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eraRm2v

w = ERFA.rm2v(r)

Express an r-matrix as an r-vector.

Given:

   r        double[3][3]    rotation matrix

Returned:

   w        double[3]       rotation vector (Note 1)

Notes:

  1. A rotation matrix describes a rotation through some angle about some arbitrary axis called the Euler axis. The "rotation vector" returned by this function has the same direction as the Euler axis, and its magnitude is the angle in radians. (The magnitude and direction can be separated by means of the function eraPn.)

  2. If r is null, so is the result. If r is not a rotation matrix the result is undefined; r must be proper (i.e. have a positive determinant) and real orthogonal (inverse = transpose).

  3. The reference frame rotates clockwise as seen looking along the rotation vector from the origin.

This revision: 2021 May 11

Copyright (C) 2013-2021, NumFOCUS Foundation. Derived, with permission, from the SOFA library.