Discussion of "axis"

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.

"axis": {
  "type": "object",
  "properties": {
    "$schema" : { "type": "string" },
    "type": { "type": "string", "enum": ["Axis"] },
    "name": { "type": "string" },
    "abbreviation": { "type": "string" },
    "direction": { "type": "string",
                   "enum": [ "north",
                             "northNorthEast",
                             "northEast",
                             "eastNorthEast",
                             "east",
                             "eastSouthEast",
                             "southEast",
                             "southSouthEast",
                             "south",
                             "southSouthWest",
                             "southWest",
                             "westSouthWest",
                             "west",
                             "westNorthWest",
                             "northWest",
                             "northNorthWest",
                             "up",
                             "down",
                             "geocentricX",
                             "geocentricY",
                             "geocentricZ",
                             "columnPositive",
                             "columnNegative",
                             "rowPositive",
                             "rowNegative",
                             "displayRight",
                             "displayLeft",
                             "displayUp",
                             "displayDown",
                             "forward",
                             "aft",
                             "port",
                             "starboard",
                             "clockwise",
                             "counterClockwise",
                             "towards",
                             "awayFrom",
                             "future",
                             "past",
                             "unspecified" ] },
    "meridian": { "$ref": "#/definitions/meridian" },

"bearing": { "$ref": "#/definitions/bearing" },

    "unit": { "$ref": "#/definitions/unit" },
    "minimum_value": { "type": "number" },
    "maximum_value": { "type": "number" },
    "range_meaning": { "type": "string", "enum": [ "exact", "wraparound"] },
    "id": { "$ref": "#/definitions/id" },
    "ids": { "$ref": "#/definitions/ids" }
  },

"required" : [ "name", "abbreviation"*, "direction" ],

  "allOf": [
    { "$ref": "#/definitions/id_ids_mutually_exclusive" }
  ],
  "additionalProperties": false
},

"$comment": "[RL] For most subtypes of CS (ordinal and temporalDateTime excepted) 19111/Topic 2 (and WKT2) has constraints requiring the axis to have units. Not clear that the above includes these constraints and the exceptions."
"$comment": "[RL] meridian is an attribute in WKT2 not found in 19111/Topic2 ..."
"$comment": "... WKT2 has a bearing attribute applied to the clockwise and counterClockwise direction values in polar CSs. (also not found in 19111/Topic 2)."
"$comment": "[RL] 19111 Topic 2 and WKT2 have constraints on axis names and abbreviations covered further in comments under the CS subtype schema holding places inserted below. Some prohibit both of axis name and axis abbreviation."

The actual definition of the missing "bearing" attribute has been added as a separate issue "Adding definition of bearing" to allow concise comments on bearing definition.

Review the proposed axis schema in the linked ProjJson v0-7 RL 2024-06-16.docx and compare its bearing, required fields, units, meridian, and naming constraints with 19111/Topic 2 and WKT2. Resolve the CRS SWG discussion and reflect the decisions in the axis definition; bearing itself is tracked in the separate "Adding definition of bearing" issue.