1. Introduction
2. The Core of An Interpreter
3. Taking out the Garbage
4. Wireless Atomic Time
5. Direction & Speed Alerts
6. Are We Fixed Yet?
7. Real-Time Satellite Tracking
8. A World-Class Interpreter
9. Final Thoughts

Comments

1. karaska143
   29 Jun 2008 at 21:50

   Hi , 

   I need the same program as well.Can you find any information.Please contact me.

   tunc@te-mob.com

    

2. Weta Hekawi
   21 Aug 2007 at 11:19

    

   The checksum routine has been modified slightly to clarify the Select statement.

   The "$" case is used to initialise Checksum and the If statement in the Else case has been removed.  This works because Checksum = value gives the same result as Checksum = 0 Xor value when processing the first byte.

    

       ' Calculates the checksum for a sentence

       Public Function GetChecksum(ByVal sentence As String) As String

           ' Loop through all chars to get a checksum

           Dim Character As Char

           Dim Checksum As Integer = 0

           For Each Character In sentence

               Select Case Character

                   Case "$"c

                       ' Ignore the dollar sign

                       Checksum = 0

                   Case "*"c

                       ' Stop processing before the asterisk

                       Exit For

                   Case Else

                       ' XOR the checksum with this character's value

                       Checksum = Checksum Xor Convert.ToByte(Character)

               End Select

           Next

           ' Return the checksum formatted as a two-character hexadecimal

           Return Checksum.ToString("X2")

       End Function

3. Weta Hekawi
   21 Aug 2007 at 11:02

   The NMEA protocol specifies that the last parameter is immediately followed by "*" and a 2-cfharacter checksum.  For example, 3.45,"W"*1A is valid as is 200804,,*1A.  In the fist case there is data in the last parameter and in the second case, because the last parameter has been omitted. we effectively have "200804,," & "" & "*" & "1A".  That is the data string upto the second last parameter and it's following comma, the omitted final parameter, the asterisc to denote both end of data and the start of  the checksum, and finally the 2-character checksum.

   Jon's excellent articles give us the start for writing our code but does say that additional error trapping is required.

   My change to the GetWords function is:

       Public Function GetWords(ByVal sentence As String) As String()

           Dim temp As String

           temp = sentence.Substring(0, sentence.IndexOf("*")) & ",*"

           Return temp.Split(","c)

       End Function

4. Imtiyaz Momin
   19 Aug 2007 at 08:01
   Try my gps string parser http://www.gpsxml.com/gpsxml/service.asmx?op=GPS2XML
   
   I need somebody to test my mobile APP. You can download the cab file from http://gps.gpsxml.com/viewtopic.php?t=4
   
   Please feel free to give any comments, suggestions or ideas
   
   Thanks
   Imtiyaz Momin
   http://gps.gpsxml.com/
   imtu80@hotmail.com
   
   
   
   
   
   
   
   
   
5. Imtiyaz Momin
   16 Aug 2007 at 06:01
   I need somebody to test my mobile APP. You can download the cab file from http://gps.gpsxml.com/viewtopic.php?t=4
   Also, added new feature where I can upload picture from the phone using my application and the picture shows up on the trail where the picture was taken.
   Check it out at http://gps.gpsxml.com/tracker.cfm?userID=1
   Please feel free to give any comments, suggestions or ideas
   
   Thanks
   Imtiyaz Momin
   http://gps.gpsxml.com/
   imtu80@hotmail.com
   
   
   
   
   
   
   
   
6. nev browitt
   28 Jun 2007 at 10:19

   I am a novice programmer and need to get my hands on some code for phone tracking which will plot a phones movement every (n) minutes then plot the position  on a map.

   Any help at all will be greatly appreciated.

   Can anyone please please help me.

   Thanks
   Nev
   

7. Imtiyaz Momin
   21 Jun 2007 at 02:48
   http://gps.imomin.com/tracker.cfm?userID=1
   
   Above link shows an example which I created for my brother for his carpc.
   It can covertly run on mobile device and send location information via internet.
   let me know what you think and anything can be done with my project.
   
   
   Imtiyaz Momin
   imtu80@hotmail.com
   http://www.imomin.com
   
   
   
   
   
   
   
   
   
8. Jean Pereira Fernandes
   10 Jun 2007 at 15:20

   Regarding with GPRMC message

   $GPRMC,040302.663,A,3939.7,N,10506.6,W,0.27,358.86,200804,,*1A

   Some antennas (like Leadtek) See quotes, transmitt the last parameter before * char like this

   $GPRMC,040302.663,A,3939.7,N,10506.6,W,0.27,358.86,200804,3.45,"W"*1A

   Other antennas (like Garmin), transmit the last parameter like this

   $GPRMC,040302.663,A,3939.7,N,10506.6,W,0.27,358.86,200804,3.45,"W",*1A

   Note that has a colon "," before * char.

   Please someone explain me this question.

   Thanks.

   Jean

9. ravi422
   19 Apr 2007 at 07:21
   Hi,
   
   Can I get the c# code for this nice article?
   
   Regards,
   Ravi
   
   
   
   
   
   
   
10. levyuk
    12 Apr 2007 at 12:31

    Well...as soon as you write a post you figure soething out.

    It seems that the error is only thrown when there isn't enough data in the nmea sentence because if I use this sentence

    $GPGSV,2,2,08,14,28,047,21,28,20,259,,19,16,156,26,23,07,254,41*71

    it seems to work fine. I think the problem is with the SNR for the first satellite in view as the previous NMEA didn't have a value for this.

    Hope this helps someone.

