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. To save space
90 in the output, and avoid confusion, the JSON never includes status
91 values of 0 or 1.
92 All error estimates (epc, epd, epe, eph, ept, epv, epx, epy) are
94 guessed to be 95% confidence, may also be 50%, one sigma, or two sigma
95 confidence. Many GNSS receivers do not specify a confidence level. None
96 specify how the value is calculated. Use error estimates with caution,
97 and only as relative "goodness" indicators. If the GPS reports a value
98 to gpsd, then gpsd will report that value. Otherwise gpsd will try to
99 compute the value from the skyview.
100 See the file include/gps.h, especially struct gps_data_t, for expanded
102 notes on the items and values in the TPV message.
103 Table 1. TPV object
105 ┌────────────┬─────────┬─────────┬──────────────────┐
106 │ │ │ │ │
107 │Name │ Always? │ Type │ Description │
108 ├────────────┼─────────┼─────────┼──────────────────┤
109 │ │ │ │ │
110 │class │ Yes │ string │ Fixed: "TPV" │
111 ├────────────┼─────────┼─────────┼──────────────────┤
112 │ │ │ │ │
113 │device │ No │ string │ Name of the │
114 │ │ │ │ originating │
115 │ │ │ │ device. │
116 ├────────────┼─────────┼─────────┼──────────────────┤
117 │ │ │ │ │
118 │mode │ Yes │ numeric │ NMEA mode: │
119 │ │ │ │ 0=unknown, │
120 │ │ │ │ 1=no fix, │
121 │ │ │ │ 2=2D, │
122 │ │ │ │ 3=3D. │
123 ├────────────┼─────────┼─────────┼──────────────────┤
124 │ │ │ │ │
125 │status │ No │ numeric │ GPS fix status: │
126 │ │ │ │ 0=Unknown, │
127 │ │ │ │ 1=Normal, │
128 │ │ │ │ 2=DGPS, │
129 │ │ │ │ 3=RTK Fixed, │
130 │ │ │ │ 4=RTK Floating, │
131 │ │ │ │ 5=DR, │
132 │ │ │ │ 6=GNSSDR, │
133 │ │ │ │ 7=Time │
134 │ │ │ │ (surveyed), │
135 │ │ │ │ 8=Simulated, │
136 │ │ │ │ 9=P(Y) │
137 ├────────────┼─────────┼─────────┼──────────────────┤
138 │ │ │ │ │
139 │time │ No │ string │ Time/date stamp │
140 │ │ │ │ in ISO8601 │
141 │ │ │ │ format, UTC. May │
142 │ │ │ │ have a │
143 │ │ │ │ fractional part │
144 │ │ │ │ of up to .001sec │
145 │ │ │ │ precision. May │
146 │ │ │ │ be absent if the │
147 │ │ │ │ mode is not 2D │
148 │ │ │ │ or 3D. May be │
149 │ │ │ │ present, but │
150 │ │ │ │ invalid, if │
151 │ │ │ │ there is no fix. │
152 │ │ │ │ Verify 3 │
153 │ │ │ │ consecutive 3D │
154 │ │ │ │ fixes before │
155 │ │ │ │ believing it is │
156 │ │ │ │ UTC. Even then │
157 │ │ │ │ it may be off by │
158 │ │ │ │ several seconds │
159 │ │ │ │ until the │
160 │ │ │ │ current leap │
161 │ │ │ │ seconds is │
162 │ │ │ │ known. │
163 ├────────────┼─────────┼─────────┼──────────────────┤
164 │ │ │ │ │
165 │altHAE │ No │ numeric │ Altitude, height │
166 │ │ │ │ above ellipsoid, │
167 │ │ │ │ in meters. │
168 │ │ │ │ Probably WGS84. │
169 ├────────────┼─────────┼─────────┼──────────────────┤
170 │ │ │ │ │
171 │altMSL │ No │ numeric │ MSL Altitude in │
172 │ │ │ │ meters. The │
173 │ │ │ │ geoid used is │
174 │ │ │ │ rarely specified │
175 │ │ │ │ and is often │
176 │ │ │ │ inaccurate. See │
177 │ │ │ │ the comments │
178 │ │ │ │ below on │
179 │ │ │ │ geoidSep. altMSL │
180 │ │ │ │ is altHAE minus │
181 │ │ │ │ geoidSep. │
182 ├────────────┼─────────┼─────────┼──────────────────┤
183 │ │ │ │ │
184 │alt │ No │ numeric │ Deprecated. │
185 │ │ │ │ Undefined. Use │
186 │ │ │ │ altHAE or │
187 │ │ │ │ altMSL. │
188 ├────────────┼─────────┼─────────┼──────────────────┤
189 │ │ │ │ │
190 │climb │ No │ numeric │ Climb (positive) │
191 │ │ │ │ or sink │
192 │ │ │ │ (negative) rate, │
193 │ │ │ │ meters per │
194 │ │ │ │ second. │
195 ├────────────┼─────────┼─────────┼──────────────────┤
196 │ │ │ │ │
197 │datum │ No │ string │ Current datum. │
198 │ │ │ │ Hopefully WGS84. │
199 ├────────────┼─────────┼─────────┼──────────────────┤
200 │ │ │ │ │
201 │depth │ No │ numeric │ Depth in meters. │
202 │ │ │ │ Probably depth │
203 │ │ │ │ below the │
204 │ │ │ │ keel... │
205 ├────────────┼─────────┼─────────┼──────────────────┤
206 │ │ │ │ │
207 │dgpsAge │ No │ numeric │ Age of DGPS │
208 │ │ │ │ data. In seconds │
209 ├────────────┼─────────┼─────────┼──────────────────┤
210 │ │ │ │ │
211 │dgpsSta │ No │ numeric │ Station of DGPS │
212 │ │ │ │ data. │
213 ├────────────┼─────────┼─────────┼──────────────────┤
214 │ │ │ │ │
215 │epc │ No │ numeric │ Estimated climb │
216 │ │ │ │ error in meters │
217 │ │ │ │ per second. │
218 │ │ │ │ Certainty │
219 │ │ │ │ unknown. │
220 ├────────────┼─────────┼─────────┼──────────────────┤
221 │ │ │ │ │
222 │epd │ No │ numeric │ Estimated track │
223 │ │ │ │ (direction) │
224 │ │ │ │ error in │
225 │ │ │ │ degrees. │
226 │ │ │ │ Certainty │
227 │ │ │ │ unknown. │
228 ├────────────┼─────────┼─────────┼──────────────────┤
229 │ │ │ │ │
230 │eph │ No │ numeric │ Estimated │
231 │ │ │ │ horizontal │
232 │ │ │ │ Position (2D) │
233 │ │ │ │ Error in meters. │
234 │ │ │ │ Also known as │
235 │ │ │ │ Estimated │
236 │ │ │ │ Position Error │
237 │ │ │ │ (epe). Certainty │
238 │ │ │ │ unknown. │
239 ├────────────┼─────────┼─────────┼──────────────────┤
240 │ │ │ │ │
241 │eps │ No │ numeric │ Estimated speed │
242 │ │ │ │ error in meters │
243 │ │ │ │ per second. │
244 │ │ │ │ Certainty │
245 │ │ │ │ unknown. │
246 ├────────────┼─────────┼─────────┼──────────────────┤
247 │ │ │ │ │
248 │ept │ No │ numeric │ Estimated time │
249 │ │ │ │ stamp error in │
250 │ │ │ │ seconds. │
251 │ │ │ │ Certainty │
252 │ │ │ │ unknown. │
253 ├────────────┼─────────┼─────────┼──────────────────┤
254 │ │ │ │ │
255 │epx │ No │ numeric │ Longitude error │
256 │ │ │ │ estimate in │
257 │ │ │ │ meters. │
258 │ │ │ │ Certainty │
259 │ │ │ │ unknown. │
260 ├────────────┼─────────┼─────────┼──────────────────┤
261 │ │ │ │ │
262 │epy │ No │ numeric │ Latitude error │
263 │ │ │ │ estimate in │
264 │ │ │ │ meters. │
265 │ │ │ │ Certainty │
266 │ │ │ │ unknown. │
267 ├────────────┼─────────┼─────────┼──────────────────┤
268 │ │ │ │ │
269 │epv │ No │ numeric │ Estimated │
270 │ │ │ │ vertical error │
271 │ │ │ │ in meters. │
272 │ │ │ │ Certainty │
273 │ │ │ │ unknown. │
274 ├────────────┼─────────┼─────────┼──────────────────┤
275 │ │ │ │ │
276 │geoidSep │ No │ numeric │ Geoid separation │
277 │ │ │ │ is the │
278 │ │ │ │ difference │
279 │ │ │ │ between the │
280 │ │ │ │ WGS84 reference │
281 │ │ │ │ ellipsoid and │
282 │ │ │ │ the geoid (Mean │
283 │ │ │ │ Sea Level) in │
284 │ │ │ │ meters. Almost │
285 │ │ │ │ no GNSS receiver │
286 │ │ │ │ specifies how │
287 │ │ │ │ they compute │
288 │ │ │ │ their geoid. │
289 │ │ │ │ gpsd │
290 │ │ │ │ interpolates the │
291 │ │ │ │ geoid from a 5x5 │
292 │ │ │ │ degree table of │
293 │ │ │ │ EGM2008 values │
294 │ │ │ │ when the │
295 │ │ │ │ receiver does │
296 │ │ │ │ not supply a │
297 │ │ │ │ geoid │
298 │ │ │ │ separation. The │
299 │ │ │ │ gpsd computed │
300 │ │ │ │ geoidSep is │
301 │ │ │ │ usually within │
302 │ │ │ │ one meter of the │
303 │ │ │ │ "true" value, │
304 │ │ │ │ but can be off │
305 │ │ │ │ as much as 12 │
306 │ │ │ │ meters. │
307 ├────────────┼─────────┼─────────┼──────────────────┤
308 │ │ │ │ │
309 │lat │ No │ numeric │ Latitude in │
310 │ │ │ │ degrees: +/- │
311 │ │ │ │ signifies │
312 │ │ │ │ North/South. │
313 ├────────────┼─────────┼─────────┼──────────────────┤
314 │ │ │ │ │
315 │leapseconds │ No │ integer │ Current leap │
316 │ │ │ │ seconds. │
317 ├────────────┼─────────┼─────────┼──────────────────┤
318 │ │ │ │ │
319 │lon │ No │ numeric │ Longitude in │
320 │ │ │ │ degrees: +/- │
321 │ │ │ │ signifies │
322 │ │ │ │ East/West. │
323 ├────────────┼─────────┼─────────┼──────────────────┤
324 │ │ │ │ │
325 │track │ No │ numeric │ Course over │
326 │ │ │ │ ground, degrees │
327 │ │ │ │ from true north. │
328 ├────────────┼─────────┼─────────┼──────────────────┤
329 │ │ │ │ │
330 │magtrack │ No │ numeric │ Course over │
331 │ │ │ │ ground, degrees │
332 │ │ │ │ magnetic. │
333 ├────────────┼─────────┼─────────┼──────────────────┤
334 │ │ │ │ │
335 │magvar │ No │ numeric │ Magnetic │
336 │ │ │ │ variation, │
337 │ │ │ │ degrees. Also │
338 │ │ │ │ known as the │
339 │ │ │ │ magnetic │
340 │ │ │ │ declination (the │
341 │ │ │ │ direction of the │
342 │ │ │ │ horizontal │
343 │ │ │ │ component of the │
344 │ │ │ │ magnetic field │
345 │ │ │ │ measured │
346 │ │ │ │ clockwise from │
347 │ │ │ │ north) in │
348 │ │ │ │ degrees, │
349 │ │ │ │ Positive is West │
350 │ │ │ │ variation. │
351 │ │ │ │ Negative is East │
352 │ │ │ │ variation. │
353 ├────────────┼─────────┼─────────┼──────────────────┤
354 │ │ │ │ │
355 │speed │ No │ numeric │ Speed over │
356 │ │ │ │ ground, meters │
357 │ │ │ │ per second. │
358 ├────────────┼─────────┼─────────┼──────────────────┤
359 │ │ │ │ │
360 │ecefx │ No │ numeric │ ECEF X position │
361 │ │ │ │ in meters. │
362 ├────────────┼─────────┼─────────┼──────────────────┤
363 │ │ │ │ │
364 │ecefy │ No │ numeric │ ECEF Y position │
365 │ │ │ │ in meters. │
366 ├────────────┼─────────┼─────────┼──────────────────┤
367 │ │ │ │ │
368 │ecefz │ No │ numeric │ ECEF Z position │
369 │ │ │ │ in meters. │
370 ├────────────┼─────────┼─────────┼──────────────────┤
371 │ │ │ │ │
372 │ecefpAcc │ No │ numeric │ ECEF position │
373 │ │ │ │ error in meters. │
374 │ │ │ │ Certainty │
375 │ │ │ │ unknown. │
376 ├────────────┼─────────┼─────────┼──────────────────┤
377 │ │ │ │ │
378 │ecefvx │ No │ numeric │ ECEF X velocity │
379 │ │ │ │ in meters per │
380 │ │ │ │ second. │
381 ├────────────┼─────────┼─────────┼──────────────────┤
382 │ │ │ │ │
383 │ecefvy │ No │ numeric │ ECEF Y velocity │
384 │ │ │ │ in meters per │
385 │ │ │ │ second. │
386 ├────────────┼─────────┼─────────┼──────────────────┤
387 │ │ │ │ │
388 │ecefvz │ No │ numeric │ ECEF Z velocity │
389 │ │ │ │ in meters per │
390 │ │ │ │ second. │
391 ├────────────┼─────────┼─────────┼──────────────────┤
392 │ │ │ │ │
393 │ecefvAcc │ No │ numeric │ ECEF velocity │
394 │ │ │ │ error in meters │
395 │ │ │ │ per second. │
396 │ │ │ │ Certainty │
397 │ │ │ │ unknown. │
398 ├────────────┼─────────┼─────────┼──────────────────┤
399 │ │ │ │ │
400 │sep │ No │ numeric │ Estimated │
401 │ │ │ │ Spherical (3D) │
402 │ │ │ │ Position Error │
403 │ │ │ │ in meters. │
404 │ │ │ │ Guessed to be │
405 │ │ │ │ 95% confidence, │
406 │ │ │ │ but many GNSS │
407 │ │ │ │ receivers do not │
408 │ │ │ │ specify, so │
409 │ │ │ │ certainty │
410 │ │ │ │ unknown. │
411 ├────────────┼─────────┼─────────┼──────────────────┤
412 │ │ │ │ │
413 │relD │ No │ numeric │ Down component │
414 │ │ │ │ of relative │
415 │ │ │ │ position vector │
416 │ │ │ │ in meters. │
417 ├────────────┼─────────┼─────────┼──────────────────┤
418 │ │ │ │ │
419 │relE │ No │ numeric │ East component │
420 │ │ │ │ of relative │
421 │ │ │ │ position vector │
422 │ │ │ │ in meters. │
423 ├────────────┼─────────┼─────────┼──────────────────┤
424 │ │ │ │ │
425 │relN │ No │ numeric │ North component │
426 │ │ │ │ of relative │
427 │ │ │ │ position vector │
428 │ │ │ │ in meters. │
429 ├────────────┼─────────┼─────────┼──────────────────┤
430 │ │ │ │ │
431 │velD │ No │ numeric │ Down velocity │
432 │ │ │ │ component in │
433 │ │ │ │ meters. │
434 ├────────────┼─────────┼─────────┼──────────────────┤
435 │ │ │ │ │
436 │velE │ No │ numeric │ East velocity │
437 │ │ │ │ component in │
438 │ │ │ │ meters. │
439 ├────────────┼─────────┼─────────┼──────────────────┤
440 │ │ │ │ │
441 │velN │ No │ numeric │ North velocity │
442 │ │ │ │ component in │
443 │ │ │ │ meters. │
444 ├────────────┼─────────┼─────────┼──────────────────┤
445 │ │ │ │ │
446 │wanglem │ No │ numeric │ Wind angle │
447 │ │ │ │ magnetic in │
448 │ │ │ │ degrees. │
449 ├────────────┼─────────┼─────────┼──────────────────┤
450 │ │ │ │ │
451 │wangler │ No │ numeric │ Wind angle │
452 │ │ │ │ relative in │
453 │ │ │ │ degrees. │
454 ├────────────┼─────────┼─────────┼──────────────────┤
455 │ │ │ │ │
456 │wanglet │ No │ numeric │ Wind angle true │
457 │ │ │ │ in degrees. │
458 ├────────────┼─────────┼─────────┼──────────────────┤
459 │ │ │ │ │
460 │wspeedr │ No │ numeric │ Wind speed │
461 │ │ │ │ relative in │
462 │ │ │ │ meters per │
463 │ │ │ │ second. │
464 ├────────────┼─────────┼─────────┼──────────────────┤
465 │ │ │ │ │
466 │wspeedt │ No │ numeric │ Wind speed true │
467 │ │ │ │ in meters per │
468 │ │ │ │ second. │
469 ├────────────┼─────────┼─────────┼──────────────────┤
470 │ │ │ │ │
471 │wtemp │ No │ numeric │ Water │
472 │ │ │ │ temperature in │
473 │ │ │ │ degrees Celsius. │
474 └────────────┴─────────┴─────────┴──────────────────┘
475 When the C client library parses a response of this kind, it will
477 assert validity bits in the top-level set member for each field
478 received; see gps.h for bitmask names and values.
