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Class 14: python - processing GPS data

TODO Outside reading

http://oceanservice.noaa.gov/podcast.html

Introduction

Today we will work on parsing GPS data

My normal log files have extra metadata on the end. Let’s start with a file that does not include this metadata.

mkdir ~/class/14
cd ~/class/14
wget http://vislab-ccom.unh.edu/~schwehr/Classes/2011/esci895-researchtools/examples/nmea.log.bz2
bunzip2 nmea.log.bz2

more notes will follow later. This class is very similar to video 13.

Parsing NMEA with python

http://gpsd.berlios.de/NMEA.txt

Final code

#!/usr/bin/env python

test_gga = '$GPGGA,024634,4308.1268,N,07056.3761,W,2,7,1.1,39.9,M,,,,*06'

def decode_gga(line):
    fields = line.split(',')
    time_string = fields[1]
    hour = int (  time_string[:2]  )
    minute = int ( time_string[2:4] )
    sec = int ( time_string[4:] )
    print 'hour:', hour, 'minute:', minute, 'sec:', sec

    # Latitude
    lat_str = fields[2]
    y = int ( lat_str[:2] ) + float(lat_str[2:]) / 60.

    if fields[3] == 'S':
        y = -y

    print 'latitude (y):', y

    # Longitude
    lon_str = fields[4]
    x = int ( lon_str[:3] ) + float ( lon_str[3:] ) / 60.
    if fields[5] == 'W':
        x = -x

    print 'longitude (x):', x

decode_gga('$GPGGA,024634,4308.1268,N,07056.3761,W,2,7,1.1,39.9,M,,,,*06')

History

1 : _ip.system("ls -F ")
2 : import gga
3 : dir(gga)
4 : _ip.system("ls -F ")
5 : _ip.system("ls -F ")
6 : _ip.system("ls -F -l")
7 : import gga
8 : reload(gga)
9 : dir(gga)
10: gga.test_gga
13: #?gga.test_gga.split
14: gga.test_gga.split(',')
15: Out[14]
16: fields = gga.test_gga.split(',')
17: who 
18: _ip.magic("who ")
19: _ip.magic("whos ")
20: _ip.magic("whos ")
21: fields
22: fields[0]
23: fields[1]
24: fields = gga.test_gga.split(',')
25: fields[-1]
26: fields
27: fields[1]
28: fields = gga.test_gga.split(',')
29: time_string = fields[1]
30: _ip.magic("whos ")
31: hour = time_string[:2]
32: hour
33: type(hour)
34: int(hour)
35: hour = int (  time_string[:2]  )
36: hour
37: type(hour)
38: _ip.magic("history ")
39: reload(gga)
40: gga.decode_gga( gga.test_gga  )
41: _ip.magic("run gga")
42: time_string
43: minute = time_string[2:4]
44: print minute
45: minute
46: minute = int ( time_string[2:4] )
47: minute
48: type (minute)
49: sec = int ( time_string[4:] )
50: print sec
51: _ip.magic("run gga")
52: reload(gga)
54: gga.decode_gga( gga.test_gga  )
56: _ip.magic("run gga")
57: fields
58: lat_str = fields[2]
59: lat_str
60: lat_str[:2]
61: int ( lat_str[:2] )
62: lat_str[2:]
63: int(lat_str[2:])
64: float(lat_str[2:])
65: float(lat_str[2:]) / 60.
66: 59/60
67: 59/60.
68: _ip.magic("history ")
69: int ( lat_str[:2] ) + float(lat_str[2:]) / 60.
70: y = int ( lat_str[:2] ) + float(lat_str[2:]) / 60.
71: fields
72: _ip.magic("run gga")
74: fields[4]
75: _ip.magic("run gga")