[NeXus-committee] Proposal for NXcrystal and NXmonochromator

[Eugen Wintersberger]

> The choice of Bragg or Laue orientation is important when calculating 
> the rocking curve profile, whether or not the crystal is used as part of 
> a monochromator.

I entirely agree with you here. However, this is a particular use case
for a crystal in connection with a monochromator. Thus, at least in my
opinion, the "usage" field belongs to NXmonochromator.

> 
> On 03/09/2015 03:14 PM, Eugen Wintersberger wrote:
> > Hi Pete
> >
> > On Sun, 2015-03-08 at 11:48 -0500, Pete Jemian wrote:
> >> Eugen:
> >>
> >> You propose to:
> >> * rename "usage" field to "type"
> >
> > I propose to remove the "usage" field entirely from NXcrystal.
> >
> >> * add "channel_cut" as another possible value
> >
> > And I propose to add a "type" field to NXmonochromator. The possible
> > values for "type" could be "Laue", "Bragg", "Pseudo Channel Cut", and
> > "Channel Cut". Or something in this way.
> >
> >>
> >> As I said before, "channel_cut" is not an alternative to "Bragg" or
> >> "Laue" in its description of crystal orientation.  Most channel cut
> >> crystals use Bragg orientation.  I suggest a new field could be added to
> >> describe "channel_cut".  Another similar term could be
> >> "pseudo_channel_cut" which describes the crystal arrangement of most
> >> synchrotron X-ray monochromators.
> >
> > This would be the "type" field for NXmonochromator. It should identify
> > what type of mono we talk about.
> >
> >>
> >> Like many things in NeXus, the field name "usage" does not seem to fit
> >> so well, as you point out.
> >>
> >> Rather than disrupt the historical use of the "usage" field in NeXus
> >> data files and however many data files have been written with this
> >> field, would it be acceptable to improve the documentation for the
> >> "usage" field?
> >
> > In the best case I would declare it as deprecated. At least from my
> > point of view NXcrystal describes a crystal and not its particular
> > application. But we can leave it there for compatibility reasons and
> > declare it as deprecated.
> >
> > I am not sure if, what I propose, is really the best approach. But for
> > the time being I have no better idea how to deal with the situation.
> >
> > regards
> >    Eugen
> >
> >
> >>
> >> Pete
> >>
> >> On 3/8/2015 10:56 AM, Eugen Wintersberger wrote:
> >>> Hi folks
> >>>     as a result of the recent discussion I would like to propose the
> >>> following changes to NXcrystal:
> >>>
> >>> remove the "usage" field from NXcrystal
> >>>
> >>> It makes no sense there as the way the crystal is used in a particular
> >>> application is entirely unimportant for the particular crystal itself.
> >>>
> >>>
> >>> Furthermore I would like to suggest the following change to
> >>> NXmonochromator
> >>>
> >>> add a "type" field to NXmonochromator
> >>>
> >>> This field should basically hold the values of "usage" from the current
> >>> NXcrystal class. I would also suggest to have an additional possible
> >>> value "channel_cut" available for this field.
> >>>
> >>> Best regards
> >>> Eugen
> >>>
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