http://dx.doi.org/10.1007/3-540-60159-7_3 Ulrich Finke Klaus Hinrichs The Quad View Data Structure - A Representation for Planar Subdivisions. 29-46 SSD/1995/P029.pdf SSD 1995 conf/ssd/95 db/conf/ssd/ssd95.html#FinkeH95