gps_decode.py

import serial, pynmea2
from math import radians, cos, sin, asin, sqrt


def haversine(ln1, lt1, ln2, lt2):
    """
    Calculate the great circle distance between two points
    on the earth (specified in decimal degrees)
    """
    # convert decimal degrees to radians
    ln1, lt1, ln2, lt2 = map(radians, [ln1, lt1, ln2, lt2])
    # haversine formula
    dlon = ln2 - ln1
    dlat = lt2 - lt1
    a = sin(dlat/2)**2 + cos(lt1) * cos(lt2) * sin(dlon/2)**2
    c = 2 * asin(sqrt(a))
    km = 6367 * c # this is in KM, use 3959 for miles
    return km

if __name__ == '__main__':

    # set up serial connection - define the COM port/rfcomm device to use
    # windows
    # ser = serial.Serial('COM3', 9600)
    # linux
    ser = serial.Serial('/dev/rfcomm0', 9600)

    streamreader = pynmea2.NMEAStreamReader()

    lat1 = None
    lat2 = None
    lon1 = None
    lon2 = None

    while True:
        gpsdata = ser.readline().decode('utf-8')

        for msg in streamreader.next(gpsdata):
            # not interested in proprietary messages
            if isinstance(msg, pynmea2.nmea.ProprietarySentence):
                continue
            else:
                if msg.sentence_type == 'GGA':
                    print('~~~~~~~~~~~~~~~')
                    # if this is the first reading then define lat2 and lon2
                    if lat2 is None:
                        lat2 = msg.latitude
                        lon2 = msg.longitude
                    else:
                        lat1 = lat2
                        lon1 = lon2
                        lat2 = msg.latitude
                        lon2 = msg.longitude
                        print('Distance travelled: ' + haversine(lon1, lat1, lon2, lat2).__str__())

                    print('Timestamp: ' + str(msg.timestamp))
                    print('Latitude: ' + msg.latitude.__str__())
                    print('Longitude: ' + msg.longitude.__str__())
                    # print('GPS quality: ' + msg.gps_qual.__str__())
                    print('Number of satellites: ' + msg.num_sats.__str__())
                    # print('Altitude: ' + msg.altitude.__str__() + msg.altitude_units.__str__())