[NeXus-definitions-tickets] [NeXusDefinitions] #130: proposal for image_exchange format

[NeXus Base Classes and Instrument Definitions]

#130: proposal for image_exchange format
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  Reporter:  Pete Jemian  |       Owner:  Pete Jemian
      Type:  task         |      Status:  reopened   
  Priority:  minor        |   Milestone:             
Resolution:               |    Keywords:             
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Comment(by Pete Jemian):

 The use of NXcollection/NXpositioners just does not work well because of
 the "axes" attribute.  The "axes" attribute indicates which positioner
 vector corresponds to each axis of the data.  In the NXdata group,
 positioner datasets are at the same level as the "data" (plottable
 dataset).  If we embed those positioners here in
 ./NXcollection/NXpositioner/value, then that "axes" attribute is no good.
 Since the NXdata/data and the  NXdata_exchange/data are hard linked, they
 have the same "axes" attribute. This means the positioners must be at the
 same elevel in NXdata_exchange as the data.

 Here's the way NeXus does the same thing in NXdata:
  1. One of the fields has an attribute signal="1" and this indicates the
 plottable dataset.
  1. The same fields has an attribute called "axes" and this contains a
 colon-delimited list of the positioner names, such as:
 axes="ttheta:energy"
  1. A field with each positioner names in the "axes" attribute must exist
 next to the plottable dataset and the length of that vector must
 correspond to the length of the corresponding axis of the plottable
 dataset.

 We should try that here.
 Extra positioners could be given in an NXcollection/NXpositioners grouping

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Ticket URL: <http://trac.nexusformat.org/definitions/ticket/130#comment:11>
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