479 Invalid or unknown floating-point values will be set to NAN. Always
481 check floating point values with isfinite() before use. isnan() is not
482 sufficient.
483 Here’s an example TPV sentence:
485 {"class":"TPV","device":"/dev/pts/1",
487 "time":"2005-06-08T10:34:48.283Z","ept":0.005,
488 "lat":46.498293369,"lon":7.567411672,"alt":1343.127,
489 "eph":36.000,"epv":32.321,
490 "track":10.3788,"speed":0.091,"climb":-0.085,"mode":3}
491 SKY
493 A SKY object reports a sky view of the GPS satellite positions. If
494 there is no GPS device available, or no skyview has been reported yet,
495 only the "class" field will reliably be present.
496 Table 2. SKY object
498 ┌───────────┬─────────┬─────────┬──────────────────┐
499 │ │ │ │ │
500 │Name │ Always? │ Type │ Description │
501 ├───────────┼─────────┼─────────┼──────────────────┤
502 │ │ │ │ │
503 │class │ Yes │ string │ Fixed: "SKY" │
504 ├───────────┼─────────┼─────────┼──────────────────┤
505 │ │ │ │ │
506 │device │ No │ string │ Name of │
507 │ │ │ │ originating │
508 │ │ │ │ device │
509 ├───────────┼─────────┼─────────┼──────────────────┤
510 │ │ │ │ │
511 │nSat │ No │ numeric │ Number of │
512 │ │ │ │ satellite │
513 │ │ │ │ objects in │
514 │ │ │ │ "satellites" │
515 │ │ │ │ array. │
516 ├───────────┼─────────┼─────────┼──────────────────┤
517 │ │ │ │ │
518 │gdop │ No │ numeric │ Geometric │
519 │ │ │ │ (hyperspherical) │
520 │ │ │ │ dilution of │
521 │ │ │ │ precision, a │
522 │ │ │ │ combination of │
523 │ │ │ │ PDOP and TDOP. A │
524 │ │ │ │ dimensionless │
525 │ │ │ │ factor which │
526 │ │ │ │ should be │
527 │ │ │ │ multiplied by a │
528 │ │ │ │ base UERE to get │
529 │ │ │ │ an error │
530 │ │ │ │ estimate. │
531 ├───────────┼─────────┼─────────┼──────────────────┤
532 │ │ │ │ │
533 │hdop │ No │ numeric │ Horizontal │
534 │ │ │ │ dilution of │
535 │ │ │ │ precision, a │
536 │ │ │ │ dimensionless │
537 │ │ │ │ factor which │
538 │ │ │ │ should be │
539 │ │ │ │ multiplied by a │
540 │ │ │ │ base UERE to get │
541 │ │ │ │ a circular error │
542 │ │ │ │ estimate. │
543 ├───────────┼─────────┼─────────┼──────────────────┤
544 │ │ │ │ │
545 │pdop │ No │ numeric │ Position │
546 │ │ │ │ (spherical/3D) │
547 │ │ │ │ dilution of │
548 │ │ │ │ precision, a │
549 │ │ │ │ dimensionless │
550 │ │ │ │ factor which │
551 │ │ │ │ should be │
552 │ │ │ │ multiplied by a │
553 │ │ │ │ base UERE to get │
554 │ │ │ │ an error │
555 │ │ │ │ estimate. │
556 ├───────────┼─────────┼─────────┼──────────────────┤
557 │ │ │ │ │
558 │prRes │ No │ numeric │ Pseudorange │
559 │ │ │ │ residue in │
560 │ │ │ │ meters. │
561 ├───────────┼─────────┼─────────┼──────────────────┤
562 │ │ │ │ │
563 │qual │ No │ numeric │ Quality │
564 │ │ │ │ Indicator │
565 │ │ │ │ 0=no signal │
566 │ │ │ │ 1=searching │
567 │ │ │ │ signal │
568 │ │ │ │ 2=signal │
569 │ │ │ │ acquired │
570 │ │ │ │ 3=signal │
571 │ │ │ │ detected but │
572 │ │ │ │ unusable │
573 │ │ │ │ 4=code locked │
574 │ │ │ │ and time │
575 │ │ │ │ synchronized │
576 │ │ │ │ 5, 6, 7=code and │
577 │ │ │ │ carrier locked │
578 │ │ │ │ and time │
579 │ │ │ │ synchronized │
580 ├───────────┼─────────┼─────────┼──────────────────┤
581 │ │ │ │ │
582 │satellites │ No │ list │ List of │
583 │ │ │ │ satellite │
584 │ │ │ │ objects in │
585 │ │ │ │ skyview │
586 ├───────────┼─────────┼─────────┼──────────────────┤
587 │ │ │ │ │
588 │tdop │ No │ numeric │ Time dilution of │
589 │ │ │ │ precision, a │
590 │ │ │ │ dimensionless │
591 │ │ │ │ factor which │
592 │ │ │ │ should be │
593 │ │ │ │ multiplied by a │
594 │ │ │ │ base UERE to get │
595 │ │ │ │ an error │
596 │ │ │ │ estimate. │
597 ├───────────┼─────────┼─────────┼──────────────────┤
598 │ │ │ │ │
599 │time │ No │ string │ Time/date stamp │
600 │ │ │ │ in ISO8601 │
601 │ │ │ │ format, UTC. May │
602 │ │ │ │ have a │
603 │ │ │ │ fractional part │
604 │ │ │ │ of up to .001sec │
605 │ │ │ │ precision. │
606 ├───────────┼─────────┼─────────┼──────────────────┤
607 │ │ │ │ │
608 │uSat │ No │ numeric │ Number of │
609 │ │ │ │ satellites used │
610 │ │ │ │ in navigation │
611 │ │ │ │ solution. │
612 ├───────────┼─────────┼─────────┼──────────────────┤
613 │ │ │ │ │
614 │vdop │ No │ numeric │ Vertical │
615 │ │ │ │ (altitude) │
616 │ │ │ │ dilution of │
617 │ │ │ │ precision, a │
618 │ │ │ │ dimensionless │
619 │ │ │ │ factor which │
620 │ │ │ │ should be │
621 │ │ │ │ multiplied by a │
622 │ │ │ │ base UERE to get │
623 │ │ │ │ an error │
624 │ │ │ │ estimate. │
625 ├───────────┼─────────┼─────────┼──────────────────┤
626 │ │ │ │ │
627 │xdop │ No │ numeric │ Longitudinal │
628 │ │ │ │ dilution of │
629 │ │ │ │ precision, a │
630 │ │ │ │ dimensionless │
631 │ │ │ │ factor which │
632 │ │ │ │ should be │
633 │ │ │ │ multiplied by a │
634 │ │ │ │ base UERE to get │
635 │ │ │ │ an error │
636 │ │ │ │ estimate. │
637 ├───────────┼─────────┼─────────┼──────────────────┤
638 │ │ │ │ │
639 │ydop │ No │ numeric │ Latitudinal │
640 │ │ │ │ dilution of │
641 │ │ │ │ precision, a │
642 │ │ │ │ dimensionless │
643 │ │ │ │ factor which │
644 │ │ │ │ should be │
645 │ │ │ │ multiplied by a │
646 │ │ │ │ base UERE to get │
647 │ │ │ │ an error │
648 │ │ │ │ estimate. │
649 └───────────┴─────────┴─────────┴──────────────────┘
650 Many devices compute dilution of precision factors but do not include
652 them in their reports. Many that do report DOPs report only HDOP,
653 two-dimensional circular error. gpsd always passes through whatever the
654 device reports, then attempts to fill in other DOPs by calculating the
655 appropriate determinants in a covariance matrix based on the satellite
656 view. DOPs may be missing if some of these determinants are singular.
657 It can even happen that the device reports an error estimate in meters
658 when the corresponding DOP is unavailable; some devices use more
659 sophisticated error modeling than the covariance calculation.
660 The satellite list objects have the following elements:
662 Table 3. Satellite object
664 ┌───────┬─────────┬─────────┬──────────────────┐
665 │ │ │ │ │
666 │Name │ Always? │ Type │ Description │
667 ├───────┼─────────┼─────────┼──────────────────┤
668 │ │ │ │ │
669 │PRN │ Yes │ numeric │ PRN ID of the │
670 │ │ │ │ satellite. 1-63 │
671 │ │ │ │ are GNSS │
672 │ │ │ │ satellites, │
673 │ │ │ │ 64-96 are │
674 │ │ │ │ GLONASS │
675 │ │ │ │ satellites, │
676 │ │ │ │ 100-164 are SBAS │
677 │ │ │ │ satellites │
678 ├───────┼─────────┼─────────┼──────────────────┤
679 │ │ │ │ │
680 │az │ No │ numeric │ Azimuth, degrees │
681 │ │ │ │ from true north. │
682 ├───────┼─────────┼─────────┼──────────────────┤
683 │ │ │ │ │
684 │el │ No │ numeric │ Elevation in │
685 │ │ │ │ degrees. │
686 ├───────┼─────────┼─────────┼──────────────────┤
687 │ │ │ │ │
688 │ss │ No │ numeric │ Signal to Noise │
689 │ │ │ │ ratio in dBHz. │
690 ├───────┼─────────┼─────────┼──────────────────┤
691 │ │ │ │ │
692 │used │ Yes │ boolean │ Used in current │
693 │ │ │ │ solution? │
694 │ │ │ │ (SBAS/WAAS/EGNOS │
695 │ │ │ │ satellites may │
696 │ │ │ │ be flagged used │
697 │ │ │ │ if the solution │
698 │ │ │ │ has corrections │
699 │ │ │ │ from them, but │
700 │ │ │ │ not all drivers │
701 │ │ │ │ make this │
702 │ │ │ │ information │
703 │ │ │ │ available.) │
704 ├───────┼─────────┼─────────┼──────────────────┤
705 │ │ │ │ │
706 │gnssid │ No │ numeric │ The GNSS ID, as │
707 │ │ │ │ defined by │
708 │ │ │ │ u-blox, not │
709 │ │ │ │ NMEA. 0=GPS, │
710 │ │ │ │ 2=Galileo, │
711 │ │ │ │ 3=Beidou, │
712 │ │ │ │ 5=QZSS, │
713 │ │ │ │ 6-GLONASS. │
714 ├───────┼─────────┼─────────┼──────────────────┤
715 │ │ │ │ │
716 │svid │ No │ numeric │ The satellite ID │
717 │ │ │ │ within its │
718 │ │ │ │ constellation. │
719 │ │ │ │ As defined by │
720 │ │ │ │ u-blox, not │
721 │ │ │ │ NMEA). │
722 ├───────┼─────────┼─────────┼──────────────────┤
723 │ │ │ │ │
724 │sigid │ No │ numeric │ The signal ID of │
725 │ │ │ │ this signal. As │
726 │ │ │ │ defined by │
727 │ │ │ │ u-blox, not │
728 │ │ │ │ NMEA. See u-blox │
729 │ │ │ │ doc for details. │
730 ├───────┼─────────┼─────────┼──────────────────┤
731 │ │ │ │ │
732 │freqid │ No │ numeric │ For GLONASS │
733 │ │ │ │ satellites only: │
734 │ │ │ │ the frequency ID │
735 │ │ │ │ of the signal. │
736 │ │ │ │ As defined by │
737 │ │ │ │ u-blox, range 0 │
738 │ │ │ │ to 13. The │
739 │ │ │ │ freqid is the │
740 │ │ │ │ frequency slot │
741 │ │ │ │ plus 7. │
742 ├───────┼─────────┼─────────┼──────────────────┤
743 │ │ │ │ │
744 │health │ No │ numeric │ The health of │
745 │ │ │ │ this satellite. │
746 │ │ │ │ 0 is unknown, 1 │
747 │ │ │ │ is OK, and 2 is │
748 │ │ │ │ unhealthy. │
749 └───────┴─────────┴─────────┴──────────────────┘
750 Note that satellite objects do not have a "class" field, as they are
752 never shipped outside of a SKY object.
