What follows is the code for a module that can be inserted into a VB.net project. Call the sub with the comm port that the GPS radio is on and you are set. Also add a Serial Port Control to your form and name it “serialPort”. Timeout is required in case an incorrect serial port has been specified.
Programming note: Even with the timeout set in the code, the application will lock up if an incorrect, but active comm port has been specified. If you know of a fix post it in the comments.
Imports System
Imports System.IO.Ports
Module gps
Public strLatitude As String = ""
Public strLongitude As String = ""
Public Sub queryGPS(ByVal cPort As String)
Dim loopCount As Integer = 0
Dim GPSOutput As String = ""
Dim GPSGPRMCStr As String = ""
Dim newLineStr As String = "$"
Dim aStrSplitItems() As String
Dim NSHemi As String = ""
Dim EWHemi As String = ""
Dim EW As Integer = 0
Dim NS As Integer = 0
Dim commQuit As Boolean = False
Dim portClosed As Boolean = False
Dim dblLatitude As Double = 0
Dim dblLongitude As Double = 0
Dim wsLatitude As String = ""
Dim wsLongitude As String = ""
'Set sentence to parse from GPS Output. Use GPRMC GPGLL, or GPGGA
Dim strSentence As String = "GPRMC"
'Reset coordinate variables()
strLatitude = ""
strLongitude = ""
On Error GoTo Errhandler
'Calls Serial Port Control on main form. Add Serial Port Control to form and name it "serialPort"
'Timeout is required in case an incorrect serial port has been specified. Application will freeze
'if timeout is missing or too lengthy.
frmMain.serialPort = New SerialPort("COM" & cPort, 4800, Parity.None, 8, StopBits.One)
frmMain.serialPort.ReadTimeout = 5
frmMain.serialPort.Open()
readLine:
Dim cCount As Integer = 0
If portClosed = True Then
frmMain.serialPort.Open()
portClosed = False
End If
'Read GPS data from Device - Geographic Position, Latitude/Longitude
GPSOutput = frmMain.serialPort.ReadLine.ToString
GPSGPRMCStr = GPSOutput
'Test string for debugging without a good GPS signal
'GPSGPRMCStr = "GPRMC,174607.000,A,3411.3450,N,07946.0365,W,0.44,160.26,020910,,*12"
If GPSGPRMCStr.Contains(strSentence) Then
commQuit = True
For i = 1 To Len(GPSGPRMCStr.ToString)
If Mid$(GPSGPRMCStr.ToString, i, 1) = "," Then cCount = cCount + 1
Select Case strSentence 'Set the line the program reads in the DIM statement above
Case "GPRMC"
Select Case cCount
Case 3 'Start collecting latitude
strLatitude = strLatitude & Mid$(GPSGPRMCStr.ToString, i, 1)
Case 4 'Get Hemisphere
NSHemi = NSHemi & Mid$(GPSGPRMCStr.ToString, i, 1)
Case 5 'Start Collecting longitude
strLongitude = strLongitude & Mid$(GPSGPRMCStr.ToString, i, 1)
Case 6 'Get Hemisphere
EWHemi = EWHemi & Mid$(GPSGPRMCStr.ToString, i, 1)
End Select
Case "GPGGA"
Select Case cCount
Case 2 'Start collecting latitude
strLatitude = strLatitude & Mid$(GPSGPRMCStr.ToString, i, 1)
Case 3 'Get Hemisphere
NSHemi = NSHemi & Mid$(GPSGPRMCStr.ToString, i, 1)
Case 4 'Start Collecting longitude
strLongitude = strLongitude & Mid$(GPSGPRMCStr.ToString, i, 1)
Case 5 'Get Hemisphere
EWHemi = EWHemi & Mid$(GPSGPRMCStr.ToString, i, 1)
End Select
Case "GPGLL"
Select Case cCount
Case 1 'Start collecting latitude
strLatitude = strLatitude & Mid$(GPSGPRMCStr.ToString, i, 1)
Case 2 'Get Hemisphere
NSHemi = NSHemi & Mid$(GPSGPRMCStr.ToString, i, 1)
Case 3 'Start Collecting longitude
strLongitude = strLongitude & Mid$(GPSGPRMCStr.ToString, i, 1)
Case 4 'Get Hemisphere
EWHemi = EWHemi & Mid$(GPSGPRMCStr.ToString, i, 1)
End Select
End Select
Next
Else
GoTo readLine
End If
