Definition of "engineering_crs" and "engineering_cs"

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.

"engineering_crs": {
  "type": "object",

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

  "properties": {
    "type": { "type": "string", "enum": ["EngineeringCRS"] },
    "name": { "type": "string" },
    "datum": { "$ref": "#/definitions/engineering_datum" },
    "coordinate_system": { "$ref": "#/definitions/coordinate_system" },
    "coordinate_system": { "$ref": "#/definitions/engineering_cs" },
    "$schema" : {},

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

    "remarks": {},
    "id": {}, "ids": {}
  },

"required" : [ "name", "datum", "coordinate system" ],

  "additionalProperties": false
},

"$comment": "[RL] See comment regarding usage under compound_crs."

"$comment": "[RL] An engineering CRS should be constrained to having an angineering_cs."

"$comment": "[RL] In 19111/Topic 2, an engineering CRS may have a datum ensemble rather than a datum. Not likely to be relevant for an engineering CRS so 19162/WKT2 spec does not offer the option. Should CRS JSON follow Topic 2 or WKT?"

"$comment": "[RL] An engineering CRS must have a datum (or a datum_ensemble, see previous comment). The schema would be clearer if this was included in the required list."

"engineering_cs": {
  "type": "object",
  "properties": {
       "oneOf": [
            { "$ref": "#/definitions/affine_cs" },
            { "$ref": "#/definitions/Cartesian_cs" }
            { "$ref": "#/definitions/cylindrical_cs" }
            { "$ref": "#/definitions/linear_cs" }
            { "$ref": "#/definitions/ordinal_cs" }
            { "$ref": "#/definitions/polar_cs" }
            { "$ref": "#/definitions/spherical_cs" }
       ]
  "additionalProperties": false
},

Start by reading the proposed engineering_crs and engineering_cs definitions in this issue and the linked ProjJson v0-7 RL 2024-06-16.docx. Review the questions about usage, datum versus datum ensemble, required fields, and allowed coordinate systems; done requires an agreed definition and corresponding schema update.