[mkgmap-dev] splitter maximum tile size

Sat Dec 1 10:26:32 GMT 2012

Hi Gerd,

Ok, we should first investigate if there really is a limit for a tile size.

Just for now it may be good if splitter issues a warning for tiles that 
exceeds a limit, e.g. "Tile xxxxx.osm.pbf covers more than n° in 
latitude. This may cause problems with mkgmap when using one of the 
options bounds, generate-sea and precomp-sea. <some hints what can be 
done to avoid that>".

I think my testcase is not ideal. I have used a polygon that covered the 
whole tile. But this causes large (too large) img sizes because the 
polygon has to be split into many subpolygons when mkgmap splits into 
subdivisions.
I think instead it is better to use one POI node in each corner of the 
bbox. I will try again and report about my findings.

WanMil

> Hi WanMil,
>
> I think the maximum values should be as large as possible. When
> splitting planet, we have a huge tile covering
> an area in the pacific, this tile has almost no nodes. If splitter has
> to create tiles with max. 20 degrees width
> we probably see tiles without nodes.
>
> Gerd
>
>
> Date: Fri, 30 Nov 2012 18:18:02 +0100
> From: wmgcnfg at web.de
> To: mkgmap-dev at lists.mkgmap.org.uk
> Subject: Re: [mkgmap-dev] splitter maximum tile size
>
>> Thorsten Kukuk wrote
>>>>
>>>> No, there is no limit for the maximum tiles size for now. Thanks for the
>>>> hint.
>>>> What is the limit? I guess it is not a constant, but depends on
>>>> resolution
>>>> and other
>>>> values? Unfortunately the test data is gone and I didn't download it.
>>>
>>> If you want to look at the problem, I can try to regenerate the
>>> data again.
>>
>> I am not sure if the problem has to be solved in splitter or in mkgmap.
>> Anyway, please try to reproduce it.
>> I also like to know why mkgmap has problems with tiles that contain only
>> very few nodes. Or is it the gps device that has problems?
>>
>> Gerd
>
> I played a little bit with a small testfile how large a tile can be. The
> attached test file has the maximum size which works for me:
>    <bounds minlat="0.0" minlon="0.0" maxlat="85.0" maxlon="179.98"/>
> Larger bounds cannot be put into a single tile.
>
> For large tiles mkgmap requires much memory problem if the bounds
> parameter is set. They need to be completely loaded with a high memory
> consumption.
>
> I don't know if there is a hard limit for the tile bounds size. Maybe
> using some limits in splitter for the maximum latitude and maximum
> longitude size would remove some problems, e.g. max lat = 20, max long = 20.
>
> WanMil
>
>
>
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