I’m posting this because it may help someone else who has Rhino become almost unresponsive.
Using MeshSplit to split a group of 7 meshes resulted in Rhino becoming almost unresponsive, because the split increased the number of meshes by a factor of 20,000. Joining the split meshes into 2 meshes restored the responsiveness but scrambled the photo texturing.
The original “mesh” was actually a group of 7 meshes with about 10 million faces in total and were photo textured. The group of meshes were created by Metashape and exported as a .obj file. I imported the meshes into Rhino, oriented and scaled them, and saved as .3dm file. I’ve opened and used that file in both Rhino 8 and Rhino 9 WIP. Both remain responsive.
I ungrouped the meshes and used MeshSplit to split the meshes with a planar surface. The result is 140427 meshes.
I grouped the meshes after splitting into two sets and saved as .3dm file. Open the file with the split meshes in Rhino 8 or Rhino 9 WIP and the result is almost unusable. Even for operations not involving the meshes, such as turning on/off layers which do not contain the meshes and simple geometry creation Rhino frequently acts as if it is locked up for ten seconds or longer. HWMoniter shows the CPU very active during these periods.
I used Join on the two groups of meshes to create 2 meshes. Unfortunately the mesh texture was completely scrambled, though it did restore the responsiveness of Rhino.