New geodetic registry from ISO

[Martin Desruisseaux <ma...@geomatys.com>]

Hello all

Geospatial softwares rely a lot of EPSG geodetic registry, for example 
with "EPSG::4326" being a well-known concise way to identify "WGS 84" 
geographic Coordinate Reference System (CRS). But recently, the 
International Organization for Standardization (ISO) also published its 
own repository:

    https://geodetic.isotc211.org/ (announced in [1])

My quick analysis: this ISO repository has both similarities and 
differences compared to EPSG geodetic registry (https://epsg.org/). On 
the similarities side, both of them allow to get a complete CRS 
definition from a concise code. Both of them can provide those 
definitions in Geographic Markup Language (GML) or Well-Known Text (WKT) 
formats. Both of term have very similar terms of use (a little bit more 
restrictive than Apache licence, which force us to provide those data in 
a separated download).

On the differences side, I didn't saw a link for downloading the 
complete ISO database. It may be on intent; this registry seems to be 
designed for online browsing only. It means that contrarily to the EPSG 
registry, it seems difficult to include the full ISO database in a 
software for off-line usage. However maybe this was not an ISO goal. 
Their announcement message on November 20 [1] said:

    The main purpose of the Registry is to serve as the primary source
    for authoritative information on reference systems and
    transformations that can be used not only by end users but also
    other registries, including the ubiquitous EPSG registry. (…snip…)
    The ISO Geodetic Registry is not meant to compete with or replace
    other registries but, rather, to complement them as an authoritative
    source for their content.

My understanding is that we may not use the ISO registry directly, but 
instead continue to use the EPSG database which itself would include 
data from ISO registry. The added value of this registry would be to 
increase confidence in those geodetic data. While I think EPSG is a very 
high quality geodetic registry, it is still considered as a secondary 
source of data rather than a primary source. ISO (in my understanding) 
aims to fill the gap by being closer to a primary source.

If we want to use the ISO registry directly instead than indirectly 
through EPSG, there is a web API. I did not explored yet, but if I 
understood correctly this API is standardized by ISO 19127:2019 
(Geographic information — Geodetic register). The GML and WKT output 
formats are both OGC and ISO standards. The WKT format is more 
up-to-date with latest ISO 19111 evolution, but GML is more complete 
because it defines all properties such as "remarks" in every corners of 
the CRS, while WKT focus on the most important properties. If the 
software can read both GML and WKT (it is the case of Apache SIS for 
example), I would suggest to give GML a try in the particular case of 
ISO registry.

     Martin

[1] https://www.iers.org/SharedDocs/Publikationen/EN/IERS/Publications/messages/IERS_Message_No_411.txt?__blob=publicationFile