Definition of "compound_crs" and all other CRS, datum and coordinate operation members of the schema

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.

"compound_crs": {
"type": "object",

"allOf": [{ "$ref": "#/definitions/object_usage" }],

  "properties": {
    "type": { "type": "string", "enum": ["CompoundCRS"] },
    "name": { "type": "string" },
    "components":  {
       "type": "array",
        "items": { "$ref": "#/definitions/crs" }
    },
    "$schema" : {},

"scope": {},
"area": {},
"bbox": {},
"vertical_extent": {},
"temporal_extent": {},
"usages": {},

    "remarks": {},
    "id": {}, "ids": {}
  },
  "required" : [ "name", "components" ],
  "additionalProperties": false

},

"$comment": "[RL] The use of both object_usage and usages in this schema is not clear - for scope and extent they seem to duplicate each other. In ISO 19111 a usage must contain one scope and one extent. The main geodetic entities (CRS, datum, all types of coordinate operation) should have at least one and may have many usages. Should the schema be something like Usage towards the end of this document?

This comment applies to all other CRS, datum and coordinate operation members in the schema."

Start with the linked ProjJson v0-7 document and the current schema definition for compound_crs, then inspect the corresponding CRS, datum, and coordinate operation members. Compare how object_usage and usages are represented and document the agreed schema direction; done means the SWG has resolved the ambiguity and the affected definitions are updated consistently.