Independent model triangulation of terrestrial laser scanner data

Transforming the coordinates of different laser scanning stations into a unique object reference system is mostly performer pairwise, using retro-reflective targets as tie points. This may lead to inconsistencies and model deformations. We propose a different approach, based on the simultaneous adjustment of all 3D models coming from different views, in a manner similar to that used in aerial triangulation by independent models. Given n models, a 7 parameters conformal transformation from each to the object system is computed using target as tie points and GCPs if available. Linearization of the equations require a set of approximate values for the unknown parameters, which are provided by an algorithm based on Hamilton Quaternions, but need a set of at least 3 points in both the scan and the object system. Provided that each model is tied to the adjacent by at least 3 tie points, a procedure is presented which computes these approximations for all the block. Tests with real and simulated data compare the effectiveness of the solution with respect to pairwise registration in several operating scenarios.