AIPS HELP file for DSKEW in 31DEC21
As of Thu Dec 2 18:47:48 2021
DSKEW: Interpolate an image to correct for input skew/rotation
INNAME Image name (name)
INCLASS Image name (class)
INSEQ 0.0 9999.0 Image name (seq. #)
INDISK 0.0 9.0 Image disk drive #
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
TRC 0.0 4096.0 Top right corner of 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)
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