[AIXM-618] Additional CRS/srsName values in the GML Profile

Description

Two additional CRS/srsName values are added in the GML profile to support the traceability of newer International Terrestrial Reference Systems.

Rationale for change

See https://aixmccb.atlassian.net/browse/AIXM-615

The Amendment 43 to ICAO Annex 15 (eff. 28 NOV 2024) introduces the updated explanation with regard to the use of WGS-84: 

“Note 1.— The latest version of the WGS-84 (G2139) reference frame is realized through coordinates of 17 GPS tracking stations which are part of the GPS Control Segment. They are aligned to IGb14 (considered to be equivalent to International Terrestrial Reference Frame 2014 (ITRF 2014)) at epoch 2005.0.

Note 2.— Another precise worldwide terrestrial coordinate system is the International Earth Rotation Service (IERS) Terrestrial Reference System (ITRS), and the realization of ITRS is the IERS ITRF. Guidance material regarding the ITRS is provided in Appendix C of Doc 9674. WGS-84 (G2139) is consistent with ITRF 2014 and in practical realization the difference between these two systems is statistically insignificant for most applications, meaning WGS-84 (G2139) and ITRF 2014 are essentially identical.”

Notwithstanding, some AIS data providers (AISP) use ITRF-originated data "as WGS-84", meaning that the data is published with WGS-84 CRS references, such as the default EPSG::4326. For traceability and data maintenance reasons, an increasing number of AISP provide in their AIS products data with reference to the ITRF terrestrial reference. 

The current GML Profile specification for AIXM includes in Annex B a limited list of CRS and srsName values. This does not include any ITRF CRS. Based on the Amendment 43 to ICAO Annex 15 and growing number of use cases, it is proposed that two additional values are added in the GML Profile list, supporting the ITRF 2014 and ITRF 2020 terrestrial coordinate systems.

Impact assessment

[FWD_1:1] No data mapping is necessary and no data loss occurs when data is exchanged from a system (A) that uses AIXM 5.1.1 for output towards a system (B) that uses AIXM 5.2 for input.

[BWD_MAP_1:1] Data mapping is possible and no data loss occurs when data is exchanged from a system (B) that uses AIXM 5.2 for output towards a system (A) that uses AIXM 5.1.1 for input.

Change Proposal details

In the GML Profile document:

• Add the following CRS / srsName values:
• For ITRF2014 - “EPSG::9000”
• For ITRF2020 - “EPSG::9990”

Mapping AIXM 5.1.1 to AIXM 5.2 (forward)

Not applicable.

Mapping AIXM 5.2 to AIXM 5.1.1 (backward)

[MAPC-01] 

For every:

• srsName="urn:ogc:def:crs:EPSG::9000” or 
• srsName="urn:ogc:def:crs:EPSG::9990” 

change into srsName="urn:ogc:def:crs:EPSG::4326”

Mapping example

(Note: for mapping test data see: https://github.com/aixm/mapping_52_511/tree/master/AIXM-xxx)