gpsd_json(5) GPSD Documentation gpsd_json(5)
NAME
gpsd_json - gpsd request/response protocol
OVERVIEW
gpsd is a service daemon that can be used to monitor GPSes, DGPS
receivers, Marine AIS broadcasts, and various other location-related
and kinematic sensors.
Clients may communicate with gpsd via textual requests and responses
over a socket. It is a bad idea for applications to speak the protocol
directly: rather, they should use the libgps client library (for C;
bindings also exist for other languages) and take appropriate care to
check in their code for the expected major and minor protocol versions.
The GPSD protocol is built on top of JSON, JavaScript Object Notation,
as specified in [RFC-7159]: The JavaScript Object Notation (JSON) Data
Interchange Format. Similar to ECMA 404.
GPSD's use of JSON is restricted in some ways that make parsing it in
fixed-extent languages (such as C) easier.
A request line is introduced by "?" and may include multiple commands.
Commands begin with a command identifier, followed either by a
terminating ';' or by an equal sign "=" and a JSON object treated as an
argument. Any ';' or newline indication (either LF or CR-LF) after the
end of a command is ignored. All request lines must be composed of
US-ASCII characters and may be no more than 80 characters in length,
exclusive of the trailing newline.
Responses are single JSON objects that have a "class" attribute the
value of which is the object type . Object types include, but are not
limited to: "TPV", "SKY", "DEVICE", and "ERROR". Objects are sent both
in response to commands, and periodically as gpsd sends reports. Each
object is terminated by a carriage return and a new line (CR-NL).
The order of JSON attributes within a response object is never
significant, and you may specify command attributes in any order.
Responses never contain the special JSON value null; instead,
attributes with empty or undefined values are omitted. The length limit
for responses and reports is currently 10240 characters, including the
trailing CR-NL. Longer responses will be truncated, so client code must
be prepared for the possibility of invalid JSON fragments.
The default maximum message length is set by GPS_JSON_RESPONSE_MAX in
include/gpsd_json.h. at compile time.
In JSON reports, if an attribute is present only if the parent
attribute is present or has a particular range, then the parent
attribute is emitted first.
There is one constraint on the order in which attributes will be
omitted. If an optional attribute is present only when a parent
attribute has a specified value or range of values, the parent
attribute will be emitted first to make parsing easier.
The next subsection section documents the core GPSD protocol.
Extensions are documented in the following subsections. The extensions
may not be supported in your gpsd instance if it has been compiled with
a restricted feature set.
The protocol was designed and documented by Eric S. Raymond.
CORE PROTOCOL RESPONSES
Here are the core-protocol responses.
TPV
A TPV object is a time-position-velocity report. The "class" and "mode"
fields will reliably be present. When "mode" is 0 (Unknown) there is
likely no usable data in the sentence. The remaining fields are
optional, their presence depends on what data the GNSS receiver has
sent, and what gpsd may calculate from that data.
A TPV object will usually be sent at least once for every measurement
epoch as determined by the "time" field. Unless the receiver has a
solid fix, and knows the current leap second, the time may be random.
Multiple TPV objects are often sent per epoch. When the receiver
dribbles data to gpsd, then gpsd has no choice but to dribble it to the
client in multiple TPV messages.
The optional "status" field (aka fix type), is a modifier (adjective)
to mode. It is not a replacement for, or superset of, the "mode" field.
It is almost, but not quite, the same as the NMEA 4.x xxGGA GPS Quality
Indicator Values. Many GNSS receivers do not supply it. Those that do
interpret the specification in various incompatible ways. To save space
in the output, and avoid confusion, the JSON never includes status
values of 0 or 1.
All error estimates (epc, epd, epe, eph, ept, epv, epx, epy) are
guessed to be 95% confidence, may also be 50%, one sigma, or two sigma
confidence. Many GNSS receivers do not specify a confidence level. None
specify how the value is calculated. Use error estimates with caution,
and only as relative "goodness" indicators. If the GPS reports a value
to gpsd, then gpsd will report that value. Otherwise gpsd will try to
compute the value from the skyview.
See the file include/gps.h, especially struct gps_data_t, for expanded
notes on the items and values in the TPV message.
Table 1. TPV object
+------------+---------+---------+------------------+
| | | | |
|Name | Always? | Type | Description |
+------------+---------+---------+------------------+
| | | | |
|class | Yes | string | Fixed: "TPV" |
+------------+---------+---------+------------------+
| | | | |
|device | No | string | Name of the |
| | | | originating |
| | | | device. |
+------------+---------+---------+------------------+
| | | | |
|mode | Yes | numeric | NMEA mode: |
| | | | 0=unknown, |
| | | | 1=no fix, |
| | | | 2=2D, |
| | | | 3=3D. |
+------------+---------+---------+------------------+
| | | | |
|status | No | numeric | GPS fix status: |
| | | | 0=Unknown, |
| | | | 1=Normal, |
| | | | 2=DGPS, |
| | | | 3=RTK Fixed, |
| | | | 4=RTK Floating, |
| | | | 5=DR, |
| | | | 6=GNSSDR, |
| | | | 7=Time |
| | | | (surveyed), |
| | | | 8=Simulated, |
| | | | 9=P(Y) |
+------------+---------+---------+------------------+
| | | | |
|time | No | string | Time/date stamp |
| | | | in ISO8601 |
| | | | format, UTC. May |
| | | | have a |
| | | | fractional part |
| | | | of up to .001sec |
| | | | precision. May |
| | | | be absent if the |
| | | | mode is not 2D |
| | | | or 3D. May be |
| | | | present, but |
| | | | invalid, if |
| | | | there is no fix. |
| | | | Verify 3 |
| | | | consecutive 3D |
| | | | fixes before |
| | | | believing it is |
| | | | UTC. Even then |
| | | | it may be off by |
| | | | several seconds |
| | | | until the |
| | | | current leap |
| | | | seconds is |
| | | | known. |
+------------+---------+---------+------------------+
| | | | |
|altHAE | No | numeric | Altitude, height |
| | | | above ellipsoid, |
| | | | in meters. |
| | | | Probably WGS84. |
+------------+---------+---------+------------------+
| | | | |
|altMSL | No | numeric | MSL Altitude in |
| | | | meters. The |
| | | | geoid used is |
| | | | rarely specified |
| | | | and is often |
| | | | inaccurate. See |
| | | | the comments |
| | | | below on |
| | | | geoidSep. altMSL |
| | | | is altHAE minus |
| | | | geoidSep. |
+------------+---------+---------+------------------+
| | | | |
|alt | No | numeric | Deprecated. |
| | | | Undefined. Use |
| | | | altHAE or |
| | | | altMSL. |
+------------+---------+---------+------------------+
| | | | |
|climb | No | numeric | Climb (positive) |
| | | | or sink |
| | | | (negative) rate, |
| | | | meters per |
| | | | second. |
+------------+---------+---------+------------------+
| | | | |
|datum | No | string | Current datum. |
| | | | Hopefully WGS84. |
+------------+---------+---------+------------------+
| | | | |
|depth | No | numeric | Depth in meters. |
| | | | Probably depth |
| | | | below the |
| | | | keel... |
+------------+---------+---------+------------------+
| | | | |
|dgpsAge | No | numeric | Age of DGPS |
| | | | data. In seconds |
+------------+---------+---------+------------------+
| | | | |
|dgpsSta | No | numeric | Station of DGPS |
| | | | data. |
+------------+---------+---------+------------------+
| | | | |
|epc | No | numeric | Estimated climb |
| | | | error in meters |
| | | | per second. |
| | | | Certainty |
| | | | unknown. |
+------------+---------+---------+------------------+
| | | | |
|epd | No | numeric | Estimated track |
| | | | (direction) |
| | | | error in |
| | | | degrees. |
| | | | Certainty |
| | | | unknown. |
+------------+---------+---------+------------------+
| | | | |
|eph | No | numeric | Estimated |
| | | | horizontal |
| | | | Position (2D) |
| | | | Error in meters. |
| | | | Also known as |
| | | | Estimated |
| | | | Position Error |
| | | | (epe). Certainty |
| | | | unknown. |
+------------+---------+---------+------------------+
| | | | |
|eps | No | numeric | Estimated speed |
| | | | error in meters |
| | | | per second. |
| | | | Certainty |
| | | | unknown. |
+------------+---------+---------+------------------+
| | | | |
|ept | No | numeric | Estimated time |
| | | | stamp error in |
| | | | seconds. |
| | | | Certainty |
| | | | unknown. |
+------------+---------+---------+------------------+
| | | | |
|epx | No | numeric | Longitude error |
| | | | estimate in |
| | | | meters. |
| | | | Certainty |
| | | | unknown. |
+------------+---------+---------+------------------+
| | | | |
|epy | No | numeric | Latitude error |
| | | | estimate in |
| | | | meters. |
| | | | Certainty |
| | | | unknown. |
+------------+---------+---------+------------------+
| | | | |
|epv | No | numeric | Estimated |
| | | | vertical error |
| | | | in meters. |
| | | | Certainty |
| | | | unknown. |
+------------+---------+---------+------------------+
| | | | |
|geoidSep | No | numeric | Geoid separation |
| | | | is the |
| | | | difference |
| | | | between the |
| | | | WGS84 reference |
| | | | ellipsoid and |
| | | | the geoid (Mean |
| | | | Sea Level) in |
| | | | meters. Almost |
| | | | no GNSS receiver |
| | | | specifies how |
| | | | they compute |
| | | | their geoid. |
| | | | gpsd |
| | | | interpolates the |
| | | | geoid from a 5x5 |
| | | | degree table of |
| | | | EGM2008 values |
| | | | when the |
| | | | receiver does |
| | | | not supply a |
| | | | geoid |
| | | | separation. The |
| | | | gpsd computed |
| | | | geoidSep is |
| | | | usually within |
| | | | one meter of the |
| | | | "true" value, |
| | | | but can be off |
| | | | as much as 12 |
| | | | meters. |
+------------+---------+---------+------------------+
