Cull skinny mesh faces ?

Replies to This Discussion

Permalink Reply by peter fotiadis on January 31, 2016 at 10:56am

If "skinny" means a cull criterion related with edge ratio ... get this attached. If means "smallish" faces I could add some lines more.

Using MeshMachine for the demo data.

But ... on the other hand the MM alone could do some stuff on that matter.

Attachments:

• massacre_due_to_edge_ratio_V1.gh, 124 KB
• massacre_due_to_edge_ratio_V1.3dm, 270 KB

Permalink Reply by Olivier Suire on February 1, 2016 at 4:34am

Hi Peter, and thanks for looking into this.

Sorry if I wasn't more clear : the idea is not to delete the faces, thus making holes and changing the topology, but rather merge them with their neighbours.

In Rhino tools terms, I'm looking for the equivalent of the "Mesh collapse" tools.

Permalink Reply by peter fotiadis on February 1, 2016 at 4:54am

But you said: cull (= kill)

Anyway ... is "skinny" a criterion related with edge ratio as used? And ... well ... "merge" means make a quad out of a "skinny" face and some (not so "skinny" - hopefully) neighbor face?

Or ... hmm... you maybe mean stuff like this attached?

Attachments:

• Mesh_check_and_reduce_V2.gh, 157 KB

Permalink Reply by David Rutten on February 1, 2016 at 5:49am

Depends on your definition of skinny.

I attached two files, one which culls faces based on longest vs shortest edge (which has a problem in some cases where a triangle contains two almost equally long short faces and one long edge), and the other culls triangles based on the ratio area^2 vs. circumference. There are many definition you could come up with.

The main problem with removing unwanted triangles from a mesh is that quite often you only want to consider triangles with at least one naked edge. This is very difficult to encode, because every time you remove a triangle you change the edge topology of the mesh.

Attachments:

• CullShortVsLongEdges.gh, 6 KB
• CullAreaVsCircumference.gh, 7 KB

Permalink Reply by Olivier Suire on February 1, 2016 at 6:27am

Hi David.

OK, here is the whole story : I use Meshmachine because at last, after 10 years of working with Rhino, I can get some decent looking meshes.

It's still a bit iffy and requires some guesswork, but I am able to output meshes that are not bound to a NURBS Iso curves, but rather produce nice close-to equilateral  triangles, smartly distributed over the topology.

Yet, the naked edges are fixed by two parameters : "FixCurves" and "FixVertices".

I'm not quite sure why both are required, but I find that if one is missing, MeshMachine will fail.

(Documentation cruelly missing here).

Anyways, WHEN I am able to output a valid mesh, I have occasionnal cases where faces along the naked edges are "Skinny" ; in that case, it means that the said faces have two edges whose lengths are comparable to the target length set in MeshMachine, and the third edge is very small.

This screws up the rest of my definition, thus my request for the equivalent of the "collapse mesh" tools found in Rhino. 

In this particular case, "Collapse by edge length" would work, but "Collapse by aspect ratio" would work as well.

Cheers,