Abstract: Spherical targets are used commonly for point cloud registrations collected by terrestrial laser scanning.To research the applicability of existing methods for robust spherical targets fitting under degradation conditions,four targets with two radii are used to test multiple robust fitting methods at different distances (10～120 m)and integrities (10%～50%).The average radius,spherical fitting accuracy,and distances between fitted center are used as indicators to evaluate the effectiveness of robust fitting methods.The results show that the methods based on angle weighting has the best effect on the larger spherical target,while the method with distance weighting has better effect on the smaller.IGGⅢ method with distance weighting controls the fitting errors under centimeter level in the range of 70 m.Spherical targets with a completeness of 40%～50% can be used for high-precision registration within a range of 70 m,while 50 m for completeness of 30%～40%.The targets with completeness below 20% cannot be used.The registration result of power infrastructure with 4 directions of views further confirms the above conclusion.

Key words: spherical target robust fitting, point cloud degradation, point cloud registration, power infrastructure measurement