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VB6 NMEA Interpreter Class for Reading GPS

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  10 years ago

  by Developer Fusion Bot

  Developer Fusion Bot

  , United Kingdom

  Joined 3 years ago

  This thread is for discussions of VB6 NMEA Interpreter Class for Reading GPS.

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  3 years ago

  by AlexE

  Alex Etchells

  , United Kingdom

  Joined 3 years ago

  As I delve deeper into NMEA sentences I am improving my understanding.
  The value that is extracted from the GGA string as 'altitude' is in fact the height
  above the WGS84 ellipsoid and not altitude.
  
  Alex
  
  
  
  
  
  

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  3 years ago

  by AlexE

  Alex Etchells

  , United Kingdom

  Joined 3 years ago

  The software in which I was using this class started throwing up the odd runtime error.
  To cut a long story short the GPS unit in question was sending truncated sentences and very occasionally the last 2 characters of the truncated sentence happened to equal the checksum resulting in an incomplete sentence being treated as valid.
  
  Here is the replacement IsValid function to prevent this from happening.

  Private Function IsValid(ByVal sentence As String) As Boolean
  ' Compare the characters after the asterisk to the calculation
  ' Returns True if a sentence's checksum matches the calculated checksum
  
  
  
  If Len(sentence) < 3 Then
      IsValid = False
      Exit Function
  End If
  
  
  If Mid$(sentence, Len(sentence) - 2, 1) <> "*" Then
      IsValid = False
      Exit Function
  End If
  
  
  
  If Right$(sentence, 2) = GetChecksum(sentence) Then
      IsValid = True
  Else
  
      IsValid = False
  End If
  
  End Function
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  

  
  Alex
  
  
  
  

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  3 years ago

  by KenFberg

  Ken Freudenberg

  , United States

  Joined 3 years ago

  Very useful code.
  However there is an a error which prevents displaying "Satellite time"
  
  The following references the "time" function instead of passing a variable:
  
  
  Private Sub gpsTimeChanged(ByVal Time As String)
  LabelTime.Caption = Time
  End Sub
  
  Accordingly the only time displayed is the system time, not the satellite time.
  
  Suggested simple change:
  
  Private Sub gpsTimeChanged(ByVal CTime As String)
  LabelTime.Caption = CTime
  End Sub
  

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  3 years ago

  by AlexE

  Alex Etchells

  , United Kingdom

  Joined 3 years ago

  Thank you for the compliment. =o)
  
  It's interesting that using Time causes an error for you.
  VB6NmeaInterpreter appends 'GMT' to the time string and this is what I see when I run the software, so I can be confident that I am seeing the satellite time.
  
  I wonder what is making things different for you.
  
  Certainly your suggested fix would avoid the issue in the test application.
  
  Changing
  
  Public Event TimeChanged(ByVal Time As String)
  
  to
  
  Public Event TimeChanged(ByVal satTime As String)
  
  in the VB6NmeaInterpreter class would prevent any future confusion, if using the class in another application.
  
  regards
  
  Alex
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  

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  2 years ago

  by radongp

  ra d

  , United States

  Joined 2 years ago
  I have a question regarding GPS bluetooth and programming in visual basic. Where and how do I specify to my VB project the port # of my GPS port? In other words my GPS's port is 41, in VB what do I need to do in order to connect to that port and get the info out of the GPS into strings in VB??
  
  Anyone's help is greatly appreciated..
  Thanks,
  R..
  
  
  
  
  
  
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