OGC GeoPackage WKT for Coordinate Reference Systems Extension Open Geospatial Consortium Submission Date: 2022-04-14 Approval Date: 2022-08-20 Publication Date: 2022-10-14 External identifier of this OGC® document: http://www.opengis.net/doc/IS/geopackage-crs-wkt/1.1 Internal reference number of this OGC® document: 21-057 Version: 1.1.0 Category: OGC® Implementation Standard Editor: Jeff Yutzler OGC GeoPackage WKT for Coordinate Reference Systems Extension Copyright notice Copyright © 2022 Open Geospatial Consortium To obtain additional rights of use, visit http://www.ogc.org/legal/ Warning This document is an OGC Member approved international standard. This document is available on a royalty free, non-discriminatory basis. Recipients of this document are invited to submit, with their comments, notification of any relevant patent rights of which they are aware and to provide supporting documentation. 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In the event any provision of this Agreement shall be deemed unenforceable, void or invalid, such provision shall be modified so as to make it valid and enforceable, and as so modified the entire Agreement shall remain in full force and effect. No decision, action or inaction by LICENSOR shall be construed to be a waiver of any rights or remedies available to it. Table of Contents 1. Scope 2. Conformance 3. References 4. Terms and Definitions 5. Conventions 5.1. Identifiers 6. WKT for Coordinate Reference Systems Extension (Informative) 6.1. Extension Author 6.2. Extension Name or Template 6.3. Extension Type 6.4. Applicability 6.5. Scope 7. Requirements (Normative) 7.1. Table Definition 7.1.1. gpkg_spatial_ref_sys 7.2. Table Data Values 7.2.1. gpkg_extensions 7.2.2. gpkg_spatial_ref_sys Annex A: Conformance Class Abstract Test Suite (Normative) A.1. Table Definition Annex B: Table Definition SQL (Normative) B.1. gpkg_spatial_ref_sys Annex C: Revision History i. Abstract This document is a revision to the GeoPackage WKT for Coordinate Reference Systems Extension that previously was published as Annex F.10 of the GeoPackage Encoding Standard 1.3.0 (OGC 12-128r17). This document replaces Annex F.10. The extension defines how to encode coordinate reference systems (CRS) in GeoPackages using the ISO/OGC Well-known text representation of coordinate reference systems [2019] (CRS WKT2) Standard. Specifically, this revision adds coordinate epochs to the encoding of coordinate reference systems in a GeoPackage. ii. Keywords The following are keywords to be used by search engines and document catalogues. ogcdoc, OGC document, geopackage, crs, srs, wkt, crs_wkt, crs_wkt2 iii. Preface Version 1 of the OGC GeoPackage Encoding Standard was adopted prior to the adoption of "12-063r5 OGC Well known text representation of Coordinate Reference Systems" [2014] (so-called WKT2). As a result, the OGC GeoPackage Encoding Standard references an older CRS WKT document ( OpenGIS® 01-009 Implementation Specification: Coordinate Transformation Services Revision 1.0 , so-called WKT1), which has known ambiguities that are being encountered by the implementation community. The CRS extension establishes a new column in the gpkg_spatial_ref_sys table to contain values that conform to the WKT2 Standard. In 2019, OGC adopted "18-010r7 OGC Well known text representation of Coordinate Reference Systems" as a revision to 12-063r5. The core (unextended) GeoPackage Encoding Standard supports the older CRS WKT [12-063r5] standard (WKT1). This extension enables both the WKT1 and WKT2 encodings to be used. However, use of the newer WKT2 encoding is strongly encouraged. GeoPackage clients are expected to use the newer encoding if both encodings are present. In a dynamic CRS, coordinates of a point on the surface of the Earth may change with time. To be unambiguous, the coordinates must always be qualified with the epoch at which they are valid (the coordinate epoch is not necessarily the epoch at which the observation was collected). In 2021, the GeoPackage SWG added coordinate epochs to gpkg_spatial_ref_sys . As this was the only substantive change to the GeoPackage Encoding Standard being considered at the time, the decision was made to split this extension into a separate document so that it could be considered separately. iv. Security Considerations No security considerations are provided for this Standard. v. Submitting organizations The following organizations submitted this Document to the Open Geospatial Consortium (OGC): Image Matters Spatialys vi. Submitters All questions regarding this submission should be directed to the editor or the submitters: Name Affiliation Jeff Yutzler Image Matters LLC Even Rouault Spatialys 1. Scope This GeoPackage extension applies to the gpkg_spatial_ref_sys table and modifies the existing requirement specified in Requirement 10 . 