[vtkusers] Delaunay surface triangulation in 3D

[Doug Hackworth]

Thanks to everyone who's replied so far.  I'm getting on the right 
track, I think, but still have a couple of questions:


1.  Bill said:
 > vtkGeometryFilter will extract surface cells from a volumetric mesh.

The documentation for vtkGeometryFilter certainly makes this sound 
promising ("All 2D faces that are used by only one 3D cell (i.e., 
boundary faces) are extracted") , but it's not clear to me how to 
actually accomplish this.  The methods presented in the class 
documentation don't make a lot of sense to me, and the examples from 
Kitware (ExtractUGrid.py and pointToCellData.py) don't make it obvious 
to me, either.

I'm imagining something of this sort:

vtkGeometryFilter* geom = vtkGeometryFilter::New();
geom->SetInput(somePolyData);
geom->SomeOtherMethods();
geom->Update();

I'm just not seeing at the moment what SomeOtherMethods() might be... 
Can someone explain this, and/or offer some sample code?


2.  Bjorn said:
 > I never tried it, but vtkSurfaceReconstructionFilter might be one way,
 > but be a little bit of overkill if it is a convex shape like a normal
 > sphere ......

This also sounds promising, since although I'm just working with spheres 
now I will ultimately want to triangulate more complex surfaces which 
may or may not be describable by a mathematical function.  Here again, 
though, I have much the same issue as with vtkGeometryFilter above.  Can 
anyone enlighten me?

Many thanks for your help.

Kindest regards,
Doug





> Doug Hackworth schrieb:
>>
>> Greetings.  I have a set of N points that reside on the surface of a 
>> sphere, and I'd like to create a triangular (not tetrahedral) mesh 
>> between these points via Delaunay triangulation.  Using vtkDelaunay2D 
>> is out because it does a different thing (ignoring the Z-coordinate 
>> during its triangulation).  And using vtkDelaunay3D only does part of 
>> the right thing -- it appears to triangulate the surface points 
>> nicely, but also creates (as its primary function) a tetrahedral mesh 
>> among all the points in 3 dimensions.
>>
>> How can I get a triangulated surface?  Just to be clear on what I 
>> want, the end result should be a hollow volume of triangles, rather 
>> like a geodesic dome.  That make sense?
>>
>> It seems as if using vtkDelaunay3D and then extracting the surface 
>> triangles only could be a promising course of action, but I have no 
>> idea how to do this (I'm also not sure that it's guaranteed to produce 
>> the right result).  Can someone offer some guidance on this?  Is there 
>> an alternative method that would be better?  Please, offer me your 
>> wisdom.  :-)
>>
>> Thanks,
>> Doug
>>