Export Step SubD

[kevin.morenogata]

I’m testing this SubD great tool, but I experienced some problems while exporting a SubD geometry.
I tried to export as an iges or step, with different configurations but I get weird trimmed surfaces (see in the picture), not respecting the main soft geometry.

[wim (Wim Dekeyser)]

Hi Kevin -

@kevin.morenogata

[…] I experienced some problems while exporting a SubD geometry.

Note that you will also see this with the ToNURBS command. When you export the SubD object to STEP, that same code is used to convert the SubD object to NURBS.

At any rate, this issue is on the list as RH-55492 and I have added this thread to be notified when that issue is resolved.

Basically, what you are seeing are rendering mesh artifacts. You can read more about that here:

SubD to Nurbs G0 continuity problem

G0 = continuous G1 = G0 + tangent continuous G2 = G1 + curvature continuous. Rhino SubDs are Catmull Clark subdivision surfaces. Below “subd” means Catmull Clark subdivision surface. For every interior point on a smooth subd edge, the subd is G2. At an ordinary smooth vertex (4 faces and 4 smooth edges), the subd is also G2. At smooth exceptional vertices (also called “star points”) the subd is G1, but often is not G2. In many cases, the corners of subd faces at exceptional vertices are…

-wim

[inju]

Isn’t that a problem with proper topology?
There are other methods of topology.

Rhino 7 WIP. Topology "star points"

[wim (Wim Dekeyser)]

Hi -

@inju

Isn’t that a problem with proper topology?

As I understand it, not necessarily, no.

@inju

There are other methods of topology.

That’s correct, yes.
And, as you show, you can avoid rendering issues at star points by using a different topology. But that doesn’t mean that the other topology isn’t “proper”.
-wim