Tetsushi Nishida Kokichi Sugihara Approximation of the Boat-Sail Voronoi Diagram and Its Application. 227-236 http://springerlink.metapress.com/openurl.asp?genre=article&issn=0302-9743&volume=3045&spage=227 2004 conf/iccsa/2004-3 ICCSA (3) db/conf/iccsa/iccsa2004-3.html#NishidaS04