[Requests] Lack of normative references to base standards in tiled matrix encodings in GeoPackage

Keith Ryden kryden at esri.com
Mon Feb 27 19:10:03 EST 2017

In 2014 the OGC Membership approved the OGC(r)GeoPackage Encoding Standard. As an encoding standard, GeoPackage specifies the requirements/rules for encoding geospatial content into a SQLite container. The requirements are themselves derived or based on other OGC and ISO standards. An example is the normative use of OGC/ISO Simple Features for the geometry features - references to the ISO 13249-3 standard as the basis for the feature encoding are prominent.
It is very important that each capability encoded into a GeoPackage have a clear lineage to the standard on which it is based - without such a clear lineage, we run into issues defining scope and proper encoding of the capability in the SQLite container.
ISSUE #1 - there is no normative reference to a base standard for the GeoPackage encoding of tiled imagery.  The encoding standards states,
"There are a wide variety of commercial and open source conventions for storing, indexing, accessing and describing tiles in tile pyramids. Unfortunately, no applicable existing consensus, national or international specifications have standardized practices in this domain. In addition, various image file formats have different representational capabilities, and include different self-descriptive metadata."
It may be possible to replace this paragraph with a statement that the GeoPackage encoding of tiled imagery is derived from the OGC WMTS Standard  The encoding defines the requirements/rules for delivery of a tiled matrix set in the SQLite container, and is consistent with the abstract model of tile matrix sets presented in the WMTS standard.
A discussion of the aspect of the WMTS Standard's tile matrix model implemented (or not) would probably need to be added to establish the scope of the encoding.

ISSUE #2 - there is no normative reference to a base standard for the GeoPackage encoding of Tiled Gridded Elevation Data proposed as Annex F.11 in the proposed 1.2 standard.
Annex F.11 - Introduction - states, " The GeoPackage Standards Working Group (SWG) has developed the ability to store 16-bit and 32-bit tiled gridded elevation data in a GeoPackage.".  This statement needs to be followed by a reference to the OGC/ISO standard on which this Tiled Gridded Elevation Data encoding is based.  If no such normative reference can be provided, the Tiled Gridded Elevation Data extension should not be part of the OGC(r)GeoPackage Encoding Standard.
This issue was raised during SWG vote to adopt the Tiled Gridded Elevation Data proposal - there was not unanimous agreement.
Keith Ryden
Esri Software Development

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