDRE values
1997 ┌──┬─────────────────────┐
1998 │ │ │
1999 │0 │ 1-sigma error ⇐ 1 m │
2000 ├──┼─────────────────────┤
2001 │ │ │
2002 │1 │ 1-sigma error ⇐ 4 m │
2003 ├──┼─────────────────────┤
2004 │ │ │
2005 │2 │ 1-sigma error ⇐ 8 m │
2006 ├──┼─────────────────────┤
2007 │ │ │
2008 │3 │ 1-sigma error > 8 m │
2009 └──┴─────────────────────┘
2010 Here’s an example:
2012 {"class":"RTCM2","type":1,
2014 "station_id":688,"zcount":843.0,"seqnum":5,"length":19,"station_health":6,
2015 "satellites":[
2016 {"ident":10,"udre":0,"iod":46,"prc":-2.400,"rrc":0.000},
2017 {"ident":13,"udre":0,"iod":94,"prc":-4.420,"rrc":0.000},
2018 {"ident":7,"udre":0,"iod":22,"prc":-5.160,"rrc":0.002},
2019 {"ident":2,"udre":0,"iod":34,"prc":-6.480,"rrc":0.000},
2020 {"ident":4,"udre":0,"iod":47,"prc":-8.860,"rrc":0.000},
2021 {"ident":8,"udre":0,"iod":76,"prc":-7.980,"rrc":0.002},
2022 {"ident":5,"udre":0,"iod":99,"prc":-8.260,"rrc":0.002},
2023 {"ident":23,"udre":0,"iod":81,"prc":-8.060,"rrc":0.000},
2024 {"ident":16,"udre":0,"iod":70,"prc":-11.740,"rrc":0.000},
2025 {"ident":30,"udre":0,"iod":4,"prc":-18.960,"rrc":-0.006},
2026 {"ident":29,"udre":0,"iod":101,"prc":-24.960,"rrc":-0.002}
2027 ]}
2028 Type 3: Reference Station Parameters
2030 Here are the payload members of a type 3 (Reference Station Parameters)
2031 message:
2032 Table 20. Reference Station Parameters
2034 ┌─────┬──────┬────────────────────┐
2035 │ │ │ │
2036 │Name │ Type │ Description │
2037 ├─────┼──────┼────────────────────┤
2038 │ │ │ │
2039 │x │ real │ ECEF X coordinate. │
2040 ├─────┼──────┼────────────────────┤
2041 │ │ │ │
2042 │y │ real │ ECEF Y coordinate. │
2043 ├─────┼──────┼────────────────────┤
2044 │ │ │ │
2045 │z │ real │ ECEF Z coordinate. │
2046 └─────┴──────┴────────────────────┘
2047 The coordinates are the position of the station, in meters to two
2049 decimal places, in Earth Centred Earth Fixed coordinates. These are
2050 usually referred to the WGS84 reference frame, but may be referred to
2051 NAD83 in the US (essentially identical to WGS84 for all except
2052 geodesists), or some other reference frame in other parts of the world.
2053 An invalid reference message is represented by a type 3 header without
2055 payload fields.