753 When the C client library parses a SKY response, it will assert the
755 SATELLITE_SET bit in the top-level set member.
756 Here’s an example:
758 {"class":"SKY","device":"/dev/pts/1",
760 "time":"2005-07-08T11:28:07.114Z",
761 "xdop":1.55,"hdop":1.24,"pdop":1.99,
762 "satellites":[
763 {"PRN":23,"el":6,"az":84,"ss":0,"used":false},
764 {"PRN":28,"el":7,"az":160,"ss":0,"used":false},
765 {"PRN":8,"el":66,"az":189,"ss":44,"used":true},
766 {"PRN":29,"el":13,"az":273,"ss":0,"used":false},
767 {"PRN":10,"el":51,"az":304,"ss":29,"used":true},
768 {"PRN":4,"el":15,"az":199,"ss":36,"used":true},
769 {"PRN":2,"el":34,"az":241,"ss":43,"used":true},
770 {"PRN":27,"el":71,"az":76,"ss":43,"used":true}]}
771 GST
773 A GST object is a pseudorange noise report.
774 Table 4. GST object
776 ┌───────┬─────────┬─────────┬──────────────────┐
777 │ │ │ │ │
778 │Name │ Always? │ Type │ Description │
779 ├───────┼─────────┼─────────┼──────────────────┤
780 │ │ │ │ │
781 │class │ Yes │ string │ Fixed: "GST" │
782 ├───────┼─────────┼─────────┼──────────────────┤
783 │ │ │ │ │
784 │device │ No │ string │ Name of │
785 │ │ │ │ originating │
786 │ │ │ │ device │
787 ├───────┼─────────┼─────────┼──────────────────┤
788 │ │ │ │ │
789 │time │ No │ string │ Time/date stamp │
790 │ │ │ │ in ISO8601 │
791 │ │ │ │ format, UTC. May │
792 │ │ │ │ have a │
793 │ │ │ │ fractional part │
794 │ │ │ │ of up to .001sec │
795 │ │ │ │ precision. │
796 ├───────┼─────────┼─────────┼──────────────────┤
797 │ │ │ │ │
798 │rms │ No │ numeric │ Value of the │
799 │ │ │ │ standard │
800 │ │ │ │ deviation of the │
801 │ │ │ │ range inputs to │
802 │ │ │ │ the navigation │
803 │ │ │ │ process (range │
804 │ │ │ │ inputs include │
805 │ │ │ │ pseudoranges and │
806 │ │ │ │ DGPS │
807 │ │ │ │ corrections). │
808 ├───────┼─────────┼─────────┼──────────────────┤
809 │ │ │ │ │
810 │major │ No │ numeric │ Standard │
811 │ │ │ │ deviation of │
812 │ │ │ │ semi-major axis │
813 │ │ │ │ of error │
814 │ │ │ │ ellipse, in │
815 │ │ │ │ meters. │
816 ├───────┼─────────┼─────────┼──────────────────┤
817 │ │ │ │ │
818 │minor │ No │ numeric │ Standard │
819 │ │ │ │ deviation of │
820 │ │ │ │ semi-minor axis │
821 │ │ │ │ of error │
822 │ │ │ │ ellipse, in │
823 │ │ │ │ meters. │
824 ├───────┼─────────┼─────────┼──────────────────┤
825 │ │ │ │ │
826 │orient │ No │ numeric │ Orientation of │
827 │ │ │ │ semi-major axis │
828 │ │ │ │ of error │
829 │ │ │ │ ellipse, in │
830 │ │ │ │ degrees from │
831 │ │ │ │ true north. │
832 ├───────┼─────────┼─────────┼──────────────────┤
833 │ │ │ │ │
834 │lat │ No │ numeric │ Standard │
835 │ │ │ │ deviation of │
836 │ │ │ │ latitude error, │
837 │ │ │ │ in meters. │
838 ├───────┼─────────┼─────────┼──────────────────┤
839 │ │ │ │ │
840 │lon │ No │ numeric │ Standard │
841 │ │ │ │ deviation of │
842 │ │ │ │ longitude error, │
843 │ │ │ │ in meters. │
844 ├───────┼─────────┼─────────┼──────────────────┤
845 │ │ │ │ │
846 │alt │ No │ numeric │ Standard │
847 │ │ │ │ deviation of │
848 │ │ │ │ altitude error, │
849 │ │ │ │ in meters. │
850 └───────┴─────────┴─────────┴──────────────────┘
851 Here’s an example:
853 {"class":"GST","device":"/dev/ttyUSB0",
855 "time":"2010-12-07T10:23:07.096Z","rms":2.440,
856 "major":1.660,"minor":1.120,"orient":68.989,
857 "lat":1.600,"lon":1.200,"alt":2.520}
858 ATT
860 An ATT object is a vehicle-attitude report. It is returned by
861 digital-compass and gyroscope sensors; depending on device, it may
862 include: heading, pitch, roll, yaw, gyroscope, and magnetic-field
863 readings. Because such sensors are often bundled as part of
864 marine-navigation systems, the ATT response may also include water
865 depth.
866 The "class" and "mode" fields will reliably be present. Others may be
868 reported or not depending on the specific device type.
869 The ATT object is synchronous to the GNSS epoch. Some devices report
871 attitude information with arbitrary, even out of order, time scales.
872 gpsd reports those in an IMU object. The ATT and IMU objects have the
873 same fields, but IMU objects are output as soon as possible. Some
874 devices output both types with arbitrary interleaving.
875 Table 5. ATT object
877 ┌─────────┬─────────┬─────────┬──────────────────┐
878 │ │ │ │ │
879 │Name │ Always? │ Type │ Description │
880 ├─────────┼─────────┼─────────┼──────────────────┤
881 │ │ │ │ │
882 │class │ Yes │ string │ Fixed: "ATT" │
883 ├─────────┼─────────┼─────────┼──────────────────┤
884 │ │ │ │ │
885 │device │ Yes │ string │ Name of │
886 │ │ │ │ originating │
887 │ │ │ │ device │
888 ├─────────┼─────────┼─────────┼──────────────────┤
889 │ │ │ │ │
890 │time │ No │ string │ Time/date stamp │
891 │ │ │ │ in ISO8601 │
892 │ │ │ │ format, UTC. May │
893 │ │ │ │ have a │
894 │ │ │ │ fractional part │
895 │ │ │ │ of up to .001sec │
896 │ │ │ │ precision. │
897 ├─────────┼─────────┼─────────┼──────────────────┤
898 │ │ │ │ │
899 │timeTag │ No │ string │ Arbitrary time │
900 │ │ │ │ tag of │
901 │ │ │ │ measurement. │
902 ├─────────┼─────────┼─────────┼──────────────────┤
903 │ │ │ │ │
904 │heading │ No │ numeric │ Heading, degrees │
905 │ │ │ │ from true north. │
906 ├─────────┼─────────┼─────────┼──────────────────┤
907 │ │ │ │ │
908 │mag_st │ No │ string │ Magnetometer │
909 │ │ │ │ status. │
910 ├─────────┼─────────┼─────────┼──────────────────┤
911 │ │ │ │ │
912 │mheading │ No │ numeric │ Heading, degrees │
913 │ │ │ │ from magnetic │
914 │ │ │ │ north. │
915 ├─────────┼─────────┼─────────┼──────────────────┤
916 │ │ │ │ │
917 │pitch │ No │ numeric │ Pitch in │
918 │ │ │ │ degrees. │
919 ├─────────┼─────────┼─────────┼──────────────────┤
920 │ │ │ │ │
921 │pitch_st │ No │ string │ Pitch sensor │
922 │ │ │ │ status. │
923 ├─────────┼─────────┼─────────┼──────────────────┤
924 │ │ │ │ │
925 │rot │ No │ numeric │ Rate of Turn in │
926 │ │ │ │ dgrees per │
927 │ │ │ │ minute. │
928 ├─────────┼─────────┼─────────┼──────────────────┤
929 │ │ │ │ │
930 │yaw │ No │ numeric │ Yaw in degrees │
931 ├─────────┼─────────┼─────────┼──────────────────┤
932 │ │ │ │ │
933 │yaw_st │ No │ string │ Yaw sensor │
934 │ │ │ │ status. │
935 ├─────────┼─────────┼─────────┼──────────────────┤
936 │ │ │ │ │
937 │roll │ No │ numeric │ Roll in degrees. │
938 ├─────────┼─────────┼─────────┼──────────────────┤
939 │ │ │ │ │
940 │roll_st │ No │ string │ Roll sensor │
941 │ │ │ │ status. │
942 ├─────────┼─────────┼─────────┼──────────────────┤
943 │ │ │ │ │
944 │dip │ No │ numeric │ Local magnetic │
945 │ │ │ │ inclination, │
946 │ │ │ │ degrees, │
947 │ │ │ │ positive when │
948 │ │ │ │ the magnetic │
949 │ │ │ │ field points │
950 │ │ │ │ downward (into │
951 │ │ │ │ the Earth). │
952 ├─────────┼─────────┼─────────┼──────────────────┤
953 │ │ │ │ │
954 │mag_len │ No │ numeric │ Scalar magnetic │
955 │ │ │ │ field strength. │
956 ├─────────┼─────────┼─────────┼──────────────────┤
957 │ │ │ │ │
958 │mag_x │ No │ numeric │ X component of │
959 │ │ │ │ magnetic field │
960 │ │ │ │ strength. │
961 ├─────────┼─────────┼─────────┼──────────────────┤
962 │ │ │ │ │
963 │mag_y │ No │ numeric │ Y component of │
964 │ │ │ │ magnetic field │
965 │ │ │ │ strength. │
966 ├─────────┼─────────┼─────────┼──────────────────┤
967 │ │ │ │ │
968 │mag_z │ No │ numeric │ Z component of │
969 │ │ │ │ magnetic field │
970 │ │ │ │ strength. │
971 ├─────────┼─────────┼─────────┼──────────────────┤
972 │ │ │ │ │
973 │acc_len │ No │ numeric │ Scalar │
974 │ │ │ │ acceleration. │
975 ├─────────┼─────────┼─────────┼──────────────────┤
976 │ │ │ │ │
977 │acc_x │ No │ numeric │ X component of │
978 │ │ │ │ acceleration │
979 │ │ │ │ (m/s^2). │
980 ├─────────┼─────────┼─────────┼──────────────────┤
981 │ │ │ │ │
982 │acc_y │ No │ numeric │ Y component of │
983 │ │ │ │ acceleration │
984 │ │ │ │ (m/s^2). │
985 ├─────────┼─────────┼─────────┼──────────────────┤
986 │ │ │ │ │
987 │acc_z │ No │ numeric │ Z component of │
988 │ │ │ │ acceleration │
989 │ │ │ │ (m/s^2). │
990 ├─────────┼─────────┼─────────┼──────────────────┤
991 │ │ │ │ │
992 │gyro_x │ No │ numeric │ X component of │
993 │ │ │ │ angular rate │
994 │ │ │ │ (deg/s) │
995 ├─────────┼─────────┼─────────┼──────────────────┤
996 │ │ │ │ │
997 │gyro_y │ No │ numeric │ Y component of │
998 │ │ │ │ angular rate │
999 │ │ │ │ (deg/s) │
1000 ├─────────┼─────────┼─────────┼──────────────────┤
1001 │ │ │ │ │
1002 │gyro_z │ No │ numeric │ Z component of │
1003 │ │ │ │ angular rate │
1004 │ │ │ │ (deg/s) │
1005 ├─────────┼─────────┼─────────┼──────────────────┤
1006 │ │ │ │ │
1007 │depth │ No │ numeric │ Water depth in │
1008 │ │ │ │ meters. │
1009 ├─────────┼─────────┼─────────┼──────────────────┤
1010 │ │ │ │ │
1011 │temp │ No │ numeric │ Temperature at │
1012 │ │ │ │ the sensor, │
1013 │ │ │ │ degrees │
1014 │ │ │ │ centigrade. │
1015 └─────────┴─────────┴─────────┴──────────────────┘
1016 The heading, pitch, and roll status codes (if present) vary by device.
1018 For the TNT Revolution digital compasses, they are coded as follows:
1019 Table 6. Device flags
1021 ┌─────┬────────────────────────────┐
1022 │ │ │
1023 │Code │ Description │
1024 ├─────┼────────────────────────────┤
1025 │ │ │
1026 │C │ magnetometer calibration │
1027 │ │ alarm │
1028 ├─────┼────────────────────────────┤
1029 │ │ │
1030 │L │ low alarm │
1031 ├─────┼────────────────────────────┤
1032 │ │ │
1033 │M │ low warning │
1034 ├─────┼────────────────────────────┤
1035 │ │ │
1036 │N │ normal │
1037 ├─────┼────────────────────────────┤
1038 │ │ │
1039 │O │ high warning │
1040 ├─────┼────────────────────────────┤
1041 │ │ │
1042 │P │ high alarm │
1043 ├─────┼────────────────────────────┤
1044 │ │ │
1045 │V │ magnetometer voltage level │
1046 │ │ alarm │
1047 └─────┴────────────────────────────┘
1048 When the C client library parses a response of this kind, it will
1050 assert ATT_IS.
