Python NMEA to GPX converter script

gistfile1.py

# NMEA to GPX converter
# Peter Pearson
# version 0.11

import csv
import sys
import time
from time import strftime

def convert_dms_to_dec(value, dir):
	dPos = value.find(".")
	
	mPos = dPos - 2
	ePos = dPos
	
	main = float(value[:mPos])	
	min1 = float(value[mPos:])
		
#	print "degrees:'%s', minutes:'%s'\n" % (main, min1)
	
	newval = float(main) + float(min1)/float(60)
	
	if dir == "W":
		newval = -newval
	elif dir == "S":
		newval = -newval
	
	return newval

def format_coord(value):
	return "%.9f" % float(round(value, 8))

def format_time(value):
	pre = strftime("%Y-%m-%dT") #"2007-04-15T"
	hour = value[:2]
	minute = value[2:4]
	second = value[4:6]
	timeval = pre + hour + ":" + minute + ":" + second + "Z"
	return timeval

def convert(inputfile, outputfile):
	reader = csv.reader(open(inputfile, "rb"))
	file = open(outputfile, 'w+')
	
	file.write("<?xml version=\"1.0\" encoding=\"UTF-8\"?>\n<gpx version=\"1.0\" creator=\"nmea_conv\"\nxmlns:xsi=\"http://www.w3.org/2001/XMLSchema-instance\" xmlns=\"http://www.topografix.com/GPX/1/0\"\nxsi:schemaLocation=\"http://www.topografix.com/GPX/1/0 http://www.topografix.com/GPX/1/0/gpx.xsd\">\n")
	
	points = []
	count = 0
	minlat = 90
	maxlat = -90
	minlon = 180
	maxlon = -180
	
	for row in reader:
		type = row[0]
		if type == "$GPGGA":
                        lat = convert_dms_to_dec(row[2], row[3])
			lon = convert_dms_to_dec(row[4], row[5])

                        # ignore dodgy values - safe to do, as it's unlikely I'm going to be in the South Atlantic anytime soon
			if lat == 0.0 && lon == 0.0:
                            continue

			points.append([])
			points[count].append(row[1])
			
			if lat < minlat:
				minlat = lat
			if lat > maxlat:
				maxlat = lat
			if lon < minlon:
				minlon = lon
			if lon > maxlon:
				maxlon = lon
			
			points[count].append(lat)
			points[count].append(lon)

			points[count].append(row[9])
			count += 1
	
	print "Points: '%i'" % (count)
	
	strbounds = "<bounds minlat=\"" + format_coord(minlat) + "\" minlon=\"" + format_coord(minlon) + "\" maxlat=\"" + format_coord(maxlat) + "\" maxlon=\"" + format_coord(maxlon) + "\"/>\n<trk>\n<trkseg>\n"
	file.write(strbounds)
		
	for point in range(count):
		time = points[point][0]
		lat_val = points[point][1]
		long_val = points[point][2]
		elev = points[point][3]
		
		strElev = "%.4f" % float(elev)
		
		strtrkpt = "<trkpt lat=\"" + format_coord(lat_val) + "\" lon=\"" + format_coord(long_val) + "\">\n  <ele>" + strElev + "</ele>\n<time>" + format_time(time) + "</time>\n</trkpt>\n"
		file.write(strtrkpt)
	
	file.write("</trkseg>\n</trk>\n</gpx>\n")
	file.close()

inputfile, outputfile = sys.argv[1], sys.argv[2]
convert(inputfile,outputfile)
print "Done!"

Thanks for this. I used it to help write some C# code to do the same thing (well, similar - I had to strip an additional timestamp surrounded by [ and ] off the start of each row in the BlackVue .gps files to get it to nmea format as an additional step)