Need a gradient expression not so dependent on mesh resolution.

[biagas]

Is your feature request related to a problem?

See Discussions #17825, #17830.

Curl (and other expressions) utilize Gradient under the covers, and it performs sampling and utilizes cell size in its calculation.

We should come up with a better way to calculate gradient.

We could possibly use vtkGradientFilter, it also has options for computing Vorticity, Divergence, QCriterion. Might be more expensive in terms of time and/or memory. Preliminary tests with customer's data from #17825 yielded smoother results.

Are there better options?