Abstract Class Name: Union Of Geometry
Subclasses
Definition
An instance of this DRM class is an aggregation of
<Geometry Representation> instances
specifying a standardized mechanism by which to organize the members
that compose the union.
Primary Page in DRM Diagram:
Secondary Pages in DRM Diagram:
Example
See concrete subclasses for examples.
FAQs
-
Consider a data provider with a polygonal representation of the
outside of a house, which has four walls and four windows.
This particular polygonal representation was developed for a
non-Zbuffered system, such that the representation groups the
polygons in a fixed order to indicate rendering order. Assuming
that the polygons are all grouped together, and that the data
provider wishes to represent this house with a
<Model> instance, how is the house represented?
The house is represented by a <Model> instance
M, such that M has a
<Geometry Model> component G and a
<Classification Data> component C,
where the tag field of C
has the value ECC_HOUSE. G has a
<Union Of Primitive Geometry> component U.
The
ordering_reason
field of U is set to
SE_ORDREAS_FIXED_LISTED.
The lowest priority
<Polygon> instances (the walls) are
specified first and the higher priority polygons (the windows)
are 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 two approaches that could be employed by the modeller
depending on how the polygons are grouped.
If all the polygons are one-sided front-facing polygons, the
house could be represented by a
<Union Of Geometry Hierarchy>
instance with
ordering_reason =
SE_ORDREAS_LAYERED_HIGH_QUALITY_RENDERING
with two
components. The first component is the base layer (all the walls) and
the second component (the first decal layer) contains all the windows.
In this case, the polygons under a
SE_ORDREAS_LAYERED_HIGH_QUALITY_RENDERING
<Union Of Geometry> instance are not coplanar,
but the rendering priority can still be resolved.
If the modeller grouped the layers into coplanar unions of
<Polygon> instances, the DRM structure might be
represented as <Union Of Geometry> instances
with four layered <Union Of Geometry>
(wall and window) lists the wall first and the window next.
-
When would a <Union Of Geometry> instance
have a <Reference Vector> component?
A <Union Of Geometry> instance U has a
<Reference Vector> component only when
U represents an environmental object, and then only when the
environmental object's representation supplies information appropriate
to such representation. An example of this is a building represented by
a <Union Of Geometry> instance, which has a
<Property Table> component
of radar cross-sections, for which a
<Reference Vector> instance
is needed to establish the zero azimuth direction.
(See Example 1).
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)
- zero or more <Alternate Hierarchy Related Geometry> instances, each through the use of a <Hierarchy Data> link object
- zero or more <Animation Related Geometry> instances
- zero or more <Classification Related Geometry> instances, each through the use of a <Classification Data> link object
- zero or one <Environment Root> instance
- zero or one <Geometry Model> instance
- zero or more <LOD Related Geometry> instances, each through the use of a <Base LOD Data> link object
- zero or more <Octant Related Geometry> instances, each through the use of a <Octant Data> link object
- zero or more <Perimeter Related Geometry> instances, each through the use of a <Perimeter Data> link object
- zero or more <Quadrant Related Geometry> instances, each through the use of a <Quadrant Data> link object
- zero or more <Separating Plane Relations> instances, each through the use of a <Separating Plane Data> link object
- zero or more <Spatial Index Related Geometry> instances, each through the use of a <Spatial Index Data> link object
- zero or more <State Related Geometry> instances, each through the use of a <State Data> link object
- zero or more <Time Related Geometry> instances, each through the use of a <Time Constraints Data> link object
- zero or more <Union Of Geometry Hierarchy> instances
Notes
Associated to 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>
link object 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>
link object on the association relationship.
Associated from 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>
link object 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>
link object on the association relationship.
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.
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
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.
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
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.
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
<Union Of Geometry> instance
was created to organize its components.
The ordering_reason
field specifies whether the ordering of the
<Geometry Representation> components of the
<Union Of Geometry> instance is semantically
significant and, if so, what that significance is.
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