2056 Here’s an example:
2058 {"class":"RTCM2","type":3,
2060 "station_id":652,"zcount":1657.2,"seqnum":2,"length":4,"station_health":6,
2061 "x":3878620.92,"y":670281.40,"z":5002093.59
2062 }
2063 Type 4: Datum
2065 Here are the payload members of a type 4 (Datum) message:
2066 Table 21. Datum
2068 ┌───────────┬─────────┬─────────────────────┐
2069 │ │ │ │
2070 │Name │ Type │ Description │
2071 ├───────────┼─────────┼─────────────────────┤
2072 │ │ │ │
2073 │dgnss_type │ string │ Either "GPS", │
2074 │ │ │ "GLONASS", │
2075 │ │ │ "GALILEO", or │
2076 │ │ │ "UNKNOWN". │
2077 ├───────────┼─────────┼─────────────────────┤
2078 │ │ │ │
2079 │dat │ integer │ 0 or 1 and │
2080 │ │ │ indicates the sense │
2081 │ │ │ of the offset shift │
2082 │ │ │ given by dx, dy, │
2083 │ │ │ dz. dat = 0 means │
2084 │ │ │ that the station │
2085 │ │ │ coordinates (in the │
2086 │ │ │ reference message) │
2087 │ │ │ are referred to a │
2088 │ │ │ local datum and │
2089 │ │ │ that adding dx, dy, │
2090 │ │ │ dz to that position │
2091 │ │ │ will render it in │
2092 │ │ │ GNSS coordinates │
2093 │ │ │ (WGS84 for GPS). If │
2094 │ │ │ dat = 1 then the │
2095 │ │ │ ref station │
2096 │ │ │ position is in GNSS │
2097 │ │ │ coordinates and │
2098 │ │ │ adding dx, dy, dz │
2099 │ │ │ will give it │
2100 │ │ │ referred to the │
2101 │ │ │ local datum. │
2102 ├───────────┼─────────┼─────────────────────┤
2103 │ │ │ │
2104 │datum_name │ string │ A standard name for │
2105 │ │ │ the datum. │
2106 ├───────────┼─────────┼─────────────────────┤
2107 │ │ │ │
2108 │dx │ real │ X offset. │
2109 ├───────────┼─────────┼─────────────────────┤
2110 │ │ │ │
2111 │dy │ real │ Y offset. │
2112 ├───────────┼─────────┼─────────────────────┤
2113 │ │ │ │
2114 │dz │ real │ Z offset. │
2115 └───────────┴─────────┴─────────────────────┘
2116 <dx> <dy> <dz> are offsets to convert from local datum to GNSS datum or
2118 vice versa. These fields are optional.
2119 An invalid datum message is represented by a type 4 header without
2121 payload fields.
2122 Type 5: Constellation Health
2124 One or more of these follow the header for type 5 messages — one for
2125 each satellite.
2126 Here is the format:
2128 Table 22. Constellation health
2130 ┌────────────┬─────────┬─────────────────────┐
2131 │ │ │ │
2132 │Name │ Type │ Description │
2133 ├────────────┼─────────┼─────────────────────┤
2134 │ │ │ │
2135 │ident │ integer │ The PRN number of │
2136 │ │ │ the satellite. │
2137 ├────────────┼─────────┼─────────────────────┤
2138 │ │ │ │
2139 │iodl │ bool │ True indicates that │
2140 │ │ │ this information │
2141 │ │ │ relates to the │
2142 │ │ │ satellite │
2143 │ │ │ information in an │
2144 │ │ │ accompanying type 1 │
2145 │ │ │ or type 9 message. │
2146 ├────────────┼─────────┼─────────────────────┤
2147 │ │ │ │
2148 │health │ integer │ 0 indicates that │
2149 │ │ │ the satellite is │
2150 │ │ │ healthy. Any other │
2151 │ │ │ value indicates a │
2152 │ │ │ problem (coding is │
2153 │ │ │ not known). │
2154 ├────────────┼─────────┼─────────────────────┤
2155 │ │ │ │
2156 │snr │ integer │ The carrier/noise │
2157 │ │ │ ratio of the │
2158 │ │ │ received signal in │
2159 │ │ │ the range 25 to 55 │
2160 │ │ │ dB(Hz). │
2161 ├────────────┼─────────┼─────────────────────┤
2162 │ │ │ │
2163 │health_en │ bool │ If set to True it │
2164 │ │ │ indicates that the │
2165 │ │ │ satellite is │
2166 │ │ │ healthy even if the │
2167 │ │ │ satellite │
2168 │ │ │ navigation data │
2169 │ │ │ says it is │
2170 │ │ │ unhealthy. │
2171 ├────────────┼─────────┼─────────────────────┤
2172 │ │ │ │
2173 │new_data │ bool │ True indicates that │
2174 │ │ │ the IOD for this │
2175 │ │ │ satellite will soon │
2176 │ │ │ be updated in type │
2177 │ │ │ 1 or 9 messages. │
2178 ├────────────┼─────────┼─────────────────────┤
2179 │ │ │ │
2180 │los_warning │ bool │ Line-of-sight │
2181 │ │ │ warning. True │
2182 │ │ │ indicates that the │
2183 │ │ │ satellite will │
2184 │ │ │ shortly go │
2185 │ │ │ unhealthy. │
2186 ├────────────┼─────────┼─────────────────────┤
2187 │ │ │ │
2188 │tou │ integer │ Healthy time │
2189 │ │ │ remaining in │
2190 │ │ │ seconds. │
2191 └────────────┴─────────┴─────────────────────┘
2192 Type 6: Null
2194 This just indicates a null message. There are no payload fields.
2195 Unknown message
2197 This format is used to dump message words in hexadecimal when the
2198 message type field doesn’t match any of the known ones.
