[Geopackage] Fwd: gpkg elevation extension question

Jeff Yutzler jeffy at imagemattersllc.com
Fri Nov 3 21:08:20 EDT 2017

Please note the question and my reply and let me know if there is anything
I should add.

---------- Forwarded message ----------
From: Jeff Yutzler <jeffy at imagemattersllc.com>
Date: Fri, Nov 3, 2017 at 9:06 PM
Subject: Re: gpkg elevation extension question
To: someone

Thank you for your note. I think your approach is reasonable but you are
correct that rows in gpkg_contents must have unique "table_name" values.
The best way to get around this might be to use views. How about inventing
a conventional suffix that you could tack onto the tiles table name to use
as the view name? Then you could register your raster tiles table normally
and register your elevation tiles table using the view.

It is probably too late to add this to the emerging tiled gridded coverage
extension but we could write it up as a separate community extension.

How does this sound?


On Fri, Nov 3, 2017 at 7:15 PM, someone wrote:

> Mr. Yutzler,
> Your work on the GeoPackage standard has been a great source of insight to
> me. Thank you. I have a question/suggestion about the gpkg elevation
> extension and thought I'd try writing.
> I am pretty sure I want to have both a "tile_data" and an
> "elevation_tile_data" column my "sample_tile_pyramid" (C.7), with the PNG
> going in tile_data and a TIFF going in elevation_tile_data. My TIFF tiles
> must align with my PNG tiles in order to support a floating-point cursor
> readout, and I think combining the columns this way would simplify my code
> use SQL more efficiently.
> The proposed elevation extension requires a separate entry for
> 2d-gridded-coverage in gpkg_contents whose primary key requires a unique
> table_name, so I think this means the proposed standard would require me to
> write code to maintain redundant tables and accept additional SQL overhead
> when querying for tiles. An "elevation shadowing" option in the extension
> that recognizes what I'm doing, while still requiring the extension schema
> and gpkg_2d_gridded_coverage_ancillary might be helpful.
> Thank you,

Jeff Yutzler
Image Matters LLC <http://www.imagemattersllc.com/>
Mobile: (703) 981-8753
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