Answer:
In RFEM, surfaces consist of a set of finite elements. Each element has its own local coordinate system. The orientation of all elements belonging to the surface is governed by the overlapping surface definition.
The centric orientation of the individual elements can be achieved by specifying the orientation to a line in the surface properties under the "Axes" tab. For this, the program requires a specification of the radial direction (x- or y-direction) and a description of the center line via two points. The program then aligns the individual element coordinate systems so that a straight line through the element origin in the radial direction on the element plane intersects the static center line.
