Definition of "ellipsoid" and "ellipsoid_cs"

Inizia con lo schema dell’ellissoide proposto e le note su ellipsoidal_cs nell’issue, quindi confronta il documento ProjJSON v0.7 collegato con i vincoli di 19111/Topic 2 e WKT2 indicati. Definisci le varianti di ellissoide richieste e completa i vincoli ellipsoidal_cs per gli assi 2D e 3D. Il lavoro è completato quando i requisiti dello schema sono concordati e rappresentati in modo coerente.

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.

"ellipsoid": {
  "type": "object",
  "oneOf":[
    {
      "properties": {
        "$schema" : { "type": "string" },
        "type": { "type": "string", "enum": ["Ellipsoid"] },
        "name": { "type": "string" },
        "semi_major_axis": { "$ref": "#/definitions/value_in_metre_or_value_and_unit" },
        "semi_minor_axis": { "$ref": "#/definitions/value_in_metre_or_value_and_unit" },
        "id": { "$ref": "#/definitions/id" },
        "ids": { "$ref": "#/definitions/ids" }
      },
      "required" : [ "name", "semi_major_axis", "semi_minor_axis" ],
      "additionalProperties": false
    },
    {
      "properties": {
        "$schema" : { "type": "string" },
        "type": { "type": "string", "enum": ["Ellipsoid"] },
        "name": { "type": "string" },
        "semi_major_axis": { "$ref": "#/definitions/value_in_metre_or_value_and_unit" },
        "inverse_flattening": { "type": "number" },
        "id": { "$ref": "#/definitions/id" },
       "ids": { "$ref": "#/definitions/ids" }
      },
      "required" : [ "name", "semi_major_axis", "inverse_flattening" ],
      "additionalProperties": false
    },
    {
      "properties": {
        "$schema" : { "type": "string" },
        "type": { "type": "string", "enum": ["Ellipsoid"] },
        "name": { "type": "string" },
        "radius": { "$ref": "#/definitions/value_in_metre_or_value_and_unit" },
        "id": { "$ref": "#/definitions/id" },
        "ids": { "$ref": "#/definitions/ids" }
      },
      "required" : [ "name", "radius" ],
     "additionalProperties": false
    }
  ],
  "allOf": [
    { "$ref": "#/definitions/id_ids_mutually_exclusive" }
  ]
},

"$comment": "[RL] This is based on the WKT2 definition which was constrained to be backward-compatible to WKT1 in allowing the ellipsoid unit to be omitted and assumed to be metre. 19111/Topic 2 requires the unit to be explicitly stated and need not be metre."

"$comment": "[RL] ProjJSON v0.7 schema omits the definition of a triaxial ellipsoid (this is noted). In 19111/Topic 2 this is provided for by an additional optional semi-median axis attribute. In WKT2 this has a different keyword and (as in 19111/Topic 2) requires unit to be given."

"ellipsoidal_cs": {

"$comment": "[RL] Definition to be completed. The definition should constrain an ellipsoidal CS to have 2 or 3 axes. 19111/Topic 2 constrains axis names to "geodetic latitude, geodetic longitude, [ellipsoidal height (if 3D)]". WKT2 constrains these to be 'latitude', 'longitude' [and 'ellipsoidal height'. WKT2 requires that axis abbreviations be from the Latin character set and recommends that conventionally-used axis abbreviations φ and θ are be replaced by 'lat' and 'lon' or by 'B' and 'L' (conventional in German). In the 3D case, WKT2 constrains the abbreviation for ellipsoidal height (if given) to be 'h'.
See vertical_cs below for a possible template for adding these constraints."