Class Name: Volume LOD Data

Superclass - <Base LOD Data>

Subclasses

Definition

An instance of this DRM class specifies a volume that governs the switching of objects by the associated branch of a volume-based <LOD Related Geometry> instance or <LOD Related Features> instance.

Primary Page in DRM Diagram:

• 9

Secondary Pages in DRM Diagram:

Example

1. Consider a geometric representation of a runway for an application for which increased detail is required as a viewer gets within 1000 metres of it, but for which a less detailed representation can be used 1000 metres or more from the runway. This geometric representation can be organized as a <LOD Related Geometry> instance, wherein the branch corresponding to the less detailed representation has a <Volume LOD Data> link object with outside set to SE_TRUE, specifying a parallelepiped volume that is aligned with the runway and extends 1000 metres from each edge. The more detailed representation's <Volume LOD Data> link object uses the same <Parallelepiped Volume Extent> instance and the same volume centre, but has outside set to SE_FALSE.

2. Consider another application, for which a geometric representation of a runway is required to provide increased detail as a viewer gets within 1000 metres of either end, but which if overflown from the side does not require detail to be switched on until the viewer is 500 metres away. In this case, the representation has the same structure as that used in the previous example, but the parallelepiped extends only 500 metres from either side of the runway, while extending 1000 metres from each end.

3. Consider a representation of a windowless building having opaque walls, such that nothing inside the building can be seen by an observer outside the building representation. Consequently, everything inside that building's representation can be switched on and off depending on whether an observer is inside or outside the building. This can be represented by organizing the representation of the building interior with a volume level of detail organization.

   Suppose that the feature representation of a building interior is being considered, so that it is being represented as one branch of a <LOD Related Features> instance in a celestiodetic SRF, and that the interior volume of the building can be represented as a parallelepiped as depicted in Figure 6.75.

   

   Figure 75 — <DRM Volume LOD Data> example

   The <Volume LOD Data> link object specifies a parallelepiped volume of the same dimensions as the building interior, and specifies the centre of that volume. The value of its outside field indicates that the feature representation of the building interior (the data represented by this branch) is active only when the viewer is inside the parallelepiped volume.

FAQs

Why does Level Of Detail need to be controlled by a volume?

A spherical boundary, defined by a distance from a centre point, may not be appropriate for some objects. For example, long, thin objects such as runways. In such cases, Levels Of Detail shall be switched at different distances from the centre of the object, depending on the direction the object is approached from. A volume allows such a non-spherical boundary to be specified.

Constraints

• <<Publishable Object>>
• <<LOD Related Organizing Principle>>
• <<Inheritance Rule For Location>>

Composed of (two-way)

• one <Location 3D> instance¹
• one <Volume Extent> instance²

Component of (two-way) (inherited)

• zero or more <Aggregate Feature> instances
• zero or more <Aggregate Geometry> instances
• zero or more <Property Grid Hook Point> instances

Inherited Field Elements

Field Elements

Notes

Composed of Notes

Location_3D

Volume_Extent

Fields Notes

outside

If the value of outside is SE_TRUE, the branch is active when the observer is outside the volume and off when the observer is inside the volume. If the value of outside is SE_FALSE, the branch is active when the observer is inside the volume and off when the observer is outside the volume.