Pocket GPS - Windows Mobile App

#Region "ParseNMEA0183"

Private Sub ParseNMEA(ByVal nmeaSentence As String)

        Dim _CRPosition As Integer
        Dim _CurrentSentence As String

        If nmeaSentence.Length = 0 Then Exit Sub

        Try

            _CRPosition = nmeaSentence.IndexOf(vbCr, 0)

            Do While _CRPosition > 0

                _CurrentSentence = nmeaSentence.Substring(0, _CRPosition - 1)
                If _CRPosition < nmeaSentence.Length - 1 Then
                    nmeaSentence = nmeaSentence.Substring(_CRPosition + 2)
                    _CRPosition = nmeaSentence.IndexOf(vbCr)
                Else
                    _CRPosition = -1
                End If

                If _CurrentSentence.IndexOf("$GPGGA") >= 0 Then ParseGGA(_CurrentSentence)
                If _CurrentSentence.IndexOf("$GPGSV") >= 0 Then ParseGSV(_CurrentSentence)
                If _CurrentSentence.IndexOf("$GPRMC") >= 0 Then ParseRMC(_CurrentSentence)

            Loop

        Catch ex As Exception

            ' Ignore parse errors.

        End Try

    End Sub

#End Region

#Region "ParseGGA"

    ' NMEA 0183 GGA sentences contain global positioning system fix data.
    '
    ' Seq.  Field                       Description
    ' 1     Sentence Id                 Talker ID and sentence ID: GP = GPS, GGA = fix data
    ' 2     UTC time                    UTC time at which fix was taken. Format: hhmmss.sss
    ' 3     Latitude                    Latitude ddmm.mmmm
    ' 4     Latitude hemisphere         Latitude hempisphere: N = North, S = South
    ' 5     Longitude                   Longitude: dddmm.mmmm
    ' 6     Longitude hempishere        Longitude hemisphere: E = East, W = West
    ' 7     Position fix                Fix quality: 0 = Invalid, 1 = Valid SPS, 2 = Valid DGPS, 3 = Valid PPS
    ' 8     Satellites used             Number of satellites being tracked (0-12)
    ' 9     HDOP                        Horizontal dilution of precision
    ' 10    Altitude                    Altitude above mean sea level according to WGS-84 ellipsoid
    ' 11    Altitude units              M = Meters
    ' 12    Geoid separation            Geoid separation above mean sea level according to WGS-84 ellipsoid
    ' 13    Geoid separation units      M = Meters
    ' 14    DGPS age                    Age of DGPS data in seconds (empty field)
    ' 15    DGPS station Id             DGPS station ID number (empty field)
    ' 16    Checksum                    Checksums are optional for most sentences
    '
    ' Samples:
    '   Signal not acquired:
    '       $GPGGA,235947.000,0000.0000,N,00000.0000,E,0,00,0.0,0.0,M,,,,0000*00
    '   Signal acquired:
    '       $GPGGA,092204.999,4250.5589,S,14718.5084,E,1,04,24.4,19.7,M,,,,0000*1F

    Private Sub ParseGGA(ByVal ggaSentence As String)

        Dim _Position As Integer = -1
        Dim _OldPosition As Integer = 0
        Dim _UnparsedSentence As String = ggaSentence
        Dim _CurrentSentence As String = String.Empty
        Dim _Item As String = String.Empty
        Dim _Delimiter As String = String.Empty

        Try

            For i As Integer = 1 To 15

                If i = 15 Then
                    _Delimiter = NMEA_CHECKSUMSTARTCHAR
                Else
                    _Delimiter = NMEA_VALUEDELIMITER
                End If

                _Position = _UnparsedSentence.IndexOf(_Delimiter, _OldPosition + 1)
                _CurrentSentence = _UnparsedSentence.Substring(_OldPosition + 1, _Position - _OldPosition - 1)

                If _CurrentSentence.Length > 0 Then
                    Select Case i
                        Case 2
                            _Item = "UTC Time"
                            Time_Label.Text = TimeSerial( _
                                                    Convert.ToInt32(_CurrentSentence.Substring(0, 2)), _
                                                    Convert.ToInt32(_CurrentSentence.Substring(2, 2)), _
                                                    Convert.ToInt32(_CurrentSentence.Substring(4, 2))).ToLongTimeString
                        Case 3
                            _Item = "Latitude"
                            Latitude_Label.Text = FormatNumber(ToDegrees(_CurrentSentence), 6)
                        Case 4
                            _Item = "Latitude Hemisphere"
                            Latitude_Label.Text += " " & _CurrentSentence
                        Case 5
                            _Item = "Longitude"
                            Longitude_Label.Text = FormatNumber(ToDegrees(_CurrentSentence), 6)
                        Case 6
                            _Item = "Longitude Hempsphere"
                            Longitude_Label.Text += " " & _CurrentSentence
                        Case 10
                            _Item = "Altitude"
                            Altitude_Label.Text = FormatNumber(Convert.ToSingle(_CurrentSentence), 2)
                    End Select
                End If

