#306 g-obj does not output facet data

[Christopher Pitts]

Running g-obj with version 7.20.0 shows "triangulated successfully: 100%" but no facet data is sent to the output.

g-obj havoc.g r.t_bum1

output from g-obj:
......
didn't find trapezoid for hole-start point at:
10530.2 80.2126 2513.42
nmg_stash_model_to_file('tri_lone_hole.g', x16c5e40, lone hole start)
nmg_stash_model_to_file(): wrote error.s to 'tri_lone_hole.g'

bombing

FAILED in triangulator: /r.t_bum1
# BRL-CAD generated Wavefront OBJ file (Units mm)
# BRL-CAD model: havoc.g
# BRL_CAD objects: r.t_bum1
Tried 1 regions, 1 conv. to NMG's 1 conv. to tri. nmgper = 100.00% triper = 100.00%
Tried 1 regions, 1 converted to NMG's successfully. 100%
1 triangulated successfully. 100%

[Sean Morrison]

Presume that's a typo and you ran with the -o option to specify the output file?

Have you tried other (simpler) database files or was the failure specific to havoc.g?

That said, there are several situations where polygonal conversion of our traditional CSG files is highly problematic (i.e., it'll fail) .. particularly for a model like our havoc example database. That particular region failure in havoc is a known issue that has already been fixed (but not yet publicly unveiled).

It's an ongoing development effort to improve our tessellation performance (which changes and improvements occurring pretty much every month for the past year) with a LOT more to go, but things are slowly improving.

Related:
https://sourceforge.net/mailarchive/message.php?msg_id=26694114
https://sourceforge.net/mailarchive/message.php?msg_id=26894272

[Christopher Pitts]

I have seen that failure in other files (not necessarily simpler ones) with the last several versions of brlcad.

[Sean Morrison]

There are a lot of changes that have been under development the past few months affecting how geometry is tessellated. Basically, all of our polygonal exporters (including g-obj) are getting an overhaul that is expected to be unveiled in the 7.22 release so there is hope coming down the pipeline.

We're painfully aware of the pains users have to go through exporting geometry. The problem runs deep in all CAD software when converting between geometric representation formats (from implicit CSG to polygonal mesh in this instance) and it's a hard problem to address, but hopefully our upcoming changes will at least make things better.