[Nexus] Beamline description using Nexus

Benjamin Watts benjamin.watts at psi.ch
Mon Jan 22 14:30:30 GMT 2018

Hi Heike,
    Just a quick answer on your final question: To describe a beamline, 
you should focus on the NXinstument base class:

An application definition describes the necessary components/ingredients 
required to adequately define a particular type of experiment. Hence, an 
application definition might give some requirements for the instrument 
description, but it is also possible that it doesn't (just certain data 
types being recorded could be enough to satisfy the application 
definition). So while the application definition for a particular 
experiment is worth checking when you want to describe a beamline that 
performs the corresponding experiment, don't expect it to give you a 
simple checklist you can complete and declare the job is "done". I would 
recommend that you just go through each component of the beamline and 
add items to the NXinstrument until you are satisfied.

It is also very likely you will find shortcomings in the NeXus base 
classes. You are doing the right thing by asking for advice on this 
list, but please also be prepared to make extensions to the base classes 
in order to make your apparatus correctly specified. We don't expect 
NeXus to be complete and we will be happy to update the standard with 
any reasonable extension you propose.


On 22/01/18 15:06, Heike Görzig wrote:
> Hi,
> I am Heike Görzig working at HZB in Berlin in a BMBF financed project on
> data management with focus on metadata.
> To begin with, I want to describe the BESSY II beamlines using nexus. As
> starting point we found useful using the XML file generated by the
> simulation software RAY-UI, which is available for many beamlines at
> At the beamlines at BESSY II we are using gratings quiet often.
> NXgrating is defined as a base class in the Nexus definitions, but I
> can't create a NXgrating using nexpy or nexusformat in python3. Normally
> it should be possible, or am I wrong here?
> The other question I have, might be a bit out of scope of the intention
> nexus was created for, but I believe some of you might have run into the
> same challenges and it would be great to get advices from you and not
> adding more variety to the list a common challenge can be dealt with.
> There are three very concrete questions:
> In the simulation software the size of e.g. a mirror or grating is very
> important as well as the slope error, but therefore I can't find
> anything in the nexus definition. Has someone of you managed this?
> The other question I have is about the layers in mirrors. For substrate
> and coating there is a roughness defined, but not so for the layers.
> Otherwise, the coating is lacking a thickness. Has someone tackled this?
> The next question is more general, if someone of you has created an
> application definition for describing beamlines at their facility and
> how are you relating the beamline description to an experiment?
> Thank you,
> Heike
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