DS9 and IMALIGN

1. Pick your stars
   Pick your stars

   1. Use the DS9 regions tool: Edit:Pointer
   2. Select the arrow point (or a point of your choice): Regions:Shape:Arrow Point
      
   3. Click on a selection of non-saturated but bright point sources (stars)
      
2. Output your star list to a text file
   Output your star list to a text file

   1. Change the output format for the DS9 Region File: Regions:File Format:X Y
   2. Change the file coordinate system: Regions:File Coordinate System:Image
      
   3. Save the region file: Regions:Save Regions...
      (e.g. starcoords.txt)
3. Find relative shifts between images
   Find relative shifts between images

   1. Load all of your images into DS9 (either Frame:New Frame and File:Open or ds9 ngc6888_4m_Ha_[0-3].fits & )
   2. Load regions (Regions:Load Regions...) or select all, copy, and paste
   3. Tab key or Frame:Next to switch between frames
   4. Create a Ruler region (Regions:Shape:Ruler), draw it between a star and the point region associated with that star
      
   5. Double-click the ruler and find its X,Y dimensions
   6. Record delta-X and delta-Y from the ruler. Remember that you want the signs that match REF-IMAGE and that the shifts only have to be accurate to within a few (about 5) pixels
      (e.g. shiftlist.txt)
   7. Copy and paste all regions, modify your ruler region, and repeat the previous two steps for each image

   
   Alternatively, just use the 'c' key to find the coordinates of your cursor and write that to the 'Coordinates' screen in DS9. You can then put that into a file and do (ref-coordinate) for each line using awk:
   awk '{printf("%5i %5i", refx-$1, refy-$2)}' ds9coordlist > shiftlist.txt
   
   
4. Run imalign
   Run imalign

   1. Make the fits input/output lists
      e.g. ls target1_[1-3].fits > inlist.txt
cat inlist.txt | sed 's/.fits/_align.fits/' > outlist.txt
   2. Run imalign:
      imalign @inlist.txt target1_1.fits starcoords.txt @outlist.txt shifts=shiftlist.txt