NEO-6M GPS module

I ordered a few of these to find out whether they would be any use for robot positioning and my conclusion is a very definite NO!

The reason being that the values indicate an inaccuracy of up to 10 meters.

Here is the setup.

The Arduino Nano is loaded with a blank sketch, the TXD pin on the breakout board is connected to the TX pin on the Nano.

One minute of latitude equals one nautical mile equals 1800 meters, one second of latitude is equal to 1800/60 i.e. 30 meters. And using the python program below the seconds' values are dancing around by some 0.3 of a second i.e. 10 meters.

#!/usr/bin/python3

#coded by Stephen Clements aka Pugwash 2019

#please use and/or modify as you please

#any feedback to pugwash429@gmail.com would be appreciated

import serial

# change to your COM port

gps_comm_port = '/dev/cu.wchusbserial1460'; # *nix comm port notation

# change to suit your timezone

timeOffset = 2

try:

    # Change the baud rate here if not 9600

    ser = serial.Serial(port=gps_comm_port, baudrate=9600)

except IOError:

    print("Invalid comm port, Comm port not found for GPS.")

    exit (1)

# validate the checksum

def validateChecksum(gpsData):

    gpsData = gpsData.lstrip('$')

    gpsList = gpsData.split('*')

    gpsHex = gpsList[1]

    gpsString = gpsList[0]

    checksumResult = 0

    for character in gpsString:

       checksumResult ^= ord(character)

       if checksumResult ==int(gpsHex, 16):

          returnTrue

       else:

          returnFalse

# format and correct time to display UTC & local time

def formatTime(timeString, tempOffset):

    tempTime = timeString.split('.') # split the decimal part from the time string

    tempTime = tempTime[0] # discard decimal part

    tempTime = tempTime.lstrip('0') # strip leading zeros

    # if GPS time is later than 9:59 am

    if len(tempTime) ==6:

        iTemp = int(tempTime[0:2]) # extract hours

        iTemp =+ iTemp + tempOffset

        if iTemp >=24: # correct for day change

            iTemp = iTemp -24

        hrs = str(iTemp)

        mins = tempTime[2:4]

        secs = tempTime[4:6]

    # if GPS time is before than 10:00 am

    if len(tempTime) ==5:

        iTemp = int(tempTime[0]) # extract hours

        iTemp =+ tempOffset

        hrs = str(iTemp)

        mins = tempTime[1:3]
 
        secs = tempTime[3:5]

    formattedTime = "%s:%s:%s" % (hrs, mins, secs)

    return formattedTime


# format longitude and latitude

def formattedPosition(posString):

    tempPos = posString.lstrip('0') # strip leading zeros

    tempPos = tempPos.split('.') # split the decimal part from the position string

    # extract degrees and minutes

    if len(tempPos[0]) ==5:

       tempStr = tempPos[0]

       degrees = int(tempStr[0:3], base=10)

       minutes = int(tempStr[3:5], base=10)


    if len(tempPos[0]) ==4:

       tempStr = tempPos[0]

       degrees = int(tempStr[0:2], base=10)

       minutes = int(tempStr[2:4], base=10)


    if len(tempPos[0]) ==3:

       tempStr = tempPos[0]

       degrees = int(tempStr[0:1], base=10)

       minutes = int(tempStr[1:3], base=10)

    # calculate seconds

    seconds = float(tempPos[1]) * 0.00001

    seconds = seconds * 60


    # format string for output

    formattedPosition = "%i° %i' %.3f\"" % (degrees, minutes, seconds)

    return formattedPosition


# display extracted values

def showValues(gpsData):

    gpsList = gpsData.split(',')

    print("Time(UTC): "+ formatTime(gpsList[1], 0))

    print("Local Time: "+ formatTime(gpsList[1], timeOffset))

    print("Longitude: "+ formattedPosition(gpsList[2]) +" "+ gpsList[3])

    print("Latitude: "+ formattedPosition(gpsList[4]) +" "+ gpsList[5])

    print("Altitude: "+ gpsList[9] +" "+ gpsList[10])

    print("No. of satellites visible: "+str(int(gpsList[7])))

    print()

    return


def main():

    print()

    print("Starting...")

    while1:
        data = ser.readline()

        data = data.decode('utf-8', errors='ignore')

        data = data.rstrip('\n')

        if data.startswith('$GPGGA'):

           if validateChecksum(data):

              showValues(data)

        else:

           print("Checksum not valid")


if __name__ == '__main__':

    main ()

Most of the time the above code works fine, but sometimes crashes out of the program, with a "List index out of range error." for tempPos[1] on line 91. I think this only happens when the number of visible satellites goes really low.

This what the output should look like when up and running:-

Time(UTC): 12:44:18
Local Time: 14:44:18
Longitude: xx° xx' 19.138" N
Latitude: x° xx' 6.168" E
Altitude: 20.6 M
No. of satellites visible: 9