Help unrolling complex polysurface

211119_Balustrade_Unroll.3dm (693.2 KB)

Hi all,

I have a series of complex polysurfaces (including and similar to the one attached) which I am trying to unroll so that I can extract a set of 2D curves that plan out each surface, unrolled and in sequence as if the whole polysurface was gradually unrolled surface by surface. I’ve tried unrolling and UVcrvs but can’t seem to get anywhere - can anybody help?

try squish or smash- smash may work better for this surface.

Unfortunately not successful - any other ideas welcome.

post the file?

Has been attached to the original post.

move your model to the origin, it’s very far away now…

then run extractbadsrf to see the degenerate surfaces in the model. repair them, then smash-

it smashed fine here once the bad stuff was rebuilt-

here is the same file with explode= no

@theoutside Why do you recommend Smash or Squish instead of UnrollSrf or UnrollSrfUV? My experience is for developable surfaces UnrollSrf and UnrollSrfUV are generally more accurate than Smash or Squish.


It is important to understand why the unroll command failed at first.

The bottom curve you extruded seems to have vertical segments. Extruding those vertical lines creates bad surfaces.

You can avoid the problems by just extruding the segments which are not vertical.

The resulting polysurface can be unrolled without problems.

… file deleted …


@martinsiegrist It looks like you uploaded the original file, not a file with the fix.

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You’re right, I didn’t notice the warning about saving a Rhino 6 file.

211119_Balustrade_Unroll.3dm (263.7 KB)

PS: prior to deleting vertical lines I pulled two edges away from their original position because they would have created invalid surfaces too.

Excellent. Find the root cause and fix it.

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Thank you. At least half of that problem was caused by vertical segments.

ExrtrudeCrv will refuse to make a bad object if the input curve has vertical segments. It is possible to Loft between two curves with vertical segments and create a bad object.

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The original file contains a single polyline. I assume the polysurface was created with Gumball Extrude, which in contrast to the ExtrudeCrv command extrudes the curves no matter what.

that is likely true, I’ve always used smash for this type pf stuff, so I stuck with what I know.

the main issue with the file is several bad surfaces. Once they are repaired, the model behaves as expected.

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Thanks very much, this is great. When you say repair the degenerate surfaces, did you literally just re-draw them or is it something else you did to fix them?

Just a simple extract srf and rebuild with the same degree and u and v span count.

Thanks for all you help, that’s been grand.

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