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The SEDRIS Data Representation Model
APPENDIX A - Classes Union Of Primitive Geometry |
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An instance of this DRM class is a <Union Of Geometry> that is composed of solely of <Primitive Geometry>.
Consider a typical geometric representation of an airport runway, in which the runway surface is represented by a layer of polygons, overlaid by stripes (decal polygons).
To ensure that the necessary rendering order is followed, the data provider creates a <Union Of Primitive Geometry> UPG, and attaches each <Polygon> as a component of UPG, in order of increasing relative rendering priority (the <Polygon> with the lowest relative rendering priority is attached first).
After all the <Polygon> instances in the underlying layer have been attached, the decal <Polygon> instances are processed in the order in in which they will be rendered.
If a specific method is used for the ordering, the data provider specifies it in UPG's ordering_reason field. In this case, the data was created for a Z-buffered rendering system that supports layers, so ordering_reason is set to SE_ORDRNG_REASON_LYR_HIGH_QUALITY_RENDERING.
A collection of <Polygon> instances making up the graphical representation of a forest canopy.
A 10 kilometre by 20 kilometre triangulated irregular network of <Polygon> instances.
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| SE_Boolean | unique_descendants; | (notes) |
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| SE_Boolean | strict_organizing_principle; | (notes) |
| SE_Union_Reason | union_reason; | (notes) |
| SE_Ordering_Reason | ordering_reason; | (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.
The union_reason field specifies the reason why the given instance of <Union Of Geometry> was created to organize its components.
The ordering_reason field specifies whether the ordering of the component <Geometry Representation> instances of the given <Union Of Geometry> instance is semantically significant, and if so, what that significance is.
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