Liu Xin Liu Wen-bao Li Cheng-ming Qualitative Representation and Reasoning of Combined Direction and Distance Relationships in Three-Dimensional GIS. 119-123 2008 CSSE (1) http://dx.doi.org/10.1109/CSSE.2008.1279 conf/csse/2008-1 db/conf/csse/csse2008-1.html#XinWC08