[Nexus] Geometric information in NeXus

[Johnson, G (Greg)]

 Hi folks,
  I met a number of you at NOBUGS a few weeks back. While I am 
  more a user than a beamline scientist, we are interested in colocating 
  datasets gathered on a variety of different instruments as part of our
Engineering
  Body Scanner project.  For example, we'd like to be able to overlay our
x-ray 
  tomography renderings with x-ray or neutron strain maps.

  Although I've got a number of thoughts and questions about NeXus
  (which we've decided to use as our core data format) this particular
  email is about adding a new instrument definition (or perhaps a
  sample description - I'm not sure).  In order for us to be able to
  co-locate datasets, we obviously need to know exactly where in the
  sample the data was measured.  So we have a need to store some
  fairly detailed geometric information about the sample.  In the
  first instance, the sample could be modelled as a primitive piece of
  geometry (cylinder, plate, cuboid, etc.)  But we have a CMM (3d
  digitiser) that we will use to generate quite accurate surface
  models - storing that surface data (a set of polygons/points) is the
  subject of my query.

  Could we treat the geometric data similar to that from any other
  instrument?  Require an NXentry for it, using a NXinstrument called
  'NXgeometry'|'NXdigitiser'|'NXsurface' (any suggestions?) and then
  store the surface itself in the NXdata element?

  But the NXdata element doesn't really seem to be the right place for
  the geometric info - at least, it would require entirely new fields
  to store them in (vertices, topology, precision, fiducial markings,
  etc).  Could NXdata be extended dramatically to incorporate spatial
  information like this?


  I've been trying to look at example files, and found Peter
  Peterson's TOF XML def'n very helpful (using XML Spy - are there
  other XML editors that are widely used?)  I can certainly craft
  something on the basis of that and submit it for substantial
  revision that would be helpful.  (Who can I burden with it???)

Many thanks for your time!

cheers,
greg  

============================================================================
Greg Johnson                              Manchester Materials Science
Centre

Phone (Manchester): +44(0)161 2008959     Manchester University
Fax (Manchester):   +44(0)161 2003586     Grosvenor Street
Phone (St Andrews): +44(0)1334 463080     Manchester M1 7HS
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Email:          greg.johnson at ieee.org
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