Experimental comparison of filter algorithms for bare-Earth extraction from airborne laser scanning point clouds $ George Sithole * , George Vosselman Department of Earth Observation and Space Systems, Faculty of Aerospace Engineering, Delft University of Technology, P.O. Box 5058, 2600 GB Delft, The Netherlands Accepted 7 May 2004 Available online Abstract Over the past years, several filters have been developed to extract bare-Earth points from point clouds. ISPRS Working Group III/3 conducted a test to determine the performance of these filters and the influence of point density thereon, and to identify directions for future research. Twelve selected datasets have been processed by eight participants. In this paper, the test results are presented. The paper describes the characteristics of the provided datasets and the used filter approaches. The filter performance is analysed both qualitatively and quantitatively. All filters perform well in smooth rural landscapes, but all produce errors in complex urban areas and rough terrain with vegetation. In general, filters that estimate local surfaces are found to perform best. The influence of point density could not well be determined in this experiment. Future research should be directed towards the usage of additional data sources, segment-based classification, and self-diagnosis of filter algorithms. D 2004 Elsevier B.V. All rights reserved. Keywords: laser scanning; LIDAR; digital surface models; digital elevation models; point cloud; filtering; performance analysis; tests 1. Introduction While commercial airborne laser scanning sys- tems have come a long way, processing the huge point clouds for the purpose of modelling system- atic errors, filtering, feature extraction and thinning often requires a large amount of human interaction. For the production of digital elevation models, the manual classification (filtering) and quality control pose the greatest challenges, consuming an estimat- ed 60–80% of processing time (Flood, 2001), and thus underlining the necessity for research in this area. Algorithms have been developed for semi- automatically/automatically extracting the bare-Earth from point clouds obtained by airborne laser scan- ning and InSAR. Some comparison of known filtering algorithms and difficulties have been men- tioned in Huising and Gomes Pereira (1998), Hau- gerud and Harding (2001) and Tao and Hu (2001). However, an experimental comparison was not 0924-2716/$ - see front matter D 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.isprsjprs.2004.05.004 $ This paper is an extended and improved version of the paper presented at the ISPRS WG III/3 workshop on ‘‘3D Reconstruction from Airborne Laser Scanner and InSAR Data’’, Dresden, Germany, 8 – 10 October 2003. * Corresponding author. Tel.: +31-15-27-88337; fax: +31-15- 27-82348. E-mail address: g.sithole@lr.tudelft.nl (G. Sithole). www.elsevier.com/locate/isprsjprs ISPRS Journal of Photogrammetry & Remote Sensing 59 (2004) 85 – 101