2. Conformance This OGC GeoPackage WKT for Coordinate Reference Systems Extension defines requirements for encoding coordinate reference systems and coordinate epochs in a GeoPackage. Conformance with this standard shall be checked using all the relevant tests specified in Annex A (normative) of this document. The framework, concepts, and methodology for testing, and the criteria to be achieved to claim conformance are specified in the OGC Compliance Testing Policies and Procedures and the OGC Compliance Testing web site [ 1 ] . 3. References The following normative documents contain provisions that, through reference in this text, constitute provisions of this document. For dated references, subsequent amendments to, or revisions of, any of these publications do not apply. For undated references, the latest edition of the normative document referred to applies. OGC: OGC 12-128r17 OGC GeoPackage Encoding Standard 1.3.0, http://www.geopackage.org/spec130/ (2020) OGC: OGC 19-005r4 OGC Abstract Specification Topic 2: Referencing by coordinates, https://docs.ogc.org/as/18-005r4/18-005r4.html (2019) OGC: OGC 18-010r7 Geographic information — Well-known text representation of coordinate reference systems 2.0.6, https://docs.ogc.org/is/18-010r7/18-010r7.html (2019) 4. Terms and Definitions This document used the terms defined in OGC Policy Directive 49 , which is based on the ISO/IEC Directives, Part 2, Rules for the structure and drafting of International Standards. In particular, the word “shall” (not “must”) is the verb form used to indicate a requirement to be strictly followed to conform to this standard and OGC documents do not use the equivalent phrases in the ISO/IEC Directives, Part 2. This document also uses terms defined in the OGC Standard for Modular specifications ( OGC 08-131r3 ), also known as the 'ModSpec'. The definitions of terms such as standard, specification, requirement, and conformance test are provided in the ModSpec. For the purposes of this document, the following additional terms and definitions apply. coordinate epoch A property of coordinates referenced to a dynamic coordinate reference system indicating the date at which the coordinates are valid. (SOURCE: OGC 18-005r4) Coordinate Reference System (CRS) A coordinate reference system is a set of mathematical rules for specifying how coordinates are to be assigned to a point that is related to an object by a datum. (SOURCE: ISO 19111:2019) Note The GeoPackage Encoding Standard (GES) uses the term "spatial reference system (SRS)," though technically an SRS is a spatial reference either by coordinates (CRS) or by geographic identifier (e.g., post code / zip code or street address). In the GES, a spatial reference system is realized through a row in the gpkg_spatial_ref_sys table. well-known text (WKT) A compact machine- and human-readable representation of geometric objects that may also be used for succinctly describing the critical elements of CRS definitions. (SOURCE: OGC 18-010r7) Note CRS WKT2 specifically refers to a document conforming to the latest revision of OGC 18-010. 5. Conventions This section provides details and examples for any conventions used in the document. Examples of conventions are symbols, abbreviations, use of XML schema, or special notes regarding how to read the document. 5.1. Identifiers The normative provisions in this Standard are denoted by the URI http://www.opengis.net/spec/{standard}/{m.n} All requirements and conformance tests that appear in this document are denoted by partial URIs which are relative to this base. 6. WKT for Coordinate Reference Systems Extension (Informative) Following is the information required by the GeoPackage Extension Template . 6.1. Extension Author GeoPackage SWG, author_name gpkg . 