Release Notes for OGC GeoPackage Encoding Standard v1.2

GeoPackage is an open, standards-based, platform-independent, portable, self-describing, compact format for transferring geospatial information.

Over the course of 2016, the GeoPackage Standards Working Group (SWG) made a number of changes to the GeoPackage Encoding Standard Version 1.1 (OGC 12-128r12). These changes have been aggregated into version 1.2 of the GeoPackage Encoding Standard (12-128r13).

GeoPackage 1.2 is a minor revision to version 1.1. The minor revision designation is being used because of a number of substantive changes that alter conformance requirements. However, all of these changes were carefully considered for impact on existing implementations. Changes that were considered to have a significant impact were rejected or recast in order to limit their impact.

All changes were all managed via the GeoPackage GitHub repository. All substantive issues and most administrative issues were raised in the GitHub Issue Tracker and discussed by the SWG. Once the issue was resolved, a pull request was generated and merged into the repository. Some administrative issues such as typos were corrected directly through a commit on the master branch.

A large number of the changes in this version were initiated through official change requests. In addition, a new extension was added as a result of the GeoPackage Elevation Extension Interoperability Experiment (see [B1]).

All questions regarding this document should be directed to the editor or the contributors:

No future work is planned to this document.

Attention is drawn to the possibility that some of the elements of this document may be the subject of patent rights. The Open Geospatial Consortium shall not be held responsible for identifying any or all such patent rights.

Recipients of this document are requested to submit, with their comments, notification of any relevant patent claims or other intellectual property rights of which they may be aware that might be infringed by any implementation of the standard set forth in this document, and to provide supporting documentation.

An administrative change is a change that does not alter the abstract tests for any requirements. It includes typographical errors, changes in wording to improve clarity or consistency, and perfunctory changes like changes in version numbers.

A critical change is a change that alters requirements in a way that is known to cause reverse compatibility issues.

A substantive change is a change that alters requirements in a way that is not deemed to have a high risk for causing reverse compatibility issues.

See Description of Critical Changes for more information on critical changes and Description of Substantive Changes for more information on substantive changes.

A strict read of GeoPackage v1.1 does not allow non-spatial attribute values. However, in practice data providers routinely need to deliver data that does not contain geometry properties. Requiring any GeoPackage that contains non-spatial tables to be declared and documented as an "Extended GeoPackage" is not reasonable and does not promote interoperability. Therefore, the specification has been modified to allow non-spatial attribute tables in a basic GeoPackage. This change is considered to be low-risk because it creates a new encoding option that would be ignored by previous versions of the standard.

It was determined that it is difficult, if not impossible, to comply with Req 69 "SQL functions that operate on GeoPackageBinary geometries as specified in other extensions SHALL operate correctly on the non-linear geometries specified in this extension." because the functions could have been loaded via an extension such SpatiaLite which cannot be changed, and does not support the non-linear geometries. The removal of this requirement will allow for interoperable storage and retrieval of the geometries, while not requiring but allowing existing functions to work with the geometries.

The GeoPackage SWG agreed to remove the “User Defined Geometry Types Extension of GeoPackageBinary Geometry Encoding” extension from the encoding standard for the following reasons:

The SWG also agreed to remove two addition extensions, “Geometry Type Triggers” and “Geometry SRS ID Triggers”, from the encoding standard as they directly relate to User-Defined Geometry Types Extension and will no longer be required.

The SWG believes that content contained in these extensions would be better suited in a best practice document. This document could outline how to create a complete and interoperable User Defined Geometry Type Extension, including the details of the geometry encoding and how it can be used with existing spatial functions. This would allow two independent developers to create User-Defined Geometry Type extensions that follow the same template and make it easier for clients of the extensions to adopt.

After successful completion of the GeoPackage Elevation Extension Interoperability Experiment (see [B1]), the SWG agreed to add a new extension to the standard. The "Tiled Gridded Elevation Data" extension stores tiled gridded elevation data in a GeoPackage. The tiles contain elevation values and may be 16-bit PNG files or 32-bit TIFF files. The extension defines two ancillary data tables, one for coverages and one for tiles. When using the PNG encoding, a scale and offset may be applied. The extension also allows for a TIFF encoding but it constrains many of the TIFF options that are available to simplify development.

In GeoPackage 1.1 and earlier, Requirement 2 specifies an exact string as the application identifier. This string is also supposed to be added to SQLite’s magic.txt file ([B3]). The SWG determined that updating this file is unsustainable. Instead, GeoPackage will now use the original application ID (GPKG) and use the user_version header to indicate the version. In addition, it is reasonable to for clients designed to comply with a specific version of the standard to interoperate with GeoPackages that comply with a later version. In response, Requirement 2 was reworded to allow for version increments and the associated abstract test was updated. This change should improve interoperability as well as make it more reasonable for GeoPackage producers to pass CITE tests.

The “WKT for Coordinate Reference Systems” extension was designed to align to a new OGC Encoding Standard, OGC 12-063r5 (see [B2]). The text in GPKG 1.1 (including the column name) incorrectly references “12-163” instead. This change corrects all references to the proper “12-063”. The GeoPackage SWG regrets the error. This change is considered to be low-risk. At worst, implementers may need to populate a redundant column to satisfy clients that use this extension but only support GPKG 1.1.

An approach has been developed for storing geometries for multiple resolutions. However, it was determined to be premature to add this approach to the standard as an extension. It is being considered for OGC Testbed 13.

Changes that were considered to be "breaking" or had great risk to interoperability were rejected for this release. These issues may be found in GitHub at https://github.com/opengeospatial/geopackage/milestone/11.