1) Converts between direction definitions in VITESS:
Cartesian: X = main propagation axis,
Y = horizontal axis (left positive),
Z = vertical axis (upward positive).
Spherical: Theta = Angle with the +X axis,
Phi = Angle of the YZ projection with the +Y axis.
Euler: How to transform vector into (1 0 0 )?
Rotates +X into chosen direction i.e. +X''= direction.
Alpha = First frame rotation angle around the Z axis,
Beta = Second frame rotation angle around the new Y axis.
2) Performs Euler frame rotations as next option.
IMPORTANT: Positive rotation of frame means rotation of one positive
axis towards a higher index positive axis : +X->+Y, +Y->+Z, +X->+Z
Last modified: Thu Jan 29
15:15:00 MET 2004, G.Zs.