[Nexus] Triple Axis Spectrometer definition

Peterson, Peter F. petersonpf at ornl.gov
Tue Aug 5 16:01:15 BST 2003


First I would like to put in a plug for the NeXus swiki at <http://www.neutron.anl.gov.:8080/NeXus> which would be a better place to post the definition since people can edit it without sending the file back and forth (under 'NeXus instrument definitions'). This also allows for definitions to be pulled out and added to the NeXus site at a later date.

Correct me if I misread your message,  but it seems as though you want to store the data with redundant axes. I agree with Mark that only quatities that are varying in the scan should be in the NXdata, but redundant axes could be very useful. This is a very interesting idea since who knows better how to convert detector positions to (Qx,Qy,Qz,E) than the person running the instrument and writting out the data? Would it make sense to have a 'signal'-like attribute on the axes as well as the data to sort out which set of redundant axes go together? Of course, the more flexible you make the standard, the tougher you make life for those trying to make a generic reader, so we should be careful.

About the TAS definition in particular (WARNING I have limited TAS knowledge): could the instrument borrow definitions from other instruments depending on the mode it is running in. For example, if you are performing an elastic powder measurement you could use 'mononxpd'. Only in the case when your measurement cannot be described by something else would you fall back on the TAS definition. Remember that each NXentry can be a different analysis type.

Finally, some notes about your file NXmononxtas.xml:
  - Any tag that does not start with 'NX' is assumed to denote the name of the group. If you do not define a type it is assumed to be 'NX_CHAR'.
  - For your 'NXdata' you have some coments describing what is going on. I recommend that you change the 'NXdata' start tag to be:
    <NXdata name="off-off|off-on|on-off|on-on">
That way validation code can more easily use it.

Peter Peterson

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