Imports System.Text
 
Module EncodeDecode
 
    Public Structure stcLatLon
        Public Lat As Integer
        Public Lon As Integer
    End Structure
 
    '''<summary>
    '''encoded a list of latlon objects into a string
    '''</summary>
    '''<param name="points">the list of latlon objects to encode</param>
    '''<returns>the encoded string</returns>
    Public Function EncodeLatLong(ByVal points As List(Of stcLatLon)) As String
        Dim plat As Integer = 0
        Dim plng As Integer = 0
        Dim len As Integer = points.Count
 
        Dim encoded_points As New StringBuilder()
        For i As Integer = 0 To len - 1
 
            'Round to 5 decimal places and drop the decimal
            Dim late5 As Integer = CInt((points(i).Lat * 100000))
            Dim lnge5 As Integer = CInt((points(i).Lon * 100000))
 
            'encode the differences between the points
            encoded_points.Append(encodeSignedNumber(late5 - plat))
            encoded_points.Append(encodeSignedNumber(lnge5 - plng))
 
            'store the current point
            plat = late5
            plng = lnge5
        Next
        Return encoded_points.ToString()
    End Function
 
 
    ''' <summary>
    ''' Encode a signed number in the encode format.
    ''' </summary>
    ''' <param name="num">the signed number</param>
    ''' <returns>the encoded string</returns>
    Private Function encodeSignedNumber(ByVal num As Integer) As String
        Dim sgn_num As Integer = num << 1
        'shift the binary value
        If num < 0 Then
            'if negative invert
            sgn_num = Not (sgn_num)
        End If
        Return (encodeNumber(sgn_num))
    End Function
 
 
    ''' <summary>
    ''' Encode an unsigned number in the encode format.
    ''' </summary>
    ''' <param name="num">the unsigned number</param>
    ''' <returns>the encoded string</returns>
    Private Function encodeNumber(ByVal num As Integer) As String
        Dim encodeString As New StringBuilder()
        While num >= 32
            'while another chunk follows
            encodeString.Append(CChar(((32 Or (num And 31)) + minASCII)))
            'OR value with 0x20, convert to decimal and add 63
            'shift to next chunk
            num >>= binaryChunkSize
        End While
        encodeString.Append(CChar((num + minASCII)))
        Return encodeString.ToString()
    End Function
 
End Module