Helmut Pottmann Stefan Leopoldseder Michael Hofer Approximation with Active B-Spline Curves and Surfaces. 8-25 2002 conf/pg/2002 Pacific Conference on Computer Graphics and Applications http://csdl.computer.org/comp/proceedings/pg/2002/1784/00/17840008abs.htm db/conf/pg/pg2002.html#PottmannLH02