1051 Here’s an example:
1053 {"class":"ATT","time":1270938096.843,
1055 "heading":14223.00,"mag_st":"N",
1056 "pitch":169.00,"pitch_st":"N", "roll":-43.00,"roll_st":"N",
1057 "dip":13641.000,"mag_x":2454.000}
1058 IMU
1060 The IMU object is asynchronous to the GNSS epoch. It is reported with
1061 arbitrary, even out of order, time scales.
1062 The ATT and IMU objects have the same fields, but IMU objects are
1064 output as soon as possible.
1065 Seee the ATT onject description for field details.
1067 TOFF
1069 This message is emitted on each cycle and reports the offset between
1070 the host’s clock time and the GPS time at top of the second (actually,
1071 when the first data for the reporting cycle is received).
1072 This message exactly mirrors the PPS message.
1074 The TOFF message reports the GPS time as derived from the GPS serial
1076 data stream. The PPS message reports the GPS time as derived from the
1077 GPS PPS pulse.
1078 A TOFF object has the following elements:
1080 Table 7. TOFF object
1082 ┌───────────┬─────────┬─────────┬──────────────────┐
1083 │ │ │ │ │
1084 │Name │ Always? │ Type │ Description │
1085 ├───────────┼─────────┼─────────┼──────────────────┤
1086 │ │ │ │ │
1087 │class │ Yes │ string │ Fixed: "TOFF" │
1088 ├───────────┼─────────┼─────────┼──────────────────┤
1089 │ │ │ │ │
1090 │device │ Yes │ string │ Name of the │
1091 │ │ │ │ originating │
1092 │ │ │ │ device │
1093 ├───────────┼─────────┼─────────┼──────────────────┤
1094 │ │ │ │ │
1095 │real_sec │ Yes │ numeric │ seconds from the │
1096 │ │ │ │ GPS clock │
1097 ├───────────┼─────────┼─────────┼──────────────────┤
1098 │ │ │ │ │
1099 │real_nsec │ Yes │ numeric │ nanoseconds from │
1100 │ │ │ │ the GPS clock │
1101 ├───────────┼─────────┼─────────┼──────────────────┤
1102 │ │ │ │ │
1103 │clock_sec │ Yes │ numeric │ seconds from the │
1104 │ │ │ │ system clock │
1105 ├───────────┼─────────┼─────────┼──────────────────┤
1106 │ │ │ │ │
1107 │clock_nsec │ Yes │ numeric │ nanoseconds from │
1108 │ │ │ │ the system clock │
1109 └───────────┴─────────┴─────────┴──────────────────┘
1110 This message is emitted once per second to watchers of a device and is
1112 intended to report the timestamps of the in-band report of the GPS and
1113 seconds as reported by the system clock (which may be NTP-corrected)
1114 when the first valid time stamp of the reporting cycle was seen.
1115 The message contains two second/nanosecond pairs: real_sec and
1117 real_nsec contain the time the GPS thinks it was at the start of the
1118 current cycle; clock_sec and clock_nsec contain the time the system
1119 clock thinks it was on receipt of the first timing message of the
1120 cycle. real_nsec is always to nanosecond precision. clock_nsec is
1121 nanosecond precision on most systems.
1122 Here’s an example:
1124 {"class":"TOFF","device":"/dev/ttyUSB0",
1126 "real_sec":1330212592, "real_nsec":343182,
1127 "clock_sec":1330212592,"clock_nsec":343184,
1128 "precision":-2}
1129 PPS
1131 This message is emitted each time the daemon sees a valid PPS (Pulse
1132 Per Second) strobe from a device.
1133 This message exactly mirrors the TOFF message.
1135 The TOFF message reports the GPS time as derived from the GPS serial
1137 data stream. The PPS message reports the GPS time as derived from the
1138 GPS PPS pulse.
1139 There are various sources of error in the reported clock times. The
1141 speed of the serial connection between the GPS and the system adds a
1142 delay to the start of cycle detection. An even bigger error is added by
1143 the variable computation time inside the GPS. Taken together the time
1144 derived from the start of the GPS cycle can have offsets of 10
1145 milliseconds to 700 milliseconds and combined jitter and wander of 100
1146 to 300 milliseconds.
1147 See the NTP documentation for their definition of precision.
1149 A PPS object has the following elements:
1151 Table 8. PPS object
1153 ┌───────────┬─────────┬─────────┬──────────────────┐
1154 │ │ │ │ │
1155 │Name │ Always? │ Type │ Description │
1156 ├───────────┼─────────┼─────────┼──────────────────┤
1157 │ │ │ │ │
1158 │class │ Yes │ string │ Fixed: "PPS" │
1159 ├───────────┼─────────┼─────────┼──────────────────┤
1160 │ │ │ │ │
1161 │device │ Yes │ string │ Name of the │
1162 │ │ │ │ originating │
1163 │ │ │ │ device │
1164 ├───────────┼─────────┼─────────┼──────────────────┤
1165 │ │ │ │ │
1166 │real_sec │ Yes │ numeric │ seconds from the │
1167 │ │ │ │ PPS source │
1168 ├───────────┼─────────┼─────────┼──────────────────┤
1169 │ │ │ │ │
1170 │real_nsec │ Yes │ numeric │ nanoseconds from │
1171 │ │ │ │ the PPS source │
1172 ├───────────┼─────────┼─────────┼──────────────────┤
1173 │ │ │ │ │
1174 │clock_sec │ Yes │ numeric │ seconds from the │
1175 │ │ │ │ system clock │
1176 ├───────────┼─────────┼─────────┼──────────────────┤
1177 │ │ │ │ │
1178 │clock_nsec │ Yes │ numeric │ nanoseconds from │
1179 │ │ │ │ the system clock │
1180 ├───────────┼─────────┼─────────┼──────────────────┤
1181 │ │ │ │ │
1182 │precision │ Yes │ numeric │ NTP style │
1183 │ │ │ │ estimate of PPS │
1184 │ │ │ │ precision │
1185 ├───────────┼─────────┼─────────┼──────────────────┤
1186 │ │ │ │ │
1187 │shm │ Yes │ string │ shm key of this │
1188 │ │ │ │ PPS │
1189 ├───────────┼─────────┼─────────┼──────────────────┤
1190 │ │ │ │ │
1191 │qErr │ No │ numeric │ Quantization │
1192 │ │ │ │ error of the │
1193 │ │ │ │ PPS, in │
1194 │ │ │ │ picoseconds. │
1195 │ │ │ │ Sometimes called │
1196 │ │ │ │ the "sawtooth" │
1197 │ │ │ │ error. │
1198 └───────────┴─────────┴─────────┴──────────────────┘
1199 This message is emitted once per second to watchers of a device
1201 emitting PPS, and reports the time of the start of the GPS second (when
1202 the 1PPS arrives) and seconds as reported by the system clock (which
1203 may be NTP-corrected) at that moment.
1204 The message contains two second/nanosecond pairs: real_sec and
1206 real_nsec contain the time the GPS thinks it was at the PPS edge;
1207 clock_sec and clock_nsec contain the time the system clock thinks it
1208 was at the PPS edge. real_nsec is always to nanosecond precision.
1209 clock_nsec is nanosecond precision on most systems.
1210 There are various sources of error in the reported clock times. For PPS
1212 delivered via a real serial-line strobe, serial-interrupt latency plus
1213 processing time to the timer call should be bounded above by about 10
1214 microseconds; that can be reduced to less than 1 microsecond if your
1215 kernel supports [RFC-2783]. USB1.1-to-serial control-line emulation is
1216 limited to about 1 millisecond. seconds.
1217 Here’s an example:
1219 {"class":"PPS","device":"/dev/ttyUSB0",
1221 "real_sec":1330212592, "real_nsec":343182,
1222 "clock_sec":1330212592,"clock_nsec":343184,
1223 "precision":-3}
1224 OSC
1226 This message reports the status of a GPS-disciplined oscillator
1227 (GPSDO). The GPS PPS output (which has excellent long-term stability)
1228 is typically used to discipline a local oscillator with much better
1229 short-term stability (such as a rubidium atomic clock).
1230 An OSC object has the following elements:
1232 Table 9. OSC object
1234 ┌────────────┬─────────┬─────────┬──────────────────┐
1235 │ │ │ │ │
1236 │Name │ Always? │ Type │ Description │
1237 ├────────────┼─────────┼─────────┼──────────────────┤
1238 │ │ │ │ │
1239 │class │ Yes │ string │ Fixed: "OSC" │
1240 ├────────────┼─────────┼─────────┼──────────────────┤
1241 │ │ │ │ │
1242 │device │ Yes │ string │ Name of the │
1243 │ │ │ │ originating │
1244 │ │ │ │ device. │
1245 ├────────────┼─────────┼─────────┼──────────────────┤
1246 │ │ │ │ │
1247 │running │ Yes │ boolean │ If true, the │
1248 │ │ │ │ oscillator is │
1249 │ │ │ │ currently │
1250 │ │ │ │ running. │
1251 │ │ │ │ Oscillators may │
1252 │ │ │ │ require warm-up │
1253 │ │ │ │ time at the │
1254 │ │ │ │ start of the │
1255 │ │ │ │ day. │
1256 ├────────────┼─────────┼─────────┼──────────────────┤
1257 │ │ │ │ │
1258 │reference │ Yes │ boolean │ If true, the │
1259 │ │ │ │ oscillator is │
1260 │ │ │ │ receiving a GPS │
1261 │ │ │ │ PPS signal. │
1262 ├────────────┼─────────┼─────────┼──────────────────┤
1263 │ │ │ │ │
1264 │disciplined │ Yes │ boolean │ If true, the GPS │
1265 │ │ │ │ PPS signal is │
1266 │ │ │ │ sufficiently │
1267 │ │ │ │ stable and is │
1268 │ │ │ │ being used to │
1269 │ │ │ │ discipline the │
1270 │ │ │ │ local │
1271 │ │ │ │ oscillator. │
1272 ├────────────┼─────────┼─────────┼──────────────────┤
1273 │ │ │ │ │
1274 │delta │ Yes │ numeric │ The time │
1275 │ │ │ │ difference (in │
1276 │ │ │ │ nanoseconds) │
1277 │ │ │ │ between the │
1278 │ │ │ │ GPS-disciplined │
1279 │ │ │ │ oscillator PPS │
1280 │ │ │ │ output pulse and │
1281 │ │ │ │ the most recent │
1282 │ │ │ │ GPS PPS input │
1283 │ │ │ │ pulse. │
1284 └────────────┴─────────┴─────────┴──────────────────┘
1285 Here’s an example:
1287 {"class":"OSC","running":true,"device":"/dev/ttyUSB0",
1289 "reference":true,"disciplined":true,"delta":67}
1290
1292 And here are the commands you can send to gpsd.
1293 ?VERSION;
1295 Returns an object with the following attributes:
1296 Table 10. VERSION object
1298 ┌────────────┬─────────┬─────────┬──────────────────┐
1299 │ │ │ │ │
1300 │Name │ Always? │ Type │ Description │
1301 ├────────────┼─────────┼─────────┼──────────────────┤
1302 │ │ │ │ │
1303 │class │ Yes │ string │ Fixed: "VERSION" │
1304 ├────────────┼─────────┼─────────┼──────────────────┤
1305 │ │ │ │ │
1306 │release │ Yes │ string │ Public release │
1307 │ │ │ │ level │
1308 ├────────────┼─────────┼─────────┼──────────────────┤
1309 │ │ │ │ │
1310 │rev │ Yes │ string │ Internal │
1311 │ │ │ │ revision-control │
1312 │ │ │ │ level. │
1313 ├────────────┼─────────┼─────────┼──────────────────┤
1314 │ │ │ │ │
1315 │proto_major │ Yes │ numeric │ API major │
1316 │ │ │ │ revision level. │
1317 ├────────────┼─────────┼─────────┼──────────────────┤
1318 │ │ │ │ │
1319 │proto_minor │ Yes │ numeric │ API minor │
1320 │ │ │ │ revision level. │
1321 ├────────────┼─────────┼─────────┼──────────────────┤
1322 │ │ │ │ │
1323 │remote │ No │ string │ URL of the │
1324 │ │ │ │ remote daemon │
1325 │ │ │ │ reporting this │
1326 │ │ │ │ version. If │
1327 │ │ │ │ empty, this is │
1328 │ │ │ │ the version of │
1329 │ │ │ │ the local │
1330 │ │ │ │ daemon. │
1331 └────────────┴─────────┴─────────┴──────────────────┘
1332 The daemon ships a VERSION response to each client when the client
1334 first connects to it.
1335 When the C client library parses a response of this kind, it will
1337 assert the VERSION_SET bit in the top-level set member.
