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Mesh triangulation quality

Andrea Venturoli's picture
Forums: 

Hello.

I'm using BRepMesh_IncrementalMesh to tessellate faces and I'm getting a weird behaviour: whenever a edge requires a finer set of triangles the whole U and V strips are using that smaller triangle size (see attached picture).
I agree I should get a higher number of triangles near the round borders, but I wouldn't expect the corresponding horizontal and vertical strips to be over-triangularized. Other meshers still use the same tessellation as in other areas there.

The code:
> BRepMesh_IncrementalMesh M(MyFace,Tol,Standard_False,M_PI/2.,Standard_True);

Are my parameters not optimal?  Am I doing something wrong?
Is there any way to achieve what I'd like to get?
Is BRepMesh_IncrementalMesh the correct class to use for this?

Thanks in advance.

Attachments: 
Qr Qr's picture

Hi Andrea,

This tool is designed to generate visualization facets only. If you want to have more regular tessellation, it is definitely not a good choice. What about Netgen?

Qr.

Andrea Venturoli's picture

Hello Qr and thanks for your reply.

My problem is not a "regularity" one; in fact I'm asking the mesh to be less regular, but faster to process later: what we are getting is more than acceptable tolerance-wise, but features a lot of triangles which are not really needed. Is there anything we can do to tweak this class to achieve this?

As for Netgen, it's a different product we'd need to integrate; I'll have a look into it, anyway.

Bye

Qr Qr's picture

Andrea, can you attach the CAD file of your test model so that I can do some experiments with it?

Andrea Venturoli's picture

Sure: here it is.

Thanks.

Attachments: 
Qr Qr's picture

I've tried to run it for a very coarse setting: I've set 1 for linear deflection and 15 degrees for the angular deflection. The result I obtained is at the picture attached. For Netgen, people say it is quite slow.

Attachments: 
Andrea Venturoli's picture

I don't care much for angular deflection, so I set it at M_PI/2 (it should be in radiants, shouldn't it?).

Anyway, I tried with your settings and, of course, I'm getting what you get; unfortunately 1 (assuming it means 1mm) is too big a deflection for us (we need 0.01mm).

As a test, I tried starting with 1 and lowering it:

_ at 0.5 the mesh still looks fine (as in your pictures);

_ at 0.25 some triangles start appearing which should not IMHO be needed;

_ at 0.125 the situation is like in my original picture (with way too many triangles added).

In the end, you confirm there is no way to achieve what we want?

 bye & Thanks

Qr Qr's picture

No way here. I tried all parameters it offers and see no gradation in element size from boundary to interior. Visualization mesh is not targeted for that. Personally, I believe, NetGen will give you the expected level of quality.

Andrea Venturoli's picture

Thanks, I'll try NetGen.

Mikhail Sazonov's picture

The OCCT bug #27693 registered after this topic has been fixed. In the current master the picture is the following. Linear deflection is 0.01, angular is pi/2.

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