NMEA Parser

The NMEA parser will decode any NMEA protocol message (official or not) and will allow you to create custom NMEA messages.

Note

The NMEA_parser class supports NMEA messages up to 120 characters

Methods

class NMEA_parser(cb=None, split_payload=False, verbose=0)

The NMEA_parser class needs to be initialized with the following parameters:

Parameter name	Value	Description
cb	Any function. Default value is None.	Callback function to be called when a NMEA message is parsed. Callback function argument is a variable containing the NMEA message fields in an array.
split_payload	True, False. Default value is False.	If True, splits the message payload and returns a list where each element is a NMEA field.
verbose	0, 1, default value is 0	If set to 1 parser will print in the terminal a CRC failed message if the parsed message is not valid

Class Attributes:

payload: NMEA message payload from which the CRC is calculated.
This is the complete NMEA message contained between the $ and * characters (excluded).

parse(buf)

Parse NMEA message

Args:

buf: Variable containing one or many NMEA messages. This variable may contain messages in other procotols, which will be ignored by the NMEA parser.

Return:

Array of NMEA messages contained in buf.

Example to parse a string with mixed NMEA and non-NMEA messages:

>>> import sbc
>>> nmea = sbc.NMEA_parser()
>>> buf = b'$GPGGA,172814.0,3723.46587704,N,12202.26957864,W,2,6,1.2,18.893,M,-25.669,M,2.0,0031*4F'
>>> buf = buf + b'This is not a NMEA message'
>>> buf = buf + b'$GPGST,172814.0,0.006,0.023,0.020,273.6,0.023,0.020,0.031*6A'
>>> msg = nmea.parse(buf)
>>> print(msg)
['GPGGA,172814.0,3723.46587704,N,12202.26957864,W,2,6,1.2,18.893,M,-25.669,M,2.0,0031', 'GPGST,172814.0,0.006,0.023,0.020,273.6,0.023,0.020,0.031']
>>> print(msg[0])
GPGGA,172814.0,3723.46587704,N,12202.26957864,W,2,6,1.2,18.893,M,-25.669,M,2.0,0031
>>> nmea = sbc.NMEA_parser(split_payload = True)
>>> msg = nmea.parse(buf)
>>> print(msg)
[['GPGGA', '172814.0', '3723.46587704', 'N', '12202.26957864', 'W', '2', '6', '1.2', '18.893', 'M', '-25.669', 'M', '2.0', '0031'], ['GPGST', '172814.0', '0.006', '0.023', '0.020', '273.6', '0.023', '0.020', '0.031']]
>>> print(msg[0][0],msg[1][0])
GPGGA GPGST

Example to use a callback function that prints GPGGA message received if a GPGGA message is received:

>>> import sbc
>>> def callback_nmea(msg):
>>>    if msg[0] == 'GPGGA':
>>>        print('GPGGA message received')
>>> nmea = sbc.NMEA_parser(cb = callback_nmea, split_payload = True)
>>> buf = b'$GPGGA,172814.0,3723.46587704,N,12202.26957864,W,2,6,1.2,18.893,M,-25.669,M,2.0,0031*4F'
>>> buf = buf + b'This is not a NMEA message'
>>> buf = buf + b'$GPGST,172814.0,0.006,0.023,0.020,273.6,0.023,0.020,0.031*6A'
>>> msg = nmea.parse(buf)  
GPGGA message received

chksum_nmea()

Calculates the two checksum bytes of the NMEA message payload.

Return:

NMEA message checksum.

Example to calculate the NMEA checksum of a payload and build a NMEA message from it:

>>> import sbc
>>> nmea = sbc.NMEA_parser()
>>> nmea.payload = b'GPGGA,172814.0,3723.46587704,N,12202.26957864,W,2,6,1.2,18.893,M,-25.669,M,2.0,0031'
>>> nmea.payload_len = len(nmea.payload)
>>> print(nmea.chksum_nmea())  
b'4F'
>>> msg = b'$' + nmea.payload + b'*' + nmea.chksum_nmea()
>>> print(msg.decode())
$GPGGA,172814.0,3723.46587704,N,12202.26957864,W,2,6,1.2,18.893,M,-25.669,M,2.0,0031*4F