about marching cubes

[Emmanuelle Bourrat]

Greetings,

I am a new user of vtk.
I need a surface representation of a volume and I need to compute things
on each cell of the surface representation, but I can't access the
vtkCellArray.

First I am drawing a volume (I put it into a structuredPoints), then I
am applying a MarchinCubes object, as follows :
marching_cubes->DebugOn();
marching_cubes->SetValue(0, 100);
marching_cubes->SetInput(volume);

Then, I would like to access the the output of marching_cubes by
marching_cubes->GetOutPut(), this method returns a vtkPolyData *, and
then I would like to access the vtkCellArray* with GetPolys(). 
The problem is that what I get with this method is an empty
vtkCellArray., it is allocated, but empty.

Can anybody help?
Thanks,

Emmanuelle.


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