                _OldPosition = _Position

            Next

        Catch ex As Exception

            Throw New Exception("Error processing GGA. " & _Item & ": " & _CurrentSentence & vbCrLf & ex.Message)

        End Try

    End Sub

#End Region

#Region "ParseGSV"

    ' NMEA 0183 GSV sentences contain data about satellites currently in view.
    '
    ' Seq.  Field                       Description
    ' 1     Sentence Id                 Talker ID: GP = GPS, Sentence ID: GSV = satellites in view
    ' 2     Number of messages          Number of messages in complete message (1 to 3)
    ' 3     Sequence number             Sequence number of this message (1 to 3)
    ' 4     Satellites in view          Total number of satellites currently in view
    ' 5     Satellite Id 1              Range is 1 to 32
    ' 6     Elevation 1                 Satellite elevation in degrees (0 to 90)
    ' 7     Azimuth 1                   Azimuth in degrees (0 to 359)
    ' 8     SNR 1                       Signal to noise ratio in dBHZ (0 to 99)
    ' 9     Satellite Id 2              Range is 1 to 32
    ' 10    Elevation 2                 Satellite elevation in degrees (0 to 90)
    ' 11    Azimuth 2                   Azimuth in degrees (0 to 359)
    ' 12    SNR 2                       Signal to noise ratio in dBHZ (0 to 99)
    ' 13    Satellite Id 3              Range is 1 to 32
    ' 14    Elevation 3                 Satellite elevation in degrees (0 to 90)
    ' 15    Azimuth 3                   Azimuth in degrees (0 to 359)
    ' 16    SNR 3                       Signal to noise ratio in dBHZ (0 to 99)
    ' 17    Satellite Id 4              Range is 1 to 32
    ' 18    Elevation 4                 Satellite elevation in degrees (0 to 90)
    ' 19    Azimuth 4                   Azimuth in degrees (0 to 359)
    ' 20    SNR 4                       Signal to noise ratio in dBHZ (0 to 99)
    ' 21    Checksum                    Checksums are optional for most sentences
    '
    ' Samples:
    '   Signal not acquired:
    '       $GPGGA,235947.000,0000.0000,N,00000.0000,E,0,00,0.0,0.0,M,,,,0000*00
    '   Signal acquired:
    '       $GPGGA,092204.999,4250.5589,S,14718.5084,E,1,04,24.4,19.7,M,,,,0000*1F

    Public Sub ParseGSV(ByVal gsvSentence As String)

        Dim _Position As Integer = -1
        Dim _OldPosition As Integer = 0
        Dim _UnparsedSentence As String = gsvSentence
        Dim _CurrentSentence As String = ""
        Dim _EndSent As Boolean = False
        Dim _Item As String = String.Empty
        Dim _Satellite As Satellite = Nothing
        Dim _SatsInView As Integer = 0

        Try

            ' GSV token
            _Item = "GSV Token"
            _Position = _UnparsedSentence.IndexOf(NMEA_VALUEDELIMITER, _OldPosition + 1)
            _CurrentSentence = _UnparsedSentence.Substring(_OldPosition + 1, _Position - _OldPosition - 1)
            _OldPosition = _Position

            ' total GSV messages in block
            _Item = "Total GSV Messages"
            _Position = _UnparsedSentence.IndexOf(NMEA_VALUEDELIMITER, _OldPosition + 1)
            _OldPosition = _Position

            ' current GSV message number
            _Item = "Current GSV Message"
            _Position = _UnparsedSentence.IndexOf(NMEA_VALUEDELIMITER, _OldPosition + 1)
            _OldPosition = _Position

            ' Sats in view
            _Item = "Satellites in View"
            _Position = _UnparsedSentence.IndexOf(NMEA_VALUEDELIMITER, _OldPosition + 1)
            _CurrentSentence = _UnparsedSentence.Substring(_OldPosition + 1, _Position - _OldPosition - 1)
            _SatsInView = Convert.ToInt32(_CurrentSentence)
            _OldPosition = _Position

