
Mark wrote:

      Another issue is storing data for our four circle diffractometer.      
      At each step of the measurement, a set of angles has to be stored together
      with a histogram. This collection is what I call a frame. I'am going
      to store this as a NXdata vGroup per frame. No new entry as should be,
      but I feel the overhead is to big. This looks like:
      entry1, NXentry
	      TRICS, NXinstrument 
		      ............
	      sample, NXsample

	      frame1, NXdata
	      frame2, NXdata
		   .
		   .
		   .
	      framen, NXdata
      Any outcries on this one?

Yes, here's mine:
	
	AAAARGH! 

Actually, I am not that upset. However, because of overhead/performance/simplicity issues,
I'd personally go for 

      entry1, NXentry
	      TRICS, NXinstrument 
		      ............
	      sample, NXsample

	      data, NXdata
		 phi   SDS (vector, n points)
		 theta SDS (vector, n points)
		 omega SDS (vector, n points)
		 datahist SDS (2D array, dimensions n x histSize)

My idea of NXdata is that it is just like a Vtable (except that we
can't use Vtable) with as many rows as there are 'points' in an
experiment. Every column contains a different variable (differentiated
by, say, physical unit---i.e. angles could be in separate columns, as
above, or collected into one 2D array of size n x #OfAngles).

One of columns has the 'signal', which used to be a scalar count (a
point, or 0D detector), but could be a vector (for 1D detector) or
even image (for 2D detectors). The total dimension of this particular
'column' SDS is then one greater than the dimensionality of the
detector.

Then again, I haven't had to store data from anything but 0D detector yet.
Is there any fundamental problem with this approach?

			przemek klosowski <przemek@nist.gov>  (301) 975-6249
			NIST Center for Neutron Research (bldg. 235), E111 
			National Institute of Standards and Technology
			Gaithersburg, MD 20899,      USA
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