[gdal-dev] Geopackage raster and empty tile matrix

[Andrea Aime]

Hi,
I've exported a TIFF to geopackage raster, and noticed that while the
exported data only cover
zoom level 7, the tile matrix definition ranges from 0 to 7.

>From the reader point of view, it seems that in order to get the
effectively populated tile
matrix levels one would have to run a select distinct on the zoom level in
the tile table,
which seems rather inefficient.

I checked the spec and while it demands a tile matrix spec for populated
levels, it does not
seem to require omitting it for non populated levels. Can you confirm?

I think I'm seeing in the code a check verifying that indeed at least one
tile is present before
listing a particular zoom level:

// In read-only mode, only lists non empty zoom levels
    else if( !bUpdate )
    {
        osSQL += CPLSPrintf(" AND EXISTS(SELECT 1 FROM %s WHERE zoom_level
= tm.zoom_level LIMIT 1)",
                            osQuotedTableName.c_str());
    }

Cheers
Andrea

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Ing. Andrea Aime
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