1. Department of Forest Inventory, Austrian Research Centre for Forests (BFW), Seckendorff-Gudent-Weg 8, 1130 Vienna, Austria
2. Research Unit Photogrammetry, Department of Geodesy and Geoinformation, TU Wien, Wiedner Hauptstraße 8-10, 1040 Vienna, Austria
3. Department of Basic Sciences in Engineering Sciences, University of Innsbruck, Technikerstraße 13, 6020 Innsbruck, Austria