[Nexus] UB matrix in NXsample

[Koennecke Mark (PSI)]

Hi,


> Am 10.04.2017 um 19:40 schrieb Osborn, Raymond <rosborn at anl.gov>:
> 
> Dear Armando,
> Busing and Levy is quite specific in calling U the orientation matrix, so the description in the NeXus base class, i.e., "Orientation matrix of single crystal sample using Busing-Levy convention: W. R. Busing and H. A. Levy (1967). Acta Cryst. 22, 457-464”, implies that we are talking about U. Whether everyone else uses it that way, I can’t say.
> 
> In our own software, we assume that orientation_matrix refers to U and then dynamically generate B from the unit cell parameters. That way, the orientation matrix should, at least in principle, be fixed during an experiment while heating or cooling the sample. Of course, tweaks might be necessary if the sample shifts. I suppose we could add a UB matrix to the list of stored parameters in a NeXus file even though it is technically redundant.
> 

Oops. I have to reread the Busing Levy paper in order to verify that orientation_matrix is so strictly defined. I always use the field 
for storing the UB. Because that is the data which is usually available. The nComp is really for describing the case when there are multiple 
crystals. Thus in the most common case nComp = 1. 

I am also not familiar with the orientation_angle. It is definitely not the angles as angles are stored elsewhere. There are fields for 
rotation_angle (omega) chi and phi. And this goes into NXtransformations anyway. The only thing I can think of what it could relate to 
is the plane normal in the Lumsden triple axis calculation. 


Best Regards,

     Mark

> We have another issue to do with where we store the orientation matrix (sample or detector). In principle, the NXsample group is the correct location, but there are circumstances where we would prefer it to be in the NXdetector group, but that should be the subject of another thread. 
> 
> With best regards,
> Ray
> 
>> On Apr 10, 2017, at 10:44 AM, V. Armando Solé <sole at esrf.fr> wrote:
>> 
>> 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
>> 
>> 
>> 
>> 
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> 
> -- 
> Ray Osborn, Senior Scientist
> Materials Science Division
> Argonne National Laboratory
> Argonne, IL 60439, USA
> Phone: +1 (630) 252-9011
> Email: ROsborn at anl.gov
> 
> 
> 
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