Decoding GPS with C#

[C222]

I have a fairly old GPS receiver that communicates with my desktop through COM1.

I found some code on the internet to decode the strings i get from the receiver which look something like:

Code: Select all

$GPGSA,A,1,,,,,,,,,,,,,1.27,0.75,1.03*04
$GPRMC,215606,V,3511.1990,N,12904.2725,W,0.000,0.0,151208,15.0,E*45
$PRWIZCH,29,6,12,0,12,0,31,0,24,6,31,0,16,0,31,0,31,0,31,0,31,0,12,0*44
$GPGGA,,,,,,0,00,,,,,,,*66
$GPGSA,A,1,,,,,,,,,,,,,1.27,0.75,1.03*04
$GPGSV,3,1,12,29,70,024,34,24,70,006,39,30,50,190,,21,48,264,*79
$GPGSV,3,2,12,10,34,052,,05,28,173,,18,21,194,,12,20,163,*73
$GPGSV,3,3,12,16,11,321,,31,11,268,,15,09,124,,26,07,108,*73
$GPRMC,215607,V,3511.1990,N,12904.2725,W,0.000,0.0,151208,15.0,E*44
$PRWIZCH,29,6,12,0,12,0,31,0,24,6,31,0,16,0,31,0,31,0,31,0,31,0,12,0*44
$GPGGA,,,,,,0,00,,,,,,,*66

The code if found here.
Using a resource I found on the internet i can tell that the GPS is working and giving me a fairly accurate location (once i get a fix).
However, this is over a terminal application called Tera Term and my GPS requires me to broadcast the command "ASTRAL" before any useful data is sent. The problem is, the code from the link above has no command to submit the command "ASTRAL". I tried:

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private void button3_Click(object sender, EventArgs e)
        {
            if (comport.IsOpen)
            {
                //byte astral;
                //astral = Convert.ToByte("ASTRAL");
                comport.Write("ASTRAL");
                comport.WriteLine("ASTRAL");
            }
            else
            {
            }
        }

But that didn't work. Any suggestions?

[wing]

NMEA 0813

That'll be your standard for GPS-over-serial (also GPS over USB - most USB GPS units just have a silly little USB=>Serial chip glued in them and will load up a virtual serial port driver)

The serial port library in .NET works great - I've used it several times (though not for GPS yet), go ahead and write your own device interaction layer. GPS isn't THAT hard.

http://www.kh-gps.de/nmea-faq.htm
A handy little resource for you to start with writing a parser.

Edit: Okay, I'm bored, I have a receiver, and I have a need to write this code for a project anyway. Give me a little bit and I'll post what I come up with.



I've never seen a GPS requiring you to send a command to start off the process - in fact, 0813 is technically unidirectional. Mine just spits out data, happy as can be, across the serial port even if there isn't anything bloody connected. Mind posting up some of the data that you see before sending the command? Your GPS may be trying to emulate another signaling method from older equipment, or something.

[C222]

Yes, my receiver is NMEA 0183 and yes, generally the data flow is one-way.
However, the Delorme Tripmate is weird. It will send the string "ASTRAL" until it runs out of power or receives the same string "ASTRAL".

My source:
http://bevhoward.com/TripMate.htm

[hotaru]

Code: Select all

                comport.Write("ASTRAL");
                comport.WriteLine("ASTRAL");

are you really writing "ASTRAL" and then "ASTRAL\n" to it? if so, are you supposed to be doing that?

[C222]

It was only "ASTRAL"
However, I just tried "ASTRAL\n", "ASTRAL\r", "ASTRAL\n\r", and "ASTRAL\r\n"
None worked.

[wing]

I don't see why it would, but C# may be trying to write Unicode to the serial port, which would be decidedly not-right. (this DOES work if you're using teraterm or hyperterm or some other direct ASCII-native serial app, right?)

Try sending the raw ASCII bits. Also, you need to terminate in CR/LF (both, not one or the other)