[gdal-dev] C# version of gdallocationinfo

[Paul Meems]

Hi list,

I need to get the pixel value of my tiff-file.
Using gdallocationinfo.exe I can get the correct value:
gdallocationinfo -wgs84 -valonly 201612021600.tif 5.22543631866552
51.2581472440154

Now I need to do this in my C# code. Using examples I found with Google I
came up with this piece of code, I also looked at the C++ code of
gdallocationinfo

public string GdalLocate(string input, double x, double y, bool inWgs84 =
true)
{
    using (var ds = Gdal.Open(input, Access.GA_ReadOnly))
    {
        if (ds == null) throw new Exception("Can't open GDAL dataset: " +
input);

        int col;
        int row;
        if (inWgs84)
        {
            var pGT = new double[6];
            ds.GetGeoTransform(pGT);
            col = (int) Math.Floor((x - pGT[0]) / pGT[1]);
            row = (int) Math.Floor((pGT[3] - y) / -pGT[5]);
        }
        else
        {
            col = (int)Math.Floor(x);
            row = (int)Math.Floor(y);
        }

        // Check input:
        var rows = ds.RasterYSize;
        var cols = ds.RasterXSize;
        if (col < 0 || row < 0 || col > cols || row > rows)
        {
            // Location is off this file! No further details to report.
            return string.Empty;
        }

        // Get the first band:
        using (var band = ds.GetRasterBand(1))
        {
            // Creating a C# array to hold the image data
            var byteBuffer = new byte[cols * rows];
            // Read the raster
            var IsThereAnError = band.ReadRaster(row, col, 1, 1,
byteBuffer, 1, 1, 0, 0);
            if (IsThereAnError == CPLErr.CE_None) return
byteBuffer[0].ToString();

            throw new Exception("Error in reading raster using
GdalLocate.");
        }
    }
}

The command line call returns 29.
My method using the same input file and coordinates returns 1.

So I must be missing something!

Thanks in advanced for any help you can provide.

Paul

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