The SEDRIS Data Representation Model
APPENDIX A - Classes
Union Of Geometry
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Abstract Class Name: Union Of Geometry
Subclasses
Definition
An instance of one of the concrete subclasses of this abstract DRM
class is an aggregation of <Geometry> specifying
a standardized mechanism by which to organize the members that compose
the union.
Primary Page in DRM Diagram:
Secondary Pages in DRM Diagram:
This class appears on only one page of the DRM class diagram.
Example
- 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
- 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 Primitive Geometry>
with the
ordering_reason set to SE_ORDRNG_REASON_FIXED_LISTED. The lowest
priority <Polygon> instances (the walls) would be
specified first and the higher priority polygons (the windows)
would be specified 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.
- If all the polygons are one-sided front-facing polygons, then the
house could be represented with an <
Union Of Geometry Hierarchy> with
ordering_reason
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.
- 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
Associated by (one-way)(inherited)
Associated with (two-way)(inherited)
Composed of (two-way)(inherited)
Composed of (two-way)
Composed of (two-way metadata)(inherited)
Component of (two-way)(inherited)
Notes
Associated with Notes
An association between a <Geometry Hierarchy> instance and a
<Feature> instance indicates that the <Geometry Hierarchy>
and the <Feature> are alternate representations of the same
environmental object.
An association between two <Geometry Hierarchy> instances
indicates that they are alternate representations of the same
environmental object.
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>.
Composed of Notes
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.
Fields Notes
If this value is SE_TRUE, each 'descendant' of this aggregation -
that is, each <Geometry> object 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> object
appears in more than one 'branch' of the aggregation.
If this value 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.
Prev: Union Of Features.
Next: Union Of Geometry Hierarchy.
Up:Index.
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Last updated: October 1, 2002
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Copyright © 2002 SEDRIS™
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