2199 Here is the format:
2201 Table 23. Unknown Message
2203 ┌─────┬──────┬────────────────────┐
2204 │ │ │ │
2205 │Name │ Type │ Description │
2206 ├─────┼──────┼────────────────────┤
2207 │ │ │ │
2208 │data │ list │ A list of strings. │
2209 └─────┴──────┴────────────────────┘
2210 Each string in the array is a hex literal representing 30 bits of
2212 information, after parity checks and inversion. The high two bits
2213 should be ignored.
2214 Type 7: Radio Beacon Almanac
2216 Here is the format:
2217 Table 24. Constellation health
2219 ┌───────────┬─────────┬─────────────────────┐
2220 │ │ │ │
2221 │Name │ Type │ Description │
2222 ├───────────┼─────────┼─────────────────────┤
2223 │ │ │ │
2224 │lat │ real │ Latitude in │
2225 │ │ │ degrees, of the LF │
2226 │ │ │ transmitter antenna │
2227 │ │ │ for the station for │
2228 │ │ │ which this is an │
2229 │ │ │ almanac. North is │
2230 │ │ │ positive. │
2231 ├───────────┼─────────┼─────────────────────┤
2232 │ │ │ │
2233 │lon │ real │ Longitude in │
2234 │ │ │ degrees, of the LF │
2235 │ │ │ transmitter antenna │
2236 │ │ │ for the station for │
2237 │ │ │ which this is an │
2238 │ │ │ almanac. East is │
2239 │ │ │ positive. │
2240 ├───────────┼─────────┼─────────────────────┤
2241 │ │ │ │
2242 │range │ integer │ Published range of │
2243 │ │ │ the station in km. │
2244 ├───────────┼─────────┼─────────────────────┤
2245 │ │ │ │
2246 │frequency │ real │ Station broadcast │
2247 │ │ │ frequency in kHz. │
2248 ├───────────┼─────────┼─────────────────────┤
2249 │ │ │ │
2250 │health │ integer │ <health> is the │
2251 │ │ │ health of the │
2252 │ │ │ station for which │
2253 │ │ │ this is an almanac. │
2254 │ │ │ If it is non-zero, │
2255 │ │ │ the station is │
2256 │ │ │ issuing suspect │
2257 │ │ │ data and should not │
2258 │ │ │ be used for fixes. │
2259 │ │ │ The ITU and RTCM104 │
2260 │ │ │ standards differ │
2261 │ │ │ about the mode │
2262 │ │ │ detailed │
2263 │ │ │ interpretation of │
2264 │ │ │ the <health> field │
2265 │ │ │ and even about its │
2266 │ │ │ bit width. │
2267 ├───────────┼─────────┼─────────────────────┤
2268 │ │ │ │
2269 │station_id │ integer │ The id of the │
2270 │ │ │ transmitter. This │
2271 │ │ │ is not the same as │
2272 │ │ │ the reference id in │
2273 │ │ │ the header, the │
2274 │ │ │ latter being the id │
2275 │ │ │ of the reference │
2276 │ │ │ receiver. │
2277 ├───────────┼─────────┼─────────────────────┤
2278 │ │ │ │
2279 │bitrate │ integer │ The transmitted │
2280 │ │ │ bitrate. │
2281 └───────────┴─────────┴─────────────────────┘
2282 Here’s an example:
2284 {"class":"RTCM2","type":9,"station_id":268,"zcount":252.6,
2286 "seqnum":4,"length":5,"station_health":0,
2287 "satellites":[
2288 {"ident":13,"udre":0,"iod":3,"prc":-25.940,"rrc":0.066},
2289 {"ident":2,"udre":0,"iod":73,"prc":0.920,"rrc":-0.080},
2290 {"ident":8,"udre":0,"iod":22,"prc":23.820,"rrc":0.014}
2291 ]}
2292 Type 13: GPS Time of Week
2294 Here are the payload members of a type 13 (Groumf Tramitter Parameters)
2295 message:
2296 Table 25. Ground Transmitter Parameters
2298 ┌──────────┬─────────┬─────────────────────┐
2299 │ │ │ │
2300 │Name │ Type │ Description │
2301 ├──────────┼─────────┼─────────────────────┤
2302 │ │ │ │
2303 │status │ bool │ If True, signals │
2304 │ │ │ user to expect a │
2305 │ │ │ type 16 explanatory │
2306 │ │ │ message associated │
2307 │ │ │ with this station. │
