Compute Derivatives of a scalar in a direction based on a Contour line

Hi all,
Starting from the vtk files of a 2-d case containing point data, I’ve been trying to compute the derivatives of a scalar (temperature). The Compute Derivatives or the Gradient filters, compute these in the X and Y directions.

What is important for me, is to compute these derivatives but in a direction which is normal and tangential to an isoline, which I generate using the Contour filter. With the Contour filter, as expected I get a curve, which has a variable direction.

When creating the Contour line(s), I see that there is also a “Compute Normals” check box, which according to the description it computes an extra array containing the normal values of the isoline. But I can’t locate this array. Of course I’m not sure if this is the proper way to get the derivatives in the normal direction of the isoline.

Any help is highly appreciated.

Phivos