Definition of "one_and_only_one_of_datum_or_datum_ensemble"

NOTE: Markdown does not support highlighting in color, so bold/italic has been used to highlight the material being discussed. This issue is extracted from the document submitted by Roger Lott at https://github.com/opengeospatial/CRS-JSON-Encoding/blob/main/ProjJson%20v0-7%20RL%202024-06-16.docx for discussion at the CRS SWG meeting OGC held during the Montreal June 2024 TC meeting.

"one_and_only_one_of_datum_or_datum_ensemble": {
  "allOf": [
    {
        "not": {
            "type": "object",
            "required": [ "datum", "datum_ensemble" ]
        }
    },
    {
        "oneOf": [
            { "type": "object", "required": ["datum"] },
            { "type": "object", "required": ["datum_ensemble"] }
        ]
    }
  ]
},

"$comment": "[RL] Why is the structure different to that of one of ID or IDs?"

Start with the one_and_only_one_of_datum_or_datum_ensemble JSON Schema fragment in the issue and compare it with the one for ID or IDs. Read the linked ProjJson v0-7 RL document for the source discussion. Done means the CRS SWG has decided whether the structures should match and the agreed definition is recorded.