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[mkgmap-dev] Really Serious bug when not using --route

From Felix Hartmann extremecarver at googlemail.com on Wed May 26 23:38:55 BST 2010

On 25.05.2010 14:28, NopMap wrote:
> Felix Hartmann wrote:
>> Routable maps are in no way bigger than non routable maps (if there is
>> no routable information inside, of course if you use the same style that
>> is routable and compile it without --route it gets smaller, if you
>> remove all road_class and road_speed from style, there is virtually no
>> size difference).
> This is not what I have observed. Using a style that does not have any route
> info, accidentially activating --route caused it to grow significantly.
> Maybe there is a different explanation, but until the reason is clear, I
> must assume that a compulsory --route would cause the same.
> Felix Hartmann wrote:
>>   Lazyness shouldn't break stuff. And continuing with
>> this problem is no option, as the newest Oregon Firmware and all future
>> Firmwares for other devices will crash too.
> So if you're bulding for an Oregon and if you use the latest updates, you
> need to specify --route.
> This is no reason to force the owners of all other devices to do this, too.
> Especially if you break the building of maps for older devices this way.
> A sensible solution would be to either fix the problem for good by removing
> those flags or introduce a new parameter/default behaviour that just creates
> an empty version of the required block with less side effects than a global
> --route.
> bye
>               Nop
I just rechecked your claims about --route increasing map size. I built 
austria from geofabrik using the default style but having deleted any 
occurence of road_class and road_speed once without --route and once 
with --route. --route made the each map exactly 2 bit bigger. So using 
--route and a non routable style, will exactly do what you ask for. So 
unless we find the real problem, a quick fix would be to have mkgmap 
just dropping road_class and road_speed when --route is not given, but 
otherwise behave exactly as if --route were given.

If you really want to decrease map size, there are good methods, like 
reducing levels (e.g use only 23,21,19 and skip 24 alltogether as 23 is 
usually still much better than the quality of data inside osm), using 
--reduce-point-density=10 and --reduce-point-density-polygon=20 (patch 
exists), using --merge-lines (maybe called similary), and dropping 
lines/polygons with less than x points by resolution (patch exists). Oh, 
and best work on an overview map for low resolutions inside mapsource, 
on GPS there is the basemap anyhow for theese resolutions).

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