The SEDRIS Data Representation Model
Representing models within an environment

Within this document, a local SRF is an SRF derived from one of the following SRFTs:

  1. LOCAL_SPACE_AZIMUTHAL_2D,
  2. LOCAL_SPACE_POLAR_2D,
  3. LOCAL_SPACE_RECTANGULAR_2D, and
  4. LOCAL_SPACE_RECTANGULAR_3D.

An SRF derived from any other SRF is termed a world SRF.

A <Model> instance can be defined in any SRF. A <Model> instance may be instantiated into another <Model> instance or into a <Environment Root> instance. If a <Model> instance is defined in a world SRF, it can only be instantiated in the DRM object hierarchy of a <Environment Root> instance if there exists a transformation from the model SRF to the target SRF subject to the constraints specified in <<Model SRF>>. 10 SRF operations of ISO/IEC 18026 specifies available transformations.

A <Model> instance defined with a local SRF can be instantiated in the DRM object hierarchy of a <Environment Root> with any SRF defined. In this case, an instance of <World Transformation> is used to specify a transformation from the local SRF of the <Model> instance to the target SRF of the <Environment Root> instance.

A <Transformation> instance allows a <Model> instance to be defined in a local SRF and then instantiated in another SRF, either a world SRF or another local SRF. A <Model> instance can be translated, scaled, and/or rotated as part of the instantiation process. If the model SRF and the target SRF of the other model or environment
root are both derived from a LOCAL_SPACE_RECTANGULAR SRFT, the translation, scale, and/or rotation may be specified by a <LSR Transformation>. Otherwise, the <World 3x3> component of the <World Transformation> instance specifies the rotation and/or scaling data while the <Location> component of the <World Transformation> specifies the translation. If necessary, a local tangent frame shall be constructed in which to apply the transformation specified by a <World Transformation> instance (see 4.7.5 Direction of ISO/IEC 18023-1).

A <World Transformation> instance is used only to instantiate a <Feature Model Instance> or <Geometry Model Instance> instance into a world SRF or into another local SRF. A local transformation, such as a <LSR Transformation> instance, is used by <Feature Model Instance> or <Geometry Model Instance> instances. A local transformation may be used by <Aggregate Geometry> to construct a composite geometry representation where portions of the geometry representation need to be oriented and positioned to other portions of the geometry representation. A local transformation may be also be used by <Property Grid Hook Point> instances to position and orient <Property Grid> instances with respect to other parts of a geometry representation. In a <LSR Transformation> instance, the steps used in transforming are found in the subclasses of <LSR Transformation Step>. The rotation, scaling, and translation are specified with instances of <Rotation>, <Scale>, and <Translation>, respectively.

When an <Feature Model Instance> instance or <Geometry Model Instance> instance is evaluated, the steps for applying a <World Transformation> component are as follows.

Let MI be a <Feature Model Instance> instance or <Geometry Model Instance> instance.
Let W be the <World Transformation> component of MI.
Let Sm = SRF of local model.
Let Sltf = local tangent frame LCE SRF with origin at the <Location> component of W.
Let Sw = world SRF.

Steps:

  1. If Sm is LOCAL_SPACE_AZIMUTHAL_2D, LOCAL_SPACE_POLAR_2D, or
    LOCAL_SPACE_RECTANGULAR_2D, use SRM operations (see 10 SRF Operations of ISO/IEC 18026) to convert all locations and reference vectors to LOCAL_SPACE_RECTANGULAR_3D.
  2. Left multiply all resulting model LSR_3D locations and reference vectors by the 3x3 matrix specified by the <World 3x3> component of W. Renormalize unit vectors, if necessary.
  3. Identify each location and reference vector in Sm with its corresponding location and reference vector equivalent in Sltf.
  4. Use SRM operations (see 10 SRF Operations of ISO/IEC 18026) to convert each location in Sltf to a location in Sw.


Return to:Top of this Page

Last updated: July 26, 2006 Copyright © 2006 SEDRIS