Utility that transforms 3x3 rotation matrix into rotation axis-angle 4-vector
A rotation with respect to an initial orientation has many equivalent representations. A common and important one is the 3-by-3 orthogonal rotation matrix R, where R-1 = RT and RTR = RRT = I, the 3-by-3 identity matrix. Another important representation is the combination of rotation axis (a unit vector n) and angle of rotation θ about that axis. The sign of rotation follows the right-hand-rule.
The RotationMatrix2VR block converts the 3-by-3 rotation matrix representation of orientation to its equivalent representation as a rotation axis and angle about that axis, the form used in Virtual Reality Modeling Language (VRML) for orienting bodies. The input and output signals are bundled Simulink® signals.
The most common use of rotations is to represent the orientation of a body with respect to some coordinate system (CS) axes.
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The rotation matrix R has the form:
The input signal to the RotationMatrix2VR block is the R matrix components passed column-wise and bundled into a single 9-component Simulink signal: [R11 R21 R31 R12 ...].
The output signal is the equivalent rotation represented as the axis of rotation, a unit vector n = (nx,ny,nz), with
n·n = nx2 + ny2 + nz2 = 1,
and the angle of rotation θ about that axis. The sign of the rotation follows the right-hand rule. The output signal is bundled into a single 4-component Simulink signal:
[nx ny nz θ].
For more on virtual reality and VRML, see the 3D Animation™ User's Guide.