Current Status | Installation | Reading | Parsing | Generating | Serializing | Utilities | Examples | Extensibility | Command Line Utility | Graphical Client | Author & License
pynmeagps
is an original Python 3 parser aimed primarily at the subset of the NMEA 0183 © v4 protocol relevant to GNSS/GPS receivers.
The intention is to make it as easy as possible to read, parse and utilise NMEA GNSS/GPS messages in Python applications.
The pynmeagps
homepage is located at https://github.com/semuconsulting/pynmeagps.
Companion libraries are available which handle UBX © and RTCM3 © messages:
The library implements a comprehensive set of outbound (GET) and inbound (SET/POLL) GNSS NMEA messages relating to GNSS/GPS devices, but is readily extensible. Refer to NMEA_MSGIDS
and NMEA_MSGIDS_PROP
for the complete dictionary of standard and proprietary messages currently supported. While the NMEA 0183 protocol itself is proprietary, the definitions here have been collated from public domain sources.
Sphinx API Documentation in HTML format is available at https://www.semuconsulting.com/pynmeagps.
Contributions welcome - please refer to CONTRIBUTING.MD.
Bug reports and Feature requests - please use the templates provided. For general queries and advice, post a message to one of the pynmeagps Discussions channels.
pynmeagps
is compatible with Python 3.8 - 3.13 and has no third-party library dependencies.
In the following, python3
& pip
refer to the Python 3 executables. You may need to substitute python
for python3
, depending on your particular environment (on Windows it's generally python
).
The recommended way to install the latest version of pynmeagps
is with pip:
python3 -m pip install --upgrade pynmeagps
If required, pynmeagps
can also be installed into a virtual environment, e.g.:
python3 -m pip install --user --upgrade virtualenv
python3 -m virtualenv env
source env/bin/activate (or env\Scripts\activate on Windows)
python3 -m pip install --upgrade pynmeagps
...
deactivate
For Conda users, pynmeagps
is also available from conda forge:
conda install -c conda-forge pynmeagps
class pynmeagps.nmeareader.NMEAReader(stream, **kwargs)
You can create an NMEAReader
object by calling the constructor with an active stream object.
The stream object can be any data stream which supports a read(n) -> bytes
method (e.g. File or Serial, with
or without a buffer wrapper). pynmeagps
implements an internal SocketStream
class to allow sockets to be read in the same way as other streams (see example below).
Individual input NMEA messages can then be read using the NMEAReader.read()
function, which returns both the raw data (as bytes) and the parsed data (as an NMEAMessage
object, via the parse()
method). The function is thread-safe in so far as the incoming data stream object is thread-safe. NMEAReader
also implements an iterator.
The constructor accepts the following optional keyword arguments:
msgmode
: 0 = GET (default, i.e. output from receiver), 1 = SET (i.e. input to receiver), 2 = POLL (i.e. query to receiver in anticipation of response back)nmeaonly
: True = raise error if stream contains non-NMEA data, False = ignore non-NMEA data (default)validate
: validation flagsVALCKSUM
(0x01) = validate checksum (default),VALMSGID
(0x02) = validate msgId (i.e. raise error if unknown NMEA message is received)quitonerror
:ERR_IGNORE
(0) = ignore errors,ERR_LOG
(1) = log continue,ERR_RAISE
(2) = (re)raise (1)
Examples:
- Serial input - this example will ignore any non-NMEA data.
from serial import Serial
from pynmeagps import NMEAReader
with Serial('/dev/tty.usbmodem14101', 9600, timeout=3) as stream:
nmr = NMEAReader(stream)
raw_data, parsed_data = nmr.read()
if parsed_data is not None:
print(parsed_data)
- File input (using iterator) - this example will produce a
NMEAStreamError
if non-NMEA data is encountered.
from pynmeagps import NMEAReader
with open('nmeadata.log', 'rb') as stream:
nmr = NMEAReader(stream, nmeaonly=True)
for raw_data, parsed_data in nmr:
print(parsed_data)
Example - Socket input (using iterator):
import socket
from pynmeagps import NMEAReader
with socket.socket(socket.AF_INET, socket.SOCK_STREAM) as stream:
stream.connect(("localhost", 50007))
nmr = NMEAReader(stream)
for raw_data, parsed_data in nmr:
print(parsed_data)
You can parse individual NMEA messages using the static NMEAReader.parse(message)
function, which takes a string or bytes containing an NMEA message and returns an NMEAMessage
object.
Note that latitude and longitude are parsed as signed decimal values for ease of use. Helper methods latlon2dms
and latlon2dmm
are available to convert decimal degrees to d°m′s.s″ or d°m.m′ display format.