| | | | |
|lat | No | numeric | Latitude in |
| | | | degrees: +/- |
| | | | signifies |
| | | | North/South. |
+------------+---------+---------+------------------+
| | | | |
|leapseconds | No | integer | Current leap |
| | | | seconds. |
+------------+---------+---------+------------------+
| | | | |
|lon | No | numeric | Longitude in |
| | | | degrees: +/- |
| | | | signifies |
| | | | East/West. |
+------------+---------+---------+------------------+
| | | | |
|track | No | numeric | Course over |
| | | | ground, degrees |
| | | | from true north. |
+------------+---------+---------+------------------+
| | | | |
|magtrack | No | numeric | Course over |
| | | | ground, degrees |
| | | | magnetic. |
+------------+---------+---------+------------------+
| | | | |
|magvar | No | numeric | Magnetic |
| | | | variation, |
| | | | degrees. Also |
| | | | known as the |
| | | | magnetic |
| | | | declination (the |
| | | | direction of the |
| | | | horizontal |
| | | | component of the |
| | | | magnetic field |
| | | | measured |
| | | | clockwise from |
| | | | north) in |
| | | | degrees, |
| | | | Positive is West |
| | | | variation. |
| | | | Negative is East |
| | | | variation. |
+------------+---------+---------+------------------+
| | | | |
|speed | No | numeric | Speed over |
| | | | ground, meters |
| | | | per second. |
+------------+---------+---------+------------------+
| | | | |
|ecefx | No | numeric | ECEF X position |
| | | | in meters. |
+------------+---------+---------+------------------+
| | | | |
|ecefy | No | numeric | ECEF Y position |
| | | | in meters. |
+------------+---------+---------+------------------+
| | | | |
|ecefz | No | numeric | ECEF Z position |
| | | | in meters. |
+------------+---------+---------+------------------+
| | | | |
|ecefpAcc | No | numeric | ECEF position |
| | | | error in meters. |
| | | | Certainty |
| | | | unknown. |
+------------+---------+---------+------------------+
| | | | |
|ecefvx | No | numeric | ECEF X velocity |
| | | | in meters per |
| | | | second. |
+------------+---------+---------+------------------+
| | | | |
|ecefvy | No | numeric | ECEF Y velocity |
| | | | in meters per |
| | | | second. |
+------------+---------+---------+------------------+
| | | | |
|ecefvz | No | numeric | ECEF Z velocity |
| | | | in meters per |
| | | | second. |
+------------+---------+---------+------------------+
| | | | |
|ecefvAcc | No | numeric | ECEF velocity |
| | | | error in meters |
| | | | per second. |
| | | | Certainty |
| | | | unknown. |
+------------+---------+---------+------------------+
| | | | |
|sep | No | numeric | Estimated |
| | | | Spherical (3D) |
| | | | Position Error |
| | | | in meters. |
| | | | Guessed to be |
| | | | 95% confidence, |
| | | | but many GNSS |
| | | | receivers do not |
| | | | specify, so |
| | | | certainty |
| | | | unknown. |
+------------+---------+---------+------------------+
| | | | |
|relD | No | numeric | Down component |
| | | | of relative |
| | | | position vector |
| | | | in meters. |
+------------+---------+---------+------------------+
| | | | |
|relE | No | numeric | East component |
| | | | of relative |
| | | | position vector |
| | | | in meters. |
+------------+---------+---------+------------------+
| | | | |
|relN | No | numeric | North component |
| | | | of relative |
| | | | position vector |
| | | | in meters. |
+------------+---------+---------+------------------+
| | | | |
|velD | No | numeric | Down velocity |
| | | | component in |
| | | | meters. |
+------------+---------+---------+------------------+
| | | | |
|velE | No | numeric | East velocity |
| | | | component in |
| | | | meters. |
+------------+---------+---------+------------------+
| | | | |
|velN | No | numeric | North velocity |
| | | | component in |
| | | | meters. |
+------------+---------+---------+------------------+
| | | | |
|wanglem | No | numeric | Wind angle |
| | | | magnetic in |
| | | | degrees. |
+------------+---------+---------+------------------+
| | | | |
|wangler | No | numeric | Wind angle |
| | | | relative in |
| | | | degrees. |
+------------+---------+---------+------------------+
| | | | |
|wanglet | No | numeric | Wind angle true |
| | | | in degrees. |
+------------+---------+---------+------------------+
| | | | |
|wspeedr | No | numeric | Wind speed |
| | | | relative in |
| | | | meters per |
| | | | second. |
+------------+---------+---------+------------------+
| | | | |
|wspeedt | No | numeric | Wind speed true |
| | | | in meters per |
| | | | second. |
+------------+---------+---------+------------------+
| | | | |
|wtemp | No | numeric | Water |
| | | | temperature in |
| | | | degrees Celsius. |
+------------+---------+---------+------------------+
When the C client library parses a response of this kind, it will
assert validity bits in the top-level set member for each field
received; see gps.h for bitmask names and values.
Invalid or unknown floating-point values will be set to NAN. Always
check floating point values with isfinite() before use. isnan() is not
sufficient.
Here's an example TPV sentence:
{"class":"TPV","device":"/dev/pts/1",
"time":"2005-06-08T10:34:48.283Z","ept":0.005,
"lat":46.498293369,"lon":7.567411672,"alt":1343.127,
"eph":36.000,"epv":32.321,
"track":10.3788,"speed":0.091,"climb":-0.085,"mode":3}
SKY
A SKY object reports a sky view of the GPS satellite positions. If
there is no GPS device available, or no skyview has been reported yet,
only the "class" field will reliably be present.
Table 2. SKY object
+-----------+---------+---------+------------------+
| | | | |
|Name | Always? | Type | Description |
+-----------+---------+---------+------------------+
| | | | |
|class | Yes | string | Fixed: "SKY" |
+-----------+---------+---------+------------------+
| | | | |
|device | No | string | Name of |
| | | | originating |
| | | | device |
+-----------+---------+---------+------------------+
| | | | |
|nSat | No | numeric | Number of |
| | | | satellite |
| | | | objects in |
| | | | "satellites" |
| | | | array. |
+-----------+---------+---------+------------------+
| | | | |
|gdop | No | numeric | Geometric |
| | | | (hyperspherical) |
| | | | dilution of |
| | | | precision, a |
| | | | combination of |
| | | | PDOP and TDOP. A |
| | | | dimensionless |
| | | | factor which |
| | | | should be |
| | | | multiplied by a |
| | | | base UERE to get |
| | | | an error |
| | | | estimate. |
+-----------+---------+---------+------------------+
| | | | |
|hdop | No | numeric | Horizontal |
| | | | dilution of |
| | | | precision, a |
| | | | dimensionless |
| | | | factor which |
| | | | should be |
| | | | multiplied by a |
| | | | base UERE to get |
| | | | a circular error |
| | | | estimate. |
+-----------+---------+---------+------------------+
| | | | |
|pdop | No | numeric | Position |
| | | | (spherical/3D) |
| | | | dilution of |
| | | | precision, a |
| | | | dimensionless |
| | | | factor which |
| | | | should be |
| | | | multiplied by a |
| | | | base UERE to get |
| | | | an error |
| | | | estimate. |
+-----------+---------+---------+------------------+
| | | | |
|prRes | No | numeric | Pseudorange |
| | | | residue in |
| | | | meters. |
+-----------+---------+---------+------------------+
| | | | |
|qual | No | numeric | Quality |
| | | | Indicator |
| | | | 0=no signal |
| | | | 1=searching |
| | | | signal |
| | | | 2=signal |
| | | | acquired |
| | | | 3=signal |
| | | | detected but |
| | | | unusable |
| | | | 4=code locked |
| | | | and time |
| | | | synchronized |
| | | | 5, 6, 7=code and |
| | | | carrier locked |
| | | | and time |
| | | | synchronized |
+-----------+---------+---------+------------------+
| | | | |
|satellites | No | list | List of |
| | | | satellite |
| | | | objects in |
| | | | skyview |
+-----------+---------+---------+------------------+
| | | | |
|tdop | No | numeric | Time dilution of |
| | | | precision, a |
| | | | dimensionless |
| | | | factor which |
| | | | should be |
| | | | multiplied by a |
| | | | base UERE to get |
| | | | an error |
| | | | estimate. |
+-----------+---------+---------+------------------+
| | | | |
|time | No | string | Time/date stamp |
| | | | in ISO8601 |
| | | | format, UTC. May |
| | | | have a |
| | | | fractional part |
| | | | of up to .001sec |
| | | | precision. |
+-----------+---------+---------+------------------+
| | | | |
|uSat | No | numeric | Number of |
| | | | satellites used |
| | | | in navigation |
| | | | solution. |
+-----------+---------+---------+------------------+
| | | | |
|vdop | No | numeric | Vertical |
| | | | (altitude) |
| | | | dilution of |
| | | | precision, a |
| | | | dimensionless |
| | | | factor which |
| | | | should be |
| | | | multiplied by a |
| | | | base UERE to get |
| | | | an error |
| | | | estimate. |
+-----------+---------+---------+------------------+
| | | | |
|xdop | No | numeric | Longitudinal |
| | | | dilution of |
| | | | precision, a |
| | | | dimensionless |
| | | | factor which |
| | | | should be |
| | | | multiplied by a |
| | | | base UERE to get |
| | | | an error |
| | | | estimate. |
+-----------+---------+---------+------------------+
| | | | |
|ydop | No | numeric | Latitudinal |
| | | | dilution of |
| | | | precision, a |
| | | | dimensionless |
| | | | factor which |
| | | | should be |
| | | | multiplied by a |
| | | | base UERE to get |
| | | | an error |
| | | | estimate. |
+-----------+---------+---------+------------------+
Many devices compute dilution of precision factors but do not include
them in their reports. Many that do report DOPs report only HDOP,
two-dimensional circular error. gpsd always passes through whatever the
device reports, then attempts to fill in other DOPs by calculating the
appropriate determinants in a covariance matrix based on the satellite
view. DOPs may be missing if some of these determinants are singular.
It can even happen that the device reports an error estimate in meters
when the corresponding DOP is unavailable; some devices use more
sophisticated error modeling than the covariance calculation.
