1. Graduate School of Frontier Sciences, The University of Tokyo, 5-1-5, Kashiwanoha, Kashiwa 277-8563, Japan
2. School of Business, Society and Technology, Mälardalens University, 72123 Västerås, Sweden
3. Center for Spatial Information Science, The University of Tokyo, 5-1-5, Kashiwanoha, Kashiwa 277-8568, Japan