Explanation for the mkgmap optimization options

Hi all, I'm at the point where it seems that my map overcharges the GPSr (probably too much details). mkgmap offers some optimization options: --reduce-point-density=NUM Simplifies the ways with the Douglas Peucker algorithm. NUM is the maximal allowed error distance, by which the resulting way may differ from the original one. This distance gets shifted with lower zoom levels. Recommended setting is 4, this should lead to only small differences (Default is 2.6, which should lead to invisible changes) --reduce-point-density-polygon=NUM Allows to set the maximal allowed error distance for the DP algorythm to be applied against polygons. Recommended setting is 8. --merge-lines Try to merge lines. This helps the simplify filter to straighten out longer chunks at lower zoom levels. Decreases file size more. Increases paint speed at low zoom levels. At the moment this option causes routing errors. Use only if routing is not needed in your map. --min-size-polygon=NUM Removes all polygons smaller than NUM from the map. This reduces map size and speeds up redrawing of maps. Recommended value is 8 to 15, default is 8. Questions: - Could someone explain the options more detailed ? - What are the pros and cons of the different options ? - What is your own experience with optimization ? - Is the routing affected by the options ? Thanks - Klaus -- View this message in context: http://gis.19327.n5.nabble.com/Explanation-for-the-mkgmap-optimization-optio... Sent from the Mkgmap Development mailing list archive at Nabble.com.

I use normally --reduce-point-density=1 --reduce-point-density-polygon=1 --merge-lines. I have no problems with routing. (I also use --remove-short-arcs=3) Basically --reduce-point* -options simplify the shape by removing some of the points if it does not affect the shape too much. I have no problems with drawing speed but I keep the very low optimization on to take care of any exessive details. (Consider for example a road that has points every 2m and the poor GPS trying to draw that on a moving map) Pro of optimization is faster map drawing and smaller map files. The con is reduced details and perhaps a bit coarser map (depending on how much you reduce point density). A test with my personal style file and different options (using same data for Finland and the latest mkgmap): -options at 1m: size is 110 MB -options at 4m: size is 107 MB (a bit too coarse map for my taste) -no optimization: size is 109 MB You may benifit more or less on your region. In my region I consider the result that the size is not really affected but it simplifies anything overly complicated. I have no idea why the map size is increased (by a tiny bit) with my options at 1m compared to no optimization. -- Harri
participants (2)
-
harri
-
toc-rox