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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> instances 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 through a distinct link object. The various subclasses provide different mechanisms for organizing <Feature Representation> instances, which include:
Each branch is a <Feature Hierarchy> instance through a different <Hierarchy Data> link object, representing a different way of organizing the same underlying collection of <Feature Representation> instances.
Each branch is a <Feature Hierarchy> instance through a different <Classification Data> link object, representing a different thematic layer, or a different classification of <Feature Representation> instances (e.g., roads, railroads) within a single thematic layer.
Each branch is a <Feature Hierarchy> instance through a distinct (but possibly overlapping), <Base LOD Data> link object, representing an alternative that is to be used at a specified level of detail.
The <Aggregate Feature> instance represents an octant-related organization, where each branch is a <Feature Hierarchy> instance representing an octant, as identified through its <Octant Data> link object.
Each branch is a <Feature Hierarchy> instance that is located within a different cell of an irregular spatial index, as defined through its <Perimeter Data> link object.
The <Aggregate Feature> instance represents a quadrant related organization, in which each branch is a <Feature Hierarchy> instance representing a quadrant, as identified through its <Quadrant Data> link object.
The <Aggregate Feature> instance 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> instance represents the different states of an environmental object for a specified EAC. Each branch represents the environmental object for a different state value of the specified EAC. Each branch is a <Feature Hierarchy> instance through a <State Data> link object that corresponds to the specified state value.
The <Aggregate Feature> instance represents an environmental object that has different representations for different time periods. Each branch is a <Feature Hierarchy> instance through a distinct (though possibly overlapping) <Time Constraints Data> link object representing an alternative that shall be used for the time period specified through its <Time Constraints Data> link object.
Each branch is a <Feature Representation> instance. The reason for organizing them into separate components is specified by the union_reason field.
See concrete subclasses for examples.
This class, through its subclasses, allows instances of <Feature Representation> to be hierarchically organized in a variety of different ways. The <Classification Related Features> subclass allows features to be organized according to their ECCs. The <Spatial Index Related Features>, <Perimeter Related Features>, <Quadrant Related Features>, and <Octant Related Features> subclasses allow features to be organized according to their locations. The <Alternate Hierarchy Related Features>, <LOD Related Features>, <State Related Features>, and <Time Related Features> subclasses allow multiple alternative representations of collections of <Feature Representation> instances 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; | 9 |
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| SE_Boolean | strict_organizing_principle; | 10 |
If the value of the unique_descendants field is SE_TRUE, each descendant shall be unique in the sense that it shall appear in only one branch of this aggregation. Each descendant is a <Feature Representation> instance within the component tree rooted at the <Aggregate Feature> instance. If unique_descendants is SE_FALSE, at least one <Feature Representation> instance appears in more than one branch of the aggregation.
If the value of the strict_organizing_principle field 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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