Attributes within repeating groups are parsed with a two-digit suffix (svid_01, svid_02, etc.).
The parse()
function accepts the following optional keyword arguments:
msgmode
: 0 = GET (default), 1 = SET, 2 = POLLvalidate
: validation flagsVALCKSUM
(0x01) = validate checksum (default),VALMSGID
(0x02) = validate msgId (i.e. raise error if unknown NMEA message is received)quitonerror
:ERR_IGNORE
(0) = ignore errors,ERR_LOG
(1) = log continue,ERR_RAISE
(2) = (re)raise (1)
Example:
from pynmeagps import NMEAReader
msg = NMEAReader.parse('$GNGLL,5327.04319,S,00214.41396,E,223232.00,A,A*68\r\n')
print(msg)
<NMEA(GNGLL, lat=-53.45072, NS=S, lon=2.240233, EW=E, time=22:32:32, status=A, posMode=A)>
The NMEAMessage
object exposes different public attributes depending on its message ID,
e.g. the RMC
message has the following attributes:
from pynmeagps import latlon2dms, latlon2dmm
print(msg)
print(msg.msgID)
print(msg.lat, msg.lon)
print(msg.spd)
print(latlon2dms((msg.lat, msg.lon)))
print(latlon2dmm((msg.lat, msg.lon)))
<NMEA(GNRMC, time=22:18:38, status=A, lat=52.62063, NS=N, lon=-2.16012, EW=W, spd=37.84, cog=, date=2021-03-05, mv=, mvEW=, posMode=A)>
'RMC'
(52.62063, -2.16012)
37.84
('52°37′14.268″N', '2°9′36.432″W')
('52°37.2378′N', '2°9.6072′W')
class pynmeagps.nmeamessage.NMEAMessage(talker: str, msgID: str, msgmode: int, **kwargs)
You can create an NMEAMessage
object by calling the constructor with the following parameters:
- talker (must be a valid talker from
pynmeagps.NMEA_TALKERS
) - message id (must be a valid id from
pynmeagps.NMEA_MSGIDS
orpynmeagps.NMEA_MSGIDS_PROP
) - msgmode (0=GET, 1=SET, 2=POLL)
- (optional) a series of keyword parameters representing the message payload
The 'msgmode' parameter signifies whether the message payload refers to a:
- GET message (i.e. output from the receiver - NB these would normally be generated via the NMEAReader.read() or NMEAReader.parse() methods but can also be created manually)
- SET message (i.e. command input to the receiver)
- POLL message (i.e. query input to the receiver in anticipation of a response back)
The message payload can be defined via keyword arguments in one of two ways:
- A single keyword parameter of
payload
containing the full payload as a list of string values (any other keyword parameters will be ignored). - One or more keyword parameters corresponding to individual message attributes. Any attributes not explicitly provided as keyword parameters will be set to a nominal value according to their type. For position messages, the
NS
orEW
values will be derived from the sign of thelat
orlon
values and need not be provided, e.g. iflat
= -32.4,NS
will be "S", iflon
= -1.34,EW
will be "W" (any providedNS
orEW
values will be overridden accordingly).
e.g. Create a GLL message, passing the entire payload as a list of strings in native NMEA format:
from pynmeagps import NMEAMessage, GET
pyld=['4330.00000','N','00245.000000','W','120425.234','A','A']
msg = NMEAMessage('GN', 'GLL', GET, payload=pyld)
print(msg)
<NMEA(GNGLL, lat=43.5, NS=N, lon=-2.75, EW=W, time=12:04:25.234000, status=A, posMode=A)>
e.g. Create GLL (GET) and GNQ (POLL) message, passing individual typed values as keywords, with any omitted keywords defaulting to nominal values (in the GLL example, the 'time' parameter has been omitted and has defaulted to the current time):
from pynmeagps import NMEAMessage, GET
msg = NMEAMessage('GN', 'GLL', GET, lat=43.5, lon=-2.75, status='A', posMode='A')
print(msg)
<NMEA(GNGLL, lat=43.5, NS='N', lon=-2.75, EW='W', time='12:04:25.234745', status='A', posMode='A')>
from pynmeagps import NMEAMessage, POLL
msg = NMEAMessage('EI', 'GNQ', POLL, msgId='RMC')
print(msg)
<NMEA(EIGNQ, msgId=RMC)>
By default, NMEA position message payloads store lat/lon to 5dp of minutes (i.e. (d)ddmm.mmmmm). An optional boolean keyword argument hpnmeamode
increases this to 7dp (i.e. (d)ddmm.mmmmmmm) when set to True, e.g.
