moffat/pynmea2

Python library for the NMEA 0183 protcol

pynmea2

pynmea2 is a python library for the NMEA 0183 protocol

pynmea2 is based on pynmea by Becky Lewis

Installation

The recommended way to install pynmea2 is with pip:

pip install pynmea2

Parsing

You can parse individual NMEA sentences using the parse() function, which takes a string containing a NMEA 0183 sentence and returns a NMEASentence object. Note that the leading '$' is optional and trailing whitespace is ingored when parsing a sentence.

Example:

>>> import pynmea2
>>> msg = pynmea2.parse("$GPGGA,184353.07,1929.045,S,02410.506,E,1,04,2.6,100.00,M,-33.9,M,,0000*6D")
>>> msg
<GGA(timestamp=datetime.time(18, 43, 53), lat='1929.045', lat_dir='S', lon='02410.506', lon_dir='E', gps_qual='1', num_sats='04', horizontal_dil='2.6', altitude=100.0, altitude_units='M', geo_sep='-33.9', geo_sep_units='M', age_gps_data='', ref_station_id='0000')>

The NMEASentence object has different properties, depending on its sentence type. The GGA message has the following properties:

>>> msg.timestamp
datetime.time(18, 43, 53)
>>> msg.lat
'1929.045'
>>> msg.lat_dir
'S'
>>> msg.lon
'02410.506'
>>> msg.lon_dir
'E'
>>> msg.gps_qual
'1'
>>> msg.num_sats
'04'
>>> msg.horizontal_dil
'2.6'
>>> msg.altitude
100.0
>>> msg.altitude_units
'M'
>>> msg.geo_sep
'-33.9'
>>> msg.geo_sep_units
'M'
>>> msg.age_gps_data
''
>>> msg.ref_station_id
'0000'
>>>

Additional properties besides the ones explicitly in the message data may also exist.

For example, latitude and longitude properties exist as helpers to access the geographic coordinates as python floats (DD, "decimal degrees") instead of the string DMS ("Degrees, minutes, seconds") format used in the NMEA protocol

>>> msg.latitude
-19.4840833333
>>> msg.longitude
24.1751

Generating

You can create a NMEASentence object by calling the constructor with talker, message type, and data fields:

>>> msg = pynmea2.GGA('GP', 'GGA', '184353.07', '1929.045', 'S', '02410.506', 'E', '1', '04', '2.6', '100.00', 'M', '-33.9', 'M', '', '0000')

and generate a NMEA string from a NMEASentence object:

>>> str(msg)
'$GPGGA,184353.07,1929.045,S,02410.506,E,1,04,2.6,100.00,M,-33.9,M,,0000*6D'

Streaming

pynmea2 can also process streams of NMEA sentences like so, by feeding chunks of data manually:

streamreader = pynmea2.NMEAStreamReader()
while 1:
    data = input.read()
    for msg in streamreader.next(data):
        print msg

or given a file-like device, automatically:

streamreader = pynmea2.NMEAStreamReader(input)
while 1:
    for msg in streamreader.next():
        print msg

Testing

pynmea2 can be tested with pytest

TODO

• Generate Sphinx docs
• Make extra NMEASentence properties writable
• Cleanup types