            If _SatsInView > 0 Then

                ' Up to 4 sats
                For i As Integer = 1 To 4

                    _Satellite = New Satellite

                    _Item = "Satellite ID"
                    _Position = _UnparsedSentence.IndexOf(NMEA_VALUEDELIMITER, _OldPosition + 1)
                    _CurrentSentence = _UnparsedSentence.Substring(_OldPosition + 1, _Position - _OldPosition - 1)
                    _Satellite.ID = Convert.ToInt32(_CurrentSentence)
                    _OldPosition = _Position

                    _Item = "Elevation"
                    _Position = _UnparsedSentence.IndexOf(NMEA_VALUEDELIMITER, _OldPosition + 1)
                    _CurrentSentence = _UnparsedSentence.Substring(_OldPosition + 1, _Position - _OldPosition - 1)
                    If _CurrentSentence.Length > 0 Then
                        _Satellite.Elevation = Convert.ToInt32(_CurrentSentence)
                    Else
                        _Satellite.Elevation = 0
                    End If
                    _OldPosition = _Position

                    _Item = "Azimuth"
                    _Position = _UnparsedSentence.IndexOf(NMEA_VALUEDELIMITER, _OldPosition + 1)
                    _CurrentSentence = _UnparsedSentence.Substring(_OldPosition + 1, _Position - _OldPosition - 1)
                    If _CurrentSentence.Length > 0 Then
                        _Satellite.Azimuth = Convert.ToInt32(_CurrentSentence)
                    Else
                        _Satellite.Azimuth = 0
                    End If
                    _OldPosition = _Position

                    _Item = "Signal to Noise Ratio"
                    _Position = _UnparsedSentence.IndexOf(NMEA_VALUEDELIMITER, _OldPosition + 1)
                    If _Position = -1 Then
                        _Satellite.SNR = 0
                        _EndSent = True
                    Else
                        _CurrentSentence = _UnparsedSentence.Substring(_OldPosition + 1, _Position - _OldPosition - 1)
                        If _CurrentSentence.Length > 0 Then
                            _Satellite.SNR = Convert.ToInt32(_CurrentSentence)
                        Else
                            _Satellite.SNR = 0
                        End If
                        _OldPosition = _Position
                    End If

                    If m_Satellites.IndexOf(_Satellite.ID) >= 0 Then
                        m_Satellites(m_Satellites.IndexOf(_Satellite.ID)) = _Satellite
                    ElseIf m_Satellites.Count >= 12 Then
                        Dim _OldestSatIndex As Integer
                        Dim _OldestCreateTime As Date = Now
                        For j As Integer = 0 To m_Satellites.Count - 1
                            If m_Satellites(j).Timestamp < _OldestCreateTime Then
                                _OldestSatIndex = j
                                _OldestCreateTime = m_Satellites(j).Timestamp
                            End If
                        Next
                        m_Satellites(_OldestSatIndex) = _Satellite
                    Else
                        m_Satellites.Add(_Satellite)
                    End If

                    DrawSatLocation()   ' draw satellite location on horizon
                    DrawSatStrength()   ' draw satellite signal to noise ratio

                    If _EndSent Then Exit For

                Next

            End If

        Catch ex As Exception

            Throw New Exception("Error processing GSV. " & _Item & ": " & _CurrentSentence & vbCrLf & ex.Message)

        End Try

    End Sub

#End Region

#Region "ParseRMC"

    ' NMEA 0183 RMC sentences contain recommended minimum specific GPS data.
    '
    ' Seq.  Field                       Description
    ' 1     Sentence ID                 Talker ID: GP = GPS, Sentence ID: RMC = GPS/transit date
    ' 2     UTC Time                    UTC time at which fix was taken. Format: hhmmss.sss
    ' 3     Status                      Status: A = Valid, V = Invalid
    ' 4     Latitude                    Latitude ddmm.mmmm
    ' 5     Latitude Hemisphere         Latitude hemisphere: N = North, S = South
    ' 6     Longitude                   Longitude: dddmm.mmmm
    ' 7     Longitude Hemisphere        Longitude hemisphere: E = East, W = West
    ' 8     Speed over ground           Speed over ground, measured in knots
    ' 9     Course over ground          Course over ground, in degrees (0 to 359.9)
    ' 10    UTC Date                    UTC Date in the format DDMMYY
    ' 11    Magnetic Variation          Magnetic variation measured in degrees
    '       Mag. Variation Hemisphere   Magnetic variation hemisphere: E = East, W = West
    ' 12    Checksum                    Checksums are optional for most sentences
    '
    ' Samples:
    '   Signal not acquired:
    '       $GPRMC,235947.000,V,0000.0000,N,00000.0000,E,,,041299,,*1D
    '   Signal acquired:
    '       $GPRMC,092204.999,A,4250.5589,S,14718.5084,E,0.00,89.68,211200,,*25

