{
  "$schema": "https://json-schema.org/draft/2020-12/schema",
  "description": "A Ring feature: an ordered closed loop of directed (oriented) Edge references forming a boundary. geometry must be null. Uses directed_references (not references) in its topology.",
  "allOf": [
    {
      "$ref": "https://ogcincubator.github.io/topo-feature/build/annotated/geo/topo/features/topo-feature/schema.json"
    },
    {
      "properties": {
        "geometry": {
          "type": "null"
        },
        "circumference": {
          "type": "number",
          "x-jsonld-id": "topo:circumference"
        },
        "topology": {
          "properties": {
            "type": {
              "type": "string",
              "const": "Ring"
            },
            "directed_references": {
              "type": "array",
              "description": "Ordered list of oriented Edge references forming the closed ring boundary",
              "items": {
                "$ref": "https://ogcincubator.github.io/topo-feature/build/annotated/geo/topo/datatypes/oriented-ref/schema.json"
              },
              "minItems": 3
            }
          },
          "required": [
            "type",
            "directed_references"
          ],
          "not": {
            "required": [
              "references"
            ]
          }
        }
      },
      "required": [
        "topology"
      ]
    }
  ]
}