python-gpsdshm

Overview

python-gpsdshm provides a read-only(!) Python interface to gpsd's shared memory. It provides a single class Shm that exposes the fields of the shared memory structure as attributes. The python-gpsdshm API is (loosely) modelled on gpsd version 3.16 (API 6.1). gpsd releases earlier than 3.0 are not supported.

python-gpsdshm is implemented using Swig and requires the gpsd header files for compilation. Please note that some Linux distributions contain Swig releases that are too old for working with Python 3.

Many Linux distributions ship the gpsd package without shared memory support. See Compiling gpsd with shared memory support for details how to build gpsd with shared memory support.

Status

python-gpsdshm is automatically tested against the following Python versions:

• Python 2.6
• Python 2.7
• Python 3.3
• Python 3.4
• Python 3.5

Branch	Travis-CI	Codecov	Codacy	Landscape
master
develop

Example

The gpsdshm.Shm class provides the interface to gpsd's shared memory.

>>> import gpsdshm
>>> gpsd_shm = gpsdshm.Shm()
>>> gpsd_shm.online               # Timestamp if GPS is online, 0 otherwise
1454057376.6934643
>>> gpsd_shm.status               # Do we have a fix?
1
>>> gpsd_shm.status == gpsdshm.STATUS_FIX
True
>>> gpsd_shm.status == gpsdshm.STATUS_NO_FIX
False
>>> gpsd_shm.skyview_time         # Skyview timestamp
>>> gpsd_shm.satellites_visible   # Number of satellites in view
6

GPS Fix

>>> gpsd_shm.fix.time             # Time of update
1454057448.0
>>> gpsd_shm.fix.mode             # Mode of fix (0=not seen, 1=no fix, 2=2D, 3=3D)
3
>>> gpsd_shm.fix.ept              # Expected time uncertainty
0.005
>>> gpsd_shm.fix.latitude         # Latitude in degrees (valid if mode >= 2)
-37.75859333333334
>>> gpsd_shm.fix.epy              # Latitude position uncertainty, meters
14.853882022256698
>>> gpsd_shm.fix.longitude        # Longitude in degrees (valid if mode >= 2)
144.99911
>>> gpsd_shm.fix.epx              # Longitude position uncertainty, meters
10.040781879264545
>>> gpsd_shm.fix.alitude          # Altitude in meters (valid if mode == 3)
68.2
>>> gpsd_shm.fix.epv              # Vertical position uncertainty, meters
19.55
>>> gpsd_shm.fix.track            # Course made good (relative to true north)
44.45
>>> gpsd_shm.fix.epd              # Track uncertainty, degrees
nan
>>> gpsd_shm.fix.speed            # Speed over ground, meters/sec
0.3446777748
>>> gpsd_shm.fix.eps              # Speed uncertainty, meters/sec
29.707764044513397
>>> gpsd_shm.fix.climb            # Vertical speed, meters/sec
0.0
>>> gpsd_shm.fix.epc              # Vertical speed uncertainty
nan

Dilution of precisions (DOP)

>>> gpsd_shm.dop.xdop
0.6693854586176363
>>> gpsd_shm.dop.ydop
0.9902588014837799
>>> gpsd_shm.dop.pdop
1.17
>>> gpsd_shm.dop.hdop
0.99
>>> gpsd_shm.dop.vdop
0.82
>>> gpsd_shm.dop.tdop
1.2548625723457216
>>> gpsd_shm.dop.gdop
2.4342743978108503

Satellites

Information about satellites is contained in the satellites list. The list is always gpsdshm.MAXCHANNELS entries long, even if only a few satellites are visible.

>>> gpsd_shm.satellites[0].ss         # Signal-to-noise ratio (dB)
16.0
>>> gpsd_shm.satellites[0].used       # Used in solution?
False
>>> gpsd_shm.satellites[0].prn        # PRNs of satellite
6
>>> gpsd_shm.satellites[0].elevation  # Elevation of satellite, degrees
56
>>> gpsd_shm.satellites[0].azimuth    # Azimuth, degrees
59

Devices

The devices list contains either information about all devices gpsd is currently monitoring (gpsd release 3.12 and later, gpsdshm.GPSD_API_MAJOR_VERSION == 6) or a single entry with information about the device that shipped the most recent update (gpsd release 3.11 and earlier, gpsdshm.GPSD_API_MAJOR_VERSION == 5).

>>> gpsd_shm.devices[0].path
/dev/ttyAMA0
>>> gpsd_shm.devices[0].flags && gpsdshm.SEEN_GPS
1
>>> gpsd_shm.devices[0].flags && gpsdshm.SEEN_RTCM2
0
>>> gpsd_shm.devices[0].flags && gpsdshm.SEEN_RTCM3
0
>>> gpsd_shm.devices[0].flags && gpsdshm.SEEN_AIS
0
>>> gpsd_shm.devices[0].driver
# TODO
>>> gpsd_shm.devices[0].subtype
# TODO
>>> gpsd_shm.devices[0].activated
# TODO
>>> gpsd_shm.devices[0].baudrate
4800
>>> gpsd_shm.devices[0].stopbits
1
>>> gpsd_shm.devices[0].parity         # 'N', 'O', or 'E'
N
>>> gpsd_shm.devices[0].cylce
1.0
>>> gpsd_shm.devices[0].mincylce
1.0
>>> gpsd_shm.devices[0].driver_mode
0

Compiling gpsd with shared memory support

$ git clone git://git.sv.gnu.org/gpsd.git   # git clone http://git.savannah.gnu.org/r/gpsd.git
$ cd gpsd
$ git tag
$ git checkout release-3.16
$ scons prefix=/usr/local shm_export=yes
$ sudo scons install

Then run start gpsd and check whether the shared segment has been created.

$ sudo /usr/local/sbin/gpsd -n /dev/ttyAMA0
$ ipcs -m | grep 0x47505344
------ Shared Memory Segments --------
key        shmid      owner      perms      bytes      nattch     status
0x47505344 163844     root       666        31616      1