[vtkusers] compute derivative

[tony hakki]

hello dear list;

I have a 3D image (.raw)  and  I specified 150 point on it (X,Y,Z). For each points I have calculated   normal vectors. Through a normal vector I got 50 samples( 50 grey scale values) by tri-linearintepolation . I would like to calculate these 50 samples' derivative( this is like a edge detection) . Is there a method  to calculate these 50 grey scale values derivative? I hope I wrote my problem understandably.
Thanks
Tony

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