The satellite list objects have the following elements:
Table 3. Satellite object
+-------+---------+---------+------------------+
| | | | |
|Name | Always? | Type | Description |
+-------+---------+---------+------------------+
| | | | |
|PRN | Yes | numeric | PRN ID of the |
| | | | satellite. 1-63 |
| | | | are GNSS |
| | | | satellites, |
| | | | 64-96 are |
| | | | GLONASS |
| | | | satellites, |
| | | | 100-164 are SBAS |
| | | | satellites |
+-------+---------+---------+------------------+
| | | | |
|az | No | numeric | Azimuth, degrees |
| | | | from true north. |
+-------+---------+---------+------------------+
| | | | |
|el | No | numeric | Elevation in |
| | | | degrees. |
+-------+---------+---------+------------------+
| | | | |
|ss | No | numeric | Signal to Noise |
| | | | ratio in dBHz. |
+-------+---------+---------+------------------+
| | | | |
|used | Yes | boolean | Used in current |
| | | | solution? |
| | | | (SBAS/WAAS/EGNOS |
| | | | satellites may |
| | | | be flagged used |
| | | | if the solution |
| | | | has corrections |
| | | | from them, but |
| | | | not all drivers |
| | | | make this |
| | | | information |
| | | | available.) |
+-------+---------+---------+------------------+
| | | | |
|gnssid | No | numeric | The GNSS ID, as |
| | | | defined by |
| | | | u-blox, not |
| | | | NMEA. 0=GPS, |
| | | | 2=Galileo, |
| | | | 3=Beidou, |
| | | | 5=QZSS, |
| | | | 6-GLONASS. |
+-------+---------+---------+------------------+
| | | | |
|svid | No | numeric | The satellite ID |
| | | | within its |
| | | | constellation. |
| | | | As defined by |
| | | | u-blox, not |
| | | | NMEA). |
+-------+---------+---------+------------------+
| | | | |
|sigid | No | numeric | The signal ID of |
| | | | this signal. As |
| | | | defined by |
| | | | u-blox, not |
| | | | NMEA. See u-blox |
| | | | doc for details. |
+-------+---------+---------+------------------+
| | | | |
|freqid | No | numeric | For GLONASS |
| | | | satellites only: |
| | | | the frequency ID |
| | | | of the signal. |
| | | | As defined by |
| | | | u-blox, range 0 |
| | | | to 13. The |
| | | | freqid is the |
| | | | frequency slot |
| | | | plus 7. |
+-------+---------+---------+------------------+
| | | | |
|health | No | numeric | The health of |
| | | | this satellite. |
| | | | 0 is unknown, 1 |
| | | | is OK, and 2 is |
| | | | unhealthy. |
+-------+---------+---------+------------------+
Note that satellite objects do not have a "class" field, as they are
never shipped outside of a SKY object.
When the C client library parses a SKY response, it will assert the
SATELLITE_SET bit in the top-level set member.
Here's an example:
{"class":"SKY","device":"/dev/pts/1",
"time":"2005-07-08T11:28:07.114Z",
"xdop":1.55,"hdop":1.24,"pdop":1.99,
"satellites":[
{"PRN":23,"el":6,"az":84,"ss":0,"used":false},
{"PRN":28,"el":7,"az":160,"ss":0,"used":false},
{"PRN":8,"el":66,"az":189,"ss":44,"used":true},
{"PRN":29,"el":13,"az":273,"ss":0,"used":false},
{"PRN":10,"el":51,"az":304,"ss":29,"used":true},
{"PRN":4,"el":15,"az":199,"ss":36,"used":true},
{"PRN":2,"el":34,"az":241,"ss":43,"used":true},
{"PRN":27,"el":71,"az":76,"ss":43,"used":true}]}
GST
A GST object is a pseudorange noise report.
Table 4. GST object
+-------+---------+---------+------------------+
| | | | |
|Name | Always? | Type | Description |
+-------+---------+---------+------------------+
| | | | |
|class | Yes | string | Fixed: "GST" |
+-------+---------+---------+------------------+
| | | | |
|device | No | string | Name of |
| | | | originating |
| | | | device |
+-------+---------+---------+------------------+
| | | | |
|time | No | string | Time/date stamp |
| | | | in ISO8601 |
| | | | format, UTC. May |
| | | | have a |
| | | | fractional part |
| | | | of up to .001sec |
| | | | precision. |
+-------+---------+---------+------------------+
| | | | |
|rms | No | numeric | Value of the |
| | | | standard |
| | | | deviation of the |
| | | | range inputs to |
| | | | the navigation |
| | | | process (range |
| | | | inputs include |
| | | | pseudoranges and |
| | | | DGPS |
| | | | corrections). |
+-------+---------+---------+------------------+
| | | | |
|major | No | numeric | Standard |
| | | | deviation of |
| | | | semi-major axis |
| | | | of error |
| | | | ellipse, in |
| | | | meters. |
+-------+---------+---------+------------------+
| | | | |
|minor | No | numeric | Standard |
| | | | deviation of |
| | | | semi-minor axis |
| | | | of error |
| | | | ellipse, in |
| | | | meters. |
+-------+---------+---------+------------------+
| | | | |
|orient | No | numeric | Orientation of |
| | | | semi-major axis |
| | | | of error |
| | | | ellipse, in |
| | | | degrees from |
| | | | true north. |
+-------+---------+---------+------------------+
| | | | |
|lat | No | numeric | Standard |
| | | | deviation of |
| | | | latitude error, |
| | | | in meters. |
+-------+---------+---------+------------------+
| | | | |
|lon | No | numeric | Standard |
| | | | deviation of |
| | | | longitude error, |
| | | | in meters. |
+-------+---------+---------+------------------+
| | | | |
|alt | No | numeric | Standard |
| | | | deviation of |
| | | | altitude error, |
| | | | in meters. |
+-------+---------+---------+------------------+
Here's an example:
{"class":"GST","device":"/dev/ttyUSB0",
"time":"2010-12-07T10:23:07.096Z","rms":2.440,
"major":1.660,"minor":1.120,"orient":68.989,
"lat":1.600,"lon":1.200,"alt":2.520}
ATT
An ATT object is a vehicle-attitude report. It is returned by
digital-compass and gyroscope sensors; depending on device, it may
include: heading, pitch, roll, yaw, gyroscope, and magnetic-field
readings. Because such sensors are often bundled as part of
marine-navigation systems, the ATT response may also include water
depth.
The "class" and "mode" fields will reliably be present. Others may be
reported or not depending on the specific device type.
The ATT object is synchronous to the GNSS epoch. Some devices report
attitude information with arbitrary, even out of order, time scales.
gpsd reports those in an IMU object. The ATT and IMU objects have the
same fields, but IMU objects are output as soon as possible. Some
devices output both types with arbitrary interleaving.
Table 5. ATT object
+---------+---------+---------+------------------+
| | | | |
|Name | Always? | Type | Description |
+---------+---------+---------+------------------+
| | | | |
|class | Yes | string | Fixed: "ATT" |
+---------+---------+---------+------------------+
| | | | |
|device | Yes | string | Name of |
| | | | originating |
| | | | device |
+---------+---------+---------+------------------+
| | | | |
|time | No | string | Time/date stamp |
| | | | in ISO8601 |
| | | | format, UTC. May |
| | | | have a |
| | | | fractional part |
| | | | of up to .001sec |
| | | | precision. |
+---------+---------+---------+------------------+
| | | | |
|timeTag | No | string | Arbitrary time |
| | | | tag of |
| | | | measurement. |
+---------+---------+---------+------------------+
| | | | |
|heading | No | numeric | Heading, degrees |
| | | | from true north. |
+---------+---------+---------+------------------+
| | | | |
|mag_st | No | string | Magnetometer |
| | | | status. |
+---------+---------+---------+------------------+
| | | | |
|mheading | No | numeric | Heading, degrees |
| | | | from magnetic |
| | | | north. |
+---------+---------+---------+------------------+
| | | | |
|pitch | No | numeric | Pitch in |
| | | | degrees. |
+---------+---------+---------+------------------+
| | | | |
|pitch_st | No | string | Pitch sensor |
| | | | status. |
+---------+---------+---------+------------------+
| | | | |
|rot | No | numeric | Rate of Turn in |
| | | | dgrees per |
| | | | minute. |
+---------+---------+---------+------------------+
| | | | |
|yaw | No | numeric | Yaw in degrees |
+---------+---------+---------+------------------+
| | | | |
|yaw_st | No | string | Yaw sensor |
| | | | status. |
+---------+---------+---------+------------------+
| | | | |
|roll | No | numeric | Roll in degrees. |
+---------+---------+---------+------------------+
| | | | |
|roll_st | No | string | Roll sensor |
| | | | status. |
+---------+---------+---------+------------------+
| | | | |
|dip | No | numeric | Local magnetic |
| | | | inclination, |
| | | | degrees, |
| | | | positive when |
| | | | the magnetic |
| | | | field points |
| | | | downward (into |
| | | | the Earth). |
+---------+---------+---------+------------------+
| | | | |
|mag_len | No | numeric | Scalar magnetic |
| | | | field strength. |
+---------+---------+---------+------------------+
| | | | |
|mag_x | No | numeric | X component of |
| | | | magnetic field |
| | | | strength. |
+---------+---------+---------+------------------+
| | | | |
|mag_y | No | numeric | Y component of |
| | | | magnetic field |
| | | | strength. |
+---------+---------+---------+------------------+
| | | | |
|mag_z | No | numeric | Z component of |
| | | | magnetic field |
| | | | strength. |
+---------+---------+---------+------------------+
| | | | |
|acc_len | No | numeric | Scalar |
| | | | acceleration. |
+---------+---------+---------+------------------+
| | | | |
|acc_x | No | numeric | X component of |
| | | | acceleration |
| | | | (m/s^2). |
+---------+---------+---------+------------------+
| | | | |
|acc_y | No | numeric | Y component of |
| | | | acceleration |
| | | | (m/s^2). |
+---------+---------+---------+------------------+
| | | | |
|acc_z | No | numeric | Z component of |
| | | | acceleration |
| | | | (m/s^2). |
+---------+---------+---------+------------------+
| | | | |
|gyro_x | No | numeric | X component of |
| | | | angular rate |
| | | | (deg/s) |
+---------+---------+---------+------------------+
| | | | |
|gyro_y | No | numeric | Y component of |
| | | | angular rate |
| | | | (deg/s) |
+---------+---------+---------+------------------+
| | | | |
|gyro_z | No | numeric | Z component of |
| | | | angular rate |
| | | | (deg/s) |
+---------+---------+---------+------------------+
| | | | |
|depth | No | numeric | Water depth in |
| | | | meters. |
+---------+---------+---------+------------------+
| | | | |
|temp | No | numeric | Temperature at |
| | | | the sensor, |
| | | | degrees |
| | | | centigrade. |
+---------+---------+---------+------------------+
The heading, pitch, and roll status codes (if present) vary by device.