1338 Here’s an example:
1340 {"class":"VERSION","version":"2.40dev",
1342 "rev":"06f62e14eae9886cde907dae61c124c53eb1101f",
1343 "proto_major":3,"proto_minor":1
1344 }
1345 ?DEVICES;
1347 Returns a device list object with the following elements:
1348 Table 11. DEVICES object
1350 ┌────────┬─────────┬────────┬──────────────────┐
1351 │ │ │ │ │
1352 │Name │ Always? │ Type │ Description │
1353 ├────────┼─────────┼────────┼──────────────────┤
1354 │ │ │ │ │
1355 │class │ Yes │ string │ Fixed: "DEVICES" │
1356 ├────────┼─────────┼────────┼──────────────────┤
1357 │ │ │ │ │
1358 │devices │ Yes │ list │ List of device │
1359 │ │ │ │ descriptions │
1360 ├────────┼─────────┼────────┼──────────────────┤
1361 │ │ │ │ │
1362 │remote │ No │ string │ URL of the │
1363 │ │ │ │ remote daemon │
1364 │ │ │ │ reporting the │
1365 │ │ │ │ device set. If │
1366 │ │ │ │ empty, this is a │
1367 │ │ │ │ DEVICES response │
1368 │ │ │ │ from the local │
1369 │ │ │ │ daemon. │
1370 └────────┴─────────┴────────┴──────────────────┘
1371 When the C client library parses a response of this kind, it will
1373 assert the DEVICELIST_SET bit in the top-level set member.
1374 Here’s an example:
1376 {"class"="DEVICES","devices":[
1378 {"class":"DEVICE","path":"/dev/pts/1","flags":1,"driver":"SiRF binary"},
1379 {"class":"DEVICE","path":"/dev/pts/3","flags":4,"driver":"AIVDM"}]}
1380 The daemon occasionally ships a bare DEVICE object to the client (that
1382 is, one not inside a DEVICES wrapper). The data content of these
1383 objects will be described later as a response to the ?DEVICE command.
1384 ?WATCH;
1386 This command sets watcher mode. It also sets or elicits a report of
1387 per-subscriber policy and the raw bit. An argument WATCH object changes
1388 the subscriber’s policy. The response describes the subscriber’s
1389 policy. The response will also include a DEVICES object.
1390 A WATCH object has the following elements:
1392 Table 12. WATCH object
1394 ┌────────┬─────────┬─────────┬──────────────────┐
1395 │ │ │ │ │
1396 │Name │ Always? │ Type │ Description │
1397 ├────────┼─────────┼─────────┼──────────────────┤
1398 │ │ │ │ │
1399 │class │ Yes │ string │ Fixed: "WATCH" │
1400 ├────────┼─────────┼─────────┼──────────────────┤
1401 │ │ │ │ │
1402 │enable │ No │ boolean │ Enable (true) or │
1403 │ │ │ │ disable (false) │
1404 │ │ │ │ watcher mode. │
1405 │ │ │ │ Default is true. │
1406 ├────────┼─────────┼─────────┼──────────────────┤
1407 │ │ │ │ │
1408 │json │ No │ boolean │ Enable (true) or │
1409 │ │ │ │ disable (false) │
1410 │ │ │ │ dumping of JSON │
1411 │ │ │ │ reports. Default │
1412 │ │ │ │ is false. │
1413 ├────────┼─────────┼─────────┼──────────────────┤
1414 │ │ │ │ │
1415 │nmea │ No │ boolean │ Enable (true) or │
1416 │ │ │ │ disable (false) │
1417 │ │ │ │ dumping of │
1418 │ │ │ │ binary packets │
1419 │ │ │ │ as pseudo-NMEA. │
1420 │ │ │ │ Default is │
1421 │ │ │ │ false. │
1422 ├────────┼─────────┼─────────┼──────────────────┤
1423 │ │ │ │ │
1424 │raw │ No │ integer │ Controls 'raw' │
1425 │ │ │ │ mode. When this │
1426 │ │ │ │ attribute is set │
1427 │ │ │ │ to 1 for a │
1428 │ │ │ │ channel, gpsd │
1429 │ │ │ │ reports the │
1430 │ │ │ │ unprocessed NMEA │
1431 │ │ │ │ or AIVDM data │
1432 │ │ │ │ stream from │
1433 │ │ │ │ whatever device │
1434 │ │ │ │ is attached. │
1435 │ │ │ │ Binary GPS │
1436 │ │ │ │ packets are │
1437 │ │ │ │ hex-dumped. │
1438 │ │ │ │ RTCM2 and RTCM3 │
1439 │ │ │ │ packets are not │
1440 │ │ │ │ dumped in raw │
1441 │ │ │ │ mode. When this │
1442 │ │ │ │ attribute is set │
1443 │ │ │ │ to 2 for a │
1444 │ │ │ │ channel that │
1445 │ │ │ │ processes binary │
1446 │ │ │ │ data, gpsd │
1447 │ │ │ │ reports the │
1448 │ │ │ │ received data │
1449 │ │ │ │ verbatim without │
1450 │ │ │ │ hex-dumping. │
1451 ├────────┼─────────┼─────────┼──────────────────┤
1452 │ │ │ │ │
1453 │scaled │ No │ boolean │ If true, apply │
1454 │ │ │ │ scaling divisors │
1455 │ │ │ │ to output before │
1456 │ │ │ │ dumping; default │
1457 │ │ │ │ is false. │
1458 ├────────┼─────────┼─────────┼──────────────────┤
1459 │ │ │ │ │
1460 │split24 │ No │ boolean │ If true, │
1461 │ │ │ │ aggregate AIS │
1462 │ │ │ │ type24 sentence │
1463 │ │ │ │ parts. If false, │
1464 │ │ │ │ report each part │
1465 │ │ │ │ as a separate │
1466 │ │ │ │ JSON object, │
1467 │ │ │ │ leaving the │
1468 │ │ │ │ client to match │
1469 │ │ │ │ MMSIs and │
1470 │ │ │ │ aggregate. │
1471 │ │ │ │ Default is │
1472 │ │ │ │ false. Applies │
1473 │ │ │ │ only to AIS │
1474 │ │ │ │ reports. │
1475 ├────────┼─────────┼─────────┼──────────────────┤
1476 │ │ │ │ │
1477 │pps │ No │ boolean │ If true, emit │
1478 │ │ │ │ the TOFF JSON │
1479 │ │ │ │ message on each │
1480 │ │ │ │ cycle and a PPS │
1481 │ │ │ │ JSON message │
1482 │ │ │ │ when the device │
1483 │ │ │ │ issues 1PPS. │
1484 │ │ │ │ Default is │
1485 │ │ │ │ false. │
1486 ├────────┼─────────┼─────────┼──────────────────┤
1487 │ │ │ │ │
1488 │device │ No │ string │ If present, │
1489 │ │ │ │ enable watching │
1490 │ │ │ │ only of the │
1491 │ │ │ │ specified device │
1492 │ │ │ │ rather than all │
1493 │ │ │ │ devices. Useful │
1494 │ │ │ │ with raw and │
1495 │ │ │ │ NMEA modes in │
1496 │ │ │ │ which device │
1497 │ │ │ │ responses aren’t │
1498 │ │ │ │ tagged. Has no │
1499 │ │ │ │ effect when used │
1500 │ │ │ │ with │
1501 │ │ │ │ enable:false. │
1502 ├────────┼─────────┼─────────┼──────────────────┤
1503 │ │ │ │ │
1504 │remote │ No │ string │ URL of the │
1505 │ │ │ │ remote daemon │
1506 │ │ │ │ reporting the │
1507 │ │ │ │ watch set. If │
1508 │ │ │ │ empty, this is a │
1509 │ │ │ │ WATCH response │
1510 │ │ │ │ from the local │
1511 │ │ │ │ daemon. │
1512 └────────┴─────────┴─────────┴──────────────────┘
1513 There is an additional boolean "timing" attribute which is undocumented
1515 because that portion of the interface is considered unstable and for
1516 developer use only.
1517 In watcher mode, GPS reports are dumped as TPV and SKY responses. AIS,
1519 Subframe and RTCM reporting is described in the next section.
1520 When the C client library parses a response of this kind, it will
1522 assert the POLICY_SET bit in the top-level set member.
1523 Here’s an example:
1525 {"class":"WATCH", "raw":1,"scaled":true}
1527 ?POLL;
1529 The POLL command requests data from the last-seen fixes on all active
1530 GPS devices. Devices must previously have been activated by ?WATCH to
1531 be pollable.
1532 Polling can lead to possibly surprising results when it is used on a
1534 device such as an NMEA GPS for which a complete fix has to be
1535 accumulated from several sentences. If you poll while those sentences
1536 are being emitted, the response will contain only the fix data
1537 collected so far in the current epoch. It may be as much as one cycle
1538 time (typically 1 second) stale.
1539 The POLL response will contain a timestamped list of TPV objects
1541 describing cached data, and a timestamped list of SKY objects
1542 describing satellite configuration. If a device has not seen fixes, it
1543 will be reported with a mode field of zero.
1544 Table 13. POLL object
1546 ┌───────┬─────────┬────────────┬──────────────────┐
1547 │ │ │ │ │
1548 │Name │ Always? │ Type │ Description │
1549 ├───────┼─────────┼────────────┼──────────────────┤
1550 │ │ │ │ │
1551 │class │ Yes │ string │ Fixed: "POLL" │
1552 ├───────┼─────────┼────────────┼──────────────────┤
1553 │ │ │ │ │
1554 │time │ Yes │ Numeric │ Timestamp in ISO │
1555 │ │ │ │ 8601 format. May │
1556 │ │ │ │ have a │
1557 │ │ │ │ fractional part │
1558 │ │ │ │ of up to .001sec │
1559 │ │ │ │ precision. │
1560 ├───────┼─────────┼────────────┼──────────────────┤
1561 │ │ │ │ │
1562 │active │ Yes │ Numeric │ Count of active │
1563 │ │ │ │ devices. │
1564 ├───────┼─────────┼────────────┼──────────────────┤
1565 │ │ │ │ │
1566 │tpv │ Yes │ JSON array │ Comma-separated │
1567 │ │ │ │ list of TPV │
1568 │ │ │ │ objects. │
1569 ├───────┼─────────┼────────────┼──────────────────┤
1570 │ │ │ │ │
1571 │sky │ Yes │ JSON array │ Comma-separated │
1572 │ │ │ │ list of SKY │
1573 │ │ │ │ objects. │
1574 └───────┴─────────┴────────────┴──────────────────┘
1575 Here’s an example of a POLL response:
1577 {"class":"POLL","time":"2010-06-04T10:31:00.289Z","active":1,
1579 "tpv":[{"class":"TPV","device":"/dev/ttyUSB0",
1580 "time":"2010-09-08T13:33:06.095Z",
1581 "ept":0.005,"lat":40.035093060,
1582 "lon":-75.519748733,"track":99.4319,"speed":0.123,"mode":2}],
1583 "sky":[{"class":"SKY","device":"/dev/ttyUSB0",
1584 "time":1270517264.240,"hdop":9.20,
1585 "satellites":[{"PRN":16,"el":55,"az":42,"ss":36,"used":true},
1586 {"PRN":19,"el":25,"az":177,"ss":0,"used":false},
1587 {"PRN":7,"el":13,"az":295,"ss":0,"used":false},
1588 {"PRN":6,"el":56,"az":135,"ss":32,"used":true},
1589 {"PRN":13,"el":47,"az":304,"ss":0,"used":false},
1590 {"PRN":23,"el":66,"az":259,"ss":0,"used":false},
1591 {"PRN":20,"el":7,"az":226,"ss":0,"used":false},
1592 {"PRN":3,"el":52,"az":163,"ss":32,"used":true},
1593 {"PRN":31,"el":16,"az":102,"ss":0,"used":false}
1594 ]}]}
1595 Note
1597 Client software should not assume the field inventory of the POLL
1598 response is fixed for all time. As gpsd collects and caches more
1599 data from more sensor types, those data are likely to find their
1600 way into this response.
1601 ?DEVICE; ?DEVICE=
1603 This command reports (when followed by ';') the state of a device, or
1604 sets (when followed by '=' and a DEVICE object) device-specific control
1605 bits, notably the device’s speed and serial mode and the native-mode
1606 bit. The parameter-setting form will be rejected if more than one
1607 client is attached to the channel and a device path is not specified.
1608 Pay attention to the response, because it is possible for this command
1610 to fail if the GPS does not support a command or only supports some
1611 combinations of modes. In case of failure, the daemon and GPS will
1612 continue to communicate at the old speed.
1613 Use the parameter-setting form with caution. On USB and Bluetooth GPSes
1615 it is also possible for serial mode setting to fail either because the
1616 serial adaptor chip does not support non-8N1 modes or because the
1617 device firmware does not properly synchronize the serial adaptor chip
1618 with the UART on the GPS chipset when the speed changes. These failures
1619 can hang your device, possibly requiring a GPS power cycle or (in
1620 extreme cases) physically disconnecting the NVRAM backup battery.
