Module Frame

# VITESS Module Frame

The module frame makes possible a transformation of the initial reference frame (provided by the former module) by rotation, translation and/or mirroring. This might be useful for test purposes or for composing instruments with unusual geometrical arrangements simply by using the provided standard modules and changing with this module the reference frame.

A sequence e.g. rotation -translation-mirroring covers all options for a transformation. However, in order to provide maximal flexibility and to allow for performing the most simple way of transformation, the sequence of rotation(R), transformation(T) and mirroring(M) can also be chosen (the input option "sequence" offers always one out of the six possibilities, default is RTM).

Rotation

In most of the cases only one simple rotation about Z, Y or X is needed. This can be done by giving one rotation angle for the corresponding axis while the other two values have to be set zero (default). The input values are defined in degrees.

IMPORTANT: Positive rotation of frame means rotation of one positive axis towards a higher index positive axis : +X to +Y, +Y to +Z, +X to +Z . That is: A 90° rotation about the Z axis means X+ rotated on Y+; 90° about the Y axis means X+ rotated on Z+; a 90° rotation about the X axis means Y+ rotated on Z+. Negative angle 90° means rotation in opposite direction.

For multiple rotations, it is important to realize that rotation operations are not commutative. On the other hand, three successive rotations of a 3D frame about e.g. Z, Y and X axes cover all possible orientations. This module uses the the following sequence: the first rotation performed is always around the Z axis (horizontal plane), this is followed by a rotation about the new Y (vertical plane containing new X) and finaly about the new X (beam) axes.

Translation

The input parameters are the components "x, y, z" of the translation vector in [cm] which shifts the origin of the coordinate system.
This shift is not meant as a real pysical operation, therefore the neutron time-of-flight is not recalculated according to the length of this vector.

Mirror

Mirroring relative to the YZ , ZX or XY planes means: x changes to -x , y toy or z toz. The three mirror operations can be performed alltogether. Two simultaneous mirroring operations mean a rotation of 180°.

Back to VITESS overview
vitess@helmholtz-berlin.de

Last modified: Thu Jan 29 15:02:26 MET 2004 G.Zs.