[vtkusers] BooleanOperationPolyDataFilter Problems

[David Gobbi]

The instability of vtkDelaunay2D is definitely a problem for these kinds of
filters.  It isn't just a matter of vtkDelaunay2D having bugs... the
problem is that in order for the algorithm to be robust, it must use exact
math.  So a lot of the work that has gone into fixing bugs seems to have
just changed the situations that cause it to crash.

A few years ago I wrote a filter called vtkContourTriangulator that can
sometimes be used as a stable replacement for vtkDelaunay2D.  However,
vtkContourTriangulator is not as fast as vtkDelaunay2D, nor does it produce
high-quality triangles (i.e. it does triangulation, but not Delaunay
triangulation).

 - David

On Wed, Jul 5, 2017 at 5:42 AM, updega2 <updega2 at berkeley.edu> wrote:

> Hi, I authored the LoopBoolean a few years ago because we wanted a more
> reliable vtk-based boolean to use in our software.
>
> I've mentioned this before I believe on the merge requests, but I think it
> may be helpful to say it again here. When the booleans fail (current and
> the
> LoopBoolean), it is typically during re-triangulation due to vtkDelaunay2D.
> I developed the LoopBoolean using vtk 6.0. After vtk 6.0, some changes were
> made to the vtkDelaunay2D code, which caused many more issues in the
> LoopBoolean. I tried working with the vtkDelaunay2D author to fix some of
> the Delaunay bugs, and we got a couple fixed, but a few remain.
>
> So, in our software, we actually have a copy of the vtkDelaunay2D code from
> the vtk 6.0 pipeline, and the LoopBoolean calls that. The code works well
> for our purposes. It still isn't bug free as the code is tolerance-based,
> and there are orientation tests that may fail from time to time due to
> tolerance issues. Also, I'll admit that error checking could be better. I
> would like to go back and improve this part of the code, but haven't had
> the
> time yet.
>
> Adam
>
>
>
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