Adding New File Formats to SAOtng

SAOtng supports FITS files internally, so that a standard FITS image file can be sent directly to SAOtng for display using XPA:

  xpaset SAOtng < foo.fits

Also, when a new file name is sent to SAOtng, the program checks the first 2880 bytes of the file to see if it is a FITS file and if so, processes it accordingly. Support for other image file formats (or any other image format) is added to SAOtng by writing two external file access programs:

a header access program to generate a FITS header describing the full image.
a data access program to generate a FITS image of a specified data section (given the center, dimensions, and block factor). Note that the block factor should be applied after the image extraction so that if xdim=ydim=1024 and block=2, the resulting image is 512x512.

These program pairs are made known to SAOtng at start-up time in a user-configurable ASCII file. When loading an image, the program command lines first are macro-expanded to fill in user-defined arguments and then is executed externally using the system() function (see Macro expansion in SAOtng.

When a new file name is sent to SAOtng, the appropriate header access program is run to gather the overall image dimensions.
The data access program then is run to extract the desired image section, which is scaled to the image display depth and displayed on the screen.
Finally, the data access program again extracts the data section and stores it as raw FITS data for later use (e.g., in order to re-scale the image without having to run the data extraction program again).

The ASCII file that defines the known image files consists of one or more file descriptors, each of which has the following format:

A help line describing the file types
A space-separated list of templates
A space-separated list of file types (not currently used)
The command-line of the image section program
The command-line of the FITS header generation program

Note that blank lines separate the file descriptions and should not be used as part of a description. Also, the '#' character is a comment character.

For example, the default image access file currently contains the following:

#
# File access descriptions:
#	help explanation
#	file template
#	file type
#	header access command
#	data access command

IRAF image files (qpoe, imh, etc.)
*.qp *.imh *.stf
QPOE IMH STF
uiraf x_fmgr.e -b blkfits image=$filename xcen=$xcen ycen=$ycen xdim=$xdim ydim=$ydim block=$block
uiraf x_fmgr.e -b hdrfits image=$filename

SAO cd-ROM FITS binary table X-ray event files
*.xi*
FITS
cat $filename
cat $filename

FITS image files
*.fit *.fits
FITS
fitsextract fits=$filename xcen=$xcen ycen=$ycen xdim=$xdim ydim=$ydim block=$block
fitsheader fits=$filename

New files are added to SAOtng using the -files [file access list] option on the command line. The files in the file access list are then added to the system-support file types.

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Last Updated May 1, 1995