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Array File Specifications

Array File Specifications

SAOtng can load array files containing "raw" images. In order to do so, the program needs to know the following information about the file:

This information is added to an array filename using the IRAF bracket specification: 


  foo.array[xdim=xdim,ydim=ydim,bitpix=bitpix,skip=skip]

The keywords can be placed in any order. The skip keyword is optional and defaults to 0. The bitpix keyword takes on the same value as would be used in a FITS file:

In addition you can specify unsigned short ints using:

The contents of such an array should be unsigned shorts, not signed ints that have been shifted (as is done in conventional FITS images). Of course, this use of -16 for bitpix is not legal in FITS images, but is a convenient convention for use in arrays.

Thus, one can load a 700 x 600 short int FITS image that has a 2880-byte header using: 

  foo.fits[xdim=700,ydim=600,bitpix=16,skip=2880]

Of course, the FITS header will be ignored in this case (i.e., no WCS display).

The array specification can be shortened by leaving out the brackets and using positional values instead. The meaning of the numbers entered after the filename depends on the number of values entered:

Thus, a 512 x 512 array of any type without a header can be specified as: 


  foo.arr 512
while a 600 x 700 double array with a 1024-byte header can be specified as: 
  foo.arr 600 700 -64 1024

For convenience, the above syntax can be input in a shortened form: 

  foo.arr[aa=]
where spec is of the form: 
  {type}{xdim}[.{ydim}][:{skip}][{endian}]
Type is one of the following:
Note that xdim is required, but ydim is optional and defaults to xdim. Skip is optional. Endian is optional but can be 'l' or 'b'.

Example: