FITS Spatial Region File Convention
A FITS Region binary table defines a spatial region of a 2-dimensional image.
The region file is often used to define an area that is to be included or excluded
from certain data processing operations on the image. The region is specified as
the union or intersection of geometric shapes, such as 'circle' or 'rectangle'.
The REGION table is the FITS equivalent of the ASCII region file that has long been
used by the ds9 image processing program and its predecessor, SAOimage.
August 2008 by Arnold Rots and Jonathan McDowell (Harvard/Smithsonian Center for Astrophysics)
Date and Place of First Usage:
circa 1998, within the Chandra data analysis system, CIAO.
Extent of Usage:
The FITS region files have been extensively used in the analysis of
Chandra images. This region format is supported by the
analysis program, and recently by the
CFITSIO FITS I/O software library.
Comments and/or critques:
Sample FITS File:
The primary array of this file contains a 128 x 128 pixel image that
has been spatially binned by a factor of 64 from the original high resolution
Chandra image (represented in pixel list format).
The 2nd HDU in the file is a region extension that applies to the primary
array image. It
is composed of 3 components: a circle, a box (rectangle), and an ellipse.
The coordinates of the X and Y components are give in pixel units of the original
unbinned image; the TCTYPn, TCRPXn, TCRVLn, and TCDLTn WCS keywords associated
with these columns provide the parameters needed to transform
to RA and Dec sky coordinates.
Sample Header Listing:
Last revised: Monday, 30-Jul-2012 13:00:09 EDT
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