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Great discovery Gerd! Enviado do meu iPhone
Em 16 de jul de 2016, às 14:28, Gerd Petermann <GPetermann_muenchen@hotmail.com> escreveu:
Hi all,
during the last days I tried to find more about the way how mkgmap stores polygons, esp. why we have some limits. While doing that I stumbled over an
old comment in LinePreparer.java:
// I don't care about getting the smallest possible file size so // err on the side of caution. which made me curious because I do care ;-)
I found out that Garmin offers a "trick" in the delta encoding which allows to reduce the needed bytes in some cases, the imgformat-1.0.pdf
explains this in detail, search for " only the sign bit is set ".
This "trick" helps esp. well when coastline polygons or rivers are stored.
I can explain this more detailed if somebody likes to know more,
for now I'd like to hear if the trick causes any problems, I did not find any
so far. A binary with this and a slightly improved overview_levels_v2.patch can be found here:
http://files.mkgmap.org.uk/download/301/mkgmap.jar
Depending on the data a single tile with size ~5MB may be reduced by 50 - 500+kB.
Gerd <reduceImgSize_v1.patch> _______________________________________________ mkgmap-dev mailing list mkgmap-dev@lists.mkgmap.org.uk http://www.mkgmap.org.uk/mailman/listinfo/mkgmap-dev