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The SEDRIS Data Representation Model
APPENDIX A - Classes Aggregate Feature |
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An instance of this DRM class specifies a collection of <Primitive Feature> and / or <Feature Hierarchy> instances, organized according to some organizing principle specific to the particular subclass of <Aggregate Feature> being considered.
For most subclasses of <Aggregate Feature>, each individual branch of the aggregation is explicitly identified by a distinct link object. The various subclasses provide different mechanisms for organizing <Feature> instances, which include:
Each branch is a <Feature Hierarchy> with a different <Hierarchy Data> instance, representing a different way of organizing the same underlying collection of <Feature> instances.
Each branch is a <Feature Hierarchy> with a different <Classification Data> instance, representing a different thematic layer, or a different classification of <Feature> instances (e.g., roads, railroads) within a single thematic layer.
Each branch is a <Feature Hierarchy> with a distinct (but possibly overlapping), <Base Level Of Detail Data> instance, representing an alternative that is to be used at a specified level of detail.
The <Aggregate Feature> represents an octree, where each branch is a <Feature Hierarchy> representing an octant within the octree, as identified by its <Oct Tree Data> instance.
Each branch is a <Feature Hierarchy> that is located within a different cell of an irregular spatial index, as defined by its <Perimeter Data> instance.
The <Aggregate Feature> represents a quadtree, in which each branch is a <Feature Hierarchy> representing a quadrant within the quadtree, as identified by its <Quad Tree Data> instance.
The <Aggregate Feature> represents a regularly spaced spatial index grid, in which each branch is a <Feature Hierarchy> instance representing a different cell within the spatial index.
The <Aggregate Feature> represents something that can take on different state values for a specified EDCS Attribute Code (the state_tag, which shall have the "state-related" property). Each branch is a <Feature Hierarchy> instance with a different <State Data> instance, representing an alternative that shall used to represent the <Aggregate Feature> when it takes on the specified state value.
The <Aggregate Feature> represents something that has different representations for different time periods, so that each branch is a <Feature Hierarchy> instance with a distinct (though possibly overlapping) <Time Constraints Data> instance, representing an alternative that shall be used for the time period specified by its <Time Constraints Data>.
Each branch is a <Feature>, which may be either a <Primitive Feature> or a <Feature Hierarchy> instance. The reason for organizing them into separate components is only minimally specified.
See specific subclasses for examples.
This class, through its subclasses, allows instances of <Feature> to be hierarchically organized in a 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.
| SE_Boolean | unique_descendants; | (notes) |
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| SE_Boolean | strict_organizing_principle; | (notes) |
An association between two <Feature> instances indicates that they are alternate representations of the same environmental object.
An association between a <Geometry Hierarchy> instance and a <Feature> instance indicates that the <Geometry Hierarchy> and the <Feature> are alternate representations of the same environmental object.
An association between a <Property Grid> instance and a <Feature> instance indicates that the <Feature> and the <Property Grid> (or some specific cell data within that <Property Grid>) are alternate representations of the same environmental object. Each associated <Property Grid> will indicate which is the case.
This relationship exists to support "attributes for derived objects." That is, these components are used only to specify texture mapping information for geometry that is to be derived from the <Aggregate Feature> by the consumer. These <Image Mapping Function> instances shall use <Image Anchor> components to specify the mapping.
This is needed for cases in which an <Aggregate Feature> is significant only for a particular domain, such as radar.
If this value is SE_TRUE, each 'descendant' of this aggregation - that is, each <Feature> instance that exists in the component tree rooted at the given <Aggregate Feature> - shall be unique, in the sense that it shall appear in only one 'branch' of this aggregation. If unique_descendants is SE_FALSE, at least one <Feature> instance appears in more than one 'branch' of the aggregation.
If this value is SE_TRUE, each 'branch' of this aggregation strictly complies with the organizing principle for its particular subclass. If this value is SE_FALSE, at least one 'branch' does not strictly comply with the given organizing principle. See the organizing principle constraint for each specific subclass for details.
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