[vtkusers] Gradient of structured grid

[Jose Luis Pina]

Hello:
I have a structured grid with 4 scalars defined, I want to see the gradient 
at the points of the grid of one of the scalars.
I tried the

vtkCellDerivatives
SetVectorModeToComputeGradient

and after a

vtkHedgeHog
SetVectorModeToUseVector

but an error say "no vectors in input data".
if I make vtkPointDataToCellData before, no works.

How I can see the gradient?.
How I should define the cells?
Thanks in advance.


CPS.Universidad de Zaragoza. (Spain)
Jose Luis Pina Martinez
jlpina at ivo.cps.unizar.es