I have noticed different behavior of extrusion when using Surface.CreateExtrusion and Extrusion.Create in RhinoCommon.
Based on the same polycurve Surface.CreateExtrusion gives only one surface as result while Extrusion.Create gives polysurface.
After closing both of them I got 2 solids and checked IsPointInside property. Centroid of the curve is used as a check point.
Surface.CreateExtrusion(single surface approach) gives wrong result but Extrusion.Create(polysurface) is ok.
As an input curve I used simple closed polyline curve with COG outside the curve. See enclosed.
Amy idea why it is happening?
P.S. This has been checked in R5 but same behaviour is in R6 Wip.
CurveExtrude.3dm (20.5 KB)