Closing a polysurface will flip it inside out

Rhino Rhino for Windows
1

I need to have a closed polysurface with surface direction outwards on my boat hulls to be able to use model information in subsequent plugins/software.
I can manage to get the individual surfaces to have correct direction, but when I join the last surface, I often end up with a closed surface with direction pointing inwards - i.e. direction of all surfaces have been flipped
Most of the time, I can bypass this problem by trimming the “non-essential” part of my hull (a distance above waterline) and close the polysurface by means of cap command or an imaginary deck surface.

However, for some models, I cannot manage to create a closed polysurface with direction pointing outwards, no matter what (limited) surface tools I try.

Does anyone have an idea what causes this, and how to avoid it / workaround??

-Lefty Looser-

PS! Due to client agreement I cannot upload model files

2

When you try showedges command do you have
any naked edges?
Or right click and getting detail info show that polysurf is valid?

3

No naked edges in model (polysurface cannot be closed with naked edges)
Yes, polysurface is reported to be valid

4

Hmm I was guessing it was invalid polysurface…
I just had a closed polysurf but invalid due to one invalid surface.

5

Are there any non-manifold edges?
How do you see that the model is inside-out? (do the Dir arrows point inwards?)

–Mitch

6

Hello - tech@mcneel.com and www.rhino3d.com/upload are private McNeel forums - confidential files can be attached or uploaded .

-Pascal

7

No, not any non-manifold edges
Yes, inside out is revealed by direction of Dir arrows (and negative volume reported in subsequent plugins/software)

8

What happens if you explode the model, select all the surfaces, run _RebuildEdges and then try to re-join?
(before you re-join you might want to use SelSmall and see if you have any micro-surfaces in there)

Sounds like there is a bug in any case…

9

Client says no
But I can try to recreate the error on a generic model for posting. That will have to be another day, however…

10

Commands I’ve never heard of before…:flushed:

Tried this in both v5 and v6 (use mainly v5 since the plugins are not updated for v6).
Ran the commands with default values/tolerances.
Result: v5 created two naked micro-edges (which I have to fix to be able to create a closed polysurf, so I just jumped to v6-testing, since that has the new and brilliant _RemoveAllNakedMicroEdges command)
v6 managed to rebuild edges and join surfaces to a closed polysurf without any naked edges - alas the new polysurf was also inside out :sob:

11

My guess is there is a super skinny surface, that looks like a line or curve, somewhere along another edge.

-Pascal

12

Pascal, You nailed it!
It is the nature of many of my models, that some surfaces have different extent in e.g. X-direction, which makes me end up patching the open parts - usually by means of _EdgeSrf. Even so, this occasionally results in a naked edge (which I don’t understand, since EdgeSrf should result in position accuracy?)
Anyway, my quick fix for generating the required closed polysurface, have been to simply add a EdgeSrf between these two naked edges, which seems to be sitting on top of eachother.
Strange still is the fact that some of my models having this “super skinny” surface can be closed without flipping inside out - but at least now I know the root cause when they do flip.