[vtkusers] how to get color any position of point of renderwindow and collision detection

[yas ---]

Hi

I want to detect collision with voxels of  an object,but i have a surface
of object that do not  have voxel

really ,I have two actor ,and one of them is static and another move
and I have position of actor,just!. I nead to position  of cells of actor
and
another question

how to get color any position of point of renderwindow ?(I want to use it
in my collision detecton algorithm)
please help me
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