11. levyuk
    12 Apr 2007 at 12:23

    Nice article, very useful except I've come across a problem with the GPGSV sentences. If you try and run this code

    MyInterpreter.Parse("$GPGSV,2,1,08,11,78,132,,20,63,226,,01,46,102,,17,33,308,*71")

    It will throw an error (Conversion from string "*71" to type 'Integer' is not valid.)

    This is because of this line of code

    SignalToNoiseRatio =

    CType(Words(Count * 4 + 3), Integer)

    Does anyone know how to solve this problem as it's kind of a thorn in my side and I can't get rid of it.

    Cheers

    Jon

12. Marius Sanjeewa Jayasuriya
    14 Mar 2007 at 21:31

    I like to write GPS navigating system pleas tell me what kind of hardware and signals I need, I am living in Sri Lanka, how I get that connection

13. Alex Etchells
    23 Mar 2006 at 08:32

    If you require Ordnance Survey Grid References, I have written an article on how to do so using NMEA data derived from Jon Person's excellent NMEAinterpreter class.
    

    
    GPS- Deriving British Ordnance Survey Grid Referece from NMEA data
    

    AlexE
    
    
    

14. Alex Etchells
    14 Mar 2006 at 13:08
    I spotted this slight error too and made the same correction as c_programming_guru.
    However this led to a new error as the final word in the string contained the checksum.
    ie in the example sentence
    
    $GPGSV, 3, 1, 10, 24, 82, 023, 40, 05, 62, 285, 32, 01, 62, 123, 00, 17, 59, 229, 28*70
    
    the final word would be 28*70
    this caused an error when trying to convert this to an int32 in the line
    
    SignalToNoiseRatio = Convert.ToInt32(Words[Count * 4 + 3]);
    
    My solution was to remove the checksum part of the sentence in GetWords, before splitting the sentence
     
        public string[] GetWords(string sentence)
        {
            //remove the final * + checksum
            sentence = sentence.Substring(0, sentence.IndexOf("*"));
            //now split it up
            return sentence.Split(',');
        }
    
    
    Assuming that I'm not talking out of my rear, I hope this proves useful
    Alex
     
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
15. c_programming_guru
    13 May 2005 at 18:11
    I love this product. Excellent Job on this product, Jon Person !. I'm really excited infact I am going to go buy and support your product 360%!... I just have to correct 1 minor error. I feel you should be aware or maybe your are already....don't know might have been a typo,... I'm not much of a VB coder but, I believe during the ParseGPGSV() function, which is suppose to parse the "Satellites in View" $GPGSV sentence.... If you look closesly. During the...
    
    Original Article: http://www.gpsdotnet.com/kb/article.aspx?id=10350
    Example Sentence: $GPGSV, 3, 1, 10, 24, 82, 023, 40, 05, 62, 285, 32, 01, 62, 123, 00, 17, 59, 229, 28*70
    
    Each Block consist of 4 words.. "24, 82, 023, 40"  ==  "PseudoRandomCode, Elevation, Azimuth, SignalToNoiseRatio"
    According to your Article... SNR values range from 0-50...where 50 means "Excellent Signal"...though SNR can go as high as 99, like you've stated.
    
    
    
    
    ' Yes. "Extract satellite information and report it" -- section.
    ' ERROR suspect
    
        Azimuth = CType ( Words ( Count * 4 + 2 ), Integer)
        SignalToNoiseRatio = CType( Words ( Count * 4 + 2 ), Integer)    
                                                                             '// ^--- Logical Bug, I believe it should be ....
    
    ' CORRECTION
        SignalToNoiseRatio = CType ( Words ( Count * 4 + 3), Integer)
                                                                             '// ^--- This would be correct.
    
    
    Otherwise I believe it would return the same value from the Azimuth extraction. So you wouldn't get any SNR information to be able to base precision correctly. For the future of dependability and reliability of code production, I post this correction. As far as the Signal Strength of the satellites, within the Notification, of the Event call to,...
    
             RaiseEvent SatelliteReceived ( PseudoRandomCode,  Azimuth,  Elevation,  SignalToNoiseRatio )
    
    I believe it would generate incorrect results...to what ever is going to be done with the SNR variable.
    Please feel free to e-mail me at deciphered_scripturez@yahoo.com for additional details...I really Thank you, Jon Person, for your hard work and time put into this and I really would LOVE to help as much as possible...I believe in your product. !    
    
                                                                                                                                                                  Thank You,
                                                                                                                                                                   -- c_programming_guru
16. James Crowley
    02 Apr 2005 at 20:37

    As I understand it, that should be fine... so long as you add a GPS receiver?

17. mittalpa
    11 Jan 2005 at 13:13
    Hi
    Just curious, what kind of hardware and signal service will be required to make it happen?
    I have a ViewSonic V37 pocket PC. Will that be a good instrument for this? Please advice.
    Thanks
    Pankaj
18. Steve Hilton
    08 Oct 2004 at 08:44
    Jon Person's article is a particularly interesting look into how GPS systems work.  I've been interested in GPS for a long time but not knowing how this new "black box" technology worked kept me away from delving into it.  After reading Jon's article I now realize that it's not nearly as difficult as I once thought.  I plan on buying his “GPS.NET Global Positioning SDK” component so I can begin writing applications utilizing GPS.  Who knows, perhaps I'll stumble onto a successful application with vertical market benefit.
    
    Thank you, Jon.  I look forward to your next article.
    
    Steve
    
19. Developer Fusion Bot
    01 Jan 1999 at 00:00

    This thread is for discussions of How to Write a GPS Application.