Alla Sheffer Vladislav Kraevoy Pyramid Coordinates for Morphing and Deformation. 68-75 2004 conf/3dpvt/2004 3DPVT http://csdl.computer.org/comp/proceedings/3dpvt/2004/2223/00/22230068abs.htm db/conf/3dpvt/3dpvt2004.html#ShefferK04