Trimming a mesh

I’m just now trying to figure out meshes. I’ve imported a mesh and done a little manipulation on it. I want to trim the left hand side of the piece off and mirror a new left from the right. I cannot get trim or split to work. Not sure where to start to understand what I’m doing wrong. Can someone get me pointed in the right direction?
thanks, rex

seat spacer.3dm (7.7 MB)

Hello - one thing you’ll find (have found… ) is that Rhino’s mesh intersection tools are not very strong… it looks like you may have already tried to split this mesh - do you have the original handy still? It might still be possible. On thing you can do is run DeleteMeshFaces and carefully widow around the faces to remove on one side.


@black33ford, before using Rhino’s mesh tools you better check if the mesh is bad using the _Check command. Your mesh had non manifold faces, duplicates and selfintersections. After cleaning this up a bit, _MeshSplit using a surface works.

seat spacer.3dm (2.1 MB)

Could you tell how this mesh was created ?

The mesh was created with a photogrammetry process. It was converted from a point cloud and then given to me. I did some triangle reduction and smoothing using Mecsoft’s mesh tool in RhinoCam. I did not seem to be able to fill all the holes in the mesh, so it was not a closed mesh.

Thanks Clement. I was able to split and mirror your result. Where can I find more out about the meaning of manifold faces, duplicates, and selfintersections?

If you search this forum there is a lot of info about that. To find the problematic areas like naked edges in your mesh i’ve used _Check and _ShowEdges, then used the mesh tools like _DeleteMeshFaces, _FillMeshHole, _CollapseVertex etc. finally used _Weld 180 to really close it.


non manifold faces means there are mesh edges shared by more than two faces.
duplicate mesh faces means mesh faces which are exactly on-top of each other.
self intersection means mesh faces which intersect through other faces in the same mesh.

Thanks Michael