On Oct 31, 2013, at 04:30 AM, Daniel Roßberg <[email protected]> wrote:

For a 3D modeler: No (or similar to the sketch primitive). For a CAD:
Definitely 100% yes. BRL-CAD is lacking 0 to 2 dimensional entities
which all CADs have. With the NMGs we in fact would have these if we
would allow all states of them.
 
Fair point.  I've said for years that our emphasis is on "solid modeling" (i.e., 3D) and not drafting features but even our closest counterpart solid modeling systems (like Solidworks) do indeed also support 2D entities and techniques (they're not sometimes not very good at them, or they've been retrofitted).  Looking back through old presentations on NMG recently, that was even part of NMG's original design where the n-Manifold is explicitly describe in terms of 3-manifolds, 2-, 1-, and even 0-manifolds (non-manifold geometry, e.g., a point). 

This raises an interesting issue about shotline behavior, but it's not much different from non-closed sketch or non-volume nurbs.  We either ignore them or treat them as a 0-thickness thin surface.

I love this idea actually for a number of reasons. It will probably eliminate 100+ functions that are merely the model or region iterator. It certainly simplifies the scope considerably helping to make the library more approachable by other developers.
The only problem will be that we expose model and nmgregion in numerous librt functions, and "shell" is a terrible name by itself. I'd propose shell become the 'model' terminology-wise.

I would call it "nmg" or "nmg_t" or something like this. Currently we
have a "model" which is a little bit confusing (especially because of
having a "nmgregion" but a "shell" then).

Nice.  I like nmg_t because it fits the convention we use elsewhere (but begs renaming the other nmg pieces to match that convention).  If memory serves, the only reason nmgregion is named that way is because X11 or some other library had a struct with the same name.

Since the last GCI task was a bit botched, perhaps we can break up the work and have them move code little by little (resolving any coupling along the way).  Assuming we get selected, of course.  If not, we can start hacking it up sooner.

Cheers!
Sean

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