maheshsundaramurthy/py-nmea

Python library for parsing the NMEA 0183 protocol (GPS)

pynmea2

pynmea2 is a python library for the NMEA 0183 protocol

pynmea2 is based on pynmea by Becky Lewis

The pynmea2 homepage is located at http://github.com/Knio/pynmea2

Compatibility

pynmea2 is compatable with Python 2.7 and Python 3.3

Installation

The recommended way to install pynmea2 is with pip:

pip install pynmea2

Parsing

You can parse individual NMEA sentences using the parse(data, check=False) 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 ignored when parsing a sentence.

With check=False, parse will accept NMEA messages that do not have checksums, however it will still raise pynmea2.ChecksumError if they are present. check=True will also raise ChecksumError if the checksum is missing.

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 DDDMM.MMMM ("Degrees, minutes, seconds") format used in the NMEA protocol. latitude_minutes, latitude_seconds, longitude_minutes, and longitude_seconds are also supported and allow easy creation of differently formatted location strings.

>>> msg.latitude
-19.4840833333
>>> msg.longitude
24.1751
>>> '%02d°%07.4f′' % (msg.latitude, msg.latitude_minutes)
'-19°29.0450′'
>>> '%02d°%02d′%07.4f″' % (msg.latitude, msg.latitude_minutes, msg.latitude_seconds)
"-19°29′02.7000″"

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

If your stream is noisy and contains errors, you can set some basic error handling with the errors parameter of the NMEAStreamReader constructor.