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<p>Hi all,</p>
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<p>during the last days I tried to find more about the way how mkgmap stores <br>
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<p>polygons, esp. why we have some limits. While doing that I stumbled over an</p>
<p>old comment in LinePreparer.java:</p>
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<div> // I don't care about getting the smallest possible file size so<br>
// err on the side of caution.<br>
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<p>which made me curious because I do care ;-)</p>
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<p>I found out that Garmin offers a "trick" in the delta encoding which allows <br>
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<p>to reduce the needed bytes in some cases, the <span>imgformat-1.0.pdf</span></p>
<p>explains this in detail, search for "<span> only the sign bit is set </span>".</p>
<p>This "trick" helps esp. well when coastline polygons or rivers are stored.</p>
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<p>I can explain this more detailed if somebody likes to know more,</p>
<p>for now I'd like to hear if the trick causes any problems, I did not find any</p>
<p>so far. <br>
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<p>A binary with this and a slightly improved <span>overview_levels_v2.patch</span><br>
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<p>can be found here:</p>
<p><a id="LPlnk252425" href="http://files.mkgmap.org.uk/download/301/mkgmap.jar" class="OWAAutoLink">http://files.mkgmap.org.uk/download/301/mkgmap.jar</a></p>
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<p>Depending on the data a single tile with size ~5MB may be reduced by 50 - 500+kB.<br>
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<p>Gerd<br>
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