For the TNT Revolution digital compasses, they are coded as follows:
Table 6. Device flags
+-----+----------------------------+
| | |
|Code | Description |
+-----+----------------------------+
| | |
|C | magnetometer calibration |
| | alarm |
+-----+----------------------------+
| | |
|L | low alarm |
+-----+----------------------------+
| | |
|M | low warning |
+-----+----------------------------+
| | |
|N | normal |
+-----+----------------------------+
| | |
|O | high warning |
+-----+----------------------------+
| | |
|P | high alarm |
+-----+----------------------------+
| | |
|V | magnetometer voltage level |
| | alarm |
+-----+----------------------------+
When the C client library parses a response of this kind, it will
assert ATT_IS.
Here's an example:
{"class":"ATT","time":1270938096.843,
"heading":14223.00,"mag_st":"N",
"pitch":169.00,"pitch_st":"N", "roll":-43.00,"roll_st":"N",
"dip":13641.000,"mag_x":2454.000}
IMU
The IMU object is asynchronous to the GNSS epoch. It is reported with
arbitrary, even out of order, time scales.
The ATT and IMU objects have the same fields, but IMU objects are
output as soon as possible.
Seee the ATT onject description for field details.
TOFF
This message is emitted on each cycle and reports the offset between
the host's clock time and the GPS time at top of the second (actually,
when the first data for the reporting cycle is received).
This message exactly mirrors the PPS message.
The TOFF message reports the GPS time as derived from the GPS serial
data stream. The PPS message reports the GPS time as derived from the
GPS PPS pulse.
A TOFF object has the following elements:
Table 7. TOFF object
+-----------+---------+---------+------------------+
| | | | |
|Name | Always? | Type | Description |
+-----------+---------+---------+------------------+
| | | | |
|class | Yes | string | Fixed: "TOFF" |
+-----------+---------+---------+------------------+
| | | | |
|device | Yes | string | Name of the |
| | | | originating |
| | | | device |
+-----------+---------+---------+------------------+
| | | | |
|real_sec | Yes | numeric | seconds from the |
| | | | GPS clock |
+-----------+---------+---------+------------------+
| | | | |
|real_nsec | Yes | numeric | nanoseconds from |
| | | | the GPS clock |
+-----------+---------+---------+------------------+
| | | | |
|clock_sec | Yes | numeric | seconds from the |
| | | | system clock |
+-----------+---------+---------+------------------+
| | | | |
|clock_nsec | Yes | numeric | nanoseconds from |
| | | | the system clock |
+-----------+---------+---------+------------------+
This message is emitted once per second to watchers of a device and is
intended to report the timestamps of the in-band report of the GPS and
seconds as reported by the system clock (which may be NTP-corrected)
when the first valid time stamp of the reporting cycle was seen.
The message contains two second/nanosecond pairs: real_sec and
real_nsec contain the time the GPS thinks it was at the start of the
current cycle; clock_sec and clock_nsec contain the time the system
clock thinks it was on receipt of the first timing message of the
cycle. real_nsec is always to nanosecond precision. clock_nsec is
nanosecond precision on most systems.
Here's an example:
{"class":"TOFF","device":"/dev/ttyUSB0",
"real_sec":1330212592, "real_nsec":343182,
"clock_sec":1330212592,"clock_nsec":343184,
"precision":-2}
PPS
This message is emitted each time the daemon sees a valid PPS (Pulse
Per Second) strobe from a device.
This message exactly mirrors the TOFF message.
The TOFF message reports the GPS time as derived from the GPS serial
data stream. The PPS message reports the GPS time as derived from the
GPS PPS pulse.
There are various sources of error in the reported clock times. The
speed of the serial connection between the GPS and the system adds a
delay to the start of cycle detection. An even bigger error is added by
the variable computation time inside the GPS. Taken together the time
derived from the start of the GPS cycle can have offsets of 10
milliseconds to 700 milliseconds and combined jitter and wander of 100
to 300 milliseconds.
See the NTP documentation for their definition of precision.
A PPS object has the following elements:
Table 8. PPS object
+-----------+---------+---------+------------------+
| | | | |
|Name | Always? | Type | Description |
+-----------+---------+---------+------------------+
| | | | |
|class | Yes | string | Fixed: "PPS" |
+-----------+---------+---------+------------------+
| | | | |
|device | Yes | string | Name of the |
| | | | originating |
| | | | device |
+-----------+---------+---------+------------------+
| | | | |
|real_sec | Yes | numeric | seconds from the |
| | | | PPS source |
+-----------+---------+---------+------------------+
| | | | |
|real_nsec | Yes | numeric | nanoseconds from |
| | | | the PPS source |
+-----------+---------+---------+------------------+
| | | | |
|clock_sec | Yes | numeric | seconds from the |
| | | | system clock |
+-----------+---------+---------+------------------+
| | | | |
|clock_nsec | Yes | numeric | nanoseconds from |
| | | | the system clock |
+-----------+---------+---------+------------------+
| | | | |
|precision | Yes | numeric | NTP style |
| | | | estimate of PPS |
| | | | precision |
+-----------+---------+---------+------------------+
| | | | |
|shm | Yes | string | shm key of this |
| | | | PPS |
+-----------+---------+---------+------------------+
| | | | |
|qErr | No | numeric | Quantization |
| | | | error of the |
| | | | PPS, in |
| | | | picoseconds. |
| | | | Sometimes called |
| | | | the "sawtooth" |
| | | | error. |
+-----------+---------+---------+------------------+
This message is emitted once per second to watchers of a device
emitting PPS, and reports the time of the start of the GPS second (when
the 1PPS arrives) and seconds as reported by the system clock (which
may be NTP-corrected) at that moment.
The message contains two second/nanosecond pairs: real_sec and
real_nsec contain the time the GPS thinks it was at the PPS edge;
clock_sec and clock_nsec contain the time the system clock thinks it
was at the PPS edge. real_nsec is always to nanosecond precision.
clock_nsec is nanosecond precision on most systems.
There are various sources of error in the reported clock times. For PPS
delivered via a real serial-line strobe, serial-interrupt latency plus
processing time to the timer call should be bounded above by about 10
microseconds; that can be reduced to less than 1 microsecond if your
kernel supports [RFC-2783]. USB1.1-to-serial control-line emulation is
limited to about 1 millisecond. seconds.
Here's an example:
{"class":"PPS","device":"/dev/ttyUSB0",
"real_sec":1330212592, "real_nsec":343182,
"clock_sec":1330212592,"clock_nsec":343184,
"precision":-3}
OSC
This message reports the status of a GPS-disciplined oscillator
(GPSDO). The GPS PPS output (which has excellent long-term stability)
is typically used to discipline a local oscillator with much better
short-term stability (such as a rubidium atomic clock).
An OSC object has the following elements:
Table 9. OSC object
+------------+---------+---------+------------------+
| | | | |
|Name | Always? | Type | Description |
+------------+---------+---------+------------------+
| | | | |
|class | Yes | string | Fixed: "OSC" |
+------------+---------+---------+------------------+
| | | | |
|device | Yes | string | Name of the |
| | | | originating |
| | | | device. |
+------------+---------+---------+------------------+
| | | | |
|running | Yes | boolean | If true, the |
| | | | oscillator is |
| | | | currently |
| | | | running. |
| | | | Oscillators may |
| | | | require warm-up |
| | | | time at the |
| | | | start of the |
| | | | day. |
+------------+---------+---------+------------------+
| | | | |
|reference | Yes | boolean | If true, the |
| | | | oscillator is |
| | | | receiving a GPS |
| | | | PPS signal. |
+------------+---------+---------+------------------+
| | | | |
|disciplined | Yes | boolean | If true, the GPS |
| | | | PPS signal is |
| | | | sufficiently |
| | | | stable and is |
| | | | being used to |
| | | | discipline the |
| | | | local |
| | | | oscillator. |
+------------+---------+---------+------------------+
| | | | |
|delta | Yes | numeric | The time |
| | | | difference (in |
| | | | nanoseconds) |
| | | | between the |
| | | | GPS-disciplined |
| | | | oscillator PPS |
| | | | output pulse and |
| | | | the most recent |
| | | | GPS PPS input |
| | | | pulse. |
+------------+---------+---------+------------------+
Here's an example:
{"class":"OSC","running":true,"device":"/dev/ttyUSB0",
"reference":true,"disciplined":true,"delta":67}
CORE PROTOCOL COMMANDS
And here are the commands you can send to gpsd.
?VERSION;
Returns an object with the following attributes:
Table 10. VERSION object
+------------+---------+---------+------------------+
| | | | |
|Name | Always? | Type | Description |
+------------+---------+---------+------------------+
| | | | |
|class | Yes | string | Fixed: "VERSION" |
+------------+---------+---------+------------------+
| | | | |
|release | Yes | string | Public release |
| | | | level |
+------------+---------+---------+------------------+
| | | | |
|rev | Yes | string | Internal |
| | | | revision-control |
| | | | level. |
+------------+---------+---------+------------------+
| | | | |
|proto_major | Yes | numeric | API major |
| | | | revision level. |
+------------+---------+---------+------------------+
| | | | |
|proto_minor | Yes | numeric | API minor |
| | | | revision level. |
+------------+---------+---------+------------------+
| | | | |
|remote | No | string | URL of the |
| | | | remote daemon |
| | | | reporting this |
| | | | version. If |
| | | | empty, this is |
| | | | the version of |
| | | | the local |
| | | | daemon. |
+------------+---------+---------+------------------+
The daemon ships a VERSION response to each client when the client
first connects to it.
