I don’t understand, its a simple curve made out of arcs and lines. I need it to be a surface because many operations in grasshopper such as Surface Dimension and Surface Morph require surfaces as inputs, not a polysurface.
Rebuilding the curve and extruding does give a surface, but I lose the original accuracy of the curve…
This is one BIG limitation of NURBS. I am not talking about a complex brep made out of multiple booleans and stuff, it a simple strip.
This should be a surface.
Hi @ShynnSup,
I don’t have the answer for you as to “why” but if you need a single surface:
Loft will maintain a single surface:
Blue (Gumball Extrude) & Purple Loft offset curve (Rhino):
Here’s 3 methods in GH illustrating differences:
Graph Space:
Model Space:
20230821_Curve_Extrusion_Single_Surface_Response_01a.gh (15.5 KB)
@ShynnSup In extrude curve command make sure “SplitAtTangent=No”.
UseExtrusions command and select “Polysurface” (not “Extrusion”). Then extrude the curve. The result should be a single surface. It is confusing that you need to select “Polysurface” to obtain a single surface.
Not a limitation of NURBS. Rather the result of particular choices made when the code was written and user options.
Hello- extrusion objects always split at curvature discontinuities (= tangency only, lilke lines and arcs in a rounded rectangle) Surface can have these - thus if in plain Rhino you tell it not to make extrusion objects, (UseExtrusions command) then you will see an option on the ExtrudeCrv command about splitting at tangents.
-Pascal
Thanks, the boolean at split tangents did it. Makes sense, in my mind it had to be entirely possibly to have a single surface from that curve, good thing it is 
My understanding of Rhino, is that curves which usually determine surfaces, do constitute the composition structure of said surfaces. Therefore, if your said curve is a polycurve, then said surface will be a polysurface.
Yes, rebuilding the said polycurve as you mentioned, indeed gives you the opportunity to create a single surface per say. And it’s of course tricky (depending on geometry and workflow) to maintain accuracy to the original polycurve.
In my personal experience I prefer to comprise curvatures in an efficient manner, which means there should be edge junctions near inflection points between one curvature change to another.
But as you said, maybe you’re dealing with a particular scenario where the means out weighs the cost.
I’ll have to check my settings, cause I’m not a fan of the “new” extrusion behavior lol.
haha just unchecked mine 
omg can’t wait to enjoy that new setting 
This is really helpful, had no idea, thank you
