[Geopackage] Query on gpkg_tile_matrix - matrix_width and matrix_height

Even Rouault even.rouault at spatialys.com
Thu May 28 18:54:17 EDT 2015


Hi Brad,

> Geopackage spec (2.2.7.1.1) describes the gpkg_tile_matrix table.
> 
> matrix_width and matrix_height are described as >=1.

Well, Table 9 is a bit more verbose :
matrix_width Number of columns (>= 1) in tile matrix at this zoom level
matrix_height Number of rows (>= 1) in tile matrix at this zoom level

and then Table 10 and req 55 and 56 also give a hint of the meaning.

> 
> The note below Requirement 44 says that there can be records for zoom
> levels that do not have any tiles populated.
> 
> However I can't find an authoritative reference that says what
> matrix_height and matrix_width are intended to describe. I assume that
> they're meant to be a describe the "framework" for the tiles. So if we're
> power of two, and the next higher matrix_width was 2, then this
> matrix_width will be 4 (irrespective of what tiles are actually
> populated).

Not being an authoritative voice, my understanding is that it is not 
necessary.
For example if you're interested in North America, in GoogleMaps tile matrix 
set, you could have in theory :
level 0 : matrix_width = matrix_height = 1 (world coverage)
level 1 : matrix_width = matrix_height = 1 (top-left quadrant coverage)

since you will never populate other quadrants.

As this was inspired from WMTS, the meaning of matrix_width and matrix_height 
should be the same as WMTS MatrixWidth and MatrixHeight

Even

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