1. Department of Earth Resources, International Surveys Institute for Aerospace Survey and Earth Sciences ITC, Hengelosestraat 99, PO Box 6, 7500 AA Enschede, the Netherlands.
2. Department of Geoinformatics, International Surveys Institute for Aerospace Survey and Earth Sciences ITC, Hengelosestraat 99, PO Box 6, 7500 AA Enschede, the Netherlands.