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The SEDRIS Data Representation Model
APPENDIX A - Classes Alternate Hierarchy Related Geometry |
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An instance of this DRM class is an aggregation of <Geometry Hierarchy> instances, in which each component <Geometry Hierarchy> is an alternate representation of the same environmental entity, and the corresponding <Hierarchy Data> instance indicates why that particular alternate representation was provided.
Consider a collection of <Geometry> instances representing a specific spatial region, for which there is a requirement that the <Geometry> instances shall be efficiently accessible both by location and by classification (such as ECC_ROAD, ECC_RIVER, ECC_VEGETATION).
To satisfy this requirement, the data provider has chosen to use an <Alternate Hierarchy Related Geometry> instance with two components, in which one component (in this example, a <Spatial Index Related Geometry> instance) organizes the <Geometry> instances spatially, while a second component (a <Classification Related Geometry> instance) organizes the <Geometry> instances by EDCS Classification Code (ECC).
This class allows a single collection of <Geometry> instances to be hierarchically organized in two or more different ways. In one branch, the <Geometry> instances might be organized spatially, while in another, they might be organized by classification. This provides two (or more) different access paths to the same objects, each organized to be efficient with respect to a different access pattern.
| SE_Boolean | unique_descendants; | (notes) |
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| SE_Boolean | strict_organizing_principle; | (notes) |
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 two <Geometry Hierarchy> instances indicates that they are alternate representations of the same environmental object.
An association from a <Hierarchy Summary Item> instance to a <Geometry Hierarchy> indicates that the <Hierarchy Summary Item> summarizes that <Geometry Hierarchy>.
An association from a <Reference Surface> instance to a <Geometry Hierarchy> indicates that the <Geometry Hierarchy> organizes the geometric objects that specify the resolution surface of the <Reference Surface>.
In the case where multiple <Collision Volume> components are specified for a given <Aggregate Geometry>, the union of the volumes thus specified is used in collision detection.
If this value is SE_TRUE, each 'descendant' of this aggregation - that is, each <Geometry> instance that exists in the component tree rooted at the given <Aggregate Geometry> - 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 <Geometry> 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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