[OSM-dev] [OSM-talk] Ideas for OSM enhancements

Karl Newman siliconfiend at gmail.com
Sat Dec 29 00:36:44 GMT 2007


On Dec 28, 2007 4:04 PM, Andy Allan <gravitystorm at gmail.com> wrote:
> On Dec 28, 2007 8:14 PM, Karl Newman <siliconfiend at gmail.com> wrote:
>
> > Can you enlighten me--what is the tiling problem?
>
> Steve Radcliffe or "Computerteddy" may want to correct me on this,
> since they know more than I do.
>
> There's a size limit for the garmin .img format, above which the areas
> need to be broken down into smaller tiles. As far as I'm aware, mkgmap
> doesn't do this for you. For a while, mkgmap could process the entire
> planet within one tile, and then later the UK could still fit within
> one tile, but those days are long gone. There was a technique using
> non-free software that computerteddy was using to process the data,
> but from his(?) wiki page* it seems there's a way around it now.
>
> However, the downloads that we have are generally woefully out of
> date, and most of them are from before these size limits starting
> biting.
> http://wiki.openstreetmap.org/index.php/OSM_Map_On_Garmin/Download
>
> Basically, I can't take planet.osm, run mkgmap and transfer the
> resultant .img file(s) to my GPS. This is what we should be aiming
> for. What is needed is just a Simple Matter of Programming
> (naturally), i.e. some developers and their time focussed on it.
>
> Cheers,
> Andy
>
> * http://wiki.openstreetmap.org/index.php/User:Computerteddy
>

(Crossposting to dev)

Okay, that's no big deal. It's actually astounding to me that you put
were able to the entire planet into a single img file... (obviously in
pre-TIGER days). Anyway, I'm planning on writing a tiling task for
Osmosis (probably not part of the Osmosis codebase, more likely a
plugin-type thing if BrettH helps me facilitate that), so it could
take a planet file and chunk it up into segments, probably individual
osm files. Those files could then be processed by mkgmap. Garmin
devices currently only support up to 2 GB MicroSD cards, but you're
more likely to run into the limit of 2025 map segments first. We
probably won't have the luxury of making the tiles uniform size,
because obviously urban areas will have much more road density than
rural areas. But if we were able to chunk it up into 4 degree square
sections (obviously quite large near the equator), the planet could be
covered in 4050 sections (360 x 180 / 16). Obviously, ocean areas will
subtract a significant number from that.

Anyway, once the tiles have been created, it's just a matter of
scripting their processing by mkgmap. You might be able to do it all
quickly with an ant build script or something similar.

Karl




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