[Gdal-dev] GDAL C# bindings exception: Attempted to read or write protected memory

[Ben Greene]

Hi,
 
I had a problem with the GDAL C# bindings freezing a little while ago, and Tamas managed to find the problem (I was passing in a two-element array instead of a three element for the return value).  However, now I'm having a different issue.
 
I'm working with 1.4.1 binaries compiled myself according to the instructions on this site (I can't find the most recent binaries in the FWTools distribution).  When I run the code below, I get a System.AccessViolationException:Attempted to read or write protected memory exception on the line:
transform.TransformPoint(point, px, py, 0.0)

It appears that the exception is thrown from this line:
public void TransformPoint(double[] argout, double x, double y, double z) {

osrPINVOKE.CoordinateTransformation_TransformPoint__SWIG_1(swigCPtr, argout, x, y, z);

}

The test image I'm using is:

o41078a5.tif
from
http://dl.maptools.org/dl/geotiff/samples/usgs/

Here is the VB.Net code I'm using (in VS 2005):

Imports GDAL

Imports OGR

Public Class GeoTiffReader

Private Shared image As Dataset

Public Shared Function GetGeoReference(ByVal Filename As String) As GeoReference

If Not (Filename Is Nothing) Then

'Return Nothing

'if uncommented, the code will not crash

End If

GDAL.gdal.AllRegister()

image = GDAL.gdal.Open(Filename, 0)

If (image Is Nothing) Then

Return Nothing

End If

Dim gr(6) As Double

image.GetGeoTransform(gr)

Dim topLeft() As Double = TransformWGS84(gr(0), gr(3))

Dim bottomRight() As Double = TransformWGS84(gr(0) + gr(1) * image.RasterXSize, gr(3) + gr(5) * image.RasterXSize)

If (topLeft.Length = 2 And bottomRight.Length = 2) Then

Return New GeoReference(topLeft(0), topLeft(1), bottomRight(0), bottomRight(1))

Else

Return Nothing

End If

image.Dispose()

End Function

Public Shared Function TransformWGS84(ByVal px As Double, ByVal py As Double) As Double()

Dim point() As Double

point = New Double() {0.0, 0.0, 0.0}

Dim srWGS84 As New SpatialReference("")

srWGS84.SetWellKnownGeogCS("WGS84")

If (image.GetProjection() = "") Then

Return New Double() {}

End If

Dim srCurrent As New SpatialReference(image.GetProjection())

Dim transform As New CoordinateTransformation(srCurrent, srWGS84)

If (transform Is Nothing) Then

Return New Double() {}

End If

Try

transform.TransformPoint(point, px, py, 0.0)

Catch

Return New Double() {}

End Try

Return point

End Function

End Class