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

[Even Rouault]

Le lundi 02 mai 2016 13:03:34, gunnarblom a écrit :
> 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. 

Ah ok, you can generate overviews/zoom layers with gdaladdo / 
GDALBuildOverviews().

> >> 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.

It could, but this isn't standardized

> 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?

For viewers, yes. For the reader side of the GDAL driver, this is a bit 
difference as it needs to determine a fixed resolution per zoom layer.

> 
> 
> 
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