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[mkgmap-dev] [PATCH v2] Performance improvement by removing unused elements before the style processing

From GerdP gpetermann_muenchen at hotmail.com on Wed Jan 4 09:29:43 GMT 2012

Hi WanMil,

I tested the patch with my tiles for Saarland. I can confirm a reduction of
processing time ~ 6% compared to r2160, and also a reduction for the peek
value of heap memory usage (238M -> 210M), so that's both good!
BUT I also see a difference in one of the seven output img files (plus the
resulting gmapsupp.img), and I think this is not intended. Both files have
the same size, but are different in many bytes.
Let me know when I should send details, maybe the new result is better than
the old ;-) 


WanMil wrote
> The 2nd patch fixes the remaining problems:
> 1. Ways without tags but referenced by relations are no longer removed 
> (they might be tagged by the relation style file and could therefore 
> appear in the map)
> 2. Intersection of ways with the tile bounding box is now checked 
> instead of only checking that at least one point is contained in the 
> bounding box. Only very few ways are affected by this but otherwise 
> routing problems are possible.
> The performance improvement seems to be good (measured with my test map):
> r2159: ~250s
> patched: ~225s
> I also expect (although I haven't tested) that the max memory 
> requirement of mkgmap is decreased. I think max mem is used when the 
> style file is just processed. At this stage all raw OSM elements and all 
> style file processed elements are kept in memory. With the patch the 
> number of OSM elements is noticeably reduced.
> WanMil
>> Hi,
>> this is another performance improvement:
>> Usually the mkgmap input tiles are larger than the processed bounding
>> box (splitter parameter overlap). So there are much many elements which
>> are processed but thrown away at a late step in mkgmap.
>> The patch tries to remove them much earlier before the style files are
>> processed and before the LocationHook starts (which ignores them but
>> that must also be calculated).
>> The patch contains one drawback:
>> Ways which have all its points outside the bounding box of the tile but
>> which cross the tile are also removed. If that's a point the patch must
>> be improved.
>> Have fun!
>> WanMil
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>> mkgmap-dev at .org
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