1621 A DEVICE object has the following elements:
1623 Table 14. DEVICE object
1625 ┌──────────┬─────────┬─────────┬──────────────────┐
1626 │ │ │ │ │
1627 │Name │ Always? │ Type │ Description │
1628 ├──────────┼─────────┼─────────┼──────────────────┤
1629 │ │ │ │ │
1630 │class │ Yes │ string │ Fixed: "DEVICE" │
1631 ├──────────┼─────────┼─────────┼──────────────────┤
1632 │ │ │ │ │
1633 │activated │ No │ string │ Time the device │
1634 │ │ │ │ was activated as │
1635 │ │ │ │ an ISO8601 time │
1636 │ │ │ │ stamp. If the │
1637 │ │ │ │ device is │
1638 │ │ │ │ inactive this │
1639 │ │ │ │ attribute is │
1640 │ │ │ │ absent. │
1641 ├──────────┼─────────┼─────────┼──────────────────┤
1642 │ │ │ │ │
1643 │bps │ No │ integer │ Device speed in │
1644 │ │ │ │ bits per second. │
1645 ├──────────┼─────────┼─────────┼──────────────────┤
1646 │ │ │ │ │
1647 │cycle │ No │ real │ Device cycle │
1648 │ │ │ │ time in seconds. │
1649 ├──────────┼─────────┼─────────┼──────────────────┤
1650 │ │ │ │ │
1651 │driver │ No │ string │ GPSD’s name for │
1652 │ │ │ │ the device │
1653 │ │ │ │ driver type. │
1654 │ │ │ │ Won’t be │
1655 │ │ │ │ reported before │
1656 │ │ │ │ gpsd has seen │
1657 │ │ │ │ identifiable │
1658 │ │ │ │ packets from the │
1659 │ │ │ │ device. │
1660 ├──────────┼─────────┼─────────┼──────────────────┤
1661 │ │ │ │ │
1662 │flags │ No │ integer │ Bit vector of │
1663 │ │ │ │ property flags. │
1664 │ │ │ │ Currently │
1665 │ │ │ │ defined flags │
1666 │ │ │ │ are: describe │
1667 │ │ │ │ packet types │
1668 │ │ │ │ seen so far │
1669 │ │ │ │ (GPS, RTCM2, │
1670 │ │ │ │ RTCM3, AIS). │
1671 │ │ │ │ Won’t be │
1672 │ │ │ │ reported if │
1673 │ │ │ │ empty, e.g. │
1674 │ │ │ │ before gpsd has │
1675 │ │ │ │ seen │
1676 │ │ │ │ identifiable │
1677 │ │ │ │ packets from the │
1678 │ │ │ │ device. │
1679 ├──────────┼─────────┼─────────┼──────────────────┤
1680 │ │ │ │ │
1681 │hexdata │ No │ string │ Data, in bare │
1682 │ │ │ │ hexadecimal, to │
1683 │ │ │ │ send to the GNSS │
1684 │ │ │ │ receiver. │
1685 ├──────────┼─────────┼─────────┼──────────────────┤
1686 │ │ │ │ │
1687 │mincycle │ No │ real │ Device minimum │
1688 │ │ │ │ cycle time in │
1689 │ │ │ │ seconds. │
1690 │ │ │ │ Reported from │
1691 │ │ │ │ ?DEVICE when │
1692 │ │ │ │ (and only when) │
1693 │ │ │ │ the rate is │
1694 │ │ │ │ switchable. It │
1695 │ │ │ │ is read-only and │
1696 │ │ │ │ not settable. │
1697 ├──────────┼─────────┼─────────┼──────────────────┤
1698 │ │ │ │ │
1699 │native │ No │ integer │ 0 means NMEA │
1700 │ │ │ │ mode and 1 means │
1701 │ │ │ │ alternate mode │
1702 │ │ │ │ (binary if it │
1703 │ │ │ │ has one, for │
1704 │ │ │ │ SiRF and │
1705 │ │ │ │ Evermore │
1706 │ │ │ │ chipsets in │
1707 │ │ │ │ particular). │
1708 │ │ │ │ Attempting to │
1709 │ │ │ │ set this mode on │
1710 │ │ │ │ a non-GPS device │
1711 │ │ │ │ will yield an │
1712 │ │ │ │ error. │
1713 ├──────────┼─────────┼─────────┼──────────────────┤
1714 │ │ │ │ │
1715 │parity │ No │ string │ N, O or E for no │
1716 │ │ │ │ parity, odd, or │
1717 │ │ │ │ even. │
1718 ├──────────┼─────────┼─────────┼──────────────────┤
1719 │ │ │ │ │
1720 │path │ No │ string │ Name the device │
1721 │ │ │ │ for which the │
1722 │ │ │ │ control bits are │
1723 │ │ │ │ being reported, │
1724 │ │ │ │ or for which │
1725 │ │ │ │ they are to be │
1726 │ │ │ │ applied. This │
1727 │ │ │ │ attribute may be │
1728 │ │ │ │ omitted only │
1729 │ │ │ │ when there is │
1730 │ │ │ │ exactly one │
1731 │ │ │ │ subscribed │
1732 │ │ │ │ channel. │
1733 ├──────────┼─────────┼─────────┼──────────────────┤
1734 │ │ │ │ │
1735 │readonly │ No │ boolean │ True if device │
1736 │ │ │ │ is read-only. │
1737 ├──────────┼─────────┼─────────┼──────────────────┤
1738 │ │ │ │ │
1739 │stopbits │ Yes │ string │ Stop bits (1 or │
1740 │ │ │ │ 2). │
1741 ├──────────┼─────────┼─────────┼──────────────────┤
1742 │ │ │ │ │
1743 │subtype │ No │ string │ Whatever version │
1744 │ │ │ │ information the │
1745 │ │ │ │ device driver │
1746 │ │ │ │ returned. │
1747 ├──────────┼─────────┼─────────┼──────────────────┤
1748 │ │ │ │ │
1749 │subtype1 │ No │ string │ More version │
1750 │ │ │ │ information the │
1751 │ │ │ │ device driver │
1752 │ │ │ │ returned. │
1753 └──────────┴─────────┴─────────┴──────────────────┘
1754 The serial parameters will (bps, parity, stopbits) be omitted in a
1756 response describing a TCP/IP source such as an Ntrip, DGPSIP, or AIS
1757 feed; on a serial device they will always be present.
1758 The contents of the flags field should be interpreted as follows:
1760 Table 15. Device flags
1762 ┌───────────┬───────┬─────────────────────┐
1763 │ │ │ │
1764 │C #define │ Value │ Description │
1765 ├───────────┼───────┼─────────────────────┤
1766 │ │ │ │
1767 │SEEN_GPS │ 0x01 │ GPS data has been │
1768 │ │ │ seen on this device │
1769 ├───────────┼───────┼─────────────────────┤
1770 │ │ │ │
1771 │SEEN_RTCM2 │ 0x02 │ RTCM2 data has been │
1772 │ │ │ seen on this device │
1773 ├───────────┼───────┼─────────────────────┤
1774 │ │ │ │
1775 │SEEN_RTCM3 │ 0x04 │ RTCM3 data has been │
1776 │ │ │ seen on this device │
1777 ├───────────┼───────┼─────────────────────┤
1778 │ │ │ │
1779 │SEEN_AIS │ 0x08 │ AIS data has been │
1780 │ │ │ seen on this device │
1781 └───────────┴───────┴─────────────────────┘
1782 When the C client library parses a response of this kind, it will
1784 assert the DEVICE_SET bit in the top-level set member.
1785 Here’s an example:
1787 {"class":"DEVICE","bps":4800,"parity":"N","stopbits":1,"native":0}
1789 When a client is in watcher mode, the daemon will ship it DEVICE
1791 notifications when a device is added to the pool or deactivated.
1792 When the C client library parses a response of this kind, it will
1794 assert the DEVICE_SET bit in the top-level set member.
1795 Examples
1797 A notice of a deactivated device:
1798 {"class":"DEVICE","path":"/dev/pts1","activated":0}
1800 A send a u-blox receiver at /dev/ttyUSB2 a request for a UBX-MON-VER
1802 message:
1803 ?DEVICE={"path":"/dev/ttyUSB2","hexdata":"b5620a0400000e34"}
1805 The gpsd daemon will respond with an ACK on success:
1807 {"class":"ACK"}
1809 ERROR
1811 The daemon may ship an error object in response to a syntactically
1812 invalid command line or unknown command. It has the following elements:
1813 Table 16. ERROR notification object
1815 ┌────────┬─────────┬────────┬────────────────┐
1816 │ │ │ │ │
1817 │Name │ Always? │ Type │ Description │
1818 ├────────┼─────────┼────────┼────────────────┤
1819 │ │ │ │ │
1820 │class │ Yes │ string │ Fixed: "ERROR" │
1821 ├────────┼─────────┼────────┼────────────────┤
1822 │ │ │ │ │
1823 │message │ Yes │ string │ Textual error │
1824 │ │ │ │ message │
1825 └────────┴─────────┴────────┴────────────────┘
1826 Here’s an example:
1828 {"class":"ERROR","message":"Unrecognized request '?FOO'"}
1830 When the C client library parses a response of this kind, it will
1832 assert the ERR_SET bit in the top-level set member.
1833
1835 RTCM-104 is a family of serial protocols used for broadcasting
1836 pseudorange corrections from differential-GPS reference stations. Many
1837 GPS receivers can accept these corrections to improve their reporting
1838 accuracy.
1839 RTCM-104 comes in two major and incompatible flavors, 2.x and 3.x. Each
1841 major flavor has minor (compatible) revisions.
1842 The applicable standard for RTCM Version 2.x is RTCM Recommended
1844 Standards for Differential NAVSTAR GPS Service RTCM Paper 194-93/SC
1845 104-STD. For RTCM 3.1 it is RTCM Paper 177-2006-SC104-STD. Ordering
1846 instructions for both standards are accessible from the website of the
1847 Radio Technical Commission for Maritime Services
1848 <https://www.rtcm.org/> under "Publications".
1849 RTCM WIRE TRANSMISSIONS
1851 Differential-GPS correction stations consist of a GPS reference
1852 receiver coupled to a low frequency (LF) transmitter. The GPS reference
1853 receiver is a survey-grade GPS that does GPS carrier tracking and can
1854 work out its position to a few millimeters. It generates range and
1855 range-rate corrections and encodes them into RTCM104. It ships the
1856 RTCM104 to the LF transmitter over serial rs-232 signal at 100 baud or
1857 200 baud depending on the requirements of the transmitter.
1858 The LF transmitter broadcasts the approximately 300khz radio signal
1860 that differential-GPS radio receivers pick up. Transmitters that are
1861 meant to have a higher range will need to transmit at a slower rate.
1862 The higher the data rate the harder it will be for the remote radio
1863 receiver to receive with a good signal-to-noise ration. (Higher data
1864 rate signals can’t be averaged over as long a time frame, hence they
1865 appear noisier.)
1866 RTCM WIRE FORMATS
1868 An RTCM 2.x message consists of a sequence of up to 33 30-bit words.
1869 The 24 most significant bits of each word are data and the six least
1870 significant bits are parity. The parity algorithm used is the same
1871 ISGPS-2000 as that used on GPS satellite downlinks. Each RTCM 2.x
1872 message consists of two header words followed by zero or more data
1873 words, depending upon the message type.
1874 An RTCM 3.x message begins with a fixed leader byte 0xD3. That is
1876 followed by six bits of version information and 10 bits of payload
1877 length information. Following that is the payload; following the
1878 payload is a 3-byte checksum of the payload using the Qualcomm CRC-24Q
1879 algorithm.
1880 RTCM2 JSON FORMAT
1882 Each RTCM2 message is dumped as a single JSON object per message, with
1883 the message fields as attributes of that object. Arrays of satellite,
1884 station, and constellation statistics become arrays of JSON
1885 sub-objects. Each sentence will normally also have a "device" field
1886 containing the pathname of the originating device.
1887 All attributes other than the device field are mandatory. Header
1889 attributes are emitted before others.
1890 Header portion
1892 Table 17. SKY object
1893 ┌───────────────┬─────────┬─────────────────────────────────────────────┐
1894 │ │ │ │
1895 │Name │ Type │ Description │
1896 ├───────────────┼─────────┼─────────────────────────────────────────────┤
1897 │ │ │ │
1898 │class │ string │ Fixed: "RTCM2". │
1899 ├───────────────┼─────────┼─────────────────────────────────────────────┤
1900 │ │ │ │
1901 │type │ integer │ Message type (1-9). │
1902 ├───────────────┼─────────┼─────────────────────────────────────────────┤
1903 │ │ │ │
1904 │station_id │ integer │ The id of the GPS │
1905 │ │ │ reference receiver. │
1906 │ │ │ The LF transmitters │
1907 │ │ │ also have │
1908 │ │ │ (different) id │
1909 │ │ │ numbers. │
1910 ├───────────────┼─────────┼─────────────────────────────────────────────┤
1911 │ │ │ │
1912 │zcount │ real │ The reference time │
1913 │ │ │ of the corrections │
1914 │ │ │ in the message in │
1915 │ │ │ seconds within the │
1916 │ │ │ current hour. Note │
1917 │ │ │ that it is in GPS │
1918 │ │ │ time, which is some │
1919 │ │ │ seconds ahead of │
1920 │ │ │ UTC (see the U.S. │
1921 │ │ │ Naval Observatory’s │
1922 │ │ │ table of leap │
1923 │ │ │ second │
1924 │ │ │ <ftp://maia.usno.navy.mil/ser7/tai-utc.dat> │
1925 │ │ │ corrections" ). │
1926 ├───────────────┼─────────┼─────────────────────────────────────────────┤
1927 │ │ │ │
1928 │seqnum │ integer │ Sequence number. Only 3 bits wide, wraps │
1929 │ │ │ after 7. │
1930 ├───────────────┼─────────┼─────────────────────────────────────────────┤
1931 │ │ │ │
1932 │length │ integer │ The number of words after the header that │
1933 │ │ │ comprise the message. │
1934 ├───────────────┼─────────┼─────────────────────────────────────────────┤
1935 │ │ │ │
1936 │station_health │ integer │ Station transmission status. Indicates the │
1937 │ │ │ health of the beacon as a reference source. │
1938 │ │ │ Any nonzero value means the satellite is │
1939 │ │ │ probably transmitting bad data and should │
1940 │ │ │ not be used in a fix. 6 means the │
1941 │ │ │ transmission is unmonitored. 7 means the │
1942 │ │ │ station is not working properly. Other │
1943 │ │ │ values are defined by the beacon operator. │
1944 └───────────────┴─────────┴─────────────────────────────────────────────┘
1945 <message type> is one of
1947 1
1949 full corrections — one message containing corrections for all GPS
1950 satellites in view. This is not common.
1951 3
1953 reference station parameters — the position of the reference
1954 station GPS antenna.
1955 4
1957 datum — the datum to which the DGPS data is referred.
1958 5
1960 constellation health — information about the satellites the beacon
1961 can see.
1962 6
1964 null message — just a filler.
1965 7
1967 radio beacon almanac — information about this or other beacons.
1968 9
1970 subset corrections — a message containing corrections for only a
1971 subset of the GPS satellites in view.
1972 16
1974 special message — a text message from the beacon operator.
1975 31
1977 GLONASS subset corrections — a message containing corrections for a
1978 set of the GLONASS satellites in view.
