Degree 1 Surface or Polysurface - What controls?

What controls when degree 1 surfaces are split into polysurfaces? Is there a setting in Options > Rhino Options > Advanced?

Hi David - the angle tolerance in the document - is that what you mean?


Pascal - not the Angle tolerance setting. With it set to 45 degrees extruding a degree 1 line (not polyline) with angle changes of less than 9 degrees results in a polysurface.
Polysurface01.3dm (2.8 MB)

Hm - I just did a similar test and it seemed to correspond - let me try again…

I’ve asked what that angle is, but I do not think it is directly controllable in any Rhino UI. You can only turn splitting on and off with CreaseSplitting

@davidcockey - kink-splitting is hard coded to 1 degree. What do you need to accomplish?


how is a line with several kinks not a polyline? i am confused… besides that if you are looking for a way to split narrow surfaces which do actually not want do divide than scaling with factor 20 in one direction then DivideAlongCreases and scale back with factor 0.05 will do. on the other side if you are longing to keep kinky surfaces as one which i dont believe, then you know that is usually not a good idea.

i am also a bit surprised how persistent rhino is in keeping a surface which is slightly kinky as a single surface. never noticed that before

A degree 1 NURBS curve has straight (linear) segments with C0 (position) continuity between segments.

NURBS curves of degree 2 and higher can have kinks if they have multi-knots with multiplicity equal to the degree - 1.

Nothing to do with splitting narrow surfaces. Perhaps you are thinking of a different thread?

Usually, but not always, not a good idea. There are some instances when I want a surface which is degree 1 and multispan in one direction (not a polysurface). These are typically part of a particular workflow when modeling and analyzing lapstrake/clinker and multi-chine boat hulls.

i am still not sure what your intention is.

ah right… got you. sorry forgot about all that

I found the solution. CreaseSplitting was enable. I disabled it and now degree 1 surfaces, not polysurfaces are created.

1 Like

I did not know this command !.

(_MergeSrf) with the (smooth = no) option has been my choice, in the past to merge the
surfaces and keeping their structures with the folds

but CreaseSplitting
it does not work with the extrusion command or from the gumball !!

Hello - CreaseSplitting does not apply to extrusion objects - use the UseExtrusions command to change what type of object is created by the extrusion commands.


1 Like

thank you pascal
I did not know this command too !!

but even with CreaseSplitting the exstrusion is a polysurfaces. is not a surface.
I just wanted to know if it was also possible to obtain a surface with folds with the extrusions

Hi Fares - with CreaseSplitting disabled, and UseExtrusions set to make polysurfaces, extruding polylines should make surfaces - let me test and make sure I am not lying here.

It looks like Gumball extruding makes a polysurface in the above case but ExtrudeCrv makes a kinked surface if SplitAtTangents is also set to No. Gets confusing…


1 Like

The curve in the example I posted above is a multispan degree 1 curve, not a polyurethane or polyline.