Mobile projection system for scaling and orientation of surfaces surveyed by an optical measuring system

A method of surveying a surface in a real world coordinate system, the method comprising:

• projecting a predefined pattern onto the surface, wherein the predefined pattern is projected onto the surface by parallel projection beams;
• determining positional and image data of a projected pattern on the surface, wherein the positional and image data are indicative of the predefined pattern in a measuring coordinate system;
• determining transformation data based on the predefined pattern and the determined positional and image data of the projected pattern, the transformation data allowing a transformation between the real world coordinate system and the measuring coordinate system to thereby survey the surface, wherein the determining of the transformation data further includes determining a transformation plane in the measuring coordinate system in such a way that a direction of a normal of the transformation plane is parallel with the parallel projection beams,
• projecting the projected pattern along the direction of the normal of the transformation plane onto the transformation plane, so that an undistorted pattern of the projected pattern with respect to the predefined pattern is projected onto the transformation plane in the measuring coordinate system,
• measuring a distance between reference points of the undistorted pattern on the transformation plane, and
• determining a scaling factor by determining a ratio between the distance of the reference points of the undistorted pattern on the transformation plane and a distance of the respective reference points of the predefined pattern in the real world coordinate system.