Abstract Class Name: Union of Geometry

Superclass - Aggregate Geometry

Subclasses

• Union of Geometry Hierarchy
• Union of Primitive Geometry

Definition

An aggregation of Geometry with a standardized mechanism by which to organize the members that compose the union.

Primary Page in DRM Diagram:

• 4

Example

1. An antenna assembly is contained in a weather protection enclosure. Visually, only the opaque enclosure can be seen. But at microwave frequencies, the enclosure is invisible and only the antenna can be "seen". The entire structure is contained in a Union of Geometry. What the Radar "sees" is modeled with a Radar Cross-section (RCS) Property Table. The algorithm (or field measurements) that computed the RCS table used axes that do not match the spatial reference frame (world or model as the case may be). Therefore, RCS axes of azimuth and elevation angle are misused unless some REFERENCE DIRECTIONS can be attached to the entire Union of Geometry.

FAQs

How would a typical Runway (base Polygons with stripes (decal polygons) be represented?

The polygons would be put into an Union of Geometry with the polygon with the lowest relative rendering priority listed first. The decal polygons would be listed next in the order in which they will be rendered. If there is a specific method for the ordering, then it should be specified in reason_for_ordering. If this Model is meant for a Zbuffered system that supports layers, then the reason_for_ordering might be SE_LAYERED_QUALITY.

What if a Model of the outside of a house, developed for a non-Zbuffered system, has the polygons grouped to render properly in a fixed order? Say the house has 4 walls and 4 windows. Assuming the polygons are all grouped together, how would this example be represented in the SEDRIS data representation model at the attribute level?

The fixed order of the polygons would be reflected in an Union of Geometry with the reason_for_ordering set to SE_FIXED_LISTED. The lowest priority Polygons (the walls) would be listed first and the higher priority polygons (the windows) would be listed last.

What if the house in the previous example were developed for a Zbuffered system?

The polygons would typically be grouped in layers. There are 2 approaches that could be employed by the modeler depending on how the polygons are grouped.

1. If all the polygons are one-sided front-facing polygons, then the house could be represented with an Union of Geometry Hierarchy with reason_for_ordering SE_LAYERED with 2 children. The 1st child would be the base layer (all the walls) and the 2nd child (the first decal layer) would contain all the windows. In this case, the polygons under a LAYERED Union of Geometry are not coplanar, but the rendering priority can still be resolved.
2. If the modeler grouped the layers into coplanar unions of Polygons then the SEDRIS structure might be represented as Union of Geometry with 4 layered Union of Geometry (wall and window) would list the wall first and the window next.

When would a Reference Vector be a component of a Union of Geometry?

A Reference Vector would be used when a Union of Geometry represented a "thing" in the environment. An example of this is a building represented by a Union of Geometry, and which has a Property Table of radar cross-sections. The table would need a Reference Vector to establish the zero azimuth direction. (See Example 1).

Constraints

• No Attribute Conflicts
• Non Crossing Aggregations
• Non Cyclic Aggregations
• Precedence of Attribute Set Index
• Non Crossing Associations
• Color Mapping Restrictions
• Image Mapping Functions and Texture Coordinates

Associated by (one-way)(inherited)

• optionally, a Hierarchy Summary Item
• optionally, some Reference Surfaces

Associated with (two-way)(inherited)

• optionally, some Features
• optionally, some Geometry Hierarchies

Composed of (one-way)(inherited)

• optionally, some {ordered} Attribute Set Indices
• optionally, a Classification Data
• optionally, some Property Tables
• optionally, some Property Table References
• optionally, some Property Values
• optionally, a Reference Surface
• optionally, some Sound Instances
• optionally, a Spatial Domain
• optionally, a Bounding Volume
• optionally, a Center of Buoyancy
• optionally, a Center of Mass
• optionally, a Center of Pressure
• optionally, some Collision Volumes
• optionally, a Conformal Behavior
• optionally, a LSR Transformation
• optionally, an Overload Priority Index
• optionally, some Property Descriptions
• optionally, a Stamp Behavior
• optionally, some {ordered} Colors
• optionally, a Light Rendering Properties
• optionally, a Rendering Properties
• optionally, some {ordered} Image Mapping Functions
• optionally, a Rendering Priority Level

Composed of (one-way)

• optionally, some Reference Vectors

Composed of (two-way)(inherited)

• optionally, some Hierarchical Tables
• optionally, some Light Sources

Composed of (one-way metadata)(inherited)

• optionally, a Time Constraints Data
• optionally, an Access
• optionally, some Browse Graphics
• optionally, some Cross References
• optionally, a Data Quality
• optionally, a Keywords
• optionally, a Point of Contact

Component of (two-way)(inherited)

• optionally, some Alternate Hierarchy Related Geometries through Geometry Hierarchy Data
• optionally, some Animation Related Geometries
• optionally, some Classification Related Geometries through Geometry Classification Data
• optionally, an Environment Root
• optionally, some Geometry Separating Plane Relations through Geometry Separating Plane Data
• optionally, a Geometry Model
• optionally, some Level of Detail Related Geometries through Geometry Level of Detail Data
• optionally, some Oct Tree Related Geometries through Geometry Oct Tree Data
• optionally, some Time Related Geometries through Geometry Time Constraints Data
• optionally, some Perimeter Related Geometries through Geometry Perimeter Data
• optionally, some Quad Tree Related Geometries through Geometry Quad Tree Data
• optionally, some Spatial Index Related Geometries through Geometry Spatial Index Data
• optionally, some State Related Geometries through Geometry State Data
• optionally, some Union of Geometry Hierarchies

Inherited Field Elements

Field Elements

Notes

Fields Notes

unique_descendants

 If SE_TRUE, then for any object that exists 'below' this aggregation,
 each object will appear in only one 'branch' of this aggregation.
 If SE_FALSE, then objects may appear in multiple 'branches' of this
 aggregation.

independent_topologies

 If SE_TRUE, then each 'branch' from this aggregation is its own,
 independent topology.  If SE_FALSE, then all of the branches exist
 within the same topology.

strict_organizing_principle

 If true, then each 'branch' strictly follows the rules of this
 aggregation.  If false, then each 'branch' might bend the rules a bit.
 For example, if this is a spatial aggregation, than a value of true
 indicates that objects will *not* cross the spatial extents defined
 by this aggregation relationship, and a value of false indicates
 that objects might cross those bounds.  For another example, if this
 is a time-based aggregation, then a value of true indicates that all
 branches will only contain data valid for the times specified for
 each branch, and a value of false indicates that the branches have
 the option of including data that falls outside of the specified
 time ranges for that branch.