When the C client library parses a response of this kind, it will
assert the VERSION_SET bit in the top-level set member.
Here's an example:
{"class":"VERSION","version":"2.40dev",
"rev":"06f62e14eae9886cde907dae61c124c53eb1101f",
"proto_major":3,"proto_minor":1
}
?DEVICES;
Returns a device list object with the following elements:
Table 11. DEVICES object
+--------+---------+--------+------------------+
| | | | |
|Name | Always? | Type | Description |
+--------+---------+--------+------------------+
| | | | |
|class | Yes | string | Fixed: "DEVICES" |
+--------+---------+--------+------------------+
| | | | |
|devices | Yes | list | List of device |
| | | | descriptions |
+--------+---------+--------+------------------+
| | | | |
|remote | No | string | URL of the |
| | | | remote daemon |
| | | | reporting the |
| | | | device set. If |
| | | | empty, this is a |
| | | | DEVICES response |
| | | | from the local |
| | | | daemon. |
+--------+---------+--------+------------------+
When the C client library parses a response of this kind, it will
assert the DEVICELIST_SET bit in the top-level set member.
Here's an example:
{"class"="DEVICES","devices":[
{"class":"DEVICE","path":"/dev/pts/1","flags":1,"driver":"SiRF binary"},
{"class":"DEVICE","path":"/dev/pts/3","flags":4,"driver":"AIVDM"}]}
The daemon occasionally ships a bare DEVICE object to the client (that
is, one not inside a DEVICES wrapper). The data content of these
objects will be described later as a response to the ?DEVICE command.
?WATCH;
This command sets watcher mode. It also sets or elicits a report of
per-subscriber policy and the raw bit. An argument WATCH object changes
the subscriber's policy. The response describes the subscriber's
policy. The response will also include a DEVICES object.
A WATCH object has the following elements:
Table 12. WATCH object
+--------+---------+---------+------------------+
| | | | |
|Name | Always? | Type | Description |
+--------+---------+---------+------------------+
| | | | |
|class | Yes | string | Fixed: "WATCH" |
+--------+---------+---------+------------------+
| | | | |
|enable | No | boolean | Enable (true) or |
| | | | disable (false) |
| | | | watcher mode. |
| | | | Default is true. |
+--------+---------+---------+------------------+
| | | | |
|json | No | boolean | Enable (true) or |
| | | | disable (false) |
| | | | dumping of JSON |
| | | | reports. Default |
| | | | is false. |
+--------+---------+---------+------------------+
| | | | |
|nmea | No | boolean | Enable (true) or |
| | | | disable (false) |
| | | | dumping of |
| | | | binary packets |
| | | | as pseudo-NMEA. |
| | | | Default is |
| | | | false. |
+--------+---------+---------+------------------+
| | | | |
|raw | No | integer | Controls 'raw' |
| | | | mode. When this |
| | | | attribute is set |
| | | | to 1 for a |
| | | | channel, gpsd |
| | | | reports the |
| | | | unprocessed NMEA |
| | | | or AIVDM data |
| | | | stream from |
| | | | whatever device |
| | | | is attached. |
| | | | Binary GPS |
| | | | packets are |
| | | | hex-dumped. |
| | | | RTCM2 and RTCM3 |
| | | | packets are not |
| | | | dumped in raw |
| | | | mode. When this |
| | | | attribute is set |
| | | | to 2 for a |
| | | | channel that |
| | | | processes binary |
| | | | data, gpsd |
| | | | reports the |
| | | | received data |
| | | | verbatim without |
| | | | hex-dumping. |
+--------+---------+---------+------------------+
| | | | |
|scaled | No | boolean | If true, apply |
| | | | scaling divisors |
| | | | to output before |
| | | | dumping; default |
| | | | is false. |
+--------+---------+---------+------------------+
| | | | |
|split24 | No | boolean | If true, |
| | | | aggregate AIS |
| | | | type24 sentence |
| | | | parts. If false, |
| | | | report each part |
| | | | as a separate |
| | | | JSON object, |
| | | | leaving the |
| | | | client to match |
| | | | MMSIs and |
| | | | aggregate. |
| | | | Default is |
| | | | false. Applies |
| | | | only to AIS |
| | | | reports. |
+--------+---------+---------+------------------+
| | | | |
|pps | No | boolean | If true, emit |
| | | | the TOFF JSON |
| | | | message on each |
| | | | cycle and a PPS |
| | | | JSON message |
| | | | when the device |
| | | | issues 1PPS. |
| | | | Default is |
| | | | false. |
+--------+---------+---------+------------------+
| | | | |
|device | No | string | If present, |
| | | | enable watching |
| | | | only of the |
| | | | specified device |
| | | | rather than all |
| | | | devices. Useful |
| | | | with raw and |
| | | | NMEA modes in |
| | | | which device |
| | | | responses aren't |
| | | | tagged. Has no |
| | | | effect when used |
| | | | with |
| | | | enable:false. |
+--------+---------+---------+------------------+
| | | | |
|remote | No | string | URL of the |
| | | | remote daemon |
| | | | reporting the |
| | | | watch set. If |
| | | | empty, this is a |
| | | | WATCH response |
| | | | from the local |
| | | | daemon. |
+--------+---------+---------+------------------+
There is an additional boolean "timing" attribute which is undocumented
because that portion of the interface is considered unstable and for
developer use only.
In watcher mode, GPS reports are dumped as TPV and SKY responses. AIS,
Subframe and RTCM reporting is described in the next section.
When the C client library parses a response of this kind, it will
assert the POLICY_SET bit in the top-level set member.
Here's an example:
{"class":"WATCH", "raw":1,"scaled":true}
?POLL;
The POLL command requests data from the last-seen fixes on all active
GPS devices. Devices must previously have been activated by ?WATCH to
be pollable.
Polling can lead to possibly surprising results when it is used on a
device such as an NMEA GPS for which a complete fix has to be
accumulated from several sentences. If you poll while those sentences
are being emitted, the response will contain only the fix data
collected so far in the current epoch. It may be as much as one cycle
time (typically 1 second) stale.
The POLL response will contain a timestamped list of TPV objects
describing cached data, and a timestamped list of SKY objects
describing satellite configuration. If a device has not seen fixes, it
will be reported with a mode field of zero.
Table 13. POLL object
+-------+---------+------------+------------------+
| | | | |
|Name | Always? | Type | Description |
+-------+---------+------------+------------------+
| | | | |
|class | Yes | string | Fixed: "POLL" |
+-------+---------+------------+------------------+
| | | | |
|time | Yes | Numeric | Timestamp in ISO |
| | | | 8601 format. May |
| | | | have a |
| | | | fractional part |
| | | | of up to .001sec |
| | | | precision. |
+-------+---------+------------+------------------+
| | | | |
|active | Yes | Numeric | Count of active |
| | | | devices. |
+-------+---------+------------+------------------+
| | | | |
|tpv | Yes | JSON array | Comma-separated |
| | | | list of TPV |
| | | | objects. |
+-------+---------+------------+------------------+
| | | | |
|sky | Yes | JSON array | Comma-separated |
| | | | list of SKY |
| | | | objects. |
+-------+---------+------------+------------------+
Here's an example of a POLL response:
{"class":"POLL","time":"2010-06-04T10:31:00.289Z","active":1,
"tpv":[{"class":"TPV","device":"/dev/ttyUSB0",
"time":"2010-09-08T13:33:06.095Z",
"ept":0.005,"lat":40.035093060,
"lon":-75.519748733,"track":99.4319,"speed":0.123,"mode":2}],
"sky":[{"class":"SKY","device":"/dev/ttyUSB0",
"time":1270517264.240,"hdop":9.20,
"satellites":[{"PRN":16,"el":55,"az":42,"ss":36,"used":true},
{"PRN":19,"el":25,"az":177,"ss":0,"used":false},
{"PRN":7,"el":13,"az":295,"ss":0,"used":false},
{"PRN":6,"el":56,"az":135,"ss":32,"used":true},
{"PRN":13,"el":47,"az":304,"ss":0,"used":false},
{"PRN":23,"el":66,"az":259,"ss":0,"used":false},
{"PRN":20,"el":7,"az":226,"ss":0,"used":false},
{"PRN":3,"el":52,"az":163,"ss":32,"used":true},
{"PRN":31,"el":16,"az":102,"ss":0,"used":false}
]}]}
Note
Client software should not assume the field inventory of the POLL
response is fixed for all time. As gpsd collects and caches more
data from more sensor types, those data are likely to find their
way into this response.
?DEVICE; ?DEVICE=
This command reports (when followed by ';') the state of a device, or
sets (when followed by '=' and a DEVICE object) device-specific control
bits, notably the device's speed and serial mode and the native-mode
bit. The parameter-setting form will be rejected if more than one
client is attached to the channel and a device path is not specified.
Pay attention to the response, because it is possible for this command
to fail if the GPS does not support a command or only supports some
combinations of modes. In case of failure, the daemon and GPS will
continue to communicate at the old speed.
Use the parameter-setting form with caution. On USB and Bluetooth GPSes
it is also possible for serial mode setting to fail either because the
serial adaptor chip does not support non-8N1 modes or because the
device firmware does not properly synchronize the serial adaptor chip
with the UART on the GPS chipset when the speed changes. These failures
can hang your device, possibly requiring a GPS power cycle or (in
extreme cases) physically disconnecting the NVRAM backup battery.
