Abstract Class Name: Feature Face

Superclass - Feature Topology

Subclasses

• Regular Feature Face
• Universal Feature Face

Definition

A 2-dimensional Feature Topology object used to represent the region that corresponds to an Areal Feature, bounded by one or more Feature Edges.

Primary Page in DRM Diagram:

• 12

Secondary Pages in DRM Diagram:

• 8

Example

1. An Areal Feature representing the a forest would be defined by one or more Feature Edges. At feature topology level 4, the walls of a building might be defined by a collection of Feature Faces.

FAQs

When are Feature Face objects required?

Feature Faces are required whenever there are Areal Features, regardless of the feature topology level.

Are there any geometric constraints on Feature Faces?

Yes. Feature Faces may not intersect or overlap one another. Feature Faces may meet only along one or more Feature Edges.

Can Feature Faces exist at any feature topology level?

Yes. Feature Faces may exist at any feature topology level in order to define the extents of Areal Features. At feature topology level 3, the collection of Feature Faces must exhaustively and exclusively partition the 2-dimensional topological surface, such that exactly two Feature Faces must meet at each Feature Edge. However, at feature topology level 4, this constraint no longer holds, and any number of Feature Faces may meet at a Feature Edge.

Looking at the relationships allowed for Feature Topology, we note that the Feature Edge to Feature Edge association is "many to many", and similarly the Feature Node to Feature Node association is "many to many". Why is the Feature Face to Feature Face association "optional to optional" instead of "many to many"?

These associations exist to support cross-tile topology. In SEDRIS terms, this is topology that appears in more than one branch of a lt;Spatial Index Relatedgt; or lt;Perimeter Relatedgt; aggregation, namely, in a Spatial Index Related Features, Spatial Index Related Feature Topology, Perimeter Related Features, or Perimeter Related Feature Topology).

Feature Nodes, Feature Edges, and, in 3D, Feature Faces can be located on the boundary of a tile. When this happens, they have "counterparts" in each of the adjacent tiles that share the boundary. These associations allow Feature Nodes, Feature Edges, and Feature Faces to identify their counterparts, if any.

In 2D,

• tile boundary Feature Nodes come in pairs, unless they're located at a corner where four tiles meet,
• tile boundary Feature Edges always come in pairs,
• Feature Faces are always contained within a single tile.

However, the multiplicity in the DRM is there to support 3D tiles (e.g., a regular set of rectangular blocks of space).

In 3D,

• tile boundary Feature Nodes can come in
  • pairs, if they're located within a tile boundary Feature Face,
  • fours, if they lie on a tile boundary Feature Edge, or
  • eights, if they are at a tile boundary corner.

• tile boundary Feature Edges can come in
  • pairs, if they are contained in a tile boundary Feature Face,

    or

  • fours if they lie on a tile boundary Feature Edge.

• tile boundary Feature Faces only come in pairs, so a Feature Face can have at most one counterpart.

Constraints

• No Attribute Conflicts
• Perimeter Related Feature Topology Partitioning
• Contained Node Restrictions
• Edges Bordering Faces
• Feature Edge Restrictions
• Non Crossing Associations

Associated by (one-way)

• optionally, some Bordered Feature Faces
• optionally, some Contained Within Feature Faces

Associated with (two-way)

• optionally, a Feature Face

Composed of (one-way)(inherited)

• optionally, a Feature ID
• optionally, some Property Values

Composed of (one-way)

• optionally, some Contained Feature Nodes
• optionally, some Internal Feature Face Rings
• optionally, some Same As Feature Faces

Component of (two-way)(inherited)

• optionally, some Union of Feature Topologies

Component of (two-way)

• optionally, some Areal Features through Face Directions