J. Haunert, K. Anders, and M. Sester. Proceedings of the ISPRS Workshop on Multiple Representation and Interoperability of Spatial Data, February 22--24, 2006, Hannover, Germany, volume XXXVI(Part 2/W40) of International Archives of Photogrammetry, Remote Sensing and Spatial Information Sciences, page 49--57. ISPRS, (2006)