This is just a rework of my earlier patch with the filter class renamed so that there can be no doubt as to what it does. As before, the rational behind this is to stop the DP filter from deleting the end points of lines that have been introduced by either the clipper or the polygon splitter (such lines are always horizontal or vertical). Yes, it will also preserve horizontal and vertical lines that occur in the OSM data. Whether that is good or bad, I do not know. Mark