2308 │ │ │ Probably indicates │
2309 │ │ │ some sort of │
2310 │ │ │ unusual event. │
2311 ├──────────┼─────────┼─────────────────────┤
2312 │ │ │ │
2313 │rangeflag │ bool │ If True, indicates │
2314 │ │ │ that the estimated │
2315 │ │ │ range is different │
2316 │ │ │ from that found in │
2317 │ │ │ the type 7 message │
2318 │ │ │ (which contains the │
2319 │ │ │ beacon’s listed │
2320 │ │ │ range). Generally │
2321 │ │ │ indicates a range │
2322 │ │ │ reduction due to │
2323 │ │ │ causes such as poor │
2324 │ │ │ ionospheric │
2325 │ │ │ conditions or │
2326 │ │ │ reduced │
2327 │ │ │ transmission power. │
2328 ├──────────┼─────────┼─────────────────────┤
2329 │ │ │ │
2330 │lat │ real │ Degrees latitude, │
2331 │ │ │ signed. Positive is │
2332 │ │ │ N, negative is S. │
2333 ├──────────┼─────────┼─────────────────────┤
2334 │ │ │ │
2335 │lon │ real │ Degrees longitude, │
2336 │ │ │ signed. Positive is │
2337 │ │ │ E, negative is W. │
2338 ├──────────┼─────────┼─────────────────────┤
2339 │ │ │ │
2340 │range │ integer │ Transmission range │
2341 │ │ │ in km (1-1024). │
2342 └──────────┴─────────┴─────────────────────┘
2343 This message type replaces message type 3 (Reference Station
2345 Parameters) in RTCM 2.3.
2346 Type 14: GPS Time of Week
2348 Here are the payload members of a type 14 (GPS Time of Week) message:
2349 Table 26. Reference Station Parameters
2351 ┌─────────┬─────────┬───────────────────┐
2352 │ │ │ │
2353 │Name │ Type │ Description │
2354 ├─────────┼─────────┼───────────────────┤
2355 │ │ │ │
2356 │week │ integer │ GPS week (0-123). │
2357 ├─────────┼─────────┼───────────────────┤
2358 │ │ │ │
2359 │hour │ integer │ Hour of week │
2360 │ │ │ (0-167). │
2361 ├─────────┼─────────┼───────────────────┤
2362 │ │ │ │
2363 │leapsecs │ integer │ Leap Seconds │
2364 │ │ │ (0-63). │
2365 └─────────┴─────────┴───────────────────┘
2366 Here’s an example:
2368 {"class":"RTCM2","type":14,"station_id":652,"zcount":1657.2,
2370 "seqnum":3,"length":1,"station_health":6,"week":601,"hour":109,
2371 "leapsecs":15}
2372 Type 16: Special Message
2374 Table 27. Special Message
2375 ┌────────┬────────┬─────────────────────┐
2376 │ │ │ │
2377 │Name │ Type │ Description │
2378 ├────────┼────────┼─────────────────────┤
2379 │ │ │ │
2380 │message │ string │ A text message sent │
2381 │ │ │ by the beacon │
2382 │ │ │ operator. │
2383 └────────┴────────┴─────────────────────┘
2384 Type 31: Correction data
2386 One or more GLONASS satellite objects follow the header for type 1 or
2387 type 9 messages. Here is the format:
2388 Table 28. Satellite object
2390 ┌───────┬──────────┬─────────────────────┐
2391 │ │ │ │
2392 │Name │ Type │ Description │
2393 ├───────┼──────────┼─────────────────────┤
2394 │ │ │ │
2395 │ident │ integer │ The PRN number of │
2396 │ │ │ the satellite for │
2397 │ │ │ which this is │
2398 │ │ │ correction data. │
2399 ├───────┼──────────┼─────────────────────┤
2400 │ │ │ │
2401 │udre │ integer │ User Differential │
2402 │ │ │ Range Error (0-3). │
2403 │ │ │ See the table │
2404 │ │ │ following for │
2405 │ │ │ values. │
2406 ├───────┼──────────┼─────────────────────┤
2407 │ │ │ │
2408 │change │ boolean │ Change-of-ephemeris │
2409 │ │ │ bit. │
2410 ├───────┼──────────┼─────────────────────┤
2411 │ │ │ │
2412 │tod │ uinteger │ Count of 30-second │
2413 │ │ │ periods since the │
2414 │ │ │ top of the hour. │
