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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 specifies 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 Representation> instances representing a specific spatial region, for which there is a requirement that the <Geometry Representation> 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 Representation> instances spatially, while a second component (a <Classification Related Geometry> instance) organizes the <Geometry Representation> instances by ECC.
This class allows a single collection of <Geometry Representation> instances to be hierarchically organized in two or more different ways. In one branch, the <Geometry Representation> 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 <Feature Representation> instance and a <Geometry Hierarchy> instance indicates that the environmental object(s) that they represent have the semantic relationship indicated by the <Base Association Data> instance on the association relationship.
An association between two <Geometry Hierarchy> instances indicates that the environmental object(s) that they represent have the semantic relationship indicated by the <Base Association Data> instance on the association relationship.
An association between a <Feature Representation> instance and a <Geometry Hierarchy> instance indicates that the environmental object(s) that they represent have the semantic relationship indicated by the <Base Association Data> instance on the association relationship.
An association between two <Geometry Hierarchy> instances indicates that the environmental object(s) that they represent have the semantic relationship indicated by the <Base Association Data> instance on the association relationship.
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 the value of the unique_descendants field is SE_TRUE, each descendant of this aggregation, that is, each <Geometry Representation> 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 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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