[vtkusers] Help! How to slice a volume data arbitrary?

[platogao]

Hi,
I have a volume data set. I want to get the arbitrary slice of the volume. That is: you can define your our plane function to cut or slice the volume, and then get the slice image.
I know this is very easy if use vtkCutter or vtkProbe or vtkImageReslice. But they are 'black box' to me. I cannot control every step of the operation. I need to do this operation use C++ and OpenGL.
My idea is that: use a point and a normal to define the plane. Then convert every points in the plane(use 2d coordinate,say image[i,j]) to 3d coordinate(x,y,z). Then see if (x,y,z) is in the volume. If it is in, use linear interplation to get the Value(x,y,z). 
My idea seems straight forword, but I think it is also very slow. I wonder if anyone can give me some advise on this operation, or how to convert (i,j) from a plane to world coordiante (x,y,z).
Thank you very much!
Plato Gao
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