This code puts a CCD image in the left window of a ds9 frame (frame1), and a DSS image in the right window (frame2). The DSS image is labeled USNO targets drawn from the USNO catalog (USNO-B1) via the cdfp file usno_targs.cdfp (that is assembled by running the script usno_look.
The user can set regions in the left window AND include text identification numbers. In an early version of this code, the frame1 results are dumped to a regions file named "show.reg" using fk5 coordinates. Hence, it is important to realize that for this to work the frame1 image (your CCD image) must posess WCS info in the header! If no such WCS is installed, then the "show.reg" file is not created.
% usno_identify Usage: usno_identify image_1.fits 17.0 blue 16 arg1 - name of fits image arg2 - V magnitude (faint) limits for USNO catalog arg3 - Text font color (white) arg4 - Text font size (16)In later versions, usno_identify produces a more general set of files that can be used for deriving WCS parameters or at least resetting the fiducial point (i.e. CRPIX1,CRPIX2,CRVAL1,CRVAL2) in an image with an existing, but imperfect, WCS header.
One thing to remember if that the targets in the right panel are labeled only with text names. These "names" are actually just the line numbers (after the header) in the cdfp catalog named "usno_targs.cdfp". You can always do a quick check of the positions using the routine cdfp_rd_by_name. Just plce your cursor on a numbered star in frame to to see the reported Ra,Dec. Note the star number (for example "145"), and then in some other command window just use the command line:
% cdfp_rd_by_name usno_targs.cdfp 145 145 293.17770385742 -6.92472219467 19:32:42.6480 -06:55:28.9999and the RA,DEC values should agree. If they do not, you are probably not using the correct cdfp file.