6.2. Extension Name or Template gpkg_crs_wkt 6.3. Extension Type Extension of Existing Requirement 10 . 6.4. Applicability Applies to the gpkg_spatial_ref_sys table. 6.5. Scope Read-write 7. Requirements (Normative) 7.1. Table Definition 7.1.1. gpkg_spatial_ref_sys Requirement 115 For GeoPackages conforming to this extension, the gpkg_spatial_ref_sys table SHALL have additional columns called definition_12_063 and epoch as per Table 1 and gpkg_spatial_ref_sys Table Definition SQL (CRS WKT Extension) . Table 1. Spatial Ref Sys Table Definition Column Name Column Type Column Description NOT NULL flag Key srs_name TEXT Human readable name of this SRS true srs_id INTEGER Unique identifier for each Spatial Reference System within a GeoPackage true PK organization TEXT Case-insensitive name of the defining organization e.g. EPSG or epsg true organization_coordsys_id INTEGER Numeric ID of the Spatial Reference System assigned by the organization true definition TEXT Well-known Text [I32] Representation of the Spatial Reference System true description TEXT Human readable description of this SRS false definition_12_063 TEXT Well-known Text [I34] or [I36] Representation of the Spatial Reference System true epoch DOUBLE Coordinate epoch as per https://docs.ogc.org/as/18-005r4/18-005r4.html#68 false Note Previous versions of this extension specified default values for definition and definition_12_063 . Those defaults have been removed for interoperability reasons but implementers should be aware that some GeoPackages may have these defaults in place. 7.2. Table Data Values 7.2.1. gpkg_extensions Requirement 145 GeoPackages with a row in the gpkg_extensions table with an extension_name of "gpkg_crs_wkt" SHALL comply with the extension defined in this Standard. GeoPackages complying with this extension SHALL have a row in the gpkg_extensions table as described in Table 2 (below). Warning Requirement 145 has been updated as part of GeoPackage 1.2.1. In 1.1.0 and 1.2.0, the table_name and column_name column values of the required gpkg_extensions row were inadvertently left unspecified. While the executable test suite running on an older GeoPackage version will not generate a failure due to missing gpkg_extensions column values, implementers are encouraged to update these values to comply with the updated requirement on older versions as well. Table 2. Extension Table Records table_name column_name extension_name definition scope gpkg_spatial_ref_sys definition_12_063 gpkg_crs_wkt see note below read-write gpkg_spatial_ref_sys definition_12_063 gpkg_crs_wkt_1_1 see note below read-write gpkg_spatial_ref_sys epoch gpkg_crs_wkt_1_1 see note below read-write Note For the definition column, use a hyperlink that describes the current implementation of this extension. While a URL such as http://www.geopackage.org/spec/#extension_crs_wkt is acceptable, permalinks to specific versions are provided upon publication using the URL pattern http://www.geopackage.org/specMmP/#extension_crs_wkt where M is the major version, m is the minor version, and P is the patch. For example http://www.geopackage.org/spec121/#extension_crs_wkt is the permalink for this extension for GeoPackage 1.2.1. 7.2.2. gpkg_spatial_ref_sys Requirement 116 Values of the definition_12_063 column SHALL be constructed per the WKT syntax as defined in [I34] and [I36] . Note For backwards compatibility, only use WKT values that are common to both 12-063 and 18-010. Additional WKT values specified in 18-010r7 can be used when required in the CRS definition. Requirement 117 At least one definition column SHALL be defined with a valid definition unless the value of the srs_id column is 0 or -1 . Both columns SHOULD be defined. If it is not possible to produce a valid [I32] definition then the value of the definition column MAY be undefined . If it is not possible to produce a valid [I34] or [I36] definition then the value of the definition_12_063 column MAY be undefined . Note If, for a particular row, both the definition and definition_12_063 columns are populated, the value in the definition_12_063 column takes priority. The coordinate epoch SHOULD be provided if available. As such, a GeoPackage could have multiple SRSs with the same organization and organization_coordsys_id but with