C# Google Static Maps encoded path calculation

Question

I'm writing a tool that gets GPS coordinates from a XML file and sends them to the Google Static Maps API. I'm trying to get a polyline from Google.

I've found the documentation and so far I've written this to convert a double value to a encoded value for a polyline:

private String convertDouble(Double _input)
{
    String result = String.Empty;
    //value * 1e5
    Int32 multiplication = Convert.ToInt32(Math.Floor(_input * 1e5));

    //value to binary string
    String binaryString = Convert.ToString(multiplication, 2);

    //binary to hex
    binaryString = BinaryStringToHexString(binaryString);

    //value to hex + 1
    Int32 hexConvert = Convert.ToInt32(binaryString, 16) + Convert.ToInt32("01", 16);

    //value to binary string
    binaryString = Convert.ToString(hexConvert, 2);

    //binary string zu int[] for further calculations
    Int32[] bitValues = new Int32[binaryString.Length];
    for (Int32 i = 0; i < bitValues.Length; i++)
    {
        if (binaryString[i] == '0')
        {
        bitValues[i] = 0;
        }
        else
        {
            bitValues[i] = 1;
        }
    }

    //shift binary to left
    Int32[] bitValues_2 = new Int32[bitValues.Length];
    for (Int32 i = 0; i < bitValues.Length - 1; i++)
    {
        bitValues_2[i] = bitValues[i + 1];
    }
    bitValues_2[bitValues_2.Length - 1] = 0;

    //if input value is negative invert binary
    if (_input < 0)
    {
        for (Int32 i = 0; i < bitValues.Length; i++)
        {
            if (bitValues_2[i] == 0)
            {
            bitValues_2[i] = 1;
                }
            else
            {
                bitValues_2[i] = 0;
            }
        }
    }

    //make blocks of 5
    Int32 lengthDifference = bitValues_2.Length % 5;

    Int32[] bitValues_3 = new Int32[bitValues_2.Length - lengthDifference];

    for (Int32 i = bitValues_2.Length - 1; i > (bitValues_2.Length - bitValues_3.Length); i--)
    {
        bitValues_3[i - (bitValues_2.Length - bitValues_3.Length)] = bitValues_2[i];
    }

    //twist blocks
    Int32[] bitValues_4 = new Int32[bitValues_3.Length];

    Int32 numberOfBlocks = bitValues_3.Length / 5;
    Int32 counter = 0;

    String[] stringValues = new String[numberOfBlocks];

    for (Int32 i = numberOfBlocks - 1; i >= 0; i--)
    {
        for (Int32 j = i * 5; j < (i * 5) + 5; j++)
        {
            bitValues_4[counter] = bitValues_3[j];
            counter++;
        }
    }

    counter = 0;

    //write int[] into strings for final conversion
    for (Int32 i = 0; i < bitValues_4.Length; i++)
    {
        if (i > 0 && i % 5 == 0)
        {
           counter++;
        }

        stringValues[counter] += bitValues_4[i].ToString();
    }

    // blocks ^ 0x20 (32) and convert to char
    Int32 value = 0;
    Int32[] intValues = new Int32[stringValues.Length];
    Char[] charValues = new Char[stringValues.Length];
    for (Int32 i = 0; i < stringValues.Length; i++)
    {
        value = Convert.ToInt32(stringValues[i], 2);
        if (i < stringValues.Length - 1)
        {
            intValues[i] = value ^ 32;
        }
        else
        {
            intValues[i] = value;
        }
            intValues[i] = intValues[i] + 63;
            charValues[i] = (Char)intValues[i];
            result += charValues[i];
        }

    return result;
}

If I use the value from the documentation

-179.9832104

I get the result

`~oia@

Which is fine, but if I use one of my values e.g.:

LAT: 8.7587061 LONG: 48.6331662

LAT: 8.8905152 LONG: 48.6226701

I get the wrong values. The final polyline should be in southern Germany. But with my calculation the polyline is somewhere near a cost. Maybe there is a finished class that gives me the encoded coordinates and I haven't found it yet.

And yes, I have to encode the polylines, because there will be many different coordinates in the XML (the GPS tracker runs for several hours and captures the location every 10 seconds).

Answer 1

Well, after another night of searching and testing I have found a solution. Brian Pedersen has a solution in his blog. And it works just like it should. I don't want to copy and paste the code here, but the link has it.