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<body class='hmmessage'><div dir='ltr'>Hi Alexandre,<br><br>yes, simplification happens in various places. The reasons are limits in the Garmin<br>format as well as optimization of the img file size.<br><br>1) The Garmin img format uses a raster with ~2.3 m distance at resolution 24. <br>I think of it as a bed of nails, you can draw straigt lines between any of the nails.<br>Details below this resolution are removed. We use two different algos for lines and shapes <br>here, so expect slightly different results for outlines.<br>2) The Garmin format doesn't allow a single polygon with more than 255 points, so mkgmap<br>has to split a complex polygon into smaller pieces.<br>3) For lower resolutions, the raster is less precise, means, for 23 points are ~4.6m, 22 -> ~9.6m and<br>so on. <br>4) For lower resolutions, a variant of the Douglas-Peucker-Algo is used to reduce the img size.<br>You can change the effect of this by using the "Optimization options":<br><a href="http://www.mkgmap.org.uk/doc/options" target="_blank">http://www.mkgmap.org.uk/doc/options</a><br> <br>See also<br>http://en.wikipedia.org/wiki/Ramer%E2%80%93Douglas%E2%80%93Peucker_algorithm<br><br>Gerd<br><br><div><hr id="stopSpelling">Date: Sat, 28 Feb 2015 01:33:18 -0300<br>From: alexandre.loss@gmail.com<br>To: mkgmap-dev@lists.mkgmap.org.uk<br>Subject: [mkgmap-dev] Complex ocean polygon hiding the islands<br><br><div dir="ltr"><div><div>Hi guys,</div><div><br></div><div>Please see if any of you can help me ...</div><div><br></div><div>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.</div><div>Here's an example:</div><div><br></div></div><div><img src="cid:ii_14bce6a1dbbedbf6" alt="Imagem inline 1" style=""><br></div><div><br></div><div>Showing only the contour lines, the polygon is drawn as follows:<br></div><div><div><br></div><div><br></div></div><div><img src="cid:ii_14bce6c2101d9500" alt="Imagem inline 2" style=""><br></div><div>Zooming...</div><div><img src="cid:ii_14bce6ce0f0977e6" alt="Imagem inline 3" height="350" width="558"><br></div><div><br></div><div><div>When I compile the map, the islands/holes are overlapped by the sea.</div><div>I noticed that when the polygon is less complex, this overlapping phenomena doesn't happens. Its looks like mkgmap simplifies complex polygons.<br></div><div><br></div><div>Is there any option that I can use in mkgmap to respect the layout of complex ocean polygons?</div></div><div><br></div><div>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.</div><div><br></div><div>Thanks.</div><div><br></div><div>Alexandre</div></div>
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