Footprint

Definition

A Footprint models the approximate physical extent of one or more referenced Buildings.

Feature Structure

• Footprint objects are Feature objects.
• Footprint objects MUST have an "id" member with a FEATURE-ID value
• Footprint objects MUST have a "feature_type" member with the value "footprint"
• Footprint objects MUST have a "geometry" member with a POLYGONAL value

Property Keys

Property	Type	Description
category	"aerial" , "ground", "subterranean"	The category that best describes the nature of the Footprint
name	null or LABELS	The name for the Footprint as declared by the Venue Organization. If present, assumed to be metadata not intended for rendering purposes
building_ids	JSON array of BUILDING-ID	Identifier of the Building(s) the Footprint is associated with

Examples

Ground level footprint for single Building

{
  "id": "11111111-1111-1111-1111-111111111111",
  "type": "Feature",
  "feature_type": "footprint",
  "geometry": {
    "type": "Polygon",
    "coordinates": [
      [
        [100.0, 0.0],
        [101.0, 0.0],
        [101.0, 1.0],
        [100.0, 1.0],
        [100.0, 0.0]
      ]
    ]
  },
  "properties": {
    "category": "ground",
    "name": null,
    "building_ids": ["22222222-2222-2222-2222-222222222222"]
  }
}

Composite aerial footprint

{
  "id": "11111111-1111-1111-1111-111111111111",
  "type": "Feature",
  "feature_type": "footprint",
  "geometry": {
    "type": "MultiPolygon",
    "coordinates": [
      [
        [
          [180.0, 40.0],
          [180.0, 50.0],
          [170.0, 50.0],
          [170.0, 40.0],
          [180.0, 40.0]
        ]
      ],
      [
        [
          [-170.0, 40.0],
          [-170.0, 50.0],
          [-180.0, 50.0],
          [-180.0, 40.0],
          [-170.0, 40.0]
        ]
      ]
    ]
   },
   "properties": {
    "category": "aerial",
    "name": {
      "en": "East Wing"
    },
    "building_ids": [
      "22222222-2222-2222-2222-222222222222",
      "33333333-3333-3333-3333-333333333333"
    ]
  }
}

Property Capturing Rules

BUILDING-IDS

• MUST contain one or more BUILDING-ID values
• MUST NOT contain duplicate values

Geometry Capturing Rules

See also: Footprint Illustrative Guidance

• Horizontal positional accuracy MUST be within tolerance
• When a Venue operates inside a shared physical Building that includes spaces not considered to be functionally relevant but structurally inseparable, then the inseparable spaces SHOULD be included in a Footprint to the extent necessary to support cognitive recognition. (Illustration)
• A Venue Organization SHOULD NOT attempt to derive an "aerial" or "ground" Footprint when:
  • The physical building, when observed in aerial/satellite imagery, is obscured to an extent that derivation of the Footprint would be impeded. Consequently, any derived geometries would possess a shape and spatial extent with questionable horizontal positional accuracy
  • Radial displacement would cause derived geometries to possess a shape and spatial extent with questionable horizontal positional accuracy

Category Specific Rules

"ground"

• MUST be used when the Footprint is derived from a site plan, source data, or a view that explicitly describes the physical extent of the Building at ground-level. (Illustration)
• MUST represent the totality of all portions of the floor(s) that are exposed at ground-level when physical access to a Building exists on more than one Level because of a sloped terrain

• MAY be derived from an aerial or satellite image when:

  • A data source possesses the required resolution to support the interpretation of ground features clearly and unambiguously
  • Other buildings or ground features do not impede capture of the Footprint
  • The physical building does not possess an architectural component (facade, canopy, etc.) that would block the view of the ground surface
  • Radial displacement is not detectable in the portion of the image where the physical building is located

• When a Venue is physically located below ground, and the ground-floor serves only to provide access, then the physical importance of the entrance MUST be assessed. A "ground" Footprint MAY NOT be required if the entrance is judged to be physically unimportant. (Illustration)

"aerial"

• MUST possess an extent describable as the physical Building(s) "...represented as the shadow projected downward from an overhead light at infinity." (Illustration)
• The existence of architectural components considered to be "exaggerated" or "flamboyant" do NOT qualify the building as a candidate for special treatment when capturing an aerial Footprint

"subterranean"

• MUST be derived from the maximum extent of all floors, modeled as one or more Level, that exist below ground-level