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The SEDRIS Data Representation Model
APPENDIX A - Classes Conformal Behaviour |
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An instance of <Conformal Behaviour> instance specifies how the aggregating geometry representation conforms to the surface upon which the aggregating geometry representation is applied.
The <Geometry Hierarchy> instance to which a <Conformal Behaviour> instance is attached conforms to the terrain skin automatically, either parallel to gravity (for example, ensuring that the base of a building touches the ground without warping the walls) or orthogonally to the terrain skin (for example, as in the case of a wall).
Consider a <Model> instance M being placed on terrain where the <Geometry Model Instance> instance specifies a <Conformal Behaviour> component indicating conformance to the terrain skin. The terrain skin uses a <Classification Related Geometry> instance to separate the surface to which M conforms from the rest of the terrain geometry in that area. If so, the <Conformal Behaviour> instance can associate with the terrain skin. This would help the consumer resolve ambiguities when deriving the actual 3D location. The surface to be conformed to can be further qualified by the <Property Value> instance that has been extended.
Consider a tree canopy that conforms to multiple or continuous LOD terrain. The entire collection of tree canopy <Polygon> instances and the tree wall <Polygon> instances around the canopy is aggregated into a <Classification Related Geometry> instance, which is associated with an <Areal Feature> instance.
Each <Vertex> component of the <Polygon> instances representing the tree wall around the canopy has a <Conformal Behaviour> component. The <Conformal Behaviour> component of each <Vertex> instance on the ground has parallel_gravity = SE_FALSE and offset_distance = 0, while the <Conformal Behaviour> components of the <Vertex> instances at the top have parallel_gravity = SE_TRUE and a positive offset_distance indicating the height of the tree wall. Each <Vertex> component of the <Polygon> instances representing the tree canopy has a <Conformal Behaviour> component with parallel_gravity = SE_TRUE and offset_distance indicating the height of the tree canopy.
An airplane <Model> instance might have <Geometry Representation> instances that represent the projected shadow. The <Geometry Hierarchy> instance containing the shadow could be given a <Conformal Behaviour> component so that it will hug the nominal terrain surface.
Conformal behaviour could be achieved using a <Translation Control Link> instance with a <Variable> component that represents a Zenith (HAT) test. We have chosen to represent this kind of behaviour as a class of its own because it is a well-understood (abstracted) self-contained behaviour. This is also the case with <Stamp Behaviour> instances and level of detail. The DRM has generally been designed to allow for high-level abstraction as well as lower-level descriptions to exist in the same <Model> instance.
The (possibly elaborated) classification specified by the classification field specifies the classification used to identify the applicable <Reference Surface> instance.
If the value of the parallel_gravity field is SE_TRUE, the direction of conformance is parallel to gravity; otherwise, the direction of conformance is orthogonal to the applicable geometry representation identified by the applicable <Reference Surface> instance.
The offset_distance field specifies the distance above the given surface, in metres.
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