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
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