1. Department of Forest Sciences, University of Helsinki, P.O. Box 27, Helsinki, Finland
2. Centre of Excellence in Laser Scanning Research, Finnish Geospatial Institution, Geodeetinrinne 2, Masala, Finland
3. Department of Remote Sensing and Photogrammetry, Finnish Geospatial Institution, Geodeetinrinne 2, Masala, Finland
4. School of Forest Sciences, University of Eastern Finland, P.O. Box 111, Joensuu, Finland