lowering a Polyface Mesh's quality

Steven Langhammer

Greetings,
I'm curently working with Polyface Meshes and actually this is my first work exprience with BricsCAD.

I work with BricsCAD v13.1.8 Build ID 40888 Revision 27908.

What I'm trying to do it to is:
adjust the settings of the modeler (Settings -> Settings -> Program Options -> Modeler -> Modeler properties for full ACIS development (licence Pro or higher)) to  lower the "quality" of the mesh, reduceing the number of faces and nodes.

What I do is:
I take a block, explode it, copy it with adjusted settings, paste it, explode the pasted block/solid and check a certain polyface mesh for the number of nodes and faces.
The Clipboard format is set to DWG R11/R12 (Settings -> Settings -> Program options -> Open and save)

A collegue of mine allready found out a few values that reduced the number of surfaces and nodes of oure test mesh down to: nodes: 724, faces: 734.

He used the following settings:
Use FACETERS system variable: checked
Surface tolerance: -10
Normal tolerance: 60
Maximum number of grid lines: 8
Maximum face edge length: 0
Grid aspect ratio: 0
Adjust mode: none (Leave everything alone)
Grid mode: Grids in interior
Triangulation mode: Triangulate everywhere
Minimum number of u grid lines: 0
Minimum number of v grid lines: 0.

My goal is:
to find the right settings to lower the number of nodes and faces to something around 300 + - 25(?). I assume that value to be the optimum between a low number of faces and an acceptable quality.

Now I found out:
that the values fall down to nodes: 94, faces: 104 when I unceck the option "Use FACETERS system variable", but then the quality of the 3D-model becomes too low.

Since I'm very unexperienced with BricsCAD all i can do is to "play around" with the values for surface tolerance, normal tolerance, max number of grid lines, max face edge length and grid aspect ratio. I guess changeing the number if u and v grid lines isen't any help to my problem.

Please note that I'm actually German. I excouse for possible my spelling and grammar misstakes. I'm posting this in english to reach a wider range of experienced users.  If you want to help me with my problem but don't understand some of my expressions please ask and I'll try to explain what I ment.

Knut Hohenberg

Hello Steven,
I'm actually German, too - but let's stick to English so others can jump in as well.

I don't consider myself an experienced user when it comes to ACIS specific things, but the possibility to tune mesh output is rather new in BricsCAD (introduced in v12), so maybe there just aren't really savvy users around at the moment.

Like you, I had trouble figuring out how the legacy method of influencing mesh density (FACETRES) and the new settings (modelerproperties) interact. Maybe someone from Bricsys could shed a little light on this.

My shot at it is to turn UseFacetRes off, and just use the new controls. For my needs(I use the meshes for rendering, not FEM), it is generally sufficient to change the Normal Tolerance to get the desired resolution of curved surfaces, and I leave all the Grid options off.

The only other control that I use is Triangulation mode:
- I mostly use 'Triangulate against the boundary' which will generate quads if appropriate, but make sure the adjoining edges of the mesh surfaces will have coincident vertices.
- 'No triangulation' will generate quads wherever possible, usually resulting in a model that is not 'water tight'.
- 'Triangulate everywhere' will create only tris, which - depending on the target software - might also be the best option.

Generally, I find the meshes of quite good quality.

Steven Langhammer

Many thanks!
That actually did exactly what i needed. Finding out the exact values for the Surface and Normal Tolerance for the bestt possible ballance between a low number of surfaces and an acceptable optical quality is just a matter of time now and shouldent take too long.