SubD Conversion glitch in grasshopper

Rhino SubD
1

I found a weird glitch where if I take this brep:

RH7 WIP GH Input Brep
RH7 WIP GH Input Brep1405×711 27.5 KB

… and then convert to SubD in grasshopper, I get a broken vertex in one spot, like this:

RH7 WIP GH SubD Error
RH7 WIP GH SubD Error1405×711 34.6 KB

For some reason, if I rotate the referenced brep in Rhino a little bit, it fixes it:

RH7 WIP GH Rotation Fixes It
RH7 WIP GH Rotation Fixes It1405×711 35.7 KB

Any idea why this would happen?

Here’s the definition used to convert it, with internalized data. There’s a curve object you can highlight to create a bounding box around the problem area so you can find it, and a stream filter to toggle between the input brep and the slightly rotated input brep.

Sub Glitch.gh (539.0 KB)

2

It’s a naked edge.

Moving the object 0.001 units in Y direction eliminates the issue too.

I think it has to do with the tolerance.
Putting an Align Vertices component before your NGON script solves the problem.

image
image1683×593 92.6 KB

Pretty cool object…

3

I’m confused, the input object is a closed polysurface.

Running _What returns this:

polysurface

ID: aa6f5e9d-8e39-4fec-bab3-801aac6506ba (94)
Object name: (not named)
Layer name: Work
Render Material:
source = from layer
index = -1

Geometry:
Valid polysurface.
closed solid polysurface with 389 surfaces.
Edge Tally:
905 manifold edges
Edge Tolerances: all 0.000
Vertex Tolerances: all 0.000
Render mesh: 389 basic custom meshes 2876 vertices 2009 polygons
Analysis mesh: none present

4

The problem is where you create the mesh from Brep. That new mesh has naked edges.

I had to create meshes from polylines recently too and chose to use a script. In your case creating the meshes from Brep Face boundaries directly leads to the meshes you want to turn into Ngons.

Attached file deleted, new version in my next post below

5

Ah, gotcha. When I input a mesh made by running _Mesh and _AddNgonsToMesh in rhino, it works fine.

I didn’t make the python script, I thought it was just a one-line script that used whatever the python version of Rhino’s _AddNgonsToMesh command is.

I’ll play with tolerances. I’ve had other problems with this script failing with certain tolerance conflicts and with nonmanifold edges.

6

I just found this post here where Giulio Piacentino posted a better script to turn Polylines to NGONs

Your example with that script:

20_05_25_mesh_from_polyline.gh (262.1 KB)

1 Like