For Direction and Line it is the Direction although for lines the direction is reversed and the origin of the direction is the midpoint of the line.
For nodes such as Polygon and Arc, BSplineCurve, BSPlineSurface, this is the ZDirection of the DTransform3d. In these cased the Dray3d origin is the startPoint of the node. For Planar nodes this is the normal to the node plane (Hidden).
For BSplineSurface, Cone, CoordinateSystem, Direction and Line, it is the XDirection of the DTransform3d.
