[mkgmap-dev] Idea: remove non-water polygons from the default style?

Thu Aug 25 18:20:16 BST 2011

Users have started complaining that Corine landuse imports are 
overlapping water areas in Finland. If the Garmin first draws the water 
and then the other landuse (forest, farm, etc.), the waters will be 
hidden and the map will be badly useable for navigation.

What if we separated most polygons to a separate map layer? For 
non-terrain uses, I cannot see any use of landuse polygons, possibly 
apart from building polygons.

One reason why polygons are currently needed is the --add-pois-to-areas 
option. That problem could be solved by implementing a polygon style 
file action 'add_poi'.

If we start splitting split stuff to separate map layers, another good 
candidate would be power lines, pipe lines and such. They are also 
mostly useful for navigating in terrain, I would guess. There could also 
be a separate layer for boundary=*.

But, if we start adding layers, it would be useful to generate multiple 
map layers in a single parsing pass. Otherwise the parsing time is going 
to dominate. Some time ago, a style that would generate no output would 
require 2.5 minutes or 3 minutes for processing the Geofabrik extract of 
Finland (about 90 megabytes in osm.pbf format) on my dual-core system.  
Also each routes-* style needs about this much processing time, because 
they do not generate much output. About half a minute per layer could be 
saved by disabling the processing of multipolygon relations, but I guess 
that we could reduce the processing time to 2 minutes for all routes-* 
layers if we could generate multiple *.img files from the same input 
tile using some special style action syntax.

Best regards,

	Marko