Unrolling fairly complex surfaces (like boat planks)

Hello ~
I have been using Rhino since #4 and had 7 since it was released. I have only done a few projects in 7 that may raise my issues, but I believe it is more common in 7 than it was in 6. What I have noticed is that it is harder to get plank surfaces (usually generated through Sweep, mostly, but sometimes loft) to unroll as a single surface.

One of the struggles with boats, of course, is to get the unrolled surface to be as representative of the 3D surface so that the planks can be precut and fit close. I do tend to record discrepancies on the shop floor and alter the 2D files, but of course I would like the 3D model to most closely represent the actual surfaces being bent.

Anyway, here is are two examples of nice surfaces being unrolled.

In this image the polysurf was made with UnrollSrf set to a tolerance of .04
The nicer single surface was generated with UnrollSrfUV (natural)

Same pattern here:

I understand that there may have been some changes to Unroll between 6 and 7 and that might help me understand what may be going on. It seems that in 7 I have to stick to UnrollSrfUV for the most part. That gets the surfaces to unroll’ jury is still out on accuracy of the shapes.

Thanks for any education you can give me!

Hi, have you tried _Smash? I vaguely remember that’s what I used for model hulls, which worked fine, but again they were only models (1/10 scale).

Hi Clint - we need an example - please post a file, or send to tech@mcneel.com, with a link back to this topic in your comments.


I will investigate smash but I thought that was for highly doubly curved surfaces.

Attached is a file with what was shown.
CIY20-MCNEEL.3dm (1.4 MB)

Hi Clint - well… the surface is not G2 in the long direction - it is tangent continuous only - but it seems to me only very very slightly. DivideAlongCreases > SplitAtTangents=Yes does chop it up. Including at the location you do not like on the unroll… Still poking.

@CCBB - the surface is degree 2 in the short direction - and it reverses curvature in the area of ugliness in the unroll:


Is that how it is mean to be or should it be a plank, and not curved at all across? If you ChangeDegree to 1 in V, the thing unrolls cleanly.


did not read the entire topic.
just wanted to point to
for maybe building the initial surfaces.

How do you tell it is not G2 lengthwise…it is degree 3 w/ 39 pts. I can see how things get weird in curvature graph.
Where is the info for…DivideAlongCreases > SplitAtTangents=Yes
Regarding the V direction of surface - there is a little compound curvature in the actual surface when it wraps around the boat and that is what I am trying to capture, but I did ChangeDegree to 1 in v direction and it unrolls but still a polysurface, but it unrolls…I am curious if you are getting a polysrf on your end, too.
Thank you - I have some things to think about.

edited to add: I now see Dividealongcreases> mine was set to NO but I get a same unrolled srf whether it is yes or no.

Well, just that DivideAlongCreases splits it up into multiple faces.

Unrolling after ChangeDegree does make a polysurface but it is clean and does not have the dogleg in it as you get from the original.