A DEVICE object has the following elements:
Table 14. DEVICE object
+----------+---------+---------+------------------+
| | | | |
|Name | Always? | Type | Description |
+----------+---------+---------+------------------+
| | | | |
|class | Yes | string | Fixed: "DEVICE" |
+----------+---------+---------+------------------+
| | | | |
|activated | No | string | Time the device |
| | | | was activated as |
| | | | an ISO8601 time |
| | | | stamp. If the |
| | | | device is |
| | | | inactive this |
| | | | attribute is |
| | | | absent. |
+----------+---------+---------+------------------+
| | | | |
|bps | No | integer | Device speed in |
| | | | bits per second. |
+----------+---------+---------+------------------+
| | | | |
|cycle | No | real | Device cycle |
| | | | time in seconds. |
+----------+---------+---------+------------------+
| | | | |
|driver | No | string | GPSD's name for |
| | | | the device |
| | | | driver type. |
| | | | Won't be |
| | | | reported before |
| | | | gpsd has seen |
| | | | identifiable |
| | | | packets from the |
| | | | device. |
+----------+---------+---------+------------------+
| | | | |
|flags | No | integer | Bit vector of |
| | | | property flags. |
| | | | Currently |
| | | | defined flags |
| | | | are: describe |
| | | | packet types |
| | | | seen so far |
| | | | (GPS, RTCM2, |
| | | | RTCM3, AIS). |
| | | | Won't be |
| | | | reported if |
| | | | empty, e.g. |
| | | | before gpsd has |
| | | | seen |
| | | | identifiable |
| | | | packets from the |
| | | | device. |
+----------+---------+---------+------------------+
| | | | |
|hexdata | No | string | Data, in bare |
| | | | hexadecimal, to |
| | | | send to the GNSS |
| | | | receiver. |
+----------+---------+---------+------------------+
| | | | |
|mincycle | No | real | Device minimum |
| | | | cycle time in |
| | | | seconds. |
| | | | Reported from |
| | | | ?DEVICE when |
| | | | (and only when) |
| | | | the rate is |
| | | | switchable. It |
| | | | is read-only and |
| | | | not settable. |
+----------+---------+---------+------------------+
| | | | |
|native | No | integer | 0 means NMEA |
| | | | mode and 1 means |
| | | | alternate mode |
| | | | (binary if it |
| | | | has one, for |
| | | | SiRF and |
| | | | Evermore |
| | | | chipsets in |
| | | | particular). |
| | | | Attempting to |
| | | | set this mode on |
| | | | a non-GPS device |
| | | | will yield an |
| | | | error. |
+----------+---------+---------+------------------+
| | | | |
|parity | No | string | N, O or E for no |
| | | | parity, odd, or |
| | | | even. |
+----------+---------+---------+------------------+
| | | | |
|path | No | string | Name the device |
| | | | for which the |
| | | | control bits are |
| | | | being reported, |
| | | | or for which |
| | | | they are to be |
| | | | applied. This |
| | | | attribute may be |
| | | | omitted only |
| | | | when there is |
| | | | exactly one |
| | | | subscribed |
| | | | channel. |
+----------+---------+---------+------------------+
| | | | |
|readonly | No | boolean | True if device |
| | | | is read-only. |
+----------+---------+---------+------------------+
| | | | |
|stopbits | Yes | string | Stop bits (1 or |
| | | | 2). |
+----------+---------+---------+------------------+
| | | | |
|subtype | No | string | Whatever version |
| | | | information the |
| | | | device driver |
| | | | returned. |
+----------+---------+---------+------------------+
| | | | |
|subtype1 | No | string | More version |
| | | | information the |
| | | | device driver |
| | | | returned. |
+----------+---------+---------+------------------+
The serial parameters will (bps, parity, stopbits) be omitted in a
response describing a TCP/IP source such as an Ntrip, DGPSIP, or AIS
feed; on a serial device they will always be present.
The contents of the flags field should be interpreted as follows:
Table 15. Device flags
+-----------+-------+---------------------+
| | | |
|C #define | Value | Description |
+-----------+-------+---------------------+
| | | |
|SEEN_GPS | 0x01 | GPS data has been |
| | | seen on this device |
+-----------+-------+---------------------+
| | | |
|SEEN_RTCM2 | 0x02 | RTCM2 data has been |
| | | seen on this device |
+-----------+-------+---------------------+
| | | |
|SEEN_RTCM3 | 0x04 | RTCM3 data has been |
| | | seen on this device |
+-----------+-------+---------------------+
| | | |
|SEEN_AIS | 0x08 | AIS data has been |
| | | seen on this device |
+-----------+-------+---------------------+
When the C client library parses a response of this kind, it will
assert the DEVICE_SET bit in the top-level set member.
Here's an example:
{"class":"DEVICE","bps":4800,"parity":"N","stopbits":1,"native":0}
When a client is in watcher mode, the daemon will ship it DEVICE
notifications when a device is added to the pool or deactivated.
When the C client library parses a response of this kind, it will
assert the DEVICE_SET bit in the top-level set member.
Examples
A notice of a deactivated device:
{"class":"DEVICE","path":"/dev/pts1","activated":0}
A send a u-blox receiver at /dev/ttyUSB2 a request for a UBX-MON-VER
message:
?DEVICE={"path":"/dev/ttyUSB2","hexdata":"b5620a0400000e34"}
The gpsd daemon will respond with an ACK on success:
{"class":"ACK"}
ERROR
The daemon may ship an error object in response to a syntactically
invalid command line or unknown command. It has the following elements:
Table 16. ERROR notification object
+--------+---------+--------+----------------+
| | | | |
|Name | Always? | Type | Description |
+--------+---------+--------+----------------+
| | | | |
|class | Yes | string | Fixed: "ERROR" |
+--------+---------+--------+----------------+
| | | | |
|message | Yes | string | Textual error |
| | | | message |
+--------+---------+--------+----------------+
Here's an example:
{"class":"ERROR","message":"Unrecognized request '?FOO'"}
When the C client library parses a response of this kind, it will
assert the ERR_SET bit in the top-level set member.
RTCM2
RTCM-104 is a family of serial protocols used for broadcasting
pseudorange corrections from differential-GPS reference stations. Many
GPS receivers can accept these corrections to improve their reporting
accuracy.
RTCM-104 comes in two major and incompatible flavors, 2.x and 3.x. Each
major flavor has minor (compatible) revisions.
The applicable standard for RTCM Version 2.x is RTCM Recommended
Standards for Differential NAVSTAR GPS Service RTCM Paper 194-93/SC
104-STD. For RTCM 3.1 it is RTCM Paper 177-2006-SC104-STD. Ordering
instructions for both standards are accessible from the website of the
Radio Technical Commission for Maritime Services
<https://www.rtcm.org/> under "Publications".
RTCM WIRE TRANSMISSIONS
Differential-GPS correction stations consist of a GPS reference
receiver coupled to a low frequency (LF) transmitter. The GPS reference
receiver is a survey-grade GPS that does GPS carrier tracking and can
work out its position to a few millimeters. It generates range and
range-rate corrections and encodes them into RTCM104. It ships the
RTCM104 to the LF transmitter over serial rs-232 signal at 100 baud or
200 baud depending on the requirements of the transmitter.
The LF transmitter broadcasts the approximately 300khz radio signal
that differential-GPS radio receivers pick up. Transmitters that are
meant to have a higher range will need to transmit at a slower rate.
The higher the data rate the harder it will be for the remote radio
receiver to receive with a good signal-to-noise ration. (Higher data
rate signals can't be averaged over as long a time frame, hence they
appear noisier.)
RTCM WIRE FORMATS
An RTCM 2.x message consists of a sequence of up to 33 30-bit words.
The 24 most significant bits of each word are data and the six least
significant bits are parity. The parity algorithm used is the same
ISGPS-2000 as that used on GPS satellite downlinks. Each RTCM 2.x
message consists of two header words followed by zero or more data
words, depending upon the message type.
An RTCM 3.x message begins with a fixed leader byte 0xD3. That is
followed by six bits of version information and 10 bits of payload
length information. Following that is the payload; following the
payload is a 3-byte checksum of the payload using the Qualcomm CRC-24Q
algorithm.
RTCM2 JSON FORMAT
Each RTCM2 message is dumped as a single JSON object per message, with
the message fields as attributes of that object. Arrays of satellite,
station, and constellation statistics become arrays of JSON
sub-objects. Each sentence will normally also have a "device" field
containing the pathname of the originating device.
All attributes other than the device field are mandatory. Header
attributes are emitted before others.
Header portion
Table 17. SKY object
+---------------+---------+---------------------------------------------+
| | | |
|Name | Type | Description |
+---------------+---------+---------------------------------------------+
| | | |
|class | string | Fixed: "RTCM2". |
+---------------+---------+---------------------------------------------+
| | | |
|type | integer | Message type (1-9). |
+---------------+---------+---------------------------------------------+
| | | |
|station_id | integer | The id of the GPS |
| | | reference receiver. |
| | | The LF transmitters |
| | | also have |
| | | (different) id |
| | | numbers. |
+---------------+---------+---------------------------------------------+
| | | |
|zcount | real | The reference time |
| | | of the corrections |
| | | in the message in |
| | | seconds within the |
| | | current hour. Note |
| | | that it is in GPS |
| | | time, which is some |
| | | seconds ahead of |
| | | UTC (see the U.S. |
| | | Naval Observatory's |
| | | table of leap |
| | | second |
| | | <ftp://maia.usno.navy.mil/ser7/tai-utc.dat> |
| | | corrections" ). |
+---------------+---------+---------------------------------------------+
| | | |
|seqnum | integer | Sequence number. Only 3 bits wide, wraps |
| | | after 7. |
+---------------+---------+---------------------------------------------+
| | | |
|length | integer | The number of words after the header that |
| | | comprise the message. |
+---------------+---------+---------------------------------------------+
| | | |
|station_health | integer | Station transmission status. Indicates the |
| | | health of the beacon as a reference source. |
| | | Any nonzero value means the satellite is |
| | | probably transmitting bad data and should |
| | | not be used in a fix. 6 means the |
| | | transmission is unmonitored. 7 means the |
| | | station is not working properly. Other |
| | | values are defined by the beacon operator. |
+---------------+---------+---------------------------------------------+
<message type> is one of
1
full corrections -- one message containing corrections for all GPS
satellites in view. This is not common.
3
reference station parameters -- the position of the reference
station GPS antenna.
4
datum -- the datum to which the DGPS data is referred.
5
constellation health -- information about the satellites the beacon
can see.
6
null message -- just a filler.
7
radio beacon almanac -- information about this or other beacons.
