Mesh.UnweldVertices

[pavlom (Pavlo Menshykh)]

Greetings, I have a list of mesh vertices IDs and I would like to unweld mesh at those vertices.
https://developer.rhino3d.com/api/RhinoCommon/html/M_Rhino_Geometry_Mesh_UnweldVertices.htm
Seems like a perfect solution, except I can’t get it to work.
My current mesh is completely welded with no creases, if I unweld it it doesn’t change behavior.
I have read the tips for the method and I did TopologyVertices.TopologyVertexIndex() but the provided list has the wrong indexing no matter how I approach it.

[pavlom (Pavlo Menshykh)]

I couldn’t get .UnweldVertices() to work properly, neither in python nor C#
To solve the problem I got topology edges indices for vertices (thankfully they were somewhat ordered) and .UnweldEdge() worked like a charm.
Picking vertices inside rhino on a mesh and using UnweldVertex works flawlessly as well (but is not a solution as I need this automated in gh).

[diff-arch]

For me it seems to work, however the results are pretty unpredictable!

Since you’re unwelding individual vertices, it has to guess which edges to unweld!

A better approach, depending on what you want to do, would probably be to unweld edges instead.

[diff-arch]

Here’s an example for unwelding mesh edges:

import Rhino.Geometry as rg

topo_edge_indices = []

for i in range(M.TopologyEdges.Count):
    if M.TopologyEdges.IsEdgeUnwelded(i):
        continue
    line = M.TopologyEdges.EdgeLine(i)
    pt = line.PointAt(0.5)
    rc, _ = C.ClosestPoint(pt, t)
    if rc:
        topo_edge_indices.append(i)

M.UnweldEdge(topo_edge_indices, False)

sub_meshes = list(M.ExplodeAtUnweldedEdges())  # optional

a = sub_meshes

Keep in mind that many Grasshopper components actually don’t seem to respect unwelded edges somehow. A prominent example would be Catmull-Clark Subdivision from Weaverbird.

unweld_edges.gh (7.3 KB)