As of Thu Jan 18 20:55:05 2018

DSKEW: Interpolate an image to correct for input skew/rotation


                                   Input image
INNAME                                Image name (name)
INCLASS                               Image name (class)
INSEQ              0.0      9999.0    Image name (seq. #)
INDISK             0.0         9.0    Image disk drive #
                                   Output image
OUTNAME                               Image name (name)
OUTCLASS                              Image name (class)
OUTSEQ            -1.0      9999.0    Image name (seq. #)
OUTDISK            0.0         9.0    Image disk drive #
BLC             0.0      4096.0    Bottom left corner of image
                                     0=>entire image
TRC             0.0      4096.0    Top right corner of image
                                     0=>entire image
IMSIZE          0.0                Output image size pixels
REWEIGHT        0.0         4.0    (1) Interpolation halfwidth
                                   (2) Minimum fraction of good
                                       pixels required (0->1/3)


Type: Task
Use: DSKEW does an interpolation of one image to correct for any skew
     or rotation.  FITS image files from other institutions,
     particularly optical telescopes have coordinates described by
     PCi_j or CDi_j keywords in the FITS header.  IMLOD and FITLD
     attempt to interpret these and are succesful when the coordinates
     are simple.  However, frequently some degrees of skew is found
     by the optical software when fitting the image coordinates.
     Since AIPS does not support skew in its image coordinates, DSKEW
     is intended to read the PCi_j or CDi_j keywords back out of the
     image history file and write an image interpolated onto a
     coordinate grid very similar to the input grid but without the

     Interpolation is done only in the first 2 dimensions.  Unlike
     HGEOM, DSKEW will interpolate over blanked pixels so that it can
     fill in small blanked regions and handle edges without having to
     discard image area.
     NOTE: the input subimage is read into dynamically allocated memory.
     Very large input arrays may cause swapping on your computer.

  INNAME......The input image name.   Standard defaults.
  INCLASS.....The input image class.  Standard defaults.
  INSEQ.......The input image sequence number. 0 => high
  INDISK......The input image disk drive no. 0 => any
  OUTNAME.....The output image name.  blank => Standard
              defaults based on INNAME.
  OUTCLASS....The output image class.  Standard behavior.
  OUTSEQ......The output image seq. no., 0=> highest unique
              If >0; image will be created if new,
                overwritten if image name exists.
  OUTDISK.....Output disk drive no., 0=> highest with space
  BLC.........The bottom left-hand pixel of the input image
              which becomes the bottom left corner of the
              input subimage.  The value (0,0) means (1,1).
  TRC.........The top right-hand pixel of the input image
              which becomes the top right corner of the
              subimage.  The value (0,0) means take the top
              right hand corner of the image.
  IMSIZE......Output image size.  0 -> input image size after BLC and
              TRC are applied
  REWEIGHT....Interpolation kernel parameters:
              (1) Half width of the interpolating kernel
                  (1 - 4).  Default = 1
                  Larger support sizes should produce more accurate
                  results at the cost of increased computation.
                  However, if the image contains very small features,
                  larger values may produce curious "overshoots" so
                  that the output image has a rather larger maximum
                  and rather more negative minimum than the input.
              (2) Minimum fraction of pixels in interpolation kernal
                  area required for non-blanked output.
                  <= 0 or >= 1  => 0.333