[mkgmap-dev] more refined mkgmap:skipSizeFilter=true handling

Tue May 14 22:25:24 BST 2013

Well, the skip filter function works well, but there are problems with 
it - especially on South America.
For South America geofabrik extract - the overview map gets rather 
large. Using higher polygon size on filter - would be the essential tool 
in order too keep the overview .img file to be getting too large, 
without nearly any visual deterioration.

a) A quick (or I hope that would be quick) adaption could be to have 
instead:
mkgmap:changeSizeFilter=? with ? being the number for the filter to be 
used. Even a value of 2, would have quite good effect in case of South 
America. (about 15% saving on the overview.img size with default style).

b) A more optimal solution would be the following:
mkgmap:changeSizeFilter="level:filter_strenght" so e.g. "0:12, 1:12, 
3:12, 4:12, 5:10, 6:8, 7:8, 8:4, 9:2, 10:1"
A filter working this way, would have great impact on the overview.img 
size, as well as normal map.img size - without leading to strong visual 
impact. (up to 50% saving on the overview.img size)

The effect of the polygon size filter on South America is especially 
strong, as there is a huge sea area included in the extract...

(also I still don't understand, why mkgmap makes so small squares for 
the sea, instead of larger squares - which should also save on .img size).