The SEDRIS Data Representation Model
APPENDIX A - Classes
Feature Face

Class Name: Feature Face

Superclass - <Feature Topology>

Subclasses

This DRM class is concrete and has no 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:

Secondary Pages in DRM Diagram:

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,

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

In 3D,

Constraints

Associated to (one-way)

Associated by (one-way)

Associated with (two-way)

Composed of (two-way) (inherited)

Composed of (two-way)

Component of (two-way) (inherited)

Inherited Field Elements

This class has no inherited field elements.

Field Elements

SE_Boolean universal; 5

Notes

Associated to Notes


Feature_Volume

These <Feature Volume> instances represent the front and back sides of the <Feature Face> instance, respectively.

Associated from Notes


Feature_Edge

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

Associated with Notes


Feature_Node

If specified, these <Feature Node> instances are contained within the <Feature Face> instance. See <<Contained Node Constraints>> for further details.

Composed of Notes


Location

At topology levels 4 and 5, <Feature Face> instances may contain a collection of interior points that define the three-dimensional shape of the surface represented by the <Feature Face> instance.

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.


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Last updated: July 26, 2006 Copyright © 2006 SEDRIS