iraf.net

Hi, I'm helping a student to set up Iraf to display HST images
properly -- she's been struggling to run some commands (which worked
fine on my own computer), so we found out that while the images are
1600x1600 pixels, the default ds9 display setting was to go up to
500x500. That's when it dawned on me that we had to set stdimage to
something sensible, so we added "set std image = imt2048" to the
login.cl file, restarted everything and displayed the image again --
now the actual image coordinates go up to 2048x2048 (and not to the
native size). What are we doing wrong? How can we get the display to
only go up to the native image size? Thanks!

I'm not sure I completely understand what you're seeing: The 'stdimage' sets the size of the image display buffer, if the image is larger than this then then only the central portion of the image will be displayed (i.e. the central stdimage size), if the image is smaller then the image will be centered in the frame with blank space around the outsides. Using the DISPLAY task 'fill' parameter will scale the entire image (up or down) to fill exactly in the stdimage size. In this latter case the DS9 'image' coords will report the position in terms of the frame buffer size, however the 'physical' coords will be in terms of the physical image size (and of course there are no WCS coords because DS9 is broken that way when displaying from IRAF). You could try "cl\$this->_split2($m[0]) unlearn display" in case your confusion is coming from the fill scaling.

OTOH, if you load the image from a DS9 menu or on the command line it creates its own frame buffer the size of the image. If the coordinate you're reading is from a cursor read then I'm not sure how it interacts with the stdimage size but would imagine it depends on the DS9 version since this behavior keeps changing. Note that in DS9 v7.2 cursor reads are completely broken, and in other recent releases you must use

setenv IMTDEV inet:5137

before you login to the CL to force the use of inet sockets for cursor reads to work properly.