[neutron-mc] McStas Polarisation details

[Kristian Nielsen]

"Dalgliesh, RM (Robert)" <R.M.Dalgliesh at rl.ac.uk> writes:

> It looks as if the neutron polarisation direction is rotated with the
> objects.

Now, it is admittedly a long time since I've been active with McStas :-)
But it looks to me as if you fundamentally misunderstand the use of
ROTATED in McStas.

When you say ROTATED in the instrument file, it means that you
physically change the orientation of the component. When you turn your
coffe cup upside down, certainly all other properties of the cup changes
orientation with it, _except_ for gravity which doesn't change and so
your coffe spills out!

If on the other hand you want to control the polarisation direction of a
polarised mirror relative to the mirror geometry itself, that needs to
be given as a parameter to the component, and the component code must
handle the appropriate calculation itself. That would correspond to
programming a coffe cup where the orientation of the handle could be
changed.

Hope this helps, and sorry if after five years of no McStas work I am
talking complete nonsense.

 - Kristian.