CODEWITHSUNDEEP
vb.netvisual-studio-2010gps
Bird87 ZA
Bird87 ZA

Reputation: 2160

How do I read the position data from a GPS (NMEA) device?

I'm trying to read data from a GPS device (NMEA). I am getting the data successfully. However, as soon as I start using it, it gives me gibbirish. This is what I get from the GPS:

$GPGSA,A,3,20,25,31,22,14,29,03,16,32,06,27,,1.5,0.8,1.3*33
$GPRMC,120556.000,A,2546.0985,S,02816.0193,E,0.22,276.44,291013,,,A*7A
$GPGGA,120557.000,2546.0984,S,02816.0191,E,1,11,0.8,1396.3,M,21.5,M,,0000*71
$GPGSA,A,3,20,25,31,22,14,29,03,16,32,06,27,,1.5,0.8,1.3*33
$GPGSV,3,1,12,31,50,165,19,14,48,055,27,16,43,304,42,32,36,265,38*76
$GPGSV,3,2,12,29,24,119,31,06,19,355,34,20,14,238,41,25,10,138,19*78
$GPGSV,3,3,12,27,09,351,33,22,06,008,36,03,05,341,36,23,,221,*7F
$GPRMC,120557.000,A,2546.0984,S,02816.0191,E,0.17,274.76,291013,,,A*7D
$GPGGA,120558.000,2546.0982,S,02816.0189,E,1,11,0.8,1396.0,M,21.5,M,,0000*72
$GPGSA,A,3,20,25,31,22,14,29,03,16,32,06,27,,1.5,0.8,1.3*33
$GPRMC,120558.000,A,2546.0982,S,02816.0189,E,0.07,220.52,291013,,,A*7B
$GPGGA,120559.000,2546.0981,S,02816.0187,E,1,11,0.8,1395.7,M,21.5,M,,0000*7A
$GPGSA,A,3,20,25,31,22,14,29,03,16,32,06,27,,1.5,0.8,1.3*33
$GPRMC,120559.000,A,2546.0981,S,02816.018

The above was received by doing the following:

//inside a 100ms ticker
Dim data As String = GpsPort.ReadExisting()
CommentBox.AppendText(data)

As soon as I do Dim strArr() As String = data.Split("$") then output it using:

CommentBox.AppendText(strArr(0).ToString) // inside the same ticker

the output is:

034.000,2546.0985,S,02816.0298,E,1,11,0.8,1360.6,M,21.5,M,,0000*77
3,20,29,14,22,31,25,03,16,32,06,27,,1.5,0.8,1.3*33
MC,121034.000,A,2546.0985,S,02816.0298,E,0.01,236.13,291013,,,A*75
.000,2546.0983,S,02816.0297,E,1,11,0.8,1359.9,M,21.5,M,,0000*7A
A,A,3,20,29,14,22,31,25,03,16,32,06,27,,1.5,0.8,1.3*33
,121035.000,A,2546.0983,S,02816.0297,E,0.06,283.04,291013,,,A*72
036.000,2546.0982,S,02816.0296,E,1,11,0.8,1359.3,M,21.5,M,,0000*73
3,20,29,14,22,31,25,03,16,32,06,27,,1.5,0.8,1.3*33
MC,121036.000,A,2546.0982,S,02816.0296,E,0.03,190.30,291013,,,A*72
.000,2546.0981,S,02816.0296,E,1,11,0.8,1358.6,M,21.5,M,,0000*75
A,A,3,20,29,14,22,31,25,03,16,32,06,27,,1.5,0.8,1.3*33
3,1,12,31,49,161,28,14,46,052,20,16,45,301,39,32,36,268,35*79
3,2,12,29,23,122,18,06,21,355,27,20,15,240,40,27,11,351,37*78

Can anyone assist me in getting the GPS co-ordinates from the GPGGA strings? Because splitting them clearly doesn't work.

Upvotes: 1

Views: 2894

Answers (2)

AlexWien
AlexWien

Reputation: 28727

You have to read the data line by line. Each line is one NMEA sentence.

Once you detect "$GPGGA" (or you also could use the RMC message) you have this line:

$GPGGA,120557.000,2546.0984,S,02816.0191,E,1,11,0.8,1396.3,M,21.5,M,,0000*71

Now you splitt by delimiter ","

Then this is latitude : 2546.0984,S
And this is longitude 02816.0191,E

read at NMEA spec which format the coordinates are: I think: the first to digits in latitdue are degrees, the rest is minutes: 25° 46.0984 minutes. If "S" multiply the result with -1.

slightly different for longitude: 02816.0191,E

first 3 digits degrees, rest minutes. 27° 16.0191 minutes. multiply with -1 if "W".

Upvotes: 2

Michael J. Gray
Michael J. Gray

Reputation: 9906

Basically, the messages you are seeing are part of a rather complicated message format. Each part means something different and the meanings depend on the message type.

You may want to look at some of the code in this open source project. I wrote this library with a colleague and it parses out those messages from a specific GPS device, but it should work with pretty much any device putting out the same data.

Upvotes: 0

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