Документ взят из кэша поисковой машины. Адрес оригинального документа : http://www.stsci.edu/hst/HST_overview/drizzlepac/DrizzlePac_brochure.pdf Дата изменения: Unknown Дата индексирования: Tue Feb 5 12:00:42 2013 Кодировка:

DrizzlePac
New software for aligning and drizzling HST images, with improved handling of astrometric data
DrizzlePac and its flagship task AstroDrizzle are new software, replacing the Dither package and MultiDrizzle
DrizzlePac in a nutshell:
· Identical or improved output in comparison with MultiDrizzle · All astrometric and distortion information will be included in calibrated images, removing the need for external calibration files · Multiple astrometric solutions, stored in images under uniquelynamed labels, that can be tied to another image, standard catalog, or user-created catalog · Astrometric solutions can be exchanged amongst users in the form of small FITS files called `headerlets' · Task parameter settings can be easily saved to `configuration files' for future use or to share with collaborators · Parallelization will speed up processing of images

Latest updates at

drizzlepac.stsci.edu

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TEAL, a convenient new interface for editing task parameters
DrizzlePac tasks parameters can be set using a new graphical user interface called TEAL (Task Editor and Launcher). Dependencies between parameters can be established to help prevent user errors. Users will be able to edit, save, and load `configuration files,' provided by instrument teams or collaborators that contain specific task parameter settings.

Introducing tweakreg, a powerful new DrizzlePac task for aligning dithered images using point sources
HST images in a single visit are generally well-aligned with each other. However, offsets as large as 0.5" can occur for the same pointing at different visits. tweakreg, a new DrizzlePac task, will align calibrated (flt.fits) images by matching sources between an image and reference image. Source files for each image are created using a routine similar to DAOfind, or can be supplied by the user. For images heavy with cosmic rays, a cosmic ray-cleaned image can be generated by AstroDrizzle for use in tweakreg for improved source identification.

Extended Simple Image Polynomials (SIP), a convention used for expressing image distortion corrections
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where !," are sky coordinates and #,$ are instrumental coordinates. The CD matrix fully represents linear distortion corrections. Other large-scale distortion corrections are expressed as high order polynomials % and &. Look-up tables '()contain high frequency distortion corrections. Small scale detector distortion corrections, if any, are applied to #,$ before use in the equation (only required for WFPC2 and ACS/WFC).


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New extensions in pipeline-calibrated ACS FITS images
Calibrated ACS images from the HST Archive will have additional distortion corrections stored as look-up tables in FITS image extensions. An example of this is shown below for an ACS/WFC image, using the task catfits.
--> catfits jb7310ymq_flt.fits EXT# FITSNAME FILENAME EXTVE 0 jb7310ymq_flt jb7310ymq_flt.fits 1 IMAGE SCI 2 IMAGE ERR 3 IMAGE DQ 4 IMAGE SCI 5 IMAGE ERR 6 IMAGE DQ 7 IMAGE D2IMARR 8 IMAGE WCSDVARR 9 IMAGE WCSDVARR 10 IMAGE WCSDVARR 11 IMAGE WCSDVARR DIMENS 1 1 1 2 2 2 1 1 2 3 4 BITPI OBJECT 16 4096x2048 -32 4096x2048 -32 4096x2048 16 4096x2048 -32 4096x2048 -32 4096x2048 16 4096 -32 65x33 -32 65x33 -32 65x33 -32 65x33 -32

Extensions ([0] through [6]) are familiar: the primary header followed by science, error, and data quality arrays, for chips 2 and 1, respectively. The new `D2IMARR' extension is a one-dimensional vector that holds corrections for physical distortions in the ACS/WFC CCD columns. The new `WCSDVAR' extensions, present for all ACS data, have look-up tables containing residual optical distortions not modeled by the polynomial fits. (`D2IMARR' and `WCSDVAR' distortion corrections used to be in the DGEOFILE reference image used by MultiDrizzle.)

Headerlet, a small FITS file containing a unique astrometric solution
An astrometric solution in an image header can be extracted into a `headerlet,' a small FITS file in a convenient format for sending to other users, or for retrieval from the HST Archive. For instance, users analyzing data from a Treasury program could retrieve headerlets associated with that data in order to use the same astrometric solutions created by other users.
Key references: Fruchter, A. S., Hook, R. N., 1997, "A Method for the Linear Reconstruction of Undersampled Images" PASP Fruchter, A. S., et al., BetaDrizzle: A Redesign of the MultiDrizzle Package, STScI Calib. Workshop, 2010 Gonzaga, S., et al., The DrizzlePac Handbook, STScI 2012

Information regarding DrizzlePac, including the DrizzlePac Handbook, is available at http://drizzlepac.stsci.edu. Questions can be sent to help@stsci.edu.