http://dx.doi.org/10.1007/3-540-56869-7_5 Bernd-Uwe Pagel Hans-Werner Six Heinrich Toben The Transformation Technique for Spatial Objects Revisited. 73-88 SSD/1993/P073.pdf 1993 conf/ssd/93 SSD db/conf/ssd/ssd93.html#PagelST93