Automatic orientation and merging of laser scanner acquisitions through volumetric targets: procedure description and test results

The use of volumetric targets for the automatic merging and orientation of laser scanner acquisitions has been experimented. The used procedure is fully automatic. The targets can also be used for the orientation of photogrammetric acquisitions, and allow to have a synergic coupling of different kinds of surveying. If a calibration grid is used, the absolute coordinates of the cone vertices are known; for larger objects (architecture), the vertices coordinates can be obtained by a topographic survey. The procedure described in the article, performs the automatic recognition of the targets, and allows to obtain the coordinates of the target vertices in the reference system of the laser scanner. The merging and the orientation of the laser scanner acquisitions can be easily obtained. The scans of a building facade have been used to perform a test. The coordinates of the target vertices, obtained through the described procedure, have been comparated with the coordinates obtained by a topographic survey. The distances among the vertices, obtained using the acquisitions and the topographic survey data, have been compared. The differences are about one millimeter.