Mobile projection system for scaling and orientation of surfaces surveyed by an optical measuring system
The present invention describes a device for surveying a surface ( 104 ) in a real world coordinate system ( 111 ). The device comprises a pattern projecting unit ( 101 ) adapted for projecting a predefined pattern ( 105 ) onto the surface ( 104 ), an optical measurement system ( 102 ) adapted for determining positional and image data of a projected pattern ( 106 ) on the surface ( 104 ), wherein the positional and image data are indicative of the predefined pattern ( 105 ) in a measuring coordinate system ( 112 ), and a processing unit ( 103 ) adapted for determining transformation data based on the predefined pattern ( 105 ) and the determined positional and image data of the projected pattern ( 106 ). The transformation data allow a transformation between the real world coordinate system ( 111 ) and the measuring coordinate system ( 112 ) to thereby survey the surface ( 104 ).
1. 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.
2. The method of claim 1 ,
wherein the determining of the transformation plane further comprises,
determining first ratios and/or first differences of distances between at least three reference points of the undistorted pattern on the transformation plane in the measuring coordinate system,
determining second ratios and/or second differences of distances between the at least three respective reference points of the predefined pattern in the real world coordinate system,
varying the normal of the transformation plane until a total difference between the first ratios and/or first differences with respect to the second ratios and/or second differences are minimized.
3. The method of claim 1 , further comprising:
measuring an orientation of the parallel projection beams in the real world coordinate system with respect to a reference coordinate system, and
determining a rotation matrix of the transformation data on the basis of the measured orientation of the parallel projection beams, so that by the rotation matrix the orientation of the surface in the reference coordinate system is determined.
4. The method of claim 3 ,
wherein the orientation of the parallel projection beams in the real world coordinate system with respect to the reference coordinate system is defined by an azimuth direction angle and/or by an elevation angle.