[Geopackage] Query on gpkg_tile_matrix - matrix_width and matrix_height

Brad Hards bradh at frogmouth.net
Fri May 29 20:20:02 EDT 2015


On Fri, 29 May 2015 06:00:24 PM Brachman, Micah wrote:
> There must be an agreement between the tiles present, and the bounding box
> which will ultimately determine the matrix_height and matrix_width.   There
> ought to be one tile in each of the minimal and maximal rows and
> columns(There must be a tile at row: 0, column: 0, row: (matrix_height -
> 1), and column: (matrix_width -1)).  This must hold true at any of the zoom
> levels.  If this doesn't hold true then the bounding box doesn't represent
> the minimum bounds of the data. 
That is contrary to the spec part that says the tiles don't need to be present 
at any given zoom level.

The bounding box could describe the potential locations for tiles (including 
tiles that haven't been generated / populated yet).

> The data must also comply with the following equations: 
> 
> pixel_x_size = Bounding Box width  * matrix_width  * tile_width
> pixel_y_size = Bounding Box height * matrix_height * tile_height
That can't be right. Did you mean to divide at some point, or swap the pixel 
and bounding box parts?

Dear SWG: This is looking like a bug in the spec - whatever the real intent 
is/was, it isn't apparent to implementers. Please come to some consensus and 
publish a fix.

Brad



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