Gunther
Posts: 4
Joined: Fri Aug 06, 2004 12:38 pm

more NMEA data needed ($GPGGA) for my application

Fri Aug 06, 2004 12:40 pm

Hi Johan,

thank you for your help. I think TomTom for PPC is a very strange problem and there doesn't help anything. The other question is the functionality of your PC programm for me. I have constructed some devices for GPS logging for instance as an automatic long time tracking system for cars (like a "black box"). Any serial GPS device sends its data to an embedded micro controller "BASIC-Tiger" from Wilke Technology Aachen (Germany, www.wilke-technology.com - look at applications) and this device sends its (calculated and filtered) data to a memory card (smart media card 16MB...128MB). The data format is exact the same like NMEA without invalid data. The stored file format is simply a text (.txt) file. Independently from input data I send then the data $GPGGA and $GPRMC to a serial port too. The $GPGGA is important for speed tracking. In your program, I think, is a filter that stops the $GPGGA data. The stored track I can see without your programm for instance in fugawi. Your program can show the stored track in "real time" - that's good! But for me would be better a GpsGate with $GPGGA data to show the speed simultaneously.
I hope you understand my bad english???

Best regards

Gunther

User avatar
johan
GpsGate
Posts: 14323
Joined: Wed Aug 04, 2004 10:40 pm
Location: Sweden
Contact: Website

RE: more NMEA data needed ($GPGGA) for my application

Fri Aug 06, 2004 1:33 pm

Hi Gunther!

Have I understood you correctly if I assume you have made a logfile with your "black-box", and that you try to replay that log file using the Log feature in GpsGate?

The Log feature can replay any file containing NMEA data, but it will filter out all data that is not recognized as NMEA. This may typically be becasue the checksum is false or that there simply is some "garbage" in the file, or that each line is not ended with carriage return + line feed CR/LF.

If you post some lines from your black-box logfile I can take a look at them.

/Johan

Franson Support

Gunther
Posts: 4
Joined: Fri Aug 06, 2004 12:38 pm

RE: more NMEA data needed ($GPGGA) for my application

Fri Aug 06, 2004 1:55 pm

Hi Johan,
here is a part of my NMEA data as text file. If you want I can send you a complete file (with all unvisible data). But where I can post such a file (as attachment?)

Best regards
Gunther


$GPRMC,041107.996,A,5057.6637,N,01102.9779,E,031.4,144.1,210704,001.3,E*68
$GPGGA,041108.996,5057.6565,N,01102.9862,E,1,04,02.9,00247.1,M,46.3,M,0,*68
$GPRMC,041108.996,A,5057.6565,N,01102.9862,E,031.6,144.0,210704,001.3,E*65
$GPGGA,041109.996,5057.6496,N,01102.9945,E,1,04,02.9,00246.8,M,46.3,M,0,*68
$GPRMC,041109.996,A,5057.6496,N,01102.9945,E,031.5,143.4,210704,001.3,E*6D
$GPGGA,041110.996,5057.6427,N,01103.0029,E,1,04,02.9,00246.5,M,46.3,M,0,*6C
$GPRMC,041110.996,A,5057.6427,N,01103.0029,E,030.9,143.2,210704,001.3,E*6F
$GPGGA,041111.996,5057.6357,N,01103.0110,E,1,04,02.9,00246.3,M,46.3,M,0,*60
$GPRMC,041111.996,A,5057.6357,N,01103.0110,E,030.9,143.1,210704,001.3,E*66
$GPGGA,041112.996,5057.6288,N,01103.0192,E,1,04,02.9,00246.2,M,46.3,M,0,*6B
$GPRMC,041112.996,A,5057.6288,N,01103.0192,E,030.9,143.1,210704,001.3,E*6C
$GPGGA,041113.996,5057.6219,N,01103.0274,E,1,04,02.9,00246.3,M,46.3,M,0,*68

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johan
GpsGate
Posts: 14323
Joined: Wed Aug 04, 2004 10:40 pm
Location: Sweden
Contact: Website

RE: more NMEA data needed ($GPGGA) for my application

Fri Aug 06, 2004 3:13 pm

Hi!

The reason the $GPGGA sentences are not replayed is that the checksums are incorrect. The Log replay in GpsGate does check the checksum and filters out all sentences with incorrect checksum. The checksums for the $GPRMC sentences are correct.

Johan

Franson Support

va3gy
Posts: 17
Joined: Wed May 31, 2006 6:05 am
Location: Canada

RE: more NMEA data needed ($GPGGA) for my application

Wed Jun 17, 2009 12:15 am

I need to build a GGA string manually because the positions I am getting are from a non standard device.

Is there a way to calculate the checksum for a string built like this ??

Ewan

bpokorny
Posts: 5
Joined: Thu May 28, 2009 11:49 pm

RE: more NMEA data needed ($GPGGA) for my application

Fri Jun 26, 2009 8:04 pm

Not sure if this will help since I have not had to do that before. I did a quick search and found this document from novatel.

http://www.novatel.com/Documents/Bulletins/apn030.pdf

va3gy
Posts: 17
Joined: Wed May 31, 2006 6:05 am
Location: Canada

RE: more NMEA data needed ($GPGGA) for my application

Sat Jun 27, 2009 5:54 am

Thanks bpokorny but I am glad to say I have it working

Regards


Ewan



Private Sub outTIMER_Tick(ByVal sender As Object, ByVal e As System.EventArgs) Handles outTIMER.Tick

If IsOpen = True Then

my_vPort.DataToPort("$GPVTG,054.7,T,034.4,M,005.5,N,010.2,K*48" & vbCrLf)
my_vPort.DataToPort("$GPGSV,2,1,08,01,40,083,46,02,17,308,41,12,07,344,39,14,22,228,45*75" & vbCrLf)

Dim InputString As String = "GPGGA,123519," & lastLat & "," & lastLon & ",1,08,0.9,545.4,M,46.9,M,,"

Dim chksum As Byte = CheckSum(InputString)

Dim finalSTR As String = Hex(chksum)

my_vPort.DataToPort("$" & InputString & "*" & finalSTR & vbCrLf)

End If

End Sub

Public Function CheckSum(ByVal InputString As String) As Byte

Dim characters() As Byte
Dim I As Integer
Dim C As Integer = InputString.Length
Dim chksum As Byte

Dim encoding As New System.Text.UTF8Encoding
characters = encoding.GetBytes(InputString)

chksum = 0
For I = 0 To C - 1
chksum = chksum Xor characters(I)
Next I

Return chksum

End Function

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