    Public Sub ParseRMC(ByVal rmcSentence As String)

        Dim _Position As Integer = -1
        Dim _OldPosition As Integer = 0
        Dim _UnparsedSentence As String = rmcSentence
        Dim _CurrentSentence As String = String.Empty
        Dim _Delimiter As String = String.Empty
        Dim _Item As String = String.Empty

        Try

            For i As Integer = 1 To 12

                If i = 12 Then
                    _Delimiter = NMEA_CHECKSUMSTARTCHAR
                Else
                    _Delimiter = NMEA_VALUEDELIMITER
                End If

                _Position = _UnparsedSentence.IndexOf(_Delimiter, _OldPosition + 1)
                _CurrentSentence = _UnparsedSentence.Substring(_OldPosition + 1, _Position - _OldPosition - 1)

                If _CurrentSentence.Length > 0 Then
                    Select Case i
                        Case 2
                            _Item = "UTC Time"
                            Time_Label.Text = TimeSerial( _
                                                    Convert.ToInt32(_CurrentSentence.Substring(0, 2)), _
                                                    Convert.ToInt32(_CurrentSentence.Substring(2, 2)), _
                                                    Convert.ToInt32(_CurrentSentence.Substring(4, 2))).ToLongTimeString
                        Case 3
                            _Item = "Status"
                            Select Case _CurrentSentence
                                Case "V"
                                    Status_Label.Text = "Awaiting position fix..."
                                Case "A"
                                    Status_Label.Text = "Valid position fix"
                                Case Else
                                    Status_Label.Text = "Invalid position fix"
                            End Select
                        Case 4
                            _Item = "Latitude"
                            Latitude_Label.Text = FormatNumber(ToDegrees(_CurrentSentence), 6)
                        Case 5
                            _Item = "Latitude Hemisphere"
                            Latitude_Label.Text += " " & _CurrentSentence
                        Case 6
                            _Item = "Longitude"
                            Longitude_Label.Text = FormatNumber(ToDegrees(_CurrentSentence), 6)
                        Case 7
                            _Item = "Longitude Hemisphere"
                            Longitude_Label.Text += " " & _CurrentSentence
                        Case 8
                            _Item = "Speed"
                            Speed_Label.Text = FormatNumber(Convert.ToSingle(_CurrentSentence), 2)
                        Case 9
                            _Item = "Heading"
                            Bearing_Label.Text = FormatNumber(Convert.ToSingle(_CurrentSentence), 2)
                            If Convert.ToSingle(_CurrentSentence) <> m_Bearing Then
                                m_Bearing = Convert.ToSingle(_CurrentSentence)
                                DrawSatLocation()   ' Re-draw bearing bug.
                            End If
                        Case 10
                            _Item = "UTC Date"
                            Date_Label.Text = DateSerial( _
                                                    Convert.ToInt32(_CurrentSentence.Substring(4, 2)), _
                                                    Convert.ToInt32(_CurrentSentence.Substring(2, 2)), _
                                                    Convert.ToInt32(_CurrentSentence.Substring(0, 2))).ToShortDateString
                    End Select
                End If

                _OldPosition = _Position

            Next

        Catch ex As Exception

            Throw New Exception("Error processing RMC. " & _Item & ": " & _CurrentSentence & vbCrLf & ex.Message)

        End Try

    End Sub

#End Region

#Region "Satellite"

Option Explicit On 
Option Strict On

Public Class Satellite

    ' Private instance attributes

    Private m_SatelliteId As Integer = 0
    Private m_Elevation As Integer = 0
    Private m_Azimuth As Integer = 0
    Private m_SNR As Integer = 0
    Private m_Timestamp As Date = Date.MinValue()

    ' Public instance attributes

    Public Property Id() As Integer
        Get
            Return m_SatelliteId
        End Get
        Set(ByVal Value As Integer)
            m_SatelliteId = Value
        End Set
    End Property

    Public Property Elevation() As Integer
        Get
            Return m_Elevation
        End Get
        Set(ByVal Value As Integer)
            m_Elevation = Value
        End Set
    End Property

    Public Property Azimuth() As Integer
        Get
            Return m_Azimuth
        End Get
        Set(ByVal Value As Integer)
            m_Azimuth = Value
        End Set
    End Property

    Public Property SNR() As Integer
        Get
            Return m_SNR
        End Get
        Set(ByVal Value As Integer)
            m_SNR = Value
        End Set
    End Property

    Public ReadOnly Property Timestamp() As Date
        Get
            Return m_Timestamp
        End Get
    End Property

    ' Constructors

    Public Sub New()
        MyBase.new()
        m_Timestamp = Now
    End Sub

End Class

#End Region