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[mkgmap-dev] Sensible resolutions - (or patch 5)

From Felix Hartmann extremecarver at gmail.com on Fri Mar 25 08:16:27 GMT 2011

On 25.03.2011 08:42, Marko Mäkelä wrote:
> Hi Felix,
> Finally I got time for this patch. The gmapsupp.img for Finland has 
> grown a lot, and much of it is probably due to Corine landuse 
> imports.  I hope that this patch will scratch that itch too. :-) Now 
> Finland is finally liberated from unclosed polygons, too. I even got 
> address search working again on the Edge (without --index), by 
> replacing --charset=latin1 with --code-page=1252.
>> Nope, motorways stay (at least if the default resolutions are used. 
>> By default no resolution 14 is created. But compiling Europe at 14 
>> with motorways looks crap. Been there, done that.
> Right, there should be some method of simplifying and merging polygons 
> in the lowest resolution levels. Until we are there, it is probably 
> best to drop the polygons from the widest zooms. A good use case of 
> merging polygons would be the huge lake areas in Finland. If you look 
> close, the lakes are small and scattered. From bigger distance, it 
> could be approximated with one huge lake. But, currently the map does 
> not show any lakes when zooming out.
> One thing that I do not understand in your patch is this:
> < --- styles/default/options    (revision 1902)
> < +++ styles/default/options    (working copy)
> < @@ -17,7 +17,7 @@
> < <  # The levels specification for this style
> <  # < -levels = 0:24, 1:22, 2:20, 3:18, 4:16
> < +levels = 0:24, 1:22, 2:21, 3:20, 4:19, 5:18, 6:16
> Is the "resolution" a mkgmap-only entity, which is mapped to zoom 
> layers known as "levels" in the IMG file? If that is the case, 
> wouldn't this change introduce two more zoom layers to the map, 
> potentially growing the file size?
Yes, but there is not a lot of information in those zoom levels anyhow. 
Overall I would say with the patch applied (on my tests) the 
gmapsupp.img filesize stays the same. But the GPS renders it much 
faster. The additional levels of 19 and 21 really help to make the 
zooming in much much smoother and the GPS can render the map faster. 
Quite a few people even use resolution 23 as intermediary, but I left 
that out, because 23 would increase overall gmapsupp.img size by 20-25% 
(whereas increases 21 by 3-4%, 19 is a change of under 1%)
> Regarding railways, you are lowering them to resolution 22, with one 
> exception: railway=subway&!(tunnel=yes) is resolution 21. I guess that 
> it is a typo and you meant 22. I think that this lowering is OK, 
> because Garmin would not show railways when zooming out from 500m, 
> even in the highest map detail level. They must really hate railways, 
> I guess.
Yes - that's a typo. But as long as we inside OSM have no real mean of 
identifying the main railway lines the railways should not be shown as 
early anyhow.
> Best regards,
>     Marko

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