1979 Type 1 and 9: Correction data
1981 One or more satellite objects follow the header for type 1 or type 9
1982 messages. Here is the format:
1983 Table 18. Satellite object
1985 ┌──────┬─────────┬─────────────────────┐
1986 │ │ │ │
1987 │Name │ Type │ Description │
1988 ├──────┼─────────┼─────────────────────┤
1989 │ │ │ │
1990 │ident │ integer │ The PRN number of │
1991 │ │ │ the satellite for │
1992 │ │ │ which this is │
1993 │ │ │ correction data. │
1994 ├──────┼─────────┼─────────────────────┤
1995 │ │ │ │
1996 │udre │ integer │ User Differential │
1997 │ │ │ Range Error (0-3). │
1998 │ │ │ See the table │
1999 │ │ │ following for │
2000 │ │ │ values. │
2001 ├──────┼─────────┼─────────────────────┤
2002 │ │ │ │
2003 │iod │ integer │ Issue Of Data, │
2004 │ │ │ matching the IOD │
2005 │ │ │ for the current │
2006 │ │ │ ephemeris of this │
2007 │ │ │ satellite, as │
2008 │ │ │ transmitted by the │
2009 │ │ │ satellite. The IOD │
2010 │ │ │ is a unique tag │
2011 │ │ │ that identifies the │
2012 │ │ │ ephemeris; the GPS │
2013 │ │ │ using the DGPS │
2014 │ │ │ correction and the │
2015 │ │ │ DGPS generating the │
2016 │ │ │ data must use the │
2017 │ │ │ same orbital │
2018 │ │ │ positions for the │
2019 │ │ │ satellite. │
2020 ├──────┼─────────┼─────────────────────┤
2021 │ │ │ │
2022 │prc │ real │ The pseudorange │
2023 │ │ │ error in meters for │
2024 │ │ │ this satellite as │
2025 │ │ │ measured by the │
2026 │ │ │ beacon reference │
2027 │ │ │ receiver at the │
2028 │ │ │ epoch indicated by │
2029 │ │ │ the z_count in the │
2030 │ │ │ parent record. │
2031 ├──────┼─────────┼─────────────────────┤
2032 │ │ │ │
2033 │rrc │ real │ The rate of change │
2034 │ │ │ of pseudorange │
2035 │ │ │ error in meters/sec │
2036 │ │ │ for this satellite │
2037 │ │ │ as measured by the │
2038 │ │ │ beacon reference │
2039 │ │ │ receiver at the │
2040 │ │ │ epoch indicated by │
2041 │ │ │ the z_count field │
2042 │ │ │ in the parent │
2043 │ │ │ record. This is │
2044 │ │ │ used to calculate │
2045 │ │ │ pseudorange errors │
2046 │ │ │ at other epochs, if │
2047 │ │ │ required by the GPS │
2048 │ │ │ receiver. │
2049 └──────┴─────────┴─────────────────────┘
2050 User Differential Range Error values are as follows:
2052 Table 19. UDRE values
2054 ┌──┬─────────────────────┐
2055 │ │ │
2056 │0 │ 1-sigma error ⇐ 1 m │
2057 ├──┼─────────────────────┤
2058 │ │ │
2059 │1 │ 1-sigma error ⇐ 4 m │
2060 ├──┼─────────────────────┤
2061 │ │ │
2062 │2 │ 1-sigma error ⇐ 8 m │
2063 ├──┼─────────────────────┤
2064 │ │ │
2065 │3 │ 1-sigma error > 8 m │
2066 └──┴─────────────────────┘
2067 Here’s an example:
2069 {"class":"RTCM2","type":1,
2071 "station_id":688,"zcount":843.0,"seqnum":5,"length":19,"station_health":6,
2072 "satellites":[
2073 {"ident":10,"udre":0,"iod":46,"prc":-2.400,"rrc":0.000},
2074 {"ident":13,"udre":0,"iod":94,"prc":-4.420,"rrc":0.000},
2075 {"ident":7,"udre":0,"iod":22,"prc":-5.160,"rrc":0.002},
2076 {"ident":2,"udre":0,"iod":34,"prc":-6.480,"rrc":0.000},
2077 {"ident":4,"udre":0,"iod":47,"prc":-8.860,"rrc":0.000},
2078 {"ident":8,"udre":0,"iod":76,"prc":-7.980,"rrc":0.002},
2079 {"ident":5,"udre":0,"iod":99,"prc":-8.260,"rrc":0.002},
2080 {"ident":23,"udre":0,"iod":81,"prc":-8.060,"rrc":0.000},
2081 {"ident":16,"udre":0,"iod":70,"prc":-11.740,"rrc":0.000},
2082 {"ident":30,"udre":0,"iod":4,"prc":-18.960,"rrc":-0.006},
2083 {"ident":29,"udre":0,"iod":101,"prc":-24.960,"rrc":-0.002}
2084 ]}
2085 Type 3: Reference Station Parameters
2087 Here are the payload members of a type 3 (Reference Station Parameters)
2088 message:
2089 Table 20. Reference Station Parameters
2091 ┌─────┬──────┬────────────────────┐
2092 │ │ │ │
2093 │Name │ Type │ Description │
2094 ├─────┼──────┼────────────────────┤
2095 │ │ │ │
2096 │x │ real │ ECEF X coordinate. │
2097 ├─────┼──────┼────────────────────┤
2098 │ │ │ │
2099 │y │ real │ ECEF Y coordinate. │
2100 ├─────┼──────┼────────────────────┤
2101 │ │ │ │
2102 │z │ real │ ECEF Z coordinate. │
2103 └─────┴──────┴────────────────────┘
2104 The coordinates are the position of the station, in meters to two
2106 decimal places, in Earth Centred Earth Fixed coordinates. These are
2107 usually referred to the WGS84 reference frame, but may be referred to
2108 NAD83 in the US (essentially identical to WGS84 for all except
2109 geodesists), or some other reference frame in other parts of the world.
2110 An invalid reference message is represented by a type 3 header without
2112 payload fields.
2113 Here’s an example:
2115 {"class":"RTCM2","type":3,
2117 "station_id":652,"zcount":1657.2,"seqnum":2,"length":4,"station_health":6,
2118 "x":3878620.92,"y":670281.40,"z":5002093.59
2119 }
2120 Type 4: Datum
2122 Here are the payload members of a type 4 (Datum) message:
2123 Table 21. Datum
2125 ┌───────────┬─────────┬─────────────────────┐
2126 │ │ │ │
2127 │Name │ Type │ Description │
2128 ├───────────┼─────────┼─────────────────────┤
2129 │ │ │ │
2130 │dgnss_type │ string │ Either "GPS", │
2131 │ │ │ "GLONASS", │
2132 │ │ │ "GALILEO", or │
2133 │ │ │ "UNKNOWN". │
2134 ├───────────┼─────────┼─────────────────────┤
2135 │ │ │ │
2136 │dat │ integer │ 0 or 1 and │
2137 │ │ │ indicates the sense │
2138 │ │ │ of the offset shift │
2139 │ │ │ given by dx, dy, │
2140 │ │ │ dz. dat = 0 means │
2141 │ │ │ that the station │
2142 │ │ │ coordinates (in the │
2143 │ │ │ reference message) │
2144 │ │ │ are referred to a │
2145 │ │ │ local datum and │
2146 │ │ │ that adding dx, dy, │
2147 │ │ │ dz to that position │
2148 │ │ │ will render it in │
2149 │ │ │ GNSS coordinates │
2150 │ │ │ (WGS84 for GPS). If │
2151 │ │ │ dat = 1 then the │
2152 │ │ │ ref station │
2153 │ │ │ position is in GNSS │
2154 │ │ │ coordinates and │
2155 │ │ │ adding dx, dy, dz │
2156 │ │ │ will give it │
2157 │ │ │ referred to the │
2158 │ │ │ local datum. │
2159 ├───────────┼─────────┼─────────────────────┤
2160 │ │ │ │
2161 │datum_name │ string │ A standard name for │
2162 │ │ │ the datum. │
2163 ├───────────┼─────────┼─────────────────────┤
2164 │ │ │ │
2165 │dx │ real │ X offset. │
2166 ├───────────┼─────────┼─────────────────────┤
2167 │ │ │ │
2168 │dy │ real │ Y offset. │
2169 ├───────────┼─────────┼─────────────────────┤
2170 │ │ │ │
2171 │dz │ real │ Z offset. │
2172 └───────────┴─────────┴─────────────────────┘
2173 <dx> <dy> <dz> are offsets to convert from local datum to GNSS datum or
2175 vice versa. These fields are optional.
2176 An invalid datum message is represented by a type 4 header without
2178 payload fields.
2179 Type 5: Constellation Health
2181 One or more of these follow the header for type 5 messages — one for
2182 each satellite.
2183 Here is the format:
2185 Table 22. Constellation health
2187 ┌────────────┬─────────┬─────────────────────┐
2188 │ │ │ │
2189 │Name │ Type │ Description │
2190 ├────────────┼─────────┼─────────────────────┤
2191 │ │ │ │
2192 │ident │ integer │ The PRN number of │
2193 │ │ │ the satellite. │
2194 ├────────────┼─────────┼─────────────────────┤
2195 │ │ │ │
2196 │iodl │ bool │ True indicates that │
2197 │ │ │ this information │
2198 │ │ │ relates to the │
2199 │ │ │ satellite │
2200 │ │ │ information in an │
2201 │ │ │ accompanying type 1 │
2202 │ │ │ or type 9 message. │
2203 ├────────────┼─────────┼─────────────────────┤
2204 │ │ │ │
2205 │health │ integer │ 0 indicates that │
2206 │ │ │ the satellite is │
2207 │ │ │ healthy. Any other │
2208 │ │ │ value indicates a │
2209 │ │ │ problem (coding is │
2210 │ │ │ not known). │
2211 ├────────────┼─────────┼─────────────────────┤
2212 │ │ │ │
2213 │snr │ integer │ The carrier/noise │
2214 │ │ │ ratio of the │
2215 │ │ │ received signal in │
2216 │ │ │ the range 25 to 55 │
2217 │ │ │ dB(Hz). │
2218 ├────────────┼─────────┼─────────────────────┤
2219 │ │ │ │
2220 │health_en │ bool │ If set to True it │
2221 │ │ │ indicates that the │
2222 │ │ │ satellite is │
2223 │ │ │ healthy even if the │
2224 │ │ │ satellite │
2225 │ │ │ navigation data │
2226 │ │ │ says it is │
2227 │ │ │ unhealthy. │
2228 ├────────────┼─────────┼─────────────────────┤
2229 │ │ │ │
2230 │new_data │ bool │ True indicates that │
2231 │ │ │ the IOD for this │
2232 │ │ │ satellite will soon │
2233 │ │ │ be updated in type │
2234 │ │ │ 1 or 9 messages. │
2235 ├────────────┼─────────┼─────────────────────┤
2236 │ │ │ │
2237 │los_warning │ bool │ Line-of-sight │
2238 │ │ │ warning. True │
2239 │ │ │ indicates that the │
2240 │ │ │ satellite will │
2241 │ │ │ shortly go │
2242 │ │ │ unhealthy. │
2243 ├────────────┼─────────┼─────────────────────┤
2244 │ │ │ │
2245 │tou │ integer │ Healthy time │
2246 │ │ │ remaining in │
2247 │ │ │ seconds. │
2248 └────────────┴─────────┴─────────────────────┘
2249 Type 6: Null
2251 This just indicates a null message. There are no payload fields.
2252 Unknown message
2254 This format is used to dump message words in hexadecimal when the
2255 message type field doesn’t match any of the known ones.
2256 Here is the format:
2258 Table 23. Unknown Message
2260 ┌─────┬──────┬────────────────────┐
2261 │ │ │ │
2262 │Name │ Type │ Description │
2263 ├─────┼──────┼────────────────────┤
2264 │ │ │ │
2265 │data │ list │ A list of strings. │
2266 └─────┴──────┴────────────────────┘
2267 Each string in the array is a hex literal representing 30 bits of
2269 information, after parity checks and inversion. The high two bits
2270 should be ignored.
