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Removing the '_array_element_size' category or not ?

  • To: imgcif-l@bnl.gov
  • Subject: Removing the '_array_element_size' category or not ?
  • From: Andy Hammersley <hammersl@esrf.fr>
  • Date: Thu, 26 Feb 98 17:33:24 +0100

As I mentioned in the previous e-mail, I'd like to consider putting
the '_array_element_size.size' data item into the 
'_array_structure_list' category. To me this would seem slightly simpler.

While on this aspect, I would like to add one more data item, one to
define the units of each dimension. This would be an enumerated list
of a standard list of possible units e.g. 'metres', 'kilogrammes',
'seconds', 'degrees', 'radians', 'joules', 'keV', 'scans'. 
As you can see we should presumably have standard SI units, and probably some 
commonly used alternatives. An alternative would be to use a 
general term e.g. 'distance', 'weight', 'time', etc., but using the 
units themselves seems slightly clearer to me. These are basically our 
n-dimensional axis labels, but by using a standard list they can be 
automatically processed when appropriate. '_array_structure_list.units' 
might be an appropriate data name.

e.g.

# Define dimensionality and element rastering, sizes, and units
loop_
_array_structure_list.array_id
_array_structure_list.index
_array_structure_list.dimension
_array_structure_list.precedence
_array_structure_list.direction
_array_structure_list.size
_array_structure_list.units
image_1    1      768    1    increasing    100.5e-6 metres
image_1    2      512    2    decreasing     99.5e-6 metres
image_2    1     1000    1    increasing      0.02   degrees
image_2    2      128    2    increasing     50.0    seconds

What are other peoples feelings on the category for 'element_size' and
'units' ? (It clear to me that they belong together). Perhaps, in
particular,  Paul Ellis can make a comment, since he's going to be
writing the I/O library software. 

As presently defined, the equivalent of the above example would be:

# Define dimensionality and element rastering
loop_
_array_structure_list.array_id
_array_structure_list.index
_array_structure_list.dimension
_array_structure_list.precedence
_array_structure_list.direction
image_1    1      768    1    increasing
image_1    2      512    2    decreasing
image_2    1     1000    1    increasing
image_2    2      128    2    increasing

# Define element sizes, and units
loop_
_array_element_size.array_id
_array_element_size.index
_array_element_size.size
_array_element_size.units
image_1    1      100.5e-6 metres
image_1    2       99.5e-6 metres
image_2    1        0.02   degrees
image_2    2       50.0    seconds


If, I'm the only one who feels that the categories should be combined,
then I suggest that we leave them as presently defined, and the 'units'
data item joins the '_array_element_size' category.

I think once this aspect is decided, we have everything needed to define
abstract arrays (and now slightly less abstract owing to the 'units').
Then will come the experiment geometry ...


   Andy


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