Class Name: Feature Face

Superclass - <Feature Topology>

Subclasses

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. Consider an <Areal Feature> instance representing a forest - that is, with a <Classification Data> component of ECC_FOREST. The forest has an outer boundary, which is specified by one or more <Feature Edge> instances via 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 there are <Areal Feature> instances, regardless of the feature topology level.

Are there any geometric constraints on <Feature Faces>?

Yes; see this class' constraints.

Can <Feature Faces> 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 this class' constraints for further details.

Looking at the relationships allowed for <Feature Topology>, 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 Node>, <Feature Edge>, 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>, <Feature Edge>, 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>,
  • fours, if they lie on a tile boundary <Feature Edge>, 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>,
    
    or
    
    
  • fours if they lie on a tile boundary <Feature Edge>.
  
  
  
• tile boundary <Feature Face> instances only come in pairs, so a <Feature Face> can have at most one counterpart.

Constraints

• <<Publishable Object>>
• <<No Attribute Conflicts>>
• <<Contained Node Restrictions>>
• <<Edges Bordering Faces>>
• <<Feature Edge Restrictions>>
• <<Non Crossing Associations>>

Associated to (one-way)

• a bounded set of 0..2 {ordered} <Feature Volume> instances (notes)

Associated by (one-way)

• zero or more <Feature Edge> instances (notes)
• exactly 2 <Feature Volume Shell> instances, each with a <Face Directions> link object

Associated with (two-way)

• zero or more <Areal Feature> instances, each with a <Face Directions> link object
• zero or one <Feature Face> instance
• zero or more <Feature Node> instances (notes)

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> instances

Component of (two-way) (inherited)

• zero or more <Union Of Feature Topology> instances

Inherited Field Elements

Field Elements

Notes

Associated to Notes

Feature_Volume

 The <Feature Volume> instances on the front and back sides
 of the <Feature Face>, respectively.

Associated from Notes

Feature_Edge

 These <Feature Edge> instances are those that border the
 given <Feature Face> instance. The converse of this
 relationship is that between <Feature Face Ring> and
 <Feature Edge>.

Associated with Notes

Feature_Node

 If specified, these <Feature Node> instances are contained
 within the <Feature Face>; see this class' constraints for
 further details.

Fields Notes

universal

 The universal field specifies that the given <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 at infinity,
 a <Feature Face> instance that has this field set to SE_TRUE has
 no external <Feature Face Ring> instance.