Have a look at the word document linked to in this thread http://forums.ni.com/ni/board/message?board.id=170&message.id=227405#M227405 whilst this is reading GPS data from a Bluetooth port the actual part parsing the NMEA data will be the same for you, all it does is look for an update in the GPRMC string and when that occurs it passes the data to the next portion of the vi where the speed is extracted and converted to MPH, the last known good data is then held in the shift register waiting to be updated with fresh data.
You will need Lat/ Long values which are easy to obtain from the GPRMC string - Note look for GPRMC rather than $GPRMC as the $ sign makes a mess of what the application looks for as its a wild card - This issue cost me a bit of head scratching at first!
Finally keep an eye on Baud rate if you have a 20Hz GPS system as at the lower speeds you might not get all the data from the device, most civil GPS receivers are 1Hz but there are some that can clock at 20Hz even though they cost a fortune (circa £1600 for the last 20Hz unit I had a play around with in my car) - Mike
