[vtkusers] coordinate transformation between polydata and image data

[Sara Rolfe]

Hello,

Sorry if this is a simple questions.  I have a 3D image which I  
extract a contour from using vtkContourFilter.  The output of this is  
polydata.  I'm interested in taking a point of interest from the  
polydata and finding the approximate corresponding point in the  
original image.  This seems to be a simple task, but I'm confused  
because the point locations appear to be in a different coordinate  
space.  The bounds of the polydata are greater than the region of the  
original image.  If I'm understanding this correctly, where can I find  
out what this transformation is, or how can I transform the polydata  
point locations back into voxel space?

Thanks,
Sara