DupBorder (or extract naked edges)

I'd like to (as the Rhino command dupBorder does...) extract the border of a polysurface (the naked edges).

GH components will only give me all the edge curves of every surface.

Any guidance?

Thanks,
taz

Replies to This Discussion

Permalink Reply by David Rutten on October 13, 2009 at 10:49am

Ouch.. solving this with pure GH components will be a bit of a nightmare. I can see one possible solution, but haven't tried it.

1) explode your BRep, you'll be using both the Edges [E] and the Faces [F].
2) For each edge in [E] create a point [P] in the middle.
3) Project [P] onto all faces in [F].
4) If you have only 1 projection distance which is very small (don't use zero, use 1e-3 or something instead, remember, edges only have to be within tolerance), then you're dealing with a naked edge. If you have 2 projection distances which are very small, you're dealing with an interior edge. If you have 3 or more, you're dealing with a non-manifold edge or a wonky brep.

----
This wouldn't be trivial even if you'd write a VB script for it. I actually wrote the code for the Extrude components (only naked edges are extruded), so I can easily make a DupBorder component as well.

--
David Rutten
david@mcneel.com
Seattle, WA

Permalink Reply by taz on October 13, 2009 at 11:32am

Sigh... That procedure is what I wanted to avoid thinking about.

I did, however, notice that the extrude component magically finds naked edges.

Where I was headed was to offset a polysurface and then loft the naked edges of the original and the offset to make a solid BRep. But now I realize that even Rhino doesn't offset polysurfaces as polysurfaces, only as individual surfaces.

I think this is basically the same thing the "shell" discussion people want to do (offset a (poly)surface as a closed BRep). But now I realize how difficult it would be.

I'll settle for a DupBorder component instead, if it's in the offering... It would be quite useful and more intuitive than other methods.

-taz

Permalink Reply by Evan C on August 3, 2010 at 7:33pm

I'm trying to do the exact same thing - has there been any progrss on this?

Permalink Reply by taz on August 10, 2010 at 4:00pm

Argh... I'm thirding a dupBorder request for the second time...

Permalink Reply by Daniel Piker on August 10, 2010 at 5:33pm

Do you mean something like this ? :

Attachments:

dupBorder.ghx, 158 KB

Permalink Reply by taz on August 10, 2010 at 10:27pm

Let me give 'er a shot with a coplanar polysurface...

Permalink Reply by Rémy Maurcot on November 25, 2011 at 6:19am

Hi all,

David rightly, I think a false comoosant VB: Here is an example of after an error occurs on the second BREP.

Permalink Reply by David Rutten on August 11, 2010 at 9:14am

Just added a BrepEdges component. It outputs 3 lists, the first contains all naked edges, the second all interior edges and the third all non-manifold edges.

--
David Rutten
david@mcneel.com
Poprad, Slovakia

Permalink Reply by taz on August 11, 2010 at 1:15pm

THANKS! (yes, shouting...)

That makes my day.

Permalink Reply by Benjamin Golder on September 8, 2010 at 5:05pm