[vtkusers] filling in a sphere's intersection with a plane

[David Gobbi]

On Fri, Jan 11, 2019 at 11:04 AM Andras Lasso <lasso at queensu.ca> wrote:

> In general, vtkCutter returns a random (unordered, non-continuous) list of
> line segments.
>
>
>
> Can vtkContourTriangulator deal with that (merge points and order line
> segments to form closed contours)?
>

Yes.  If given unordered line segments, vtkContourTriangulator will sort
them.  The nightly tests cover this feature.

Usually we apply vtkStripper with a very large MaximumLength on vtkCutter
> output to create polygons that can be triangulated and rendered. This works
> well almost every time, but in some cases (cutting very complex geometries
> with hundreds of thousand of points) stripping does not find closed
> polygons. It would be nice to have a somewhat simpler and more robust
> solution.
>

The vtkCountourTriangulator code has checks to deal with bad geometry.
It's not perfect, but it's much better than vtkPolygon::Triangulate().
I've avoided vtkDelaunay2D because certain geometries will cause it to
crash.

I wrote vtkClipClosedSurface specifically to deal with complex 3D
geometries (it uses vtkContourTriangulator as its final stage).  I had
meant to write a similar filter called vtkCutClosedSurface filter for
cutting (instead of clipping) but that never happened.

  David

>
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