[Paraview] Calculation of the normal gradient on a boundary face

[Nicolas Lancial]

Hi,

I have a problem with something a priori easy to calculate but in which I
really don't succeed to do...

I want to calculate a heat flux in a flat plate (with a thickness) and so I
calculate the gradient of the temperature (with
GradientOfUnstucturedDataSet). In then take the component of the gradient
which is normal to the face I want to have the heat flux.

In the solid, the values given are good (non zero) and equal to the
theoretical values, ok...

But when I want to show the normal component of gradient on a boundary face
by using ExtractBlock and then ExtractSurface, the values of the gradient
are 0 everywhere... But in the volume it is still non zero !

Here are pictures showing the problem. In the first image, I plot the
temperature on a flat plate (with thickness) and I calculate the gradient.
I have compared to the theorical values and it is okay.

In the second image, I wanted to plot the value of the gradient in a
boundary face of the flat plate but I have 0 everywhere...(which is however
calculated in the volume... I have also tried to project the values by
using "PointDataToCellData" and "Cell centers" but it doesn't work...

Is it a bug ?
I'm using Paraview 4.0 on ubuntu 12.10.
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