Categories: S60 | Python | Code Examples | Location Based Services

This page was last modified 14:42, 7 March 2008.

From Forum Nokia Wiki

Good starter code for working with GPS data:

Connects to a bluetooth GPS receiver and parses the NMEA sentence, printing the location to the screen.

From Nick's Code - check there for any updates.

# Basic script to grab the current location from an NMEA bluetooth GPS,
#  and log it to the screen
# Also optionally logs periodic location data to a file, so you can see
#  where you were
#
# GPL
#
# Nick Burch - v0.01 (15/01/2006)
 
import appuifw
import socket
 
# Bluetooth address to connect to
# Change this to your GPS's bluetooth address!
gps_addr='00:15:4B:01:14:EE'
 
# How many GGA sentences between logging
# Set to 0 to prevent logging
gga_log_interval = 10
gga_log_count = 0
 
# File to log GGA sentences into
gga_log_file = 'e:\\nmea_gga_log.txt'
 
# We want icons etc
appuifw.app.screen='normal'
 
# Define title etc
appuifw.app.title=u"NMEA Location Disp"
 
# Alert them to the GPS we're going to connect to
appuifw.note(u"Will connect to GPS %s" % gps_addr, 'info')
 
# Connect to the bluetooth GPS using the serial service
sock=socket.socket(socket.AF_BT, socket.SOCK_STREAM)
target=(gps_addr,1)
sock.connect(target)
 
appuifw.note(u"Connected to the GPS")
 
# Open the GGA log file, in append mode
gga_log_fh = open(gga_log_file,'a');
 
# This is set to 0 to request a quit
going = 1
 
#############################################################################
 
# Generate the checksum for some data
# (Checksum is all the data XOR'd, then turned into hex)
def generate_checksum(data):
	csum = 0
	for c in data:
		csum = csum ^ ord(c)
	hex_csum = "%02x" % csum
	return hex_csum.upper()
 
# Format a NMEA timestamp into something friendly
def format_time(time):
	hh = time[0:2]
	mm = time[2:4]
	ss = time[4:]
	return "%s:%s:%s UTC" % (hh,mm,ss)
 
# Format a NMEA date into something friendly
def format_date(date):
	months = ('Jan', 'Feb', 'Mar', 'Apr', 'May', 'Jun', 'Jul', 'Aug', 'Sep', 'Oct', 'Nov', 'Dec')
	dd = date[0:2]
	mm = date[2:4]
	yy = date[4:6]
	yyyy = int(yy) + 2000
	return "%s %s %d" % (dd, months[(int(mm)-1)], yyyy)
 
#############################################################################
 
def readline(sock):
	"""Read one single line from the socket"""
	line = ""
	while 1:
		char = sock.recv(1)
		if not char: break
		line += char
		if char == "\n": break
	return line
 
def exit_key_pressed():
	"""Function called when the user requests exit"""
	# TODO Figure out why going in the main thread isn't updated
	going = 0
	appuifw.app.exit_key_handler = None
 
#############################################################################
 
# Get the location from a GGA sentence
def get_gga_location(data):
	d = data.split(',')
	ret = {}
	ret['type'] = 'GGA'
	ret['lat'] = "%s%s" % (d[1],d[2])
	ret['long'] = "%s%s" % (d[3],d[4])
	ret['time'] = format_time(d[0])
	return ret
 
# Get the location from a GLL sentence
def get_gll_location(data):
	d = data.split(',')
	ret = {}
	ret['type'] = 'GLL'
	ret['lat'] = "%s%s" % (d[0],d[1])
	ret['long'] = "%s%s" % (d[2],d[3])
	ret['time'] = format_time(d[4])
	return ret
 
# Get the location from a RMC sentence
def get_rmc_location(data):
	d = data.split(',')
	ret = {}
	ret['type'] = 'RMC'
	ret['lat'] = "%s%s" % (d[2],d[3])
	ret['long'] = "%s%s" % (d[4],d[5])
	ret['time'] = format_time(d[0])
	return ret
 
#############################################################################
 
# Loop while active
appuifw.app.exit_key_handler = exit_key_pressed
while going == 1:
	rawdata = readline(sock)
	if not rawdata: break
	data = rawdata.strip()
 
	# Ensure it starts with $GP
	if not data[0:3] == '$GP':
		continue
 
	# If it has a checksum, ensure that's correct
	# (Checksum follows *, and is XOR of everything from
	#  the $ to the *, exclusive)
	if data[-3] == '*':
		exp_checksum = generate_checksum(data[1:-3])
		if not exp_checksum == data[-2:]:
			print "Invalid checksum %s, expecting %s" % (data[-2:], exp_checksum)
			continue
		
		# Strip the checksum
		data = data[:-3]
 
	# Grab the parts of the sentence
	talker = data[1:3]
	sentence_id = data[3:6]
	sentence_data = data[7:]
 
	# The NMEA sentences we're interested in are:
	#  GGA - Global Positioning System Fix Data
	#  GLL - Geographic Position
	#  RMC - GPS Transit Data
	location = {}
	if sentence_id == 'GGA':
		location = get_gga_location(sentence_data)
 
		# Log GGA packets periodically
		gga_log_count = gga_log_count + 1
		if gga_log_count == gga_log_interval:
			gga_log_count = 0
			gga_log_fh.write(rawdata)
	if sentence_id == 'GLL':
		location = get_gll_location(sentence_data)
	if sentence_id == 'RMC':
		location = get_rmc_location(sentence_data)
 
	# If we got a location, print it
	if not location == {}:
		# Check the location is valid
		if location['lat'] == '0000.0000N' and location['long'] == '0000.0000E':
			print "Invalid GPS location found"
		else:
			print "Source of location is %s" % location['type']
			print "Lat is %s" % location['lat']
			print "Long is %s" % location['long']
			print "Time is %s" % location['time']
		print ""
 
	# Future:
	#  Grab satellites in view from GSV
	#  Grab satellites in use from GSA
	#  Grab speed and direction from VTG
 
	# For debugging
	#print data
 
# All done
sock.close()
gga_log_fh.close()
 
print "All done"
appuifw.app.set_exit()