[vtkusers] Polydata volume calculation problem

[JeffreyRForsyth]

Hi Xiaopeng,

when the reconstruction filter is executed, you generate a level set
function which tells the distance of any point to the surface of the input
polydata.  If you then contour at the +5 level set for example you have a
surface which is +5 units enlarged from the original polydata.  At the -3
level set you have a surface 3 units shrunken from the original polydata. 
By selecting the 0 level set you have exactly the original polydata surface. 
So to answer your question, SetValue(0, 0) is what you need.

However, the reconstruction filter may rescale your polydata - it will
shrink it by the SampleSpacing() parameter, which I am not sure what this
defaults to.  To avoid any shrinking, set sample spacing to 1.  
Or alternatively you can set some spacing greater than 1 and scale up
afterwards by this same value with a VTK transform filter.  The reason why
you might increase the spacing during reconstruction is because this
decreases the density of the output mesh and decreases computation time.

  
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