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

[Will Schroeder]

An implicit function is f(x,y,z) = constant. If it doesn't fit that IMO it's
not an implicit function. The beauty of these beasts is that they are
simple, now you want to complexify the matter by checking validity on every
point, it would likely slow everything down, not to mention require
modifying a lot of code to do it right.

I think you need a new design not a new hack ;-)

W

On Mon, Feb 14, 2011 at 12:04 PM, Karthik Krishnan <
karthik.krishnan at kitware.com> wrote:

> 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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-- 
William J. Schroeder, PhD
Kitware, Inc.
28 Corporate Drive
Clifton Park, NY 12065
will.schroeder at kitware.com
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