Abstract Class Name: Feature Face

Superclass - <Feature Topology>

Subclasses

• <Regular Feature Face>
• <Universal Feature Face>

Definition

An instance of this DRM class is a 2-dimensional <Feature Topology> instance used to represent the region that corresponds to an <Areal Feature>, bounded by one or more <Feature Edge> instances.

Primary Page in DRM Diagram:

• 12

Secondary Pages in DRM Diagram:

• 8

Example

1. An <Areal Feature> representing a forest would be defined by one or more <Feature Edge> instances. At feature topology level 4, the walls of a building might be defined by a collection of <Feature Face> instances.

FAQs

When are <Feature Face> instances 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> shall exhaustively and exclusively partition the 2-dimensional topological surface, such that exactly two <Feature Faces> shall 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 <Spatial Index Related> or <Perimeter Related> 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>>
• <<Contained Node Restrictions>>
• <<Edges Bordering Faces>>
• <<Feature Edge Restrictions>>
• <<Non Crossing Associations>>

Associated by (one-way)

• one or more <Feature Edge> instances (notes)

Associated with (two-way)

• zero or more <Areal Feature> instances through <Face Directions>
• zero or one <Feature Face> instance
• zero or more <Feature Node> instances (notes)

Composed of (two-way)(inherited)

• zero or one <Feature ID> instance
• zero or more <Property Value> instances

Composed of (two-way)

• zero or more <Internal Feature Face Ring> instances
• zero or more <Same As Feature Face> instances

Component of (two-way)(inherited)

• zero or more <Union Of Feature Topology> instances

Inherited Field Elements

Notes

Associated with Notes

Feature_Edge

 The <Feature Edges> that border this <Feature Face>;
 the converse of this relationship is that between
 <Feature Face Ring> and <Feature Edge>.

Feature_Node

 The <Feature Nodes> contained within the <Feature Face>,
 if any.