Output coordinate frames

The output map generated by rebin will contain at least 3 output coordinate frames. They are the GRID, PIXEL and AXIS coordinate frames. For maps regridded in RJ/RB/GA or RD coordinates there will be an additional SKY coordinate frame.

They can be listed with the ndftrace command:

lapaki[M82/short]>ndftrace m82 fullwcs

   NDF structure ..../m82:
      Title:  SURF:remdbm
      Label:  Extinction corrected

   Shape:
      No. of dimensions:  2
      Dimension size(s):  256 x 256
      Pixel bounds     :  -127:128, -127:128
      Total pixels     :  65536

   Axes:
      Axis 1:
         Label : R.A. offset
         Units : arcsec
         Extent: 127.5 to -128.5

      Axis 2:
         Label : Declination offset
         Units : arcsec
         Extent: -127.5 to 128.5

   Data Component:
      Type        :  _REAL
      Storage form:  SIMPLE
      Bad pixels may be present

   Quality Component:
      Storage form :  SIMPLE
      Bad-bits mask:  3 (binary 00000011)

   World Coordinate Systems:
      Number of coordinate Frames      : 4
      Index of current coordinate Frame: 4

      Frame index: 1
        Title               : "Data grid indices; first pixel at (1,1)"
        Domain              : GRID

      Frame index: 2
        Title               : "Pixel coordinates; first pixel at (-127.5,-1..."
        Domain              : PIXEL

      Frame index: 3
        Title               : "Axis coordinates; first pixel at (127,-127)"
        Domain              : AXIS

      Frame index: 4
        Title               : "FK5 equatorial coordinates; mean equinox J20..."
        Domain              : SKY

   Extensions:
      FITS             <_CHAR*80>
      REDS             <SURF_EXT>


   History Component:
      Created    :  1999 Feb 07 17:34:41
      No. records:  9
      Last update:  1999 Jun 16 17:00:07 (MATHS           (KAPPA 0.13-6))
      Update mode:  NORMAL

In the above example, the SKY frame is the current frame (this will be used by KAPPA display) and is set to FK5 J2000. The AXIS frame contains arcsecond offsets from the regrid centre. The PIXEL frame uses pixel indices and rebin ensures that the regrid centre is always at pixel coordinate 0,0 unlike the GRID frame where the pixel origin is always at the bottom left hand corner. The PIXEL frame is used by all KAPPA commands that combine images and also the makemos command in CCDPACK.

For more information on coordinate frames please see Using World Coordinate Systems in SUN/95.