Transform NAD27 to WGS84 - data shifts ignored

Mar 2, 2010 at 11:12 PM

I am trying to get Proj.Net to transform from NAD27 to WGS84 correctly. I'm using the following code:

 

public void doConversion(object sender, RoutedEventArgs e)
        {
            CoordinateTransformationFactory ctfac = new CoordinateTransformationFactory();

            ICoordinateSystem toCS = SridReader.GetCSbyID(4326);

            ICoordinateSystem fromCS = SridReader.GetCSbyID(32024);

            ICoordinateTransformation trans = ctfac.CreateFromCoordinateSystems(fromCS, toCS);

            double[] fromPoint = new double[] { 1551935.4,199319.2 };
            double[] toPoint = trans.MathTransform.Transform(fromPoint);

            IMathTransform inversedTransform = trans.MathTransform.Inverse();
            double[] point = inversedTransform.Transform(toPoint);

        }

 

The resulting point is wrong, off by at least 100 feet: 35.58018, -99.505976 and should be more like: 35.538067, -99.50635.

I've tried creating my own projection string adding in +nadgrids=conus. I've tried adding a shift via +towgs84. Both are ignored. What do I have to do to get this transformation to work correctly?

Janene