strLatitude = Microsoft.VisualBasic.Right(strLatitude, Len(strLatitude) - 1)
NSHemi = Microsoft.VisualBasic.Right(NSHemi, Len(NSHemi) - 1)
strLongitude = Microsoft.VisualBasic.Right(strLongitude, Len(strLongitude) - 1)
EWHemi = Microsoft.VisualBasic.Right(EWHemi, Len(EWHemi) - 1)
If NSHemi <> "" Then
If NSHemi = "N" Then NSHemi = "" Else NSHemi = "-"
If EWHemi = "E" Then EWHemi = "" Else EWHemi = "-"
End If
'Convert Lat and Long to decimel
'********************************************************************
'Strip leading Zeros
dblLatitude = CDbl(strLatitude.ToString)
dblLongitude = CDbl(strLongitude.ToString)
'Add polarity
If NSHemi = "-" Then
dblLatitude = dblLatitude * -1
NS = -1
Else
NS = 1
End If
If EWHemi = "-" Then
dblLongitude = dblLongitude * -1
EW = -1
Else
EW = 1
End If
'Move decimel place two places to the left
dblLatitude = dblLatitude / 100
dblLongitude = dblLongitude / 100
'Get values left of decimel
Dim leftLat As Integer = Math.Abs(dblLatitude)
Dim leftLong As Integer = Math.Abs(dblLongitude)
'Get values right of decimel
Dim rightLat As Double = Math.Abs(dblLatitude) - Math.Abs(leftLat)
Dim rightLong As Double = Math.Abs(dblLongitude) - Math.Abs(leftLong)
'Convert to minutes
rightLat = (rightLat * 100) / 60
rightLong = (rightLong * 100) / 60
'Lat/Long in decimel, in case you need decimel degrees instead of degrees/minutes/seconds.
wsLatitude = Trim(Str(CDbl(strLatitude) * NS))
wsLongitude = Trim(Str(CDbl(strLongitude) * EW))
'Lat/long in Degrees/Minutes/Seconds in decimel form
strLatitude = Trim(Str((leftLat + rightLat) * NS))
strLongitude = Trim(Str((leftLong + rightLong) * EW))
frmMain.serialPort.ReadBufferSize = 0
frmMain.serialPort.Close()
portClosed = True
'*********************************************************************
'Comment out else section when deployed. Work with results in main sub
'*********************************************************************
'Sometimes reception is poor and it takes more than one pass of the data to get a fix
'This section forces another read of the GPS device when the coordinates are null or
'contain zeros. Note: The application as written will fail on the prime meridian when
'at the equator.
If strLatitude = "" Or strLongitude = "" Or strLatitude = "0" Or strLongitude = "0" And commQuit = True Then
loopCount = loopCount + 1
If loopCount > 10 Then
MsgBox("The GPS device is currently not getting a fix, please try again later." _
& Chr(10) & GPSOutput, vbOKOnly, "Satellite Communication Unavailable")
Exit Sub
Else
GoTo readLine
End If
Else
'Access web service from arc to return a list of addresses within a certain range of the inspector's location.
'Web Service is currently in SC stateplane.
'A google test.
'System.Diagnostics.Process.Start("http://maps.google.com/maps?q=" & strLatitude & "%2C" & strLongitude)
End If
'********************************************************************
Exit Sub
Errhandler:
Select Case Err.Number
Case 5
Resume Next
Case 13
'MsgBox(Err.Number & " " & Err.Description)
Resume Next
Case 57
'MsgBox(Err.Number & " " & Err.Description)
MsgBox("Comm Port not available", MsgBoxStyle.Exclamation, "Communication Error.")
Exit Sub
Case 91
'MsgBox(Err.Number & " " & Err.Description)
Resume Next
Case 8002
'GPSComm.PortOpen = False
MsgBox("Comm Port not available", MsgBoxStyle.Exclamation, "Communication Error.")
'GPSComm.PortOpen = True
Resume Next
Exit Sub
Case Else
MsgBox(Err.Number & " " & Err.Description)
Resume
Resume Next
End Select
End Sub
End Module
