UnrollSrf screws up joined edges in an odd way

When I unroll this polysurface (Explode=No), I get a single polysurface, but Rhino sees some internal edges as naked.
This makes no sense, because it should result in multiple surfaces or polysurfaces.
…and it should’nt happen in the first place.

Flatten makes screwy internal naked edges.3dm (180.5 KB)

Hello - the file tolerance is .1mm - I’d guess that is the problem - Rhino really prefers to be between .01 and .000001 - I’d shoot for that as a tolerance for building. these things to begin with. That said it is not clear to me how to fix it at this point…


Tolerances drive me nuts.
FYI, the object was created with a 0.001 tolerance, and since it flattened as shown, I tried to loosen-up the tolerance, and saved the file that way.

Therefor, this is not a tolerance issue.
A polysurface where you have naked edges like this should not be a single polysurface.
I call this a bug.

No, it wasn’t… If you explode, rebuild edges then Join (with .001 file tolerance) you will see the out of tolerance edges (they won’t join). They are out by a little over 0.01 tolerance. So undo after the failed join, set your file tolerance to 0.02, then Join. Then unroll. It should produce a single polysurface with no interior nakeds (at least it did here).

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I sent a file modeled by someone else who probably changed the tolerance during modeling.

Anyhow, it makes no sense that a polysurface has no interior naked edges and then when flattened has some.
It makes even less sense that the resulting polysurface is single despite those naked edges.

Well you can do all kinds of tricks to out-of-tolerance edges to make them join (like JoinEdge or resetting the file tolerance), but that doesn’t change the underlying surface geometry which Rhino needs to use to unroll. In any case, as it’s super simple, I would just remake the object by re-extruding from the original edge curves using the correct file tolerances.

Flattened.3dm (270.4 KB)


Mitch, this is not a simple extrusion as you say.

I’m not an academic, so I don’t have your amazing theoretical knowledge.
I need to focus on mundane stuff like getting the parts right so they will fit in place in the construction.