Consider an octree that is represented in a transmittal by an <Octant Related Geometry> instance. The lower left octant of the octree is a <Union Of Primitive Geometry> aggregated by the <Octant Related Geometry> as follows:
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The SEDRIS Data Representation Model
APPENDIX A - Classes Octant 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> represents a branch of an octant. The octant represented by a branch is specified by the <Octant Data> instance associated with that branch. The bounding region that the <Geometry Hierarchy> components occupy is defined by the <Spatial Extent> component of the <Octant Related Geometry> instance.
Consider an octree that is represented in a transmittal by an <Octant Related Geometry> instance. The lower left octant of the octree is a <Union Of Primitive Geometry> aggregated by the <Octant Related Geometry> as follows:
An <Octant Related Geometry> is used when an object in the hierarchy contains spatial components that occupy a certain octant. These octants might not contain <Primitive Geometry>, which is why this class can have less than 8 components.
<Octant Related Geometry> automatically has a <Spatial Extent> component, because it is a <Geometry Hierarchy>. However, unlike other classes descended from <Geometry Hierarchy>, <Octant Related Geometry> has a constraint stating that the <Spatial Extent> component is mandatory.
| 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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