A GPS receiver uses the NMEA standard to communicate within satellites. Every message it receives, called sentence, has a checksum that ensures its correctness.
Calculating the NMEA sentence checksum is simple, just xor some data (as stated for example in http://www.gpsinformation.org/dale/nmea.htm).
In Python? Is a bunch of code.
[code]
from operator import xor
# NMEA sentence, the checksum is after the '*'
# and it's represented in hex.
s = '$GPGGA,123519,4807.038,N,01131.000,'
s += 'E,1,08,0.9,545.4,M,46.9,M,,*47'
# Converts every character in the substring
# between '$' and the '*' (exclusive)
# in a sequence of integral values.
nmea = map(ord, s[1:s.index('*')])
# Reducing with xor the sequence
checksum = reduce(xor, nmea)
# Optionally converts in hex for printing
print hex(checksum)
[/code]
If you run this simple script you can see 0x47 on your terminal... the sentence is correct.
Power Up Without a Plug
8 hours ago
3 comments:
how to read the NMEA data using python and how inslall NMEA module in python envirment
My first experiment was using the pySerial (http://pyserial.sourceforge.net/) library to attach directly to a bluetooth GPS. After that I parsed the stream by hand. Right now, probably, something like Python GIS (http://pygps.org/) coulde be used... but I don't test this module yet.
Thanks dude: you just saved my bacon! I love people like you who post really useful bits of code that just do one thing correctly!
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