Definition of "coordinate system"

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.

"coordinate_system": {
  "type": "object",
  "properties": {
    "$schema" : { "type": "string" },
    "type": { "type": "string", "enum": ["CoordinateSystem"] },
    "name": { "type": "string" },
    "subtype": { "type": "string",
                 "enum": ["Cartesian",
                          "spherical",
                          "ellipsoidal",
                          "vertical",
                          "ordinal",
                          "parametric",
                          "affine",

"polar",
"linear",
"cylindrical",

                          "TemporalDateTime",
                          "TemporalCount",
                          "TemporalMeasure"]  },
    "axis": {
        "type": "array",
        "items": { "$ref": "#/definitions/axis" }
    },
    "id": { "$ref": "#/definitions/id" },
    "ids": { "$ref": "#/definitions/ids" }
  },
  "required" : [ "subtype", "axis" ],
  "allOf": [
    { "$ref": "#/definitions/id_ids_mutually_exclusive" }
  ],
  "additionalProperties": false
},

"$comment": "[RL] 3x CS subtypes missing."
"$comment": "[RL] For CS subtypes, 19111/Topic 2 has constraints on (i) dimension [number of axes] permitted (for each subtype), (ii) data type for axis unit (for several subtypes). The above enumeration and schema for 'axis' does not include these constraints."
"$comment": "[RL] 19111/Topic 2 (and WKT2) has constraints on the type of CS that may be associated with each subtype of CRS. Not clear that the above enumeration allows for these constraints: should each CS subtype be defined?"

Start with the coordinate_system schema excerpt in the issue and the linked ProjJson v0-7 document. Compare the proposed subtypes, axis definitions, and mutual-exclusion rules with ISO 19111 Topic 2 and WKT2, then clarify the required constraints and subtype definitions. Done means the project has an agreed schema treatment for the missing subtypes and stated dimensional and axis-unit constraints.