[MOAB-dev] Creating geometry from sets of triangles

[Paul Wilson]

On 01/07/2014 10:02 AM, Tim Tautges (ANL) wrote:
>
>
> 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.
Yes, the format in question has the triangles arranged in groups.
>
>>
>> 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.
That does sound useful.  I'll plan to develop something based on this.

Paul

-- 
-- ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ --
Paul Wilson ~ UW-Madison ~ 608-263-0807 ~ cal: http://bit.ly/pphw-cal
Professor, Engineering Physics. ~ http://cnerg.engr.wisc.edu
Faculty Director, Advanced Computing Infrastructure


-------------- next part --------------
A non-text attachment was scrubbed...
Name: smime.p7s
Type: application/pkcs7-signature
Size: 6244 bytes
Desc: S/MIME Cryptographic Signature
URL: <http://lists.mcs.anl.gov/pipermail/moab-dev/attachments/20140107/42aa5c13/attachment.bin>