Enhanced JSON-FG support based on use case analysis

[teezip]

Background

JSON-FG standard (or "OGC Features and Geometries JSON - Part 1: Core") has been approved in May 2026:
https://docs.ogc.org/is/21-045r1/21-045r1.html

There is initial JSON-FG support in Hakunapi, see also issue #26 and pull request #73.

As the standard is now finalized this support might need some enhancements.

Also actual use cases should be analyzed before implementation.

Possible uses cases in case "traditional geometries" are used:

• OGCFeat service is used to fetch JSON-FG file that is stored for later "offline" use and such a file contains for example crs information (different options here based on JSON-FG with "coordRefSys" and reference to older obsolete GeoJSON standard with "crs" element)
• JSON-FG file contains multiple a collection of multiple feature types instead of just one (related to OGCFeat service, how to query?)
• others?