[vtk-developers] Implicit functions - Ability to specify if it is evaluable

[Karthik Krishnan]

Hello:

I need to cut a dataset with a polyplane. So I wrote a vtkPolyPlane class
that derives from vtkImplicitFunction; so one could use it in combination
with a vtkCutter.

It does not quite work, unless the polyplane is infinite in extent. What I
need is a way for the implicit function to specify that it cannot be defined
at a certain point. The hack I have now is for the Evaluate method to return
VTK_DOUBLE_MAX and a modification to vtkCutter to avoid contouring any cells
which contain a point where the evaluated function value is VTK_DOUBLE_MAX.

I propose
- Adding a IsDefined method to vtkImplicitFunction that returns true by
default (subclasses may override it)
- Modifying vtkCutter to query IsDefined() on points in a cell before
attempting to contour a cell.

Any thoughts.

Thanks
--
karthik
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