DPlane3d
- Planar features, such as Polygons, Arcs, EllipticalArcs, Circles Follows MicroStation's anticlockwise rule in determining the normal.
- The origin of the DPlane3d is often identical to that of the DTransform3d, and is usually the same plane as the DTransform3d.XYPlane only it is often rotated.
- For a BSplineSurface the logic is not clear.