[vtkusers] detecting if surface is convex

[Bryn Lloyd]

Thanks Dominik. I also thought about the convex hull approach, but that
will mean I need to detect when the volume changes, e.g. if larger than
some epsilon. If possible I would prefer not to use such a
(data-dependent) condition.







Dominik Szczerba wrote:
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> Another idea: you can use e.g. qhull to compute the convex hull of your
> mesh. If the mesh is convex the resulting volume will not change.
> 
> Dominik
> 
> Dominik Szczerba wrote:
>> Curvature?
>>
>> But will probably not be more robust than angles.
>>
>> Dominik
>>
>> Bryn Lloyd wrote:
>>> Hi,
>>
>>> Is there any code in VTK that would help with detecting if a closed 3d
>>> surface (or equivalently a connected set of tetrahedra) is convex or
>>> concave?
>>> My own attempts have been to compute the dihedral angles at each edge on
>>> the surface. If at least one is larger than PI -> concave. This is not
>>> very robust though, especially for flat surfaces.
>>
>>> Thanks
>>> Bryn
>>
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> - --
> Dominik Szczerba, Ph.D.
> Computational Physics Group
> Foundation for Research
> on Information Technologies in Society
> http://www.itis.ethz.ch
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-- 
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Bryn Lloyd
Computer Vision Laboratory
ETH Zürich, Sternwartstrasse 7
CH - 8092 Zürich, Switzerland
Tel: +41 44 63 27690
Fax: +41 44 63 21199
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