The SEDRIS Data Representation Model
APPENDIX A - Classes
Volume Level Of Detail Data

Class Name: Volume Level Of Detail Data

Superclass - <Base Level Of Detail Data>

Subclasses

This DRM class is concrete and has no 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 < Level Of Detail Related Geometry> or < Level Of Detail Related Features> instance.

Primary Page in DRM Diagram:

Secondary Pages in DRM Diagram:

This class appears on only one page of the DRM class 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 outside that volume. This geometric representation can be organized as a < Level Of Detail Related Geometry> instance, wherein the branch corresponding to the less detailed representation has a < Volume Level Of Detail 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 Level Of Detail Data> link object would use the same <Parallelepiped Volume Extent> and the same volume centre, but would have 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 would have the same structure as that used in the previous example, but the parallelepiped would extend only 500 metres from either side of the runway, while extending 1000 metres from each end.

  4. 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 building interior's representation with a volume level of detail organization.

    Suppose that the building interior's feature representation is being considered, so that it is being represented as one branch of a < Level Of Detail Related Features> instance in a geodetic spatial reference frame, and that the interior volume of the building can be represented as a parallelepiped. 

          <Level Of Detail Related Features>
        <>
        |
        | - - - <Volume Level Of Detail Data>
        |       outside = SE_FALSE
        |                 <>
        |                  |
        |       -----------------------------------
        |       |                                 |
        |   <Parallelelpiped Volume Extent>   <GD Location 3D>
        |
        |
      (building interior's feature representation)

    The <Volume Level Of Detail Data> 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 building interior's feature representation (the data represented by this branch) is active only when the viewer is inside (that is, not outside) 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

Composed of (two-way)

Component of (two-way)(inherited)

Inherited Field Elements

This class has no inherited field elements.

Field Elements

SE_Boolean outside; (notes)

Notes

Composed of Notes


Location_3D

 This specifies the centre of the volume.

Volume_Extent

 This specifies the shape of the volume.

World_Transformation

 This locates and orients the volume within the currently scoped
 spatial reference frame.

Fields Notes


outside

 For a <Volume Level Of Detail Data> instance associated with
 a given branch of a volume-based level of detail aggregation,
 outside is SE_TRUE if that branch is switched on when the
 observer is outside the volume, and off when the observer
 is inside the volume. If outside is SE_TRUE, this behaviour
 is reversed.
Prev: Volume Geometry. Next: Volume Light Behaviour. Up:Index.

Last updated: October 1, 2002 Copyright © 2002 SEDRIS™