from pynmeagps import NMEAMessage, GET
msgsp = NMEAMessage('GN', 'GLL', GET, lat=43.123456789, lon=-2.987654321, status='A', posMode='A', hpnmeamode=0) # standard precision
print(msgsp)
msghp = NMEAMessage('GN', 'GLL', GET, lat=-43.123456789, lon=2.987654321, status='A', posMode='A', hpnmeamode=1) # high precision
print(msghp)
NMEAMessage('GN','GLL', 0, payload=['4307.40741', 'N', '00259.25926', 'W', '095045.78', 'A', 'A'])
NMEAMessage('GN','GLL', 0, payload=['4307.4074073', 'S', '00259.2592593', 'E', '094824.88', 'A', 'A'])
NB: Once instantiated, an NMEAMessage
object is immutable.
The NMEAMessage
class implements a serialize()
method to convert an NMEAMessage
object to a bytes array suitable for writing to an output stream.
from serial import Serial
from pynmeagps import NMEAMessage, POLL
stream = Serial('COM6', 38400, timeout=3)
msg = NMEAMessage('EI','GNQ', POLL, msgId='RMC')
print(msg.serialize())
stream.write(msg.serialize())
b'$EIGNQ,RMC*24\r\n'
pynmeagps
provides the following utility methods:
latlon2dms
- converts decimal lat/lon to degrees, minutes, decimal seconds format e.g. "53°20′45.6″N", "2°32′46.68″W"latlon2dmm
- converts decimal lat/lon to degrees, decimal minutes format e.g. "53°20.76′N", "2°32.778′W"llh2iso6709
- converts lat/lon and altitude (hMSL) to ISO6709 format e.g. "+27.5916+086.5640+8850CRSWGS_84/"ecef2llh
- converts ECEF (X, Y, Z) coordinates to geodetic (lat, lon, ellipsoidal height) coordinatesllh2ecef
- converts geodetic (lat, lon, ellipsoidal height) coordinates to ECEF (X, Y, Z) coordinateshaversine
- finds great circle distance in km between two sets of (lat, lon) coordinatesplanar
- finds planar distance in m between two sets of (lat, lon) coordinatesbearing
- finds bearing in degrees between two sets of (lat, lon) coordinates
See Sphinx documentation for details.
The following command line examples can be found in the /examples
folder:
-
nmeapoller.py
illustrates how to read, write and display NMEA messages 'concurrently' using threads and queues. This represents a useful generic pattern for many end user applications. -
nmeafile.py
illustrates how to implement an NMEA datalog file reader usingpynmeagps.NMEAReader
iterator functionality. -
nmeasocket.py
illustrates how to implement a TCP Socket reader for NMEA messages using NMEAReader iterator functionality. -
gpxtracker.py
illustrates a simple utility to convert an NMEA datalog file to a*.gpx
track file usingpynmeagps.NMEAReader
. -
/webserver/nmeaserver.py
illustrates a simple HTTP web server wrapper aroundpynmeagps.NMEAReader
; it presents data from selected NMEA messages as a web page http://localhost:8080 or a RESTful API http://localhost:8080/gps. -
utilities.py
illustrates how to use variouspynmeagps
utility methods.
The NMEA protocol is principally defined in the modules nmeatypes_*.py
as a series of dictionaries. Additional message types
can be readily added to the appropriate dictionary. Message payload definitions must conform to the following rules:
1. attribute names must be unique within each message class
2. avoid reserved names 'msgID', 'talker', 'payload', 'checksum'.
3. attribute types must be one of the valid types (IN, DE, CH, etc.)
4. repeating groups must be defined as a tuple ('numr', {dict}), where:
'numr' is either:
a. an integer representing a fixed number of repeats e.g. 32
b. a string representing the name of a preceding attribute containing the number of repeats e.g. 'numSv'
c. 'None' for an indeterminate repeating group. Only one such group is permitted per payload and it must be at the end.
{dict} is the nested dictionary of repeating items
A command line utility gnssdump
is available via the pygnssutils
package. This is capable of reading and parsing NMEA, UBX and RTCM3 data from a variety of input sources (e.g. serial, socket and file) and outputting to a variety of media in a variety of formats. See https://github.com/semuconsulting/pygnssutils for further details.
To install pygnssutils
:
python3 -m pip install --upgrade pygnssutils
For help with the gnssdump
utility, type:
gnssdump -h
A python/tkinter graphical GPS client which supports NMEA, UBX and RTCM3 protocols is available at:
https://github.com/semuconsulting/PyGPSClient
pynmeagps
is maintained entirely by unpaid volunteers. It receives no funding from advertising or corporate sponsorship. If you find the library useful, a small donation would be greatly appreciated!