Hi Gerd, is this trick only good for polygons or does this work with normal streets/tracks as well? Jakob Am 16.07.2016 um 19:28 schrieb Gerd Petermann:
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
_______________________________________________ mkgmap-dev mailing list mkgmap-dev@lists.mkgmap.org.uk http://www.mkgmap.org.uk/mailman/listinfo/mkgmap-dev