2271 Type 7: Radio Beacon Almanac
2273 Here is the format:
2274 Table 24. Constellation health
2276 ┌───────────┬─────────┬─────────────────────┐
2277 │ │ │ │
2278 │Name │ Type │ Description │
2279 ├───────────┼─────────┼─────────────────────┤
2280 │ │ │ │
2281 │lat │ real │ Latitude in │
2282 │ │ │ degrees, of the LF │
2283 │ │ │ transmitter antenna │
2284 │ │ │ for the station for │
2285 │ │ │ which this is an │
2286 │ │ │ almanac. North is │
2287 │ │ │ positive. │
2288 ├───────────┼─────────┼─────────────────────┤
2289 │ │ │ │
2290 │lon │ real │ Longitude in │
2291 │ │ │ degrees, of the LF │
2292 │ │ │ transmitter antenna │
2293 │ │ │ for the station for │
2294 │ │ │ which this is an │
2295 │ │ │ almanac. East is │
2296 │ │ │ positive. │
2297 ├───────────┼─────────┼─────────────────────┤
2298 │ │ │ │
2299 │range │ integer │ Published range of │
2300 │ │ │ the station in km. │
2301 ├───────────┼─────────┼─────────────────────┤
2302 │ │ │ │
2303 │frequency │ real │ Station broadcast │
2304 │ │ │ frequency in kHz. │
2305 ├───────────┼─────────┼─────────────────────┤
2306 │ │ │ │
2307 │health │ integer │ <health> is the │
2308 │ │ │ health of the │
2309 │ │ │ station for which │
2310 │ │ │ this is an almanac. │
2311 │ │ │ If it is non-zero, │
2312 │ │ │ the station is │
2313 │ │ │ issuing suspect │
2314 │ │ │ data and should not │
2315 │ │ │ be used for fixes. │
2316 │ │ │ The ITU and RTCM104 │
2317 │ │ │ standards differ │
2318 │ │ │ about the mode │
2319 │ │ │ detailed │
2320 │ │ │ interpretation of │
2321 │ │ │ the <health> field │
2322 │ │ │ and even about its │
2323 │ │ │ bit width. │
2324 ├───────────┼─────────┼─────────────────────┤
2325 │ │ │ │
2326 │station_id │ integer │ The id of the │
2327 │ │ │ transmitter. This │
2328 │ │ │ is not the same as │
2329 │ │ │ the reference id in │
2330 │ │ │ the header, the │
2331 │ │ │ latter being the id │
2332 │ │ │ of the reference │
2333 │ │ │ receiver. │
2334 ├───────────┼─────────┼─────────────────────┤
2335 │ │ │ │
2336 │bitrate │ integer │ The transmitted │
2337 │ │ │ bitrate. │
2338 └───────────┴─────────┴─────────────────────┘
2339 Here’s an example:
2341 {"class":"RTCM2","type":9,"station_id":268,"zcount":252.6,
2343 "seqnum":4,"length":5,"station_health":0,
2344 "satellites":[
2345 {"ident":13,"udre":0,"iod":3,"prc":-25.940,"rrc":0.066},
2346 {"ident":2,"udre":0,"iod":73,"prc":0.920,"rrc":-0.080},
2347 {"ident":8,"udre":0,"iod":22,"prc":23.820,"rrc":0.014}
2348 ]}
2349 Type 13: GPS Time of Week
2351 Here are the payload members of a type 13 (Groumf Tramitter Parameters)
2352 message:
2353 Table 25. Ground Transmitter Parameters
2355 ┌──────────┬─────────┬─────────────────────┐
2356 │ │ │ │
2357 │Name │ Type │ Description │
2358 ├──────────┼─────────┼─────────────────────┤
2359 │ │ │ │
2360 │status │ bool │ If True, signals │
2361 │ │ │ user to expect a │
2362 │ │ │ type 16 explanatory │
2363 │ │ │ message associated │
2364 │ │ │ with this station. │
2365 │ │ │ Probably indicates │
2366 │ │ │ some sort of │
2367 │ │ │ unusual event. │
2368 ├──────────┼─────────┼─────────────────────┤
2369 │ │ │ │
2370 │rangeflag │ bool │ If True, indicates │
2371 │ │ │ that the estimated │
2372 │ │ │ range is different │
2373 │ │ │ from that found in │
2374 │ │ │ the type 7 message │
2375 │ │ │ (which contains the │
2376 │ │ │ beacon’s listed │
2377 │ │ │ range). Generally │
2378 │ │ │ indicates a range │
2379 │ │ │ reduction due to │
2380 │ │ │ causes such as poor │
2381 │ │ │ ionospheric │
2382 │ │ │ conditions or │
2383 │ │ │ reduced │
2384 │ │ │ transmission power. │
2385 ├──────────┼─────────┼─────────────────────┤
2386 │ │ │ │
2387 │lat │ real │ Degrees latitude, │
2388 │ │ │ signed. Positive is │
2389 │ │ │ N, negative is S. │
2390 ├──────────┼─────────┼─────────────────────┤
2391 │ │ │ │
2392 │lon │ real │ Degrees longitude, │
2393 │ │ │ signed. Positive is │
2394 │ │ │ E, negative is W. │
2395 ├──────────┼─────────┼─────────────────────┤
2396 │ │ │ │
2397 │range │ integer │ Transmission range │
2398 │ │ │ in km (1-1024). │
2399 └──────────┴─────────┴─────────────────────┘
2400 This message type replaces message type 3 (Reference Station
2402 Parameters) in RTCM 2.3.
2403 Type 14: GPS Time of Week
2405 Here are the payload members of a type 14 (GPS Time of Week) message:
2406 Table 26. Reference Station Parameters
2408 ┌─────────┬─────────┬───────────────────┐
2409 │ │ │ │
2410 │Name │ Type │ Description │
2411 ├─────────┼─────────┼───────────────────┤
2412 │ │ │ │
2413 │week │ integer │ GPS week (0-123). │
2414 ├─────────┼─────────┼───────────────────┤
2415 │ │ │ │
2416 │hour │ integer │ Hour of week │
2417 │ │ │ (0-167). │
2418 ├─────────┼─────────┼───────────────────┤
2419 │ │ │ │
2420 │leapsecs │ integer │ Leap Seconds │
2421 │ │ │ (0-63). │
2422 └─────────┴─────────┴───────────────────┘
2423 Here’s an example:
2425 {"class":"RTCM2","type":14,"station_id":652,"zcount":1657.2,
2427 "seqnum":3,"length":1,"station_health":6,"week":601,"hour":109,
2428 "leapsecs":15}
2429 Type 16: Special Message
2431 Table 27. Special Message
2432 ┌────────┬────────┬─────────────────────┐
2433 │ │ │ │
2434 │Name │ Type │ Description │
2435 ├────────┼────────┼─────────────────────┤
2436 │ │ │ │
2437 │message │ string │ A text message sent │
2438 │ │ │ by the beacon │
2439 │ │ │ operator. │
2440 └────────┴────────┴─────────────────────┘
2441 Type 31: Correction data
2443 One or more GLONASS satellite objects follow the header for type 1 or
2444 type 9 messages. Here is the format:
2445 Table 28. Satellite object
2447 ┌───────┬──────────┬─────────────────────┐
2448 │ │ │ │
2449 │Name │ Type │ Description │
2450 ├───────┼──────────┼─────────────────────┤
2451 │ │ │ │
2452 │ident │ integer │ The PRN number of │
2453 │ │ │ the satellite for │
2454 │ │ │ which this is │
2455 │ │ │ correction data. │
2456 ├───────┼──────────┼─────────────────────┤
2457 │ │ │ │
2458 │udre │ integer │ User Differential │
2459 │ │ │ Range Error (0-3). │
2460 │ │ │ See the table │
2461 │ │ │ following for │
2462 │ │ │ values. │
2463 ├───────┼──────────┼─────────────────────┤
2464 │ │ │ │
2465 │change │ boolean │ Change-of-ephemeris │
2466 │ │ │ bit. │
2467 ├───────┼──────────┼─────────────────────┤
2468 │ │ │ │
2469 │tod │ uinteger │ Count of 30-second │
2470 │ │ │ periods since the │
2471 │ │ │ top of the hour. │
2472 ├───────┼──────────┼─────────────────────┤
2473 │ │ │ │
2474 │prc │ real │ The pseudorange │
2475 │ │ │ error in meters for │
2476 │ │ │ this satellite as │
2477 │ │ │ measured by the │
2478 │ │ │ beacon reference │
2479 │ │ │ receiver at the │
2480 │ │ │ epoch indicated by │
2481 │ │ │ the z_count in the │
2482 │ │ │ parent record. │
2483 ├───────┼──────────┼─────────────────────┤
2484 │ │ │ │
2485 │rrc │ real │ The rate of change │
2486 │ │ │ of pseudorange │
2487 │ │ │ error in meters/sec │
2488 │ │ │ for this satellite │
2489 │ │ │ as measured by the │
2490 │ │ │ beacon reference │
2491 │ │ │ receiver at the │
2492 │ │ │ epoch indicated by │
2493 │ │ │ the z_count field │
2494 │ │ │ in the parent │
2495 │ │ │ record. This is │
2496 │ │ │ used to calculate │
2497 │ │ │ pseudorange errors │
2498 │ │ │ at other epochs, if │
2499 │ │ │ required by the GPS │
2500 │ │ │ receiver. │
2501 └───────┴──────────┴─────────────────────┘
2502 Here’s an example:
2504 {"class":"RTCM2","type":31,"station_id":652,"zcount":1642.2,
2506 "seqnum":0,"length":14,"station_health":6,
2507 "satellites":[
2508 {"ident":5,"udre":0,"change":false,"tod":0,"prc":132.360,"rrc":0.000},
2509 {"ident":15,"udre":0,"change":false,"tod":0,"prc":134.840,"rrc":0.002},
2510 {"ident":14,"udre":0,"change":false,"tod":0,"prc":141.520,"rrc":0.000},
2511 {"ident":6,"udre":0,"change":false,"tod":0,"prc":127.000,"rrc":0.000},
2512 {"ident":21,"udre":0,"change":false,"tod":0,"prc":128.780,"rrc":0.000},
2513 {"ident":22,"udre":0,"change":false,"tod":0,"prc":125.260,"rrc":0.002},
2514 {"ident":20,"udre":0,"change":false,"tod":0,"prc":117.280,"rrc":-0.004},
2515 {"ident":16,"udre":0,"change":false,"tod":17,"prc":113.460,"rrc":0.018}
2516 ]}
2517
2519 The support for RTCM104v3 dumping is incomplete and buggy. Do not
2520 attempt to use it for production! Anyone interested in it should read
2521 the source code.
2522
2524 AIS support is an extension. It may not be present if your instance of
2525 gpsd has been built with a restricted feature set.
2526 AIS packets are dumped as JSON objects with class "AIS". Each AIS
2528 report object contains a "type" field giving the AIS message type and a
2529 "scaled" field telling whether the remainder of the fields are dumped
2530 in scaled or unscaled form. (These will be emitted before any
2531 type-specific fields.) It will also contain a "device" field naming the
2532 data source. Other fields have names and types as specified in the
2533 AIVDM/AIVDO Protocol Decoding document on the GPSD project website;
2534 each message field table may be directly interpreted as a specification
2535 for the members of the corresponding JSON object type.
2536 By default, certain scaling and conversion operations are performed for
2538 JSON output. Latitudes and longitudes are scaled to decimal degrees
2539 rather than the native AIS unit of 1/10000th of a minute of arc. Ship
2540 (but not air) speeds are scaled to knots rather than tenth-of-knot
2541 units. Rate of turn may appear as "nan" if is unavailable, or as one of
2542 the strings "fastright" or "fastleft" if it is out of the AIS encoding
2543 range; otherwise it is quadratically mapped back to the turn sensor
2544 number in degrees per minute. Vessel draughts are converted to decimal
2545 meters rather than native AIS decimeters. Various other scaling
2546 conversions are described in "AIVDM/AIVDO Protocol Decoding".
2547
2549 Subframe support is always compiled into gpsd but many GPSes do not
2550 output subframe data or the gpsd driver may not support subframes.
2551 Subframe packets are dumped as JSON objects with class "SUBFRAME". Each
2553 subframe report object contains a "frame" field giving the subframe
2554 number, a "tSV" field for the transmitting satellite number, a "TOW17"
2555 field containing the 17 MSBs of the start of the next 12-second message
2556 and a "scaled" field telling whether the remainder of the fields are
2557 dumped in scaled or unscaled form. It will also contain a "device"
2558 field naming the data source. Each SUBFRAME object will have a
2559 sub-object specific to that subframe page type. Those sub-object fields
2560 have names and types similar to those specified in the IS-GPS-200
2561 document; each message field table may be directly interpreted as a
2562 specification for the members of the corresponding JSON object type.
2563 Table 29. SUBFRAME object
2565 ┌───────┬─────────┬─────────┬──────────────────┐
2566 │ │ │ │ │
2567 │Name │ Always? │ Type │ Description │
2568 ├───────┼─────────┼─────────┼──────────────────┤
2569 │ │ │ │ │
2570 │class │ Yes │ string │ Fixed: │
2571 │ │ │ │ "SUBFRAME" │
2572 ├───────┼─────────┼─────────┼──────────────────┤
2573 │ │ │ │ │
2574 │device │ Yes │ string │ Name of the │
2575 │ │ │ │ originating │
2576 │ │ │ │ device. │
2577 ├───────┼─────────┼─────────┼──────────────────┤
2578 │ │ │ │ │
2579 │gnssId │ Yes │ integer │ Constellation of │
2580 │ │ │ │ transmitting │
2581 │ │ │ │ satellite │
2582 ├───────┼─────────┼─────────┼──────────────────┤
2583 │ │ │ │ │
2584 │tSV │ Yes │ integer │ ID of │
2585 │ │ │ │ transmitting │
2586 │ │ │ │ satellite (Not │
2587 │ │ │ │ PRN) │
2588 ├───────┼─────────┼─────────┼──────────────────┤
2589 │ │ │ │ │
2590 │TOW17 │ No │ integer │ Type 17 bits of │
2591 │ │ │ │ the next GPS │
2592 │ │ │ │ Time Of Week │
2593 ├───────┼─────────┼─────────┼──────────────────┤
2594 │ │ │ │ │
2595 │frame │ No │ integer │ Frame number │
2596 ├───────┼─────────┼─────────┼──────────────────┤
2597 │ │ │ │ │
2598 │scaled │ Yes │ boolean │ True is values │
2599 │ │ │ │ scaled │
2600 └───────┴─────────┴─────────┴──────────────────┘
2601
2603 Reading the raw JSON can be tedious. You can pretty print, and
2604 colorize, your JSON with [jq] to make reading easier. Using jq ito
2605 pretty pring a JSON file can be as simple as:
2606 $ jq . GPSD.json
2608 To grab 10 seconds of live gpsd JSON, and pretty print it:
2610 $ gpspipe -w -x 10 | jq .
2612 If you only want to see the TPV messages:
2614 $ gpspipe -w -x 10 | fgrep TPV | jq .
2616
2618 gpsd(8), libgps(3), libgpsmm(3), jq(1)
2619
2621 Project web site: https://gpsd.io/
2622 [RFC 2783]: https://datatracker.ietf.org/doc/html/rfc2783
2624 Pulse-Per-Second API for UNIX-like Operating Systems
2625 [RFC 7159]: https://datatracker.ietf.org/doc/html/rfc7159
2627 The JavaScript Object Notation (JSON) Data Interchange Format
2628 [jq]: https://github.com/stedolan/jq
2630
2632 This file is Copyright 2013 by the GPSD project
2633 SPDX-License-Identifier: BSD-2-clause
2634
2636 Eric S. Raymond
2637GPSD, Version 3.25 2023-01-10 GPSD_JSON(5)