[MOAB-dev] Creating geometry from sets of triangles

[Tim Tautges (ANL)]

On 01/06/2014 05:04 PM, Paul Wilson wrote:
> Hello MOAB team,
>
> I'm looking to write a new reader for MOAB to read wavefront (obj) files.  These are sets of triangles - I think very
> similar to STL files - that enclose volumes.  (STL may be another option here actually.) In the primary geometry of
> interest, there are nested regions of space, each enclosed by a set of triangles.  I'd like to generate a model a la
> DAGMC that correctly excludes the nested volumes from its parent, etc.

Do these wavefront files have information on the grouping of the triangles?  If so, it should be relatively easy to 
separate and nest the groups, since presumably the bounding boxes would also be nested.

>
> It seems that something like this perhaps exists already, either in MOAB, or CGM, or Cubit, and I wonder what advice the
> MOAB team has for accomplishing this.  I've thought about some algorithmic notions to do this, but didn't want to get
> too far down the implementation without checking here first.
>

I'm not sure it does completely.  If you can group the triangles, you could build that into a volume-surface topological 
structure, but that would give you almost the same thing as evaluating bounding boxes of the collections directly.

I recently added a BoundBox class to MOAB that provides a bounding box for entity sets or ranges, that would probably 
help.  I could also maybe see adding > and < operators to that class to evaluate nesting, though relying on floating 
point comparisons like that can be kind of dicey if they're close.

- tim

> Paul
>

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              Tim Tautges            Argonne National Laboratory
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