[mkgmap-dev] Idea: map layers (multiple output tiles per input tile)

Wed May 25 20:29:31 BST 2011

On Fri, Apr 08, 2011 at 11:19:17PM +0300, Marko Mäkelä wrote:
>I got an idea today: Make the style language support layers, and allow 
>the user to specify which layers to generate and in which output files.  
>This would have the benefit that you could generate all output layers 
>from a map in a single run, reducing the parsing and multipolygon 
>processing overhead, and possibly allowing more parallel processing.

I did some research on this. It looks like the concept of map layer or 
output map file would have to be added to MapCollector, MapDetails and 
GType.

Currently, I generate 5 nearly identical, very sparse layers from 
finland.osm.pbf. These use the styles 
routes-{foot,bicycle,bus,rail,ferry}. These styles could be merged into 
one if we had the concept of multiple output .img files per input tile.  
Each layer takes about 2.5 minutes to generate. The time is reduced to 2 
minutes per tile if I patch the code to ignore multipolygon relations.  
Processing a "null style" (one with no action rules) takes about the 
same time as processing one of these route styles. This leads me to 
believe that the processing time of the 5 map layers could be reduced 
from 5*2.5 = 12.5 minutes to 2 minutes, or 1/6 of the original.

Thoughts? Suggestions regarding the implementation?

	Marko