[Smtk-developers] Polygon question

[Robert Michael O'Bara]

Hi David,

The situation you described would be invalid for 2d domains.  Either there is the one large polygonal model face or there are two.  To have all three would mean that a point in space would be "owned" by more than one model entity.  If we were modeling a 3D contact type of problem then a spatial point could be owned by more than one model entity; however, those model entities could not belong to the same topological "network".  

Does that make sense?

Bob

Sent from my iPad

> On Sep 19, 2015, at 8:57 PM, David Thompson <david.thompson at kitware.com> wrote:
> 
> Hi Bob,
> 
> I have a question about how many corner cases the polygon session should handle:
> 
>  should users be allowed to create non-manifold models?
> 
> The case I am worried about is if (see attached figure) a user creates
> - face 1 with vertices A-B-C-D-F-G and then creates
> - face 2 with vertices A-B-F-G and then creates
> - face 3 with vertices B-C-D-F.
> 
> In that case, edge A-B (for example) is used twice in the same sense.
> Vertices B and F are also troublesome.
> 
> The data structure I use for vertices and edges will be different depending on what you say. If I only have to track manifold models, then it is enough to store a list of edges in CCW order at each model vertex plus a list of face IDs between pairs of adjacent edges (and nothing at edges except model vertices). If I have to handle non-manifold models, then edges will have to store lists of loops and vertices will not store faces between adjacent edges (or will have to store a map between pairs of edges and faces).
> 
> Any opinions?
> 
>    Thanks,
>    David
> <poly-example.pdf>