9
subset corrections -- a message containing corrections for only a
subset of the GPS satellites in view.
16
special message -- a text message from the beacon operator.
31
GLONASS subset corrections -- a message containing corrections for
a set of the GLONASS satellites in view.
Type 1 and 9: Correction data
One or more satellite objects follow the header for type 1 or type 9
messages. Here is the format:
Table 18. Satellite object
+------+---------+---------------------+
| | | |
|Name | Type | Description |
+------+---------+---------------------+
| | | |
|ident | integer | The PRN number of |
| | | the satellite for |
| | | which this is |
| | | correction data. |
+------+---------+---------------------+
| | | |
|udre | integer | User Differential |
| | | Range Error (0-3). |
| | | See the table |
| | | following for |
| | | values. |
+------+---------+---------------------+
| | | |
|iod | integer | Issue Of Data, |
| | | matching the IOD |
| | | for the current |
| | | ephemeris of this |
| | | satellite, as |
| | | transmitted by the |
| | | satellite. The IOD |
| | | is a unique tag |
| | | that identifies the |
| | | ephemeris; the GPS |
| | | using the DGPS |
| | | correction and the |
| | | DGPS generating the |
| | | data must use the |
| | | same orbital |
| | | positions for the |
| | | satellite. |
+------+---------+---------------------+
| | | |
|prc | real | The pseudorange |
| | | error in meters for |
| | | this satellite as |
| | | measured by the |
| | | beacon reference |
| | | receiver at the |
| | | epoch indicated by |
| | | the z_count in the |
| | | parent record. |
+------+---------+---------------------+
| | | |
|rrc | real | The rate of change |
| | | of pseudorange |
| | | error in meters/sec |
| | | for this satellite |
| | | as measured by the |
| | | beacon reference |
| | | receiver at the |
| | | epoch indicated by |
| | | the z_count field |
| | | in the parent |
| | | record. This is |
| | | used to calculate |
| | | pseudorange errors |
| | | at other epochs, if |
| | | required by the GPS |
| | | receiver. |
+------+---------+---------------------+
User Differential Range Error values are as follows:
Table 19. UDRE values
+--+----------------------+
| | |
|0 | 1-sigma error <= 1 m |
+--+----------------------+
| | |
|1 | 1-sigma error <= 4 m |
+--+----------------------+
| | |
|2 | 1-sigma error <= 8 m |
+--+----------------------+
| | |
|3 | 1-sigma error > 8 m |
+--+----------------------+
Here's an example:
{"class":"RTCM2","type":1,
"station_id":688,"zcount":843.0,"seqnum":5,"length":19,"station_health":6,
"satellites":[
{"ident":10,"udre":0,"iod":46,"prc":-2.400,"rrc":0.000},
{"ident":13,"udre":0,"iod":94,"prc":-4.420,"rrc":0.000},
{"ident":7,"udre":0,"iod":22,"prc":-5.160,"rrc":0.002},
{"ident":2,"udre":0,"iod":34,"prc":-6.480,"rrc":0.000},
{"ident":4,"udre":0,"iod":47,"prc":-8.860,"rrc":0.000},
{"ident":8,"udre":0,"iod":76,"prc":-7.980,"rrc":0.002},
{"ident":5,"udre":0,"iod":99,"prc":-8.260,"rrc":0.002},
{"ident":23,"udre":0,"iod":81,"prc":-8.060,"rrc":0.000},
{"ident":16,"udre":0,"iod":70,"prc":-11.740,"rrc":0.000},
{"ident":30,"udre":0,"iod":4,"prc":-18.960,"rrc":-0.006},
{"ident":29,"udre":0,"iod":101,"prc":-24.960,"rrc":-0.002}
]}
Type 3: Reference Station Parameters
Here are the payload members of a type 3 (Reference Station Parameters)
message:
Table 20. Reference Station Parameters
+-----+------+--------------------+
| | | |
|Name | Type | Description |
+-----+------+--------------------+
| | | |
|x | real | ECEF X coordinate. |
+-----+------+--------------------+
| | | |
|y | real | ECEF Y coordinate. |
+-----+------+--------------------+
| | | |
|z | real | ECEF Z coordinate. |
+-----+------+--------------------+
The coordinates are the position of the station, in meters to two
decimal places, in Earth Centred Earth Fixed coordinates. These are
usually referred to the WGS84 reference frame, but may be referred to
NAD83 in the US (essentially identical to WGS84 for all except
geodesists), or some other reference frame in other parts of the world.
An invalid reference message is represented by a type 3 header without
payload fields.
Here's an example:
{"class":"RTCM2","type":3,
"station_id":652,"zcount":1657.2,"seqnum":2,"length":4,"station_health":6,
"x":3878620.92,"y":670281.40,"z":5002093.59
}
Type 4: Datum
Here are the payload members of a type 4 (Datum) message:
Table 21. Datum
+-----------+---------+---------------------+
| | | |
|Name | Type | Description |
+-----------+---------+---------------------+
| | | |
|dgnss_type | string | Either "GPS", |
| | | "GLONASS", |
| | | "GALILEO", or |
| | | "UNKNOWN". |
+-----------+---------+---------------------+
| | | |
|dat | integer | 0 or 1 and |
| | | indicates the sense |
| | | of the offset shift |
| | | given by dx, dy, |
| | | dz. dat = 0 means |
| | | that the station |
| | | coordinates (in the |
| | | reference message) |
| | | are referred to a |
| | | local datum and |
| | | that adding dx, dy, |
| | | dz to that position |
| | | will render it in |
| | | GNSS coordinates |
| | | (WGS84 for GPS). If |
| | | dat = 1 then the |
| | | ref station |
| | | position is in GNSS |
| | | coordinates and |
| | | adding dx, dy, dz |
| | | will give it |
| | | referred to the |
| | | local datum. |
+-----------+---------+---------------------+
| | | |
|datum_name | string | A standard name for |
| | | the datum. |
+-----------+---------+---------------------+
| | | |
|dx | real | X offset. |
+-----------+---------+---------------------+
| | | |
|dy | real | Y offset. |
+-----------+---------+---------------------+
| | | |
|dz | real | Z offset. |
+-----------+---------+---------------------+
<dx> <dy> <dz> are offsets to convert from local datum to GNSS datum or
vice versa. These fields are optional.
An invalid datum message is represented by a type 4 header without
payload fields.
Type 5: Constellation Health
One or more of these follow the header for type 5 messages -- one for
each satellite.
Here is the format:
Table 22. Constellation health
+------------+---------+---------------------+
| | | |
|Name | Type | Description |
+------------+---------+---------------------+
| | | |
|ident | integer | The PRN number of |
| | | the satellite. |
+------------+---------+---------------------+
| | | |
|iodl | bool | True indicates that |
| | | this information |
| | | relates to the |
| | | satellite |
| | | information in an |
| | | accompanying type 1 |
| | | or type 9 message. |
+------------+---------+---------------------+
| | | |
|health | integer | 0 indicates that |
| | | the satellite is |
| | | healthy. Any other |
| | | value indicates a |
| | | problem (coding is |
| | | not known). |
+------------+---------+---------------------+
| | | |
|snr | integer | The carrier/noise |
| | | ratio of the |
| | | received signal in |
| | | the range 25 to 55 |
| | | dB(Hz). |
+------------+---------+---------------------+
| | | |
|health_en | bool | If set to True it |
| | | indicates that the |
| | | satellite is |
| | | healthy even if the |
| | | satellite |
| | | navigation data |
| | | says it is |
| | | unhealthy. |
+------------+---------+---------------------+
| | | |
|new_data | bool | True indicates that |
| | | the IOD for this |
| | | satellite will soon |
| | | be updated in type |
| | | 1 or 9 messages. |
+------------+---------+---------------------+
| | | |
|los_warning | bool | Line-of-sight |
| | | warning. True |
| | | indicates that the |
| | | satellite will |
| | | shortly go |
| | | unhealthy. |
+------------+---------+---------------------+
| | | |
|tou | integer | Healthy time |
| | | remaining in |
| | | seconds. |
+------------+---------+---------------------+
Type 6: Null
This just indicates a null message. There are no payload fields.
Unknown message
This format is used to dump message words in hexadecimal when the
message type field doesn't match any of the known ones.
Here is the format:
Table 23. Unknown Message
+-----+------+--------------------+
| | | |
|Name | Type | Description |
+-----+------+--------------------+
| | | |
|data | list | A list of strings. |
+-----+------+--------------------+
Each string in the array is a hex literal representing 30 bits of
information, after parity checks and inversion. The high two bits
should be ignored.
