In the file below, there are 4 (co)planar groups of curves that represent facades. They were just experimenting with extruding them into 3D, and noticed a small anomaly - and I can’t explain it either now that i have checked.
If you extrude each facade group individually, no problem. However if you extrude them all at once or even in groups of 2 or 3, some of the windows (always the same ones) get filled in with an additional unwanted extrusion. I cannot figure out why though, everything looks OK. Projecting to the CPlane does not help, but Explode/Join on everything does fix the issue. From that I infer that there is a problem with certain rectangles, but I still can’t explain why the extrusion works normally when only one facade is selected and not when several are selected… So I’m posting it here as a possible bug… maybe someone can find some other reason why this happens that I missed.
Changing the tolerance to a more loose one, or projecting all curves to a plane, then extrude them, seem to fix it.
I think Pascal’s first impression of some rectangles are not coplanar within tolerance is perhaps what’s going on here. Are you seeing differently?
Yes, but Projecting to a planar surface is not at all the same thing as using ProjectToCPlane or using SetPt with Z=0. It is using a different method.
The result of ProjectToCPlane or SetPt retains the original curve ID’s whereas Project to a planar surface changes them - so as far as I can tell, the curves are being remade from scratch using Project - and something in that process fixes the problem.
ProjectToCPlane and SetPt simply modify the control point Z coordinates of the existing curves, but the basic structure remains and thus the problem is still there…
This is not a (co)planarity problem IMO. The other proof of this is if you Explode/re Join all, the problem goes away as well, even without trying to project to a plane. That operation also remakes the curves. Therefore it is the reconstruction of the curves that fixes the problem…
