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:

xdim -- the width of the file in pixels
ydim -- the height of the file in pixels
bitpix -- the data type of each pixel
skip -- the size of the header to skip (in bytes)

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:

8 -- unsigned byte
16 -- 2-byte signed integer
32 -- 4-byte signed integer
-32 -- 4-byte float
-64 -- 8-byte float

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:

xdim -- assume that xdim and ydim are equal. Assume no header to skip. From this, calculate the data type based on the file size.
xdim bitpix -- assume that xdim and ydim are equal. Assume no header to skip.
xdim ydim bitpix -- use values as assigned, assume no header to skip
xdim ydim bitpix skip -- use values as assigned and skip a header

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

If an array specification is sent to SAOtng from the Unix shell, the file name and specification must be enclosed in quotes. Quotes are not required from the Load a New Image menu option.

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Last Updated May 1, 1995