The SEDRIS Data Representation Model
APPENDIX A - Classes
Continuous LOD Related Geometry
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Class Name: Continuous LOD Related 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
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 :
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)
- 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
Component of (two-way)
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.
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 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.
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Next: Control Link.
Up:Index.
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Last updated: August 23, 2005
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Copyright © 2005 SEDRIS™
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