topic sub-d Mesh import to t-splines in Fusion Support Forum

sub-d Mesh import to t-splines

adam4QNES — Mon, 08 Apr 2024 11:40:17 GMT

Hi there,

I have a problem that I did not have in older fusion versions.:

When I import a quad mesh, fusion triangulates parts of the mesh. So I cant make a T-Spline object out of it anymore, when I try to convert it.

Re: sub-d Mesh import to t-splines

TheCADWhisperer — Mon, 08 Apr 2024 11:42:35 GMT

@adam4QNES wrote:

When I import a quad mesh

@adam4QNES

Can you Attach the original mesh file here. (You might have to zip it first.)

Re: sub-d Mesh import to t-splines

adam4QNES — Mon, 08 Apr 2024 12:00:09 GMT

Her U go

Re: sub-d Mesh import to t-splines

TheCADWhisperer — Mon, 08 Apr 2024 12:39:29 GMT

@adam4QNES wrote:
. So I cant make a T-Spline object out of it anymore, when I try to convert it.

What is the source? An reference images?

This looks mostly planar geometry to me - not something that would be done with t-spline geometry?

Re: sub-d Mesh import to t-splines

adam4QNES — Mon, 08 Apr 2024 13:48:39 GMT

It is ment for T-Spline geometry. The source is rhino 7. There we created it as an Sub-D Object and I want to add some fillets in a parametric modell, and do other operations. I need it to be an T-spline object in fusion, but somehow the import into fusion splits a lot of the quad-surfaces into triangles, which therefore makes it impossible for me to convert the impoorted mesh into a T-spline object. (Screenshot is from rhino)

Re: sub-d Mesh import to t-splines

jeff_strater — Mon, 08 Apr 2024 17:02:59 GMT

I'm pretty sure that those triangles are in the OBJ file itself. As long as you have "triangulate mesh polygons" off:

Fusion will not add triangles. The fact that there are SOME quads in this mesh shows that. Any triangles that exist are kept as triangles.

Re: sub-d Mesh import to t-splines

HughesTooling — Mon, 08 Apr 2024 17:33:41 GMT

@jeff_strater It looks like Fusion doesn't like 4 sided faces that are not planar. I imported the mesh into Rhino and it comes in like this for example. These areas have 4 sides but not flat, when Fusion import it splits them into triangles.

This is Rhino

And in Fusion.

Re: sub-d Mesh import to t-splines

TrippyLighting — Mon, 08 Apr 2024 18:58:26 GMT

I am looking at this in Blender and the model is not "clean", meaning there are some internal faces in the symmetry plane and a number of N-Gons that likely cause the behavior in Fusion!

Re: sub-d Mesh import to t-splines

adam4QNES — Mon, 08 Apr 2024 20:03:06 GMT

I have triangulation deactivated in my preferences. Fusion still does it, if the angle of two vertices (sides of the quad) is to big. 3ds Max or Blender wont do that. Also a re-import into Rhino does not add any triangles.

Rhino Meshanalysis says the following:

General information about this mesh:

Mesh does not have any degenerate faces.
Mesh does not have any degenerate ngons.
Mesh does not have any extremely short edges.
Mesh does not have any non manifold edges.
Mesh does not have any naked edges.
Mesh does not have any duplicate faces.
Mesh does not have any faces with directions different from the mesh as a whole.
Mesh does not have any self intersecting faces.
Mesh does not have any disjoint pieces.
Mesh does not have any unused vertices.

ID: 6b53c359-74cf-41aa-9a02-308108d400bc (42)
Object name: (not named)
Layer name: Layer 01
Render Material:
source = from layer
index = -1

Geometry:
Valid mesh.
Closed double precision polygon mesh: 260 vertices, 354 faces with normals (64 n-gons)
Bounding box: (14.5804,45.1868,-21.4663) to (107.847,80.3249,21.4663)

Re: sub-d Mesh import to t-splines

adam4QNES — Tue, 09 Apr 2024 13:00:14 GMT

Yes that's also what I suspect, and it is a real pain that a lowpoly quad import does not work with fusion anymore, if the angle in a quad is to big )):

@adam4QNES - this post has been edited due to Community Rules & Etiquette violation.

Re: sub-d Mesh import to t-splines

TrippyLighting — Mon, 08 Apr 2024 20:16:17 GMT

@adam4QNES your suspicion is incorrect. If you address the numerous modeling problems (that also is a PITA) then this will work just fine.

However, I still missed an N-Gon:

Re: sub-d Mesh import to t-splines

jeff_strater — Tue, 09 Apr 2024 00:12:07 GMT

thanks, @HughesTooling - good to know. I learned something today. I guess that makes sense, as Fusion does not know what to do with non-planar quad patches anyway.

Re: sub-d Mesh import to t-splines

adam4QNES — Tue, 09 Apr 2024 06:53:42 GMT

What repairs did you do?

Re: sub-d Mesh import to t-splines

TrippyLighting — Tue, 09 Apr 2024 16:00:34 GMT

I looked at it again this morning and the main problem that needs fixing is duplicate vertices. Those a vertices that, within a certain tolerance, occupy the same location.

When those are removed/merged, the mesh can already be imported into Fusion and converted into a T-Spline.
then there are 2 N-gons and a couple of triangles that, when eliminated, result in better topology.

The video might still take a while to convert into the higher resolution versions on YouTube: