How to trace a curved sloping plate?

Hi Group,

I’m new to Rhino and actually doing a trial of the software and have a question.

I wanted to know how I could trace a curved sloping plate stringer to get a flattened developed surface.
Say I modeled a curved spiral staircase with some other program like AutoCAD Architecture or Revit and imported the stair into Rhino (see attached).

Any help would be appreciated.

Hello- is the path is meant to be actually curved in plan, or tessellated as in the image? I guess either way, extracting the very outer or inner ‘curved’ faces into a spearate polysurface

and UnrollSrf > Explode=No would be where I’d start. If that is not on the right track, please post a file with the objects and some clear explanation of what you would like to accomplish.



How would you extract the faces of the inner or outer surface?
is there a way to trace this curved surface somehow with like a 3D polyline in AutoCAD?

Ideally I would like to extract the surface of the inside face of the stringer to show the riser and tread profile. Here is a developed view from another stair along with a screen shot of the 3D model.

Here are a couple of stair models.
One was an imported DWG (Helix) and the other is an imported STP (Core).

The Core model was created with SDS2, which have too many faces.
Not sure if it’s possible to edit within Rhino to reduce them or just easier to trace and re-create the surface.

Helix Stair.3dm (313.2 KB)
Core Wynwood.3dm (12.0 MB)

Hi Ed - the second one is a little simpler in that it is an arc in plan, the Helix one looks like two arcs plus some transition. You can certainly reverse engineer these to clean curves and surfaces but it is a bit of work I’d say.
For the helix, I’d weld the mesh at say 10 -15 degrees then Explode to get the outer faces as one or two meshes. You can then DupBorder to get a polyline and flatten that to the CPlane but I’d guess that curve must be availble from the original confstruction process that you can import directly…


Hi Pascal,

Thanks for the advice.
I will research and try your suggestions.