The SEDRIS Data Representation Model
APPENDIX A - Classes
Local 4x4

Class Name: Local 4x4

Superclass - <SEDRIS Abstract Base>

Subclasses

This DRM class is concrete and has no subclasses.

Definition

An instance of this DRM class specifies a 4×4 matrix that is used to scale, orient, and position DRM objects in the scope of its aggregate <LSR Transformation> instance. The direction of rotation is determined by the right-hand rule. The translation parameters are always in the rightmost column of the matrix.

Since a <Local 4x4> instance only appears as a component of an <LSR Transformation> instance and an <LSR Transformation> instance only appears in the scope of an LSR SRF, the DRM objects to which a <Local 4x4> instance is applied are always specified in an LSR SRF.

The matrix multiplication order is defined by w = M × v, where M is the matrix of the <Local 4x4> instance, v is the original location vector, and w is the resulting location vector.

Primary Page in DRM Diagram:

Secondary Pages in DRM Diagram:

This class appears on only one page of the DRM class diagram.

Example

  1. Let A be a <Model> instance representing an airport, and let C be a separate <Model> instance representing a control tower, where A and C are specified in matching LSR SRFs, and A contains a <Geometry Model Instance> instance G that is a reference to C.

    G in A shall have an <LSR Transformation> component, where the position and orientation of the control tower G in A is specified by the <Local 4x4> component of that <LSR Transformation> instance.

FAQs

How is the transformation matrix specified?

The DRM specifies matrices in row major order; that is, the first four elements correspond to the first row of the matrix, the following four elements correspond to the second row of the matrix, and so on (just as a float[4][4] in C is organized). Hence, if mat[][] is the matrix being used, mat[i][j] is the element in row i and column j of the matrix.

What is the multiplication order for the matrices of <Local 4x4> instances?

If M is the transformation matrix of a <Local 4x4> instance and v is a column location vector, the Level 0 API transforms v to a column location vector w by setting w = M × v.

Local 4x4 FAQ, post-multiply

Figure 30 — <DRM Local 4x4> example

Is a matrix in the DRM the same as a matrix in OpenGL?

No. A matrix in the DRM is specified in row major order, while in OpenGL, matrices are specified in column major order (as in the glMultMatrix function). Consequently, to correctly apply DRM transformations in OpenGL programs, each matrix shall be reordered.

Constraints

Component of (two-way)

Inherited Field Elements

This class has no inherited field elements.

Field Elements

SRM_Matrix_4x4 matrix; 1

Notes

Fields Notes

matrix

The matrix field specifies a standard 4 × 4 transformation matrix.


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Last updated: July 26, 2006 Copyright © 2006 SEDRIS