[Nexus] UB matrix in NXsample

[V. Armando Solé]

Dear colleagues,

I am trying to map the orientation matrix (UB in the SPEC jargon) to the
appropriate place in the NXsample group
(http://download.nexusformat.org/doc/html/classes/base_classes/NXsample.html#nxsample)

My understanding is that it should be under orientation_matrix however I
face some difficulties:

- The format is [n_comp, 3, 3]. I would be expecting a 3x3 matrix. So, I
guess if there is only one composition or type of crystal, the format
has to be [1,3,3]

- Do you call orientation_matrix to the UB product in Busing and Levy or
just the matrix U? Very often one just has the product UB and it would
be cumbersome to have different meanings as function of having the
(optional) cell parameters or not in order to build the B matrix. If you
actually mean the U matrix, I would strongly advice to add the
ub[n_comp, 3, 3] representing UB as a sample dataset field.

As a side question, what is the NXsample/sample_orientation that has
three floats? The only thing I find in Busing and Levy corresponding to
three floats is hkl. If it is that, hkl would have been more explicit.
If it is not that, what is it?

Thanks a lot for your help.

Best regards,

Armando