[Nexus] NeXus update

[Pete Jemian]

On 1/21/2015 11:25 AM, V. Armando Sole wrote:
> To store x and y as (n_rows, ncolumns) with the product n_rows *
> n_columns equal to n_points is *not* convenient.

This is exactly the case for multi-dimensional data acquired with the 
EPICS "sscan" record and stored in APS "MDA" data files.  We have many 
beam lines at the APS using this.

In many cases, saving x as float[n_rows] is just fine.  In some cases, x 
is from a readback device with jitter or drift.  That's when x must be 
stored as float[n_rows * ncolumns].  It's a real nuisance to store this 
and visualize, but that is the real-world situation.

Prior to December 2014, NeXus had no tools to describe this structure 
for visualization.  NeXus should make it possible to represent this type 
of data but it should not be required for all data to use this 
structure.  The 1% case should not require the 99% to abide by the same 
requirements but the 99% should not rule out the possibility of the 1%.

Pete

-- 
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Pete R. Jemian, Ph.D.                <jemian at anl.gov>
Beam line Controls and Data Acquisition, Group Leader
Advanced Photon Source,   Argonne National Laboratory
Argonne, IL  60439                   630 - 252 - 3189
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