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<p>Hi Gerd,</p>
<br>
is this trick only good for polygons or does this work with normal
streets/tracks as well?<br>
<br>
Jakob<br>
<br>
<div class="moz-cite-prefix">Am 16.07.2016 um 19:28 schrieb Gerd
Petermann:<br>
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<p>Hi all,</p>
<p><br>
</p>
<p>during the last days I tried to find more about the way how
mkgmap stores <br>
</p>
<p>polygons, esp. why we have some limits. While doing that I
stumbled over an</p>
<p>old comment in LinePreparer.java:</p>
<div> // I don't care about getting the smallest possible
file size so<br>
// err on the side of caution.<br>
</div>
<p>which made me curious because I do care ;-)</p>
<p><br>
</p>
<p>I found out that Garmin offers a "trick" in the delta
encoding which allows <br>
</p>
<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>
<p><br>
</p>
<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>
</p>
<p>A binary with this and a slightly improved <span>overview_levels_v2.patch</span><br>
</p>
<p>can be found here:</p>
<p><a moz-do-not-send="true" 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>
<p><br>
</p>
<p>Depending on the data a single tile with size ~5MB may be
reduced by 50 - 500+kB.<br>
</p>
<p><br>
</p>
<p>Gerd<br>
</p>
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