[gdal-dev] Questions about MBTiles write support @ GDAL 2.1 RC4

gunnarblom gunnarblom at mail.com
Mon May 2 04:03:34 PDT 2016

Even Rouault-2 wrote
>> 1) When creating a MBTiles file, only one layer is written. Can you use
>> GDAL to populate other layers?
> I'm not sure what you call "layer". AFAIK MBTiles files do not have a
> concept 
> of storing tiles for different layers. (you could use GeoPackage for that)

I'm talking about zoom layers. E.g. when using gdal2tiles.py you choose what
zoom layers you want to create. Now with the API when only one layer is
created, many MBTiles readers will not show anything until you zoom in to
the exact zoom layer that was decided to include. So the output MBTiles file
doesn't really function as supposed to in a MBTiles reader/viewer.

Even Rouault-2 wrote
>> 2) Can you choose to create 512*512px tiles
>> instead of the 256*256px default? Would increase quality on retina
>> devices. 
> It is true that the spec doesn't say anyting about tile size, but are
> there 
> MBTiles files with tiles not 256x256 ? This isn't supported by the driver.
> On 
> writing this shouldn't be a big problem. On reading this might be a bit
> more 
> tricky as you could potentially have a mix of tiles of different sizes !

I guess the MBTiles format could have metadata about what resolution the
tiles are in. But also the readers/viewers should just draw the tiles in
their correct place and shouldn't be dependent on what resolution they have?
Isn't that how it works with a regular TMS folder structure anyway?

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