Figure 1

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Figure 1 Global Positioning Codes

RMC - GPS/Transit Data
Example:
$GPRMC,180258,A,4056.4604,N,07216.9673,W,3.965,263.0,130800, 14.8,W*41
Fields: Time of fix (hhmmss), Status (A=OK, V=warning), latitude, N/S, longitude, E/W, ground speed (knots), course, date of fix (ddmmyy), magnetic variation, E/W, checksum
GGA - Global Positioning Fix Data
Example:
$GPGGA,180300,4056.4602,N,07216.9702,W,1,06,1.34,8.4,M, -34.6,M,,*43
Fields: Time of fix (hhmmss), latitude, N/S, longitude, E/W, Quality (0=invalid, 1=GPS fix, 2=DGPS fix), number of satellites tracked, horizontal dilution of position, altitude, M (for meters), height of geoid above WGS84 ellipsoid, seconds since last DGPS update, DGPS station ID, checksum
GSA - Active Satellites and Dilution of Precision
Example:
$GPGSA,A,3,17,23,09,29,26,,,,,,,,2.48,1.34,2.09*00
Fields: Selection of 2D/3D fix (A=automatic, M=manual), Fix type (2=2D, 3=3D), pseudo-random number (PRN) ID of satellites, position dilution of precision (PDOP), horizontal dilution of precision (HDOP), vertical dilution of precision (VDOP), checksum
GSV - Satellites in View
Example:
$GPGSV,3,2,09,21,21,298,33,15,18,319,28,29,16,246,36,03, 10,299,28*7D
Fields: Number of GSV sentences in this group, number of this sentence, number of satellites in view, satellite PRN, elevation, azimuth, signal strength (all repeated up to four times per sentence), checksum

Figure 2 CommCheck

  Dim flag ' Is input currently being read?
Dim strUnparsed As String ' All the input data that needs to be broken into 
                          ' phrases

Private Sub btnGo_Click()

If flag = 0 Then ' you're turning on input
    If MSComm1.PortOpen = False Then
        MSComm1.CommPort = 1
        MSComm1.Settings = "4800,N,8,1"
        MSComm1.PortOpen = True
    End If

    flag = 1
    txtDisplay.Text = ""
    btnGo.Caption = "Stop"
Else ' you're turning off input
    flag = 0
    If MSComm1.PortOpen = True Then MSComm1.PortOpen = False
    btnGo.Caption = "Go"
End If

End Sub

Private Sub Form_Load()
    flag = 0
    Timer1.Interval = 1000 ' Every second, poll the GPS device
End Sub
Private Sub Timer1_Timer()

If flag = 1 Then
    FetchInput
    ParseInput
End If

End Sub

Sub FetchInput()
On Error Resume Next
     
If flag = 1 Then ' Only parse while comm port is open
     b$ = MSComm1.Input
     strUnparsed = strUnparsed + b$
End If

End Sub

Sub ParseInput() ' Only parse complete phrases
Dim strCurrent As String  ' All the input data in the current string
Dim crpos As Integer

If Len(strUnparsed) = 0 Then Exit Sub ' Nothing new to parse!

crpos = InStr(1, strUnparsed, vbCr) ' Find the EOL in the current input

Do While crpos > 0 ' Loop thru the current input, breaking phrases at EOLs
   strCurrent = Left(strUnparsed, crpos - 1)
   strUnparsed = Mid(strUnparsed, crpos + 2)
   crpos = InStr(1, strUnparsed, vbCr)
   
   ' Add current input to the textbox
   txtDisplay.Text = txtDisplay.Text & strCurrent & vbCrLf
   
   ' If the textbox is getting long, only show the last 1500 chars
   If Len(txtDisplay.Text) > 1500 Then txtDisplay.Text = _
       Right(txtDisplay.Text, 1500)
   
   ' Move the selection to the end of the textbox
   txtDisplay.SelStart = Len(txtDisplay.Text)
Loop

End Sub

Figure 4 TripMate Initialization Codes

PRWIINIT - TripMate Initialization
Example:
$PRWIINIT,V,,,3338.6000,N,11155.0000,W,0,0,M,0,T, 190500,021000
Fields: Status (A=cycle unit off, V=init string), null, null, null, latitude, N/S, longitude, E/W, speed, altitude, M, bearing, compass true? (T=true),date (ddmmyy),GMT (hhmmss)
PRWIILOG - Request Specific Strings Only
Example:
$PRWIILOG,RMC,A,T,1,0
Fields: Message to turn on/off, status (A=string on, V=off), T, interval in seconds, 0

Figure 5 Plotting Satellites

  Sub PlotSat(satelev As Integer, satazim As Integer)

Dim x, y
pi = 3.14159265358979

' Correct so that N = up
satazim = (satazim - 90) Mod 360

x = 180 + satelev * Cos((satazim * pi / 180))
y = 180 + satelev * Sin((satazim * pi / 180))
picCompass.ForeColor = RGB(255, 0, 0)
picCompass.PSet (x, y), RGB(255, 0, 0)

End Sub