Version 1505 was commited by markb on 2010-01-20 22:15:29 +0000 (Wed, 20 Jan 2010) Preserve the end points of horizontal and vertical lines. This stops the DP filter from discarding the end points of an edge that has been generated by either the clipper or by the polygon splitter. The benefit of this is that it removes some artifacts from polygons that have been clipped or split. It will err on the safe side in that it preserves all edges that are horizontal or vertical but the number of those occurring naturally in the data must be quite small so it should not spoil the filtering effort.