Class Name: Feature Face

Superclass - <Feature Topology>

Subclasses

Definition

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

Primary Page in DRM Diagram:

• 12

Secondary Pages in DRM Diagram:

• 8

Example

1. Consider an <Areal Feature> instance representing a forest; that is, one with a <Classification Data> component with tag = ECC_FOREST. The forest (topologically represented by a <Feature Face> instance) has an outer boundary, which is specified by one or more <Feature Edge> instances using a <Feature Face Ring> instance.

2. 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 Face> instances are required whenever <Areal Feature> instances exist, regardless of the feature topology level.

Are there any geometric constraints on <Feature Face> instances?

Yes; see the constraints on this class for details.

Can <Feature Face> instances exist at any feature topology level?

Yes. <Feature Face> instances may exist at any feature topology level in order to define the extents of <Areal Feature> instances. See the constraints on this class for details.

Looking at the relationships allowed for <Feature Topology> instances, 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 DRM 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> instance, a <Spatial Index Related Feature Topology> instance, a <Perimeter Related Features> instance, or a <Perimeter Related Feature Topology> instance).

<Feature Node> instances, <Feature Edge> instances, and, in 3D, <Feature Face> instances 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 Node> instances, <Feature Edge> instances, and <Feature Face> instances to identify their counterparts, if any.

In 2D,

• tile boundary <Feature Node> instances come in pairs, unless they're located at a corner where four tiles meet,
• tile boundary <Feature Edge> instances always come in pairs,
• <Feature Face> instances 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 Node> instances can come in
  • pairs, if they're located within a tile boundary <Feature Face> instance,
  • fours, if they lie on a tile boundary <Feature Edge> instance, or
  • eights, if they are at a tile boundary corner.
• tile boundary <Feature Edge> instances can come in
  • pairs, if they are contained in a tile boundary <Feature Face> instance, or
  • fours if they lie on a tile boundary <Feature Edge> instance.
• tile boundary <Feature Face> instances only come in pairs, so a <Feature Face> instance can have at most one counterpart.

Constraints

• <<Publishable Object>>
• <<Property Constraints>>
• <<Constraints On Associates>>
• <<Contained Node Constraints>>
• <<Edges Bordering Faces>>
• <<Feature Edge Constraints>>

Associated to (one-way)

• a bounded set of 0..2 {ordered} <Feature Volume> instances¹

Associated by (one-way)

• zero or more <Feature Edge> instances²
• exactly 2 <Feature Volume Shell> instances, each through the use of a <Face Directions> link object

Associated with (two-way)

• zero or more <Areal Feature> instances, each through the use of a <Face Directions> link object
• zero or one <Feature Face> instance
• zero or more <Feature Node> instances³

Composed of (two-way) (inherited)

• zero or more <Property Value> instances

Composed of (two-way)

• zero or more {ordered} <Feature Face Ring> instances
• zero or more <Location> instances⁴

Component of (two-way) (inherited)

• zero or more <Union Of Feature Topology> instances

Inherited Field Elements

Field Elements

Notes

Associated to Notes

Feature_Volume

Associated from Notes

Feature_Edge

Associated with Notes

Feature_Node

Composed of Notes

Location

Fields Notes

universal

The universal field specifies that the <Feature Face> instance is the universal <Feature Face> instance. Within a 2D or 3D tile that has feature topology level 3, the universal <Feature Face> instance lies outside any other faces. Since the external boundary of the universal <Feature Face> instance is conceptually at infinity, a <Feature Face> instance that has this field set to SE_TRUE has no external <Feature Face Ring> component.