GPStoUVZ.py

import numpy as np
import pynmea2

gps_samples=2048
badValue=999

def getUVZ(gpsfile):
    
    u = np.empty(gps_samples)
    u.fill(badValue)
    v = np.empty(gps_samples)
    v.fill(badValue)
    z = np.empty(gps_samples)
    z.fill(badValue)
    lat = np.empty(gps_samples)
    lat.fill(badValue)
    lon = np.empty(gps_samples)
    lon.fill(badValue)
    
    ipos=0
    ivel=0
    
    with open(gpsfile, 'r') as file:
    
        for line in file:
            if "GPGGA" in line:
                gpgga = pynmea2.parse(line,check=True)   #grab gpgga sentence and parse
                #check to see if we have lost GPS fix, and if so, continue to loop start. a badValue will remain at this index
                if gpgga.gps_qual < 1:
                    ipos+=1
                    continue
                z[ipos] = gpgga.altitude
                lat[ipos] = gpgga.latitude
                lon[ipos] = gpgga.longitude
                ipos+=1
            elif "GPVTG" in line:
                if gpgga.gps_qual < 1:
                    continue
                gpvtg = pynmea2.parse(line,check=True)   #grab gpvtg sentence
                u[ivel] = gpvtg.spd_over_grnd_kmph*np.cos(gpvtg.true_track) #units are kmph
                v[ivel] = gpvtg.spd_over_grnd_kmph*np.sin(gpvtg.true_track) #units are kmph
                ivel+=1
            else: #if not GPGGA or GPVTG, continue to start of loop
                continue
           
    print('GPGGA lines: {}.'.format(ipos))
    print('GPVTG lines: {}'.format(ivel))

    return u,v,z,lat,lon

if __name__ == "__main__":

    import sys

    if len(sys.argv) != 2:
        print("Provide the path to the GPS file.")
        sys.exit(1)

    gpsfile = sys.argv[1]
    
    u,v,z,lat,lon = getUVZ(gpsfile)