Type 7: Radio Beacon Almanac
Here is the format:
Table 24. Constellation health
+-----------+---------+---------------------+
| | | |
|Name | Type | Description |
+-----------+---------+---------------------+
| | | |
|lat | real | Latitude in |
| | | degrees, of the LF |
| | | transmitter antenna |
| | | for the station for |
| | | which this is an |
| | | almanac. North is |
| | | positive. |
+-----------+---------+---------------------+
| | | |
|lon | real | Longitude in |
| | | degrees, of the LF |
| | | transmitter antenna |
| | | for the station for |
| | | which this is an |
| | | almanac. East is |
| | | positive. |
+-----------+---------+---------------------+
| | | |
|range | integer | Published range of |
| | | the station in km. |
+-----------+---------+---------------------+
| | | |
|frequency | real | Station broadcast |
| | | frequency in kHz. |
+-----------+---------+---------------------+
| | | |
|health | integer | <health> is the |
| | | health of the |
| | | station for which |
| | | this is an almanac. |
| | | If it is non-zero, |
| | | the station is |
| | | issuing suspect |
| | | data and should not |
| | | be used for fixes. |
| | | The ITU and RTCM104 |
| | | standards differ |
| | | about the mode |
| | | detailed |
| | | interpretation of |
| | | the <health> field |
| | | and even about its |
| | | bit width. |
+-----------+---------+---------------------+
| | | |
|station_id | integer | The id of the |
| | | transmitter. This |
| | | is not the same as |
| | | the reference id in |
| | | the header, the |
| | | latter being the id |
| | | of the reference |
| | | receiver. |
+-----------+---------+---------------------+
| | | |
|bitrate | integer | The transmitted |
| | | bitrate. |
+-----------+---------+---------------------+
Here's an example:
{"class":"RTCM2","type":9,"station_id":268,"zcount":252.6,
"seqnum":4,"length":5,"station_health":0,
"satellites":[
{"ident":13,"udre":0,"iod":3,"prc":-25.940,"rrc":0.066},
{"ident":2,"udre":0,"iod":73,"prc":0.920,"rrc":-0.080},
{"ident":8,"udre":0,"iod":22,"prc":23.820,"rrc":0.014}
]}
Type 13: GPS Time of Week
Here are the payload members of a type 13 (Groumf Tramitter Parameters)
message:
Table 25. Ground Transmitter Parameters
+----------+---------+---------------------+
| | | |
|Name | Type | Description |
+----------+---------+---------------------+
| | | |
|status | bool | If True, signals |
| | | user to expect a |
| | | type 16 explanatory |
| | | message associated |
| | | with this station. |
| | | Probably indicates |
| | | some sort of |
| | | unusual event. |
+----------+---------+---------------------+
| | | |
|rangeflag | bool | If True, indicates |
| | | that the estimated |
| | | range is different |
| | | from that found in |
| | | the type 7 message |
| | | (which contains the |
| | | beacon's listed |
| | | range). Generally |
| | | indicates a range |
| | | reduction due to |
| | | causes such as poor |
| | | ionospheric |
| | | conditions or |
| | | reduced |
| | | transmission power. |
+----------+---------+---------------------+
| | | |
|lat | real | Degrees latitude, |
| | | signed. Positive is |
| | | N, negative is S. |
+----------+---------+---------------------+
| | | |
|lon | real | Degrees longitude, |
| | | signed. Positive is |
| | | E, negative is W. |
+----------+---------+---------------------+
| | | |
|range | integer | Transmission range |
| | | in km (1-1024). |
+----------+---------+---------------------+
This message type replaces message type 3 (Reference Station
Parameters) in RTCM 2.3.
Type 14: GPS Time of Week
Here are the payload members of a type 14 (GPS Time of Week) message:
Table 26. Reference Station Parameters
+---------+---------+-------------------+
| | | |
|Name | Type | Description |
+---------+---------+-------------------+
| | | |
|week | integer | GPS week (0-123). |
+---------+---------+-------------------+
| | | |
|hour | integer | Hour of week |
| | | (0-167). |
+---------+---------+-------------------+
| | | |
|leapsecs | integer | Leap Seconds |
| | | (0-63). |
+---------+---------+-------------------+
Here's an example:
{"class":"RTCM2","type":14,"station_id":652,"zcount":1657.2,
"seqnum":3,"length":1,"station_health":6,"week":601,"hour":109,
"leapsecs":15}
Type 16: Special Message
Table 27. Special Message
+--------+--------+---------------------+
| | | |
|Name | Type | Description |
+--------+--------+---------------------+
| | | |
|message | string | A text message sent |
| | | by the beacon |
| | | operator. |
+--------+--------+---------------------+
Type 31: Correction data
One or more GLONASS satellite objects follow the header for type 1 or
type 9 messages. Here is the format:
Table 28. Satellite object
+-------+----------+---------------------+
| | | |
|Name | Type | Description |
+-------+----------+---------------------+
| | | |
|ident | integer | The PRN number of |
| | | the satellite for |
| | | which this is |
| | | correction data. |
+-------+----------+---------------------+
| | | |
|udre | integer | User Differential |
| | | Range Error (0-3). |
| | | See the table |
| | | following for |
| | | values. |
+-------+----------+---------------------+
| | | |
|change | boolean | Change-of-ephemeris |
| | | bit. |
+-------+----------+---------------------+
| | | |
|tod | uinteger | Count of 30-second |
| | | periods since the |
| | | top of the hour. |
+-------+----------+---------------------+
| | | |
|prc | real | The pseudorange |
| | | error in meters for |
| | | this satellite as |
| | | measured by the |
| | | beacon reference |
| | | receiver at the |
| | | epoch indicated by |
| | | the z_count in the |
| | | parent record. |
+-------+----------+---------------------+
| | | |
|rrc | real | The rate of change |
| | | of pseudorange |
| | | error in meters/sec |
| | | for this satellite |
| | | as measured by the |
| | | beacon reference |
| | | receiver at the |
| | | epoch indicated by |
| | | the z_count field |
| | | in the parent |
| | | record. This is |
| | | used to calculate |
| | | pseudorange errors |
| | | at other epochs, if |
| | | required by the GPS |
| | | receiver. |
+-------+----------+---------------------+
Here's an example:
{"class":"RTCM2","type":31,"station_id":652,"zcount":1642.2,
"seqnum":0,"length":14,"station_health":6,
"satellites":[
{"ident":5,"udre":0,"change":false,"tod":0,"prc":132.360,"rrc":0.000},
{"ident":15,"udre":0,"change":false,"tod":0,"prc":134.840,"rrc":0.002},
{"ident":14,"udre":0,"change":false,"tod":0,"prc":141.520,"rrc":0.000},
{"ident":6,"udre":0,"change":false,"tod":0,"prc":127.000,"rrc":0.000},
{"ident":21,"udre":0,"change":false,"tod":0,"prc":128.780,"rrc":0.000},
{"ident":22,"udre":0,"change":false,"tod":0,"prc":125.260,"rrc":0.002},
{"ident":20,"udre":0,"change":false,"tod":0,"prc":117.280,"rrc":-0.004},
{"ident":16,"udre":0,"change":false,"tod":17,"prc":113.460,"rrc":0.018}
]}
RTCM3 DUMP FORMAT
The support for RTCM104v3 dumping is incomplete and buggy. Do not
attempt to use it for production! Anyone interested in it should read
the source code.
AIS DUMP FORMATS
AIS support is an extension. It may not be present if your instance of
gpsd has been built with a restricted feature set.
AIS packets are dumped as JSON objects with class "AIS". Each AIS
report object contains a "type" field giving the AIS message type and a
"scaled" field telling whether the remainder of the fields are dumped
in scaled or unscaled form. (These will be emitted before any
type-specific fields.) It will also contain a "device" field naming the
data source. Other fields have names and types as specified in the
AIVDM/AIVDO Protocol Decoding document on the GPSD project website;
each message field table may be directly interpreted as a specification
for the members of the corresponding JSON object type.
By default, certain scaling and conversion operations are performed for
JSON output. Latitudes and longitudes are scaled to decimal degrees
rather than the native AIS unit of 1/10000th of a minute of arc. Ship
(but not air) speeds are scaled to knots rather than tenth-of-knot
units. Rate of turn may appear as "nan" if is unavailable, or as one of
the strings "fastright" or "fastleft" if it is out of the AIS encoding
range; otherwise it is quadratically mapped back to the turn sensor
number in degrees per minute. Vessel draughts are converted to decimal
meters rather than native AIS decimeters. Various other scaling
conversions are described in "AIVDM/AIVDO Protocol Decoding".
SUBFRAME DUMP FORMATS
Subframe support is always compiled into gpsd but many GPSes do not
output subframe data or the gpsd driver may not support subframes.
Subframe packets are dumped as JSON objects with class "SUBFRAME". Each
subframe report object contains a "frame" field giving the subframe
number, a "tSV" field for the transmitting satellite number, a "TOW17"
field containing the 17 MSBs of the start of the next 12-second message
and a "scaled" field telling whether the remainder of the fields are
dumped in scaled or unscaled form. It will also contain a "device"
field naming the data source. Each SUBFRAME object will have a
sub-object specific to that subframe page type. Those sub-object fields
have names and types similar to those specified in the IS-GPS-200
document; each message field table may be directly interpreted as a
specification for the members of the corresponding JSON object type.
Table 29. SUBFRAME object
+-------+---------+---------+------------------+
| | | | |
|Name | Always? | Type | Description |
+-------+---------+---------+------------------+
| | | | |
|class | Yes | string | Fixed: |
| | | | "SUBFRAME" |
+-------+---------+---------+------------------+
| | | | |
|device | Yes | string | Name of the |
| | | | originating |
| | | | device. |
+-------+---------+---------+------------------+
| | | | |
|gnssId | Yes | integer | Constellation of |
| | | | transmitting |
| | | | satellite |
+-------+---------+---------+------------------+
| | | | |
|tSV | Yes | integer | ID of |
| | | | transmitting |
| | | | satellite (Not |
| | | | PRN) |
+-------+---------+---------+------------------+
| | | | |
|TOW17 | No | integer | Type 17 bits of |
| | | | the next GPS |
| | | | Time Of Week |
+-------+---------+---------+------------------+
| | | | |
|frame | No | integer | Frame number |
+-------+---------+---------+------------------+
| | | | |
|scaled | Yes | boolean | True is values |
| | | | scaled |
+-------+---------+---------+------------------+
READING
Reading the raw JSON can be tedious. You can pretty print, and
colorize, your JSON with [jq] to make reading easier. Using jq ito
pretty pring a JSON file can be as simple as:
$ jq . GPSD.json
To grab 10 seconds of live gpsd JSON, and pretty print it:
$ gpspipe -w -x 10 | jq .
If you only want to see the TPV messages:
$ gpspipe -w -x 10 | fgrep TPV | jq .
SEE ALSO
gpsd(8), libgps(3), libgpsmm(3), jq(1)
RESOURCES
Project web site: https://gpsd.io/
[RFC 2783]: https://datatracker.ietf.org/doc/html/rfc2783
Pulse-Per-Second API for UNIX-like Operating Systems
[RFC 7159]: https://datatracker.ietf.org/doc/html/rfc7159
The JavaScript Object Notation (JSON) Data Interchange Format
[jq]: https://github.com/stedolan/jq
COPYING
This file is Copyright 2013 by the GPSD project
SPDX-License-Identifier: BSD-2-clause
AUTHOR
Eric S. Raymond
GPSD, Version 3.25 2023-01-10 gpsd_json(5)
gpsd 3.25 - Generated Thu Feb 2 15:28:14 CST 2023