[NeXus-committee] More DECTRIS

[Mark Koennecke]

Hi,

Let us assume that NP is the number of frames.

Then the optimal solution in terms of NeXus (and may be HDF-5) would be 
to have an
array data[NP,xsize,ysize]. The problem is that we cannot have the 
optimum because
HDF-5 cannot compress in parallel and DECTRIS does not get the write 
performance
they want without compression and accepting the limitation that they get 
to define the
computer delivered with the detector and are in no position to force 
parallel file systems
on their users. So we need to settle for second best.

This leaves us with the option to put all the links into one NXdata or 
have a NXdata per chunk.
I prefer the NXdata per chunk (but I do not feel strongly about this). 
DECTRIS has
arranged for each of the data chunks to have two attributes: 
image_nr_low, image_nr_high
which makes it clear how to stitch together the data.

Pete: the napimount attribute. This is a historical feature we used to 
support external linking
in HDF-4 and XML which cannot do it natively. NAPI still uses this 
attribute. So, in order to
maintain full NAPI compatibility I ask for this attribute.

Regards,

         Mark

P.S. someone else was already pointing out the image_nr_low etc thing