Gerg, Once again, thank you very much for you prompt, super detailed, complete and instructive answer.
Best regards, Alexandre 2015-02-28 4:45 GMT-03:00 Gerd Petermann <[email protected]>: > Hi Alexandre, > > yes, simplification happens in various places. The reasons are limits in > the Garmin > format as well as optimization of the img file size. > > 1) The Garmin img format uses a raster with ~2.3 m distance at resolution > 24. > I think of it as a bed of nails, you can draw straigt lines between any of > the nails. > Details below this resolution are removed. We use two different algos for > lines and shapes > here, so expect slightly different results for outlines. > 2) The Garmin format doesn't allow a single polygon with more than 255 > points, so mkgmap > has to split a complex polygon into smaller pieces. > 3) For lower resolutions, the raster is less precise, means, for 23 points > are ~4.6m, 22 -> ~9.6m and > so on. > 4) For lower resolutions, a variant of the Douglas-Peucker-Algo is used to > reduce the img size. > You can change the effect of this by using the "Optimization options": > http://www.mkgmap.org.uk/doc/options > > See also > > http://en.wikipedia.org/wiki/Ramer%E2%80%93Douglas%E2%80%93Peucker_algorithm > > Gerd > > ------------------------------ > Date: Sat, 28 Feb 2015 01:33:18 -0300 > From: [email protected] > To: [email protected] > Subject: [mkgmap-dev] Complex ocean polygon hiding the islands > > > Hi guys, > > Please see if any of you can help me ... > > I have an ocean polygon with multiple edges and in the middle of these > there are several islands that are in fact holes in the polygon. > Here's an example: > > [image: Imagem inline 1] > > Showing only the contour lines, the polygon is drawn as follows: > > > [image: Imagem inline 2] > Zooming... > [image: Imagem inline 3] > > When I compile the map, the islands/holes are overlapped by the sea. > I noticed that when the polygon is less complex, this overlapping > phenomena doesn't happens. Its looks like mkgmap simplifies complex > polygons. > > Is there any option that I can use in mkgmap to respect the layout of > complex ocean polygons? > > By the way, if this isn't the right list to ask this kind of question, > please let me know cause I'm new here. > > Thanks. > > Alexandre > > _______________________________________________ mkgmap-dev mailing list > [email protected] > http://www.mkgmap.org.uk/mailman/listinfo/mkgmap-dev > > _______________________________________________ > mkgmap-dev mailing list > [email protected] > http://www.mkgmap.org.uk/mailman/listinfo/mkgmap-dev >
_______________________________________________ mkgmap-dev mailing list [email protected] http://www.mkgmap.org.uk/mailman/listinfo/mkgmap-dev
