The SEDRIS Data Representation Model
APPENDIX A - Classes
Continuous LOD Related Geometry

Class Name: Continuous LOD Related Geometry

Superclass - <Aggregate Geometry>

Subclasses

This DRM class is concrete and has no subclasses.

Definition

An instance of this DRM class is used to represent continuous terrain or continuous adaptive terrain, by replacing a <Polygon> instance that represents all or part of an environmental object with a set of <Polygon> instances that represent the same environmental object or part of an environmental object tessellated to a finer level of detail.

Primary Page in DRM Diagram:

Secondary Pages in DRM Diagram:

This class appears on only one page of the DRM class diagram.

Example

  1. Consider a spaceship attempting to land on a planet. As it gets closer and closer to the planet, the terrain should be viewed in more and more detail as the spaceship descends. For smooth transitions of this detail, <Continuous LOD Related Geometry> instances are used to provide the transitions in detail.

    The geometry represented by a <Continuous LOD Related Geometry> instance can be represented in finer detail by using one or more <Continuous LOD Related Geometry> components each of which contains that finer detail in its <Union Of Primitive Geometry> component, and will then itself have zero or more <Continuous LOD Related Geometry> components. Any <Continuous LOD Related Geometry> components that contain <Continuous LOD Related Geometry> components under it will have the terminating_node flag set to SE_FALSE. The <Union Of Primitive Geometry> component will contain <Polygon> components. If a <Continuous LOD Related Geometry> instance is encountered with the terminating_node flag set to SE_TRUE, only a <Union Of Primitive Geometry> component will exist under it, as depicted in Figure 10:

    Continuous LOD Related Geometry, Example 1

    Figure 10 — <DRM Continuous LOD Related Geometry> example

    NOTE  This example only shows two levels of polygon fragmentation. Each <Continuous LOD Related Geometry> instance could contain <Continuous LOD Related Geometry> components, but that would make a huge picture. Only the idea is represented here.

FAQs

How can a consumer find the finest fragmentation of polygons?

Follow all Continuous LOD chains. Wherever a continuous LOD node with terminating_node set to SE_TRUE is encountered, that identifies the finest fragmentation of <Polygon> instances under the <Union Of Primitive Geometry> at that Continuous LOD.

What do the "terminating" <Polygon> instances represent?

The combination of polygons from the continuous LOD nodes with terminating_node set to SE_TRUE make up the <Polygon> identified under the <Union Of Primitive Geometry> from the continuous LOD node with terminating_node set to SE_FALSE.

Since <Continuous LOD Related Geometry> instances are not organized with link objects, such as <Base LOD Data> instances, how can consumers determine the range between fine and coarse data?

The uniqueness of Continuous LOD data is that it is not based on range data for an entire area to blend in. Rather, the blending of data is performed typically at the IG. In source data, all potential polygon fragmentations have been identified. Therefore, it is not necessary to have range data stored in a link class.

Constraints

Associated to (one-way) (inherited)

Associated by (one-way) (inherited)

Composed of (two-way) (inherited)

Composed of (two-way)

Composed of (two-way metadata) (inherited)

Component of (two-way) (inherited)

Component of (two-way)

Inherited Field Elements

SE_Boolean

unique_descendants;

9

SE_Boolean

strict_organizing_principle;

10

Field Elements

SE_Boolean

terminating_node;

11

Notes

Associated to Notes


Feature_Representation

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> link object on the association relationship.


Geometry_Hierarchy

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> link object on the association relationship.

Associated from Notes


Feature_Representation

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> link object on the association relationship.


Geometry_Hierarchy

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> link object on the association relationship.


Hierarchy_Summary_Item

An association from a <Hierarchy Summary Item> instance to a <Geometry Hierarchy> instance indicates that the <Hierarchy Summary Item> instance summarizes that <Geometry Hierarchy> instance.


Reference_Surface

An association from a <Reference Surface> instance to a <Geometry Hierarchy> instance indicates that the <Geometry Hierarchy> instance organizes the geometric objects that specify the reference surface geometry of the <Reference Surface> instance.

Composed of Notes


Collision_Volume

In the case where multiple <Collision Volume> components are specified for the <Aggregate Geometry> instance, the union of the volumes thus specified is used in collision detection.


LSR_Transformation

An <Aggregate Geometry> instance can have an <LSR Transformation> component only when the <Aggregate Geometry> instance is within the scope of an LSR 3D SRF.

Fields Notes

unique_descendants

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 <Aggregate Geometry> instance 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.

strict_organizing_principle

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.

terminating_node

The terminating_node field specifies whether the current level of tessellation is the finest level of tessellation. This flag is set to SE_TRUE if no other <Continuous LOD Related Geometry> instances are found below this level.

Prev: Contact Point. Next: Control Link. Up:Index.

Last updated: July 1, 2011 Copyright © 2011 SEDRIS™