Thorsten Graf Kamakoti Veezhinathan An Optimal Algorithm for Computing Vissible Nearest Foreign Neighbors Among Colored Line Segments. 59-70 http://link.springer.de/link/service/series/0558/bibs/1432/14320059.htm 1998 conf/swat/1998 SWAT db/conf/swat/swat98.html#GrafV98