See the
WFPC2 Drizzling overview and general tips,
to find a cookbook and/or sample dataset that
best represents your dataset, with regards to
target placement and
pointing strategy.
Cookbook for single images with the target placed on the PC chip (only)
These instructions are intended for single images or sets of images where
it is undesireable to combine multiple images,
for example, datasets involving moving targets or transient phenomena.
De-archive the science and data quality FITS files to your working
directory. Make a uref directory and download the distortion reference files
(IDCTAB and OFFTAB in your image headers) into it, and define your uref
directory (set uref). Convert the files to GEIS format (with strfits):
> set uref = "/data/mymachine/uref/"
> strfits *c0f.fits "" ""
> strfits *c1f.fits "" ""
PyDrizzle parameters
The following are sample parameters (with some rationale in the comments)
for applying the geometric distortion correction to single images
(no image combination).
Some of the default parameters
are not listed here.
> unlearn pydrizzle # reset all parameters to default values first
pydrizzle.input = 'u9xb0101m.c0h'
pydrizzle.output = 'jupiter_f410m' # target_filter filenaming
pydrizzle.section = '1' # process PC chip only
pydrizzle.kernel = 'square'
pydrizzle.units = 'cps' # counts or cps
pydrizzle.pixfrac = 1.0
pydrizzle.rotate = yes # if you want North up
pydrizzle.orient = 0.0 # if you want North up
pydrizzle.psize = '0.0455' # PC pixel scale
pydrizzle.xsize = 1024
pydrizzle.ysize = 1024
pydrizzle.bits_single = 0
pydrizzle.bits_final = 0
pydrizzle.wt_scl = 'exptime'
pydrizzle.fillval = 0.0
pydrizzle.idckey = 'idctab'
pydrizzle.single = no
pydrizzle.clean = yes
pydrizzle.save = no
pydrizzle.build = no
Inspect your output and iterate as needed
You may wish to set fillval=INDEF, or set bits to include some types of
flagged pixels,
rather than having empty pixels in the output image.
There are several methods available to remove cosmic rays and detector artifacts
from single images, and/or cosmetically interpolate over them. This
is beyond the scope of this cookbook, but one method is illustrated in the
Jupiter example (see the README file).
Send any questions or concerns to the STScI Help Desk (help@stsci.edu).
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