Aggregate Feature

Abstract Class Name: Aggregate Feature

Superclass - Feature Hierarchy

Subclasses

Definition

A collection of Features and/or Feature Hierarchies, possibly including Feature Model Instances. In most cases each of the individual components is explicitly labeled by a link data object. The various subclasses provide different mechanisms for organizing Features, which include:

ALTERNATE_HIERARCHY:
Each of the components is a collection of Features with a different Feature Hierarchy Data value, representing different ways of organizing the same collection of Features.
CLASSIFICATION:
Each of the components is a collection of Features with a different Feature Classification Data value, representing different thematic layers, or different classifications of Features (e.g. roads, railroads) within a single thematic layer.
LEVEL_OF_DETAIL:
Each of the components is a collection of Features with a different, possibly overlapping, Feature Level of Detail Data value, representing alternatives that should be used at different viewing ranges or map scales.
OCT_TREE:
Each of the components is a collection of Features that are located within a different cell of an octree, as identified by its Feature Oct Tree Data value.
PERIMETER:
Each of the components is a collection of Features that are located within a different cell of an irregular spatial index, as defined by its Feature Perimeter Data value.
QUADTREE:
Each of the components is a collection of Features that are located within a different cell of a quadtree, as identified by its Feature Quad Tree Data value.
SPATIAL_INDEX:
Each of the components is a collection of Features that are located within a different cell of a regularly spaced spatial index grid.
STATE:
Each of the components is a collection of Features with a different Feature State Data value, representing alternatives that should be used when the Aggregate Feature is in different states.
TIME:
Each of the components is a collection of Features with a different, possibly overlapping, Feature Time Constraints Data value, representing alternatives that should be used during different time periods.
UNION:
Each of the components is a Feature or collection of Features. The reason for organizing them into separate components is not specified.

Primary Page in DRM Diagram:

Secondary Pages in DRM Diagram:

Example

An airport could be represented as a Union of Features that includes Linear Features for the runways; a Point Feature for the control tower; and Areal Features for the terminal and parking lots.
A forested area could be represented at two levels of detail using a Level of Detail Related Features object, with two component Unions of Features having different scale ranges, each containing a single Areal Feature. The Areal Feature to be used at smaller scales would be simpler than the Areal Feature to be used at larger scales.
In the previous example, a third component Union of Features could be added to be used at even larger scales, where the single Areal Feature is replaced by a large number of Point Features representing individual trees.
A lake that varies in size significantly with the seasons could be represented as a Time Related Features object, with two (or more) component Union of Features objects, each containing a single Areal Feature representing the lake.
A large collection of features might be organized using a Classification Related Features object, with multiple component Union of Features objects, containing cultural, vegetation, and surface drainage features, respectively.

FAQs

What is the purpose of this class?: This class, through its subclasses, allows Features to be hierarchically organized in a wide variety of different ways. The Classification Related Features subclass allows features to be organized according to their classification codes. The Spatial Index Related Features, Perimeter Related Features, Quad Tree Related Features, and Oct Tree Related Features subclasses allow features to be organized according to their locations. The Alternate Hierarchy Related Features, Level of Detail Related Features, State Related Features, and Time Related Features subclasses allow multiple alternative representations of collections of Features to be created, with different alternatives used under different conditions. Finally, the Union of Features subclass allows features to be grouped arbitrarily.

Constraints

Associated by (one-way)(inherited)

optionally, a Hierarchy Summary Item

Associated with (two-way)(inherited)

optionally, some Features
optionally, some Geometry Hierarchies
optionally, some Property Grids

Composed of (one-way)(inherited)

optionally, some {ordered} Attribute Set Indices
optionally, a Classification Data
optionally, some Colors
optionally, some {ordered} Image Mapping Functions (notes)
optionally, some Labels
optionally, some Property Tables
optionally, some Property Table References
optionally, some Property Values
optionally, a Rendering Priority Level
optionally, a Spatial Domain
optionally, a Reference Surface
optionally, some Sound Instances

Composed of (one-way)

optionally, some Property Descriptions

Composed of (two-way)

optionally, some Topology Hierarchies

Composed of (one-way metadata)(inherited)

optionally, an Access
optionally, some Browse Graphics
optionally, some Cross References
optionally, a Data Quality
optionally, a Keywords
optionally, a Point of Contact
optionally, a Time Constraints Data

Component of (two-way)(inherited)

optionally, some Union of Features
optionally, some Alternate Hierarchy Related Features through Feature Hierarchy Data
optionally, some Classification Related Features through Feature Classification Data
optionally, an Environment Root
optionally, a Feature Model
optionally, some Time Related Features through Feature Time Constraints Data
optionally, some Level of Detail Related Features through Feature Level of Detail Data
optionally, some Oct Tree Related Features through Feature Oct Tree Data
optionally, some Perimeter Related Features through Feature Perimeter Data
optionally, some Quad Tree Related Features through Feature Quad Tree Data
optionally, some Spatial Index Related Features through Feature Spatial Index Data
optionally, some State Related Features through Feature State Data

Inherited Field Elements

SE_FEATURE_TOPOLOGY_LEVEL_ENUM	feature_topology_level;

Field Elements

SE_BOOLEAN	unique_descendants;	(notes)
SE_BOOLEAN	independent_topologies;	(notes)
SE_BOOLEAN	strict_organizing_principle;	(notes)

Notes

Composed of Notes

Image_Mapping_Function

 Added to support "attributes for derived objects."
 That is, these components are used only to specify
 texture mapping information for geometry that
 is derived from the <Feature> by the consumer.
 These <Image Mapping Functions> must use
 <Image Anchor> components to specify the mapping.

Fields Notes

unique_descendants

 If true, then for any object that exists 'below' this aggregation,
 each object will appear in only one 'branch' of this aggregation.
 If false, then objects may appear in multiple 'branches' of this
 aggregation.

independent_topologies

 If true, then each 'branch' from this aggregation is its own,
 independent topology.  If false, then all of the branches exist
 within the same topology.

strict_organizing_principle

 If true, then each 'branch' strictly follows the rules of this
 aggregation.  If false, then each 'branch' might bend the rules a bit.
 For example, if this is a spatial aggregation, than a value of true
 indicates that objects will *not* cross the spatial extents defined
 by this aggregation relationship, and a value of false indicates
 that objects might cross those bounds.  For another example, if this
 is a time-based aggregation, then a value of true indicates that all
 branches will only contain data valid for the times specified for
 each branch, and a value of false indicates that the branches have
 the option of including data that falls outside of the specified
 time ranges for that branch.

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