Help cropping a complex mesh

New to meshes in Rhino.

I have scanned an object in Meshroom. Came out great, though it seems to be comprised of a number of patches that are not grouped and not contiguous yet many select at the same time.

I would like to trim this beast with a few simple planes, yet I am stymied at every turn. Main problem is that many of these non-contiguous patches disappear when I have a successful trim on one of its “kin”.

Maybe the screen-shots will help. You can see in the “after” pic all the missing triangles from below the plane after boolean diff w/ the surface to trim the end clean. Seems like it would be such a simple operation, but meshes sure are a different beast than solids…

Opine please thanks!!

Hi David -

Use SplitDisjointMesh to split this in separate meshes.

I’d activate a selection filter (SelectionFilterFaces) and then just window-select the part that you don’t want and hit Delete. [Remember to turn off the selection filter with the SelectionFilterNone command].

Thanks so much Wim.

I used split disjoint mesh, which was certainly helpful.

The output then yields many new jagged faces, all co-planar with the trimming surfaces (btw the highlighted surfaces were the ones successfully deleted after trimming, it is the multitude of slender faces both in and outside of the trimmed perimeter both on the top and bottom trims that are the issue).

Deleting these manually is just not tenable: Is there a factor I can address to help avoid generating these new faces?
Thanks again,

Hi David - what does Check have to say about the meshes to be split?