Methods for the Automatic Geometric Registration of Terrestrial Laser Scanner Point Clouds in Forest Stands

A combined analysis of multiple terrestrial laser scanner point clouds recorded from different positions requires a geometric registration of these scans. In most applications of terrestrial laser scanning, artificial tie points, which can be recognized automatically by proprietary scanner software, are placed in the scanning area. In this case, the scan positions have to be chosen in a way that they ensure a clear view to the tie points. These pre-scanning tasks may be often labour-intensive and time-consuming. Therefore, an automatic registration process without pre-assigned artificial tie points is aspired. This paper will discuss two methods for the registration of terrestrial laser scanner point clouds in forestry applications: In a first step, our automatic registration procedure on the basis of an intensity image of a laser scanner data will be presented. The tie points (in this case white spheres) are detected in the intensity image. Corresponding points are found by calculating a distance pattern of all detected spheres on the basis of their centres derived from the range data. In a second step towards avoiding artificial tie points, a novel method to register two laser scanner datasets on the basis of extracted tree axis and only one tie point is introduced. Finally the results of three different registration processes (interactive, sphere detection, tree axes) are compared and discussed.