different epochs. While the epoch should theoretically go in the dataset metadata (per ISO 19111 / OGC Topic 2 as approved by the OGC in March 2021), there is not currently a standard metadata profile that would be suitable. Annex A: Conformance Class Abstract Test Suite (Normative) A.1. Table Definition Table Definition Test Case ID /extension_crs_wkt/table_def Test Purpose Verify that the gpkg_spatial_ref_sys table exists and has the correct definition. Extends /base/core/gpkg_spatial_ref_sys/data/table_def . Test Method PRAGMA table_info('gpkg_spatial_ref_sys') Fail if returns an empty result set Fail if result set does not include a column named 'definition_12_063' or if the column is not of type 'TEXT', notnull 1, and dflt_value 'undefined'. Fail if result set does not include a column named 'epoch' or if the column is not of type 'DOUBLE' and notnull 0. Pass if no failures. Reference Req 115 Test Type Basic Table Data Values Test Case ID /extensions/crs_wkt/extensions/data_values Test Purpose Verify that the gpkg_extensions table has the required rows. Test Method SELECT table_name, column_name, scope FROM gpkg_extensions WHERE extension_name = 'gpkg_crs_wkt'; Not testable if returns an empty result set Fail if there is not exactly one row Fail if scope is not "read-write" Fail if column_name is not "definition_12_063" Fail if table_name is not "gpkg_spatial_ref_sys" Pass if no fails Reference Req 145 Test Type: Capabilities Test Case ID /extensions/crs_wkt/extensions/data_values_1_1 Test Purpose Verify that the gpkg_extensions table has the required rows for the revised extension. Test Method SELECT table_name, column_name, scope FROM gpkg_extensions WHERE extension_name = 'gpkg_crs_wkt_1_1'; Not testable if returns an empty result set Fail if there is not exactly two rows Fail if scope for both rows is not "read-write" Fail if column_name is not "definition_12_063" or "epoch" Fail if table_name for both rows is not "gpkg_spatial_ref_sys" Pass if no fails Reference Req 145 Test Type: Capabilities Test Case ID /extension_crs_wkt/data_values_default Test Purpose Verify that the gpkg_spatial_ref_sys table contains the required default contents. Extends /base/core/gpkg_spatial_ref_sys/data_values_default . Test Method SELECT organization, organization_coordsys_id, definition, definition_12_063 FROM gpkg_spatial_ref_sys WHERE srs_id = -1 Confirm that this returns "NONE" -1 "undefined" "undefined" SELECT srs_id, organization, organization_coordsys_id, definition, definition_12_063 FROM gpkg_spatial_ref_sys WHERE srs_id = 0 Confirm that this returns "NONE" 0 "undefined" "undefined" SELECT definition FROM gpkg_spatial_ref_sys WHERE organization IN ("epsg","EPSG") AND organization_coordsys_id 4326 Confirm that this is a valid CRS SELECT definition_12_063 FROM gpkg_spatial_ref_sys WHERE organization IN ("epsg","EPSG") AND organization_coordsys_id 4326 Confirm that this is a valid 12-063/18-010 CRS Pass if tests 1-4 are met Fail otherwise Reference Req 116 Test Type Capability Test Case ID /extension_crs_wkt/data_values_required Test Purpose Verify that the spatial_ref_sys table contains rows to define all srs_id values used by features and tiles in a GeoPackage. Extends /base/core/gpkg_spatial_ref_sys/data_values_required . Test Method SELECT definition, definition_12_063 FROM gpkg_spatial_ref_sys WHERE srs_id NOT IN (0, -1) For each result Fail if both definition values are 'undefined' Pass if no failures Reference Req 117 Test Type Capability Annex B: Table Definition SQL (Normative) B.1. gpkg_spatial_ref_sys gpkg_spatial_ref_sys Table Definition SQL (CRS WKT Extension) CREATE TABLE gpkg_spatial_ref_sys ( srs_name TEXT NOT NULL , srs_id INTEGER NOT NULL PRIMARY KEY , organization TEXT NOT NULL , organization_coordsys_id INTEGER NOT NULL , definition TEXT NOT NULL , description TEXT , definition_12_063 TEXT NOT NULL , epoch DOUBLE ); Annex C: Revision History Date Release Editor Primary clauses modified Description 2021-08-20 0.1 J. Yutzler all initial version 2022-04-15 0.90 R. Lott preface, 4, 7 input from open comment period 2022-05-10 0.91 C. Reed multiple input from open comment period 2022-05-23 0.92 A. Youmans 4 clarification 2022-06-06 0.93 J. Yutzler all final cleanup 1 . www.opengeospatial.org/cite Last updated 2022-10-14 12:30:46 -0400