|
The SEDRIS Data Representation Model
APPENDIX A - Classes Aggregate Geometry |
|---|
An instance of this DRM class specifies a collection of <Primitive Geometry> instances or <Geometry Hierarchy> instances organized according to some organizing principle specific to the particular subclass of <Aggregate Geometry> being considered.
For most subclasses of <Aggregate Geometry>, each individual branch of the aggregation is explicitly identified through a distinct link object. The various subclasses provide the following different mechanisms for organizing <Geometry Representation> instances:
Each branch is a <Geometry Hierarchy> component through a different <Hierarchy Data> link object, representing a different way of organizing the same underlying collection of <Geometry Representation> instances.
Each branch is a <Geometry Hierarchy> component representing a different frame in an animation sequence. This organizing principle has no counterpart in the <Aggregate Feature> class.
Each branch is a <Geometry Hierarchy> component through a different <Classification Data> link object, representing either a different thematic layer, or a different classification of <Geometry Representation> instances (e.g., roads, railroads) within a single thematic layer.
Each branch is either a <Union Of Primitive Geometry> component (usually a collection of <Polygon> instances), or a set of <Polygon> instances that represent the terrain at a finer level of detail at close range (or alternatively, with a coarser level of detail at long range). This mechanism is used to represent continuous terrain or continuous adaptive terrain. This organizing principle has no counterpart in the <Aggregate Feature> class.
Each branch is a <Geometry Hierarchy> component through a different (but possibly overlapping) <Base LOD Data> link object, representing an alternative that shall be used at a specified level of detail.
The <Aggregate Geometry> instance represents an octant-related organization, in which each branch is a <Geometry Hierarchy> component representing an octant as identified through its <Octant Data> link object.
Each branch is a <Geometry Hierarchy> component that is located within a different cell of an irregular spatial index, as defined through its <Perimeter Data> link object.
The <Aggregate Geometry> instance represents a quadrant related organization, in which each branch is a <Geometry Hierarchy> component representing a quadrant, as identified through its <Quadrant Data> link object.
Each branch is a <Separating Plane Relations> component. Each <Separating Plane Relations> component specifies a <Separating Plane> component P and up to two <Geometry Hierarchy> components each representing the data on either the positive or the negative side of P as indicated through the corresponding <Separating Plane Data> link object. This organizing principle has no counterpart in the <Aggregate Feature> class.
The <Aggregate Geometry> instance represents a regularly spaced spatial index grid, in which each branch is a <Geometry Hierarchy> component representing a different cell within the spatial index.
The <Aggregate Geometry> instance represents an environmental object that can take on different state values for a specified EAC (the state_tag, which shall have the "state related" property). Each branch is a <Geometry Hierarchy> component through a different <State Data> link object, representing an alternative that shall be used to represent the <Aggregate Geometry> instance when it takes on the specified state value.
The <Aggregate Geometry> instance represents an environmental object that has different representations for different time periods. Each branch is a <Geometry Hierarchy> component through a distinct (though possibly overlapping) <Time Constraints Data> link object, representing an alternative that shall be used for the time period specified through its <Time Constraints Data> link object.
Each branch is a <Geometry Hierarchy> component. The reason for organizing them into separate components is only minimally specified. The counterpart of this mechanism among the subclasses of <Aggregate Feature> is the <Union Of Features> class.
Each branch is a <Primitive Geometry> component; <Primitive Geometry> instances can be included in a transmittal only as components of <Union Of Primitive Geometry> instances. The counterpart of this mechanism among the subclasses of <Aggregate Feature> is the <Union Of Features> class.
See concrete subclasses for examples.
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.
|