2415 ├───────┼──────────┼─────────────────────┤
2416 │ │ │ │
2417 │prc │ real │ The pseudorange │
2418 │ │ │ error in meters for │
2419 │ │ │ this satellite as │
2420 │ │ │ measured by the │
2421 │ │ │ beacon reference │
2422 │ │ │ receiver at the │
2423 │ │ │ epoch indicated by │
2424 │ │ │ the z_count in the │
2425 │ │ │ parent record. │
2426 ├───────┼──────────┼─────────────────────┤
2427 │ │ │ │
2428 │rrc │ real │ The rate of change │
2429 │ │ │ of pseudorange │
2430 │ │ │ error in meters/sec │
2431 │ │ │ for this satellite │
2432 │ │ │ as measured by the │
2433 │ │ │ beacon reference │
2434 │ │ │ receiver at the │
2435 │ │ │ epoch indicated by │
2436 │ │ │ the z_count field │
2437 │ │ │ in the parent │
2438 │ │ │ record. This is │
2439 │ │ │ used to calculate │
2440 │ │ │ pseudorange errors │
2441 │ │ │ at other epochs, if │
2442 │ │ │ required by the GPS │
2443 │ │ │ receiver. │
2444 └───────┴──────────┴─────────────────────┘
2445 Here’s an example:
2447 {"class":"RTCM2","type":31,"station_id":652,"zcount":1642.2,
2449 "seqnum":0,"length":14,"station_health":6,
2450 "satellites":[
2451 {"ident":5,"udre":0,"change":false,"tod":0,"prc":132.360,"rrc":0.000},
2452 {"ident":15,"udre":0,"change":false,"tod":0,"prc":134.840,"rrc":0.002},
2453 {"ident":14,"udre":0,"change":false,"tod":0,"prc":141.520,"rrc":0.000},
2454 {"ident":6,"udre":0,"change":false,"tod":0,"prc":127.000,"rrc":0.000},
2455 {"ident":21,"udre":0,"change":false,"tod":0,"prc":128.780,"rrc":0.000},
2456 {"ident":22,"udre":0,"change":false,"tod":0,"prc":125.260,"rrc":0.002},
2457 {"ident":20,"udre":0,"change":false,"tod":0,"prc":117.280,"rrc":-0.004},
2458 {"ident":16,"udre":0,"change":false,"tod":17,"prc":113.460,"rrc":0.018}
2459 ]}
2460
2462 The support for RTCM104v3 dumping is incomplete and buggy. Do not
2463 attempt to use it for production! Anyone interested in it should read
2464 the source code.
2465
2467 AIS support is an extension. It may not be present if your instance of
2468 gpsd has been built with a restricted feature set.
2469 AIS packets are dumped as JSON objects with class "AIS". Each AIS
2471 report object contains a "type" field giving the AIS message type and a
2472 "scaled" field telling whether the remainder of the fields are dumped
2473 in scaled or unscaled form. (These will be emitted before any
2474 type-specific fields.) It will also contain a "device" field naming the
2475 data source. Other fields have names and types as specified in the
2476 AIVDM/AIVDO Protocol Decoding document on the GPSD project website;
2477 each message field table may be directly interpreted as a specification
2478 for the members of the corresponding JSON object type.
2479 By default, certain scaling and conversion operations are performed for
2481 JSON output. Latitudes and longitudes are scaled to decimal degrees
2482 rather than the native AIS unit of 1/10000th of a minute of arc. Ship
2483 (but not air) speeds are scaled to knots rather than tenth-of-knot
2484 units. Rate of turn may appear as "nan" if is unavailable, or as one of
2485 the strings "fastright" or "fastleft" if it is out of the AIS encoding
2486 range; otherwise it is quadratically mapped back to the turn sensor
2487 number in degrees per minute. Vessel draughts are converted to decimal
2488 meters rather than native AIS decimeters. Various other scaling
2489 conversions are described in "AIVDM/AIVDO Protocol Decoding".
