Serengeti has been what I would call “aggressively” splitting my surfaces apart at different times, despite turning off that feature in advanced settings.
It seems to happen when filleting certain surfaces. Note that when I run RemoveMultiKnot on the upper surface, I get a single fillet and no broken apart surface, but I haven’t had to do that in previous Rhino versions.
@Gijs@menno When current V9 WIP FilletSrf with the Trim option is used on a surface containing multiknots that surface is converted to a polysurface (split at the multiknots). It does not occur without the Trim option. It does not occur with V8.
Example: Blue surface has multiknots created by changing degree from 2 to 3. FilletSrfMultiKnot.3dm (2.2 MB)
I agree, the Trim option should behave like the Trim command. The command bypasses the setting of CreaseSplitting and returns a trimmed fully-multiple knot result, and not a polysurface. FilletSrf and related commands should do the same.
For now, as a workaround until this is fixed, you can (temporarily) disable this by issuing _CreaseSplitting _Disable prior to using FilletSrf and restore it with _CreaseSplitting _Enable. It is generally a good idea to keep crease splitting enabled.
@menno It is interesting that CreaseSplitting is affecting a surface without fully multiple knots. The surface in my example above does not have any creases (no fully multiple knots). It is a degree 3 surface and the knots have a multiplicity of 2, not 3 as needed for tangential discontinuity in a degree 3 surface.