vtkImageData* vtk_image = image->GetVTK< vtkImageData >( );
if( vtk_image == NULL )
return( "MarchingCubes: Input does not have a valid VTK conversion." );
vtkImageData* vtk_image = image->GetVTK< vtkImageData >( );
if( vtk_image == NULL )
return( "MarchingCubes: Input does not have a valid VTK conversion." );