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uchscale stsdas.hst_calib.wfpc



uchscale -- Update plate scales of WFPC2 (or WF/PC) images


uchscale infile newscale


The task updates the plate scales of WFPC2 (or WF/PC, if necessary) images by updating the CD matrices. The plate scale values used by the pipeline to populate WFPC2 files have undergone changes since the instrument was first commissioned. This task can be used to update the CD matrices of earlier observations to the more accurate plate scales and therefore cohere with images obtained at different epoches. A history of the updating will be added to the image header.


infile [string]
Input images.
newscale [string]
New plate scales to be used in the image(s). The plate scale values should be delimited by commas or spaces. If this parameter is given a null value, the task will simply print out the current plate scales for the user to examine and nothing is updated.

The input plate scales can be in either arcseconds per pixel or degrees per pixel. The task recognizes which unit to use from the plate scale's numerical range. On the other hand, this capability restricts this task's application to WFPC2 and WF/PC only. Unreasonable plate scale values will stop the task.

If the input image has more groups than the input plate scales, the last plate scale in the list will be repeated for the subsequent groups. For example, if newscale="0.046 0.0997", then group 2, 3, and 4 will all use 0.0997 as the new plate scale.


1. Change the plate scales of abc.c0h to 0.046, 0.101, 0.102, 0.103 (arcseconds per pixel).

wf> uchscale abc.c0h "0.046 0.101 0.102 0.103"

2. Examine the plate scales of all .c0h files.

wf> uchscale *.c0h ""

3. Update the plate scale of group 2 of all .c0h files to 2.7694^-5 deg/pixel.

wf> uchscale *.c0h[2] "2.7694e-5" 



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