[vtkusers] Bug fix for boolean operations filter

[Cory Quammen]

Hi all,

Today I committed a bug fix to vtkImplicitPolyDataDistance that should fix
at least some of the known problems with vtkBooleanOperationPolyDataFilter.

commit 67122e8421c833769fff90c8a0a113007e0383cf
Author: Cory Quammen <cory.quammen at kitware.com>
Date:   Wed Apr 29 23:02:34 2015 -0400

    BUG: Fixed error in area-weighted normal

    When the closest point on a surface to a test point is on an edge, the
    area-weighted normal is the average of the normals of the faces
    adjacent to the edge. The contribution from one of the faces was being
    added twice, producing the incorrect area-weighted normal. This
    resulted in the wrong sign for the signed distance in some cases.
    This patch fixes the error.

    Changed TestImplicitPolyDataDistance.cxx to fail prior to this change
    and pass after the change. The previous test exercised
    vtkImplicityPolyDataDistance but did not check the results. The new
    test checks against a baseline.


For anyone who has tried to use the boolean operations filter but found it
to be buggy, especially where it added extraneous triangles to the output,
I encourage you to check out the current VTK master branch and see if this
fixes your problem. If not, please let me know.

There is still a known problem for input geometries that have long skinny
triangles [1], but I think today's bug fix should take care of many of the
problems people have reported.

Thanks,
Cory

[1] http://www.paraview.org/Bug/view.php?id=13708

-- 
Cory Quammen
R&D Engineer
Kitware, Inc.
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