Brep.Flip(), Brep.Face.Reverse(), Brep.Surface.Reverse Inconsistencies

[kev.r (Kevin)]

Some posts explaining this topic:

Brep.Flip without swamping UVs and vice versa

BrepFaces have a reverse orientation flag, which allows you to flip the normal without affecting the underlying surface. This is an important optimisation because half the time a brep-face needs to be flipped when it is joined with other faces, so this flipping needs to be as minimal an intervention as possible. Surfaces do not have this. The normal direction of a surface is determine by the right-hand-rule and the UV directions. When you convert a BrepFace into a Surface, you lose the Orientat…

Box surface Normal pointing inwards... huh?

A Surface is a fairly simple object, basically just a rectangle that can be stretched and bend into some other shape. Some types of surfaces supported in Rhino are PlaneSurface (a literal rectangle with interior), Revolution (one curve swept (partially) in a circle, SumSurface (one curve swept along another curve), and NurbsSurface. When a surface becomes part of a Brep, it needs additional information and it is wrapped up into a BrepFace. BrepFaces add additional functionality such as trimmin…

Reverse surface normals (Like Dir command)

TL;DR: I think you may want to use BrepFace.IsOrientationReversed (see http://developer.rhino3d.com/api/RhinoCommonWin/html/P_Rhino_Geometry_BrepFace_OrientationIsReversed.htm The situation with normals and polysurfaces is a bit complex, but I’ll try to explain. A surface has one normal direction, which is defined as the vector product of the tangents in U- and V-direction. Therefore the normal is determined by the direction of U and V (which can be changed by the Dir command by the way). But …

-Kevin