2490
2492 Subframe support is always compiled into gpsd but many GPSes do not
2493 output subframe data or the gpsd driver may not support subframes.
2494 Subframe packets are dumped as JSON objects with class "SUBFRAME". Each
2496 subframe report object contains a "frame" field giving the subframe
2497 number, a "tSV" field for the transmitting satellite number, a "TOW17"
2498 field containing the 17 MSBs of the start of the next 12-second message
2499 and a "scaled" field telling whether the remainder of the fields are
2500 dumped in scaled or unscaled form. It will also contain a "device"
2501 field naming the data source. Each SUBFRAME object will have a
2502 sub-object specific to that subframe page type. Those sub-object fields
2503 have names and types similar to those specified in the IS-GPS-200
2504 document; each message field table may be directly interpreted as a
2505 specification for the members of the corresponding JSON object type.
2506 Table 29. SUBFRAME object
2508 ┌───────┬─────────┬─────────┬──────────────────┐
2509 │ │ │ │ │
2510 │Name │ Always? │ Type │ Description │
2511 ├───────┼─────────┼─────────┼──────────────────┤
2512 │ │ │ │ │
2513 │class │ Yes │ string │ Fixed: │
2514 │ │ │ │ "SUBFRAME" │
2515 ├───────┼─────────┼─────────┼──────────────────┤
2516 │ │ │ │ │
2517 │device │ Yes │ string │ Name of the │
2518 │ │ │ │ originating │
2519 │ │ │ │ device. │
2520 ├───────┼─────────┼─────────┼──────────────────┤
2521 │ │ │ │ │
2522 │gnssId │ Yes │ integer │ Constellation of │
2523 │ │ │ │ transmitting │
2524 │ │ │ │ satellite │
2525 ├───────┼─────────┼─────────┼──────────────────┤
2526 │ │ │ │ │
2527 │tSV │ Yes │ integer │ ID of │
2528 │ │ │ │ transmitting │
2529 │ │ │ │ satellite (Not │
2530 │ │ │ │ PRN) │
2531 ├───────┼─────────┼─────────┼──────────────────┤
2532 │ │ │ │ │
2533 │TOW17 │ No │ integer │ Type 17 bits of │
2534 │ │ │ │ the next GPS │
2535 │ │ │ │ Time Of Week │
2536 ├───────┼─────────┼─────────┼──────────────────┤
2537 │ │ │ │ │
2538 │frame │ No │ integer │ Frame number │
2539 ├───────┼─────────┼─────────┼──────────────────┤
2540 │ │ │ │ │
2541 │scaled │ Yes │ boolean │ True is values │
2542 │ │ │ │ scaled │
2543 └───────┴─────────┴─────────┴──────────────────┘
2544
2546 Reading the raw JSON can be tedious. You can pretty print, and
2547 colorize, your JSON with [jq] to make reading easier. Using jq ito
2548 pretty pring a JSON file can be as simple as:
2549 $ jq . GPSD.json
2551 To grab 10 seconds of live gpsd JSON, and pretty print it:
2553 $ gpspipe -w -x 10 | jq .
2555 If you only want to see the TPV messages:
2557 $ gpspipe -w -x 10 | fgrep TPV | jq .
2559
2561 gpsd(8), libgps(3), libgpsmm(3), jq(1)
2562
2564 Project web site: https://gpsd.io/
2565 [RFC 2783]: https://datatracker.ietf.org/doc/html/rfc2783
2567 Pulse-Per-Second API for UNIX-like Operating Systems
2568 [RFC 7159]: https://datatracker.ietf.org/doc/html/rfc7159
2570 The JavaScript Object Notation (JSON) Data Interchange Format
2571 [jq]: https://github.com/stedolan/jq
2573
2575 This file is Copyright 2013 by the GPSD project
2576 SPDX-License-Identifier: BSD-2-clause
2577
2579 Eric S. Raymond
2580GPSD, Version 3.24 2022-04-27 GPSD_JSON(5)