Rhino5 - First order single multiface surface

Hi, I’m looking for help in following issue how to create first order - made of planar faces - single surface in Rhino? I was trying to use point grid command, but quality of the surface is not good. Idea is to create stepwise surface like stairs, but in two perpendicular directions as one surface (not joined, not polysurface). In simplest model is look like small box is putted on the top of bigger box and I need single surface which cover both boxes. Corners and edges need to be sharp. Anyone knows if is it possible and which command I can use?

Two ways to do do this -


  1. Turn Extrusion creation off - Set UseExtrusions to Polysurfaces
  2. Draw your stair step profile as a polyline
  3. Temporarily turn off crease splitting - type CreaseSplitting and set SplitAlongCreases to No.
  4. Extrude your polyline - set SplitAtTangents=No. It will be one single creased surface.
  5. Don’t forget to turn crease splitting back on afterward, it is not a good idea to have it on all the time.


  1. Draw your polyline and extrude as above (Crease splitting still set to No), then Explode the polysurface, or draw some individual surfaces that are joinable (but don’t join them).
  2. Run MergeSrf with Smooth=No and merge the corresponding edges at each joint.

Kinked surfaces are special objects not generally used, they may cause problems with other Rhino operations downstream or on export, and possibly exhibit display artifacts.

Thanks Helvetosaur for help, but this is not exactly what I want. I’ll try describe it better. Please see on the attached picture. There is shown that control points of the surface are exactly in position of input (starting) points. Now I’m able to make it only manually putting control points in correct positions. I’d like to be able move from step - planar surface to step - single surface in somehow automatic way. Let’s say I have complex model build of planar surfaces (50-100) and I’d like to convert them into single surface. Any thoughts?

Yep. Don’t. A likely recipe for an unusable model.

If it’s all planar surfaces in your polysurface and you are concerned with editing it - what about using SolidPtOn? There is also subObject selection of individual faces and edges which works pretty well for editing these types of objects.

Thank you for SolidPtOn I wasn’t aware about this command, preaty usefull.
However reason why I need it as single surface is that it’ll be used as boundary condition for volume definition in another software. As long as it is treated as one surface all further definitions are much simpler (or even possible).

Hello - can it be a mesh?


Hi! Unfortunately no, it can’t be mesh. Object need to be exported from Rhino as iges-format file.

Why does a boundary condition imply a single surface? BREP (what Rhino polysurfaces are) is “Boundary Representation”

While certain structures may be modeled as kinked single surfaces, others may not. But in any case, IMO, they are more curiosity items than real, workable solutions. Below is a single surface cube. You can have fun playing with it…

SS_Cube.3dm (618.3 KB)

SS_CubeV5.3dm (542.8 KB)

This is why:

IGES trimmed NURBS surfaces are represented as an entity 128, which contains the surface geometry,
together with an entity 144, which contains only the trimming information.
Maxsurf can only read the entity 128 data, but does not support importing the entity 144
trimming data.

If I import polysurface to Maxsurf I’ll get list of single surfaces, which I’ll need to trim and join manually. For simple shapes it’s not a problem, but for complex shapes it is really time-consuming and tedious work. That is why I’m looking how to workaround this issue.

Sounds like you need to construct all your surfaces as untrimmed. If they are all planar and have linear edges, this is not difficult with the Rhino toolset. Then all you need to do is join the untrimmed surfaces in MaxSurf.