The images have a very slightly lossy compression applied, and are subsequently very efficiently losslessly compressed with bzip2.
Convert image format atlas how to#
The astrometry algorithms page describes how to use the astrometric calibration information. In case the full astrometric solution is desired, it is included as an HDU in the file. The image headers have WCS headers that have been corrected to align correctly with the final astrometric solution, but without the polynomial distortion terms. The effective smoothing length for the sky background used in these images is around 2 field widths, or 20 arcmin, as opposed to about 2 arcmin for the photometric pipeline. The 'global' method used for creating these images is different from, and far less aggressive than, that applied by the photometric pipeline. The sky-subtraction is described in the algorithms page. When searching for RA and DEC, SAS will return the field which is 'primary' at that location according to the resolve algorithm.
The SAS provides an image search tool, using RUN, CAMCOL, FIELD or RA, DEC, that returns these corrected frames. The information about the calibration and sky-subtraction is provided, and can thus be backed-out if necessary. These images are calibrated in nanomaggies per pixel, and have had a sky-subtraction applied. See the frame datamodel, which explains the format in detail.
Convert image format atlas archive#
The Science Archive Server provides the survey images, called 'corrected frames', as 'frames-*.fits.bz2' files. Additionally, the SAS is able to produce and return an arbitrary FITS mosaic using the corrected frames. The SDSS photo software has estimated the PSF from the images, and this information is described in the PSF section below.Ĭonvenient tools for searching for images of interest are available on SAS as well (by run, camcol, field, or by RA and Dec). To use the images, it is useful to know the point-spread function (PSF). The atlas images correspond to what the imaging catalog actually measured its parameters from.
atlas images for each object (sky-subtracted, but uncalibrated).corrected frames for each field and band (sky-subtracted, calibrated).The Science Archive Server provides two versions of the FITS images, which can be used for quantitative analysis: The data access page links to various query forms on CAS to get images by coordinates, or to search for objects from the imaging and spectroscopic catalogs by redshift, object magnitude, color etc., and to retrieve the corresponding data from the SAS. See its documentation (or just browse the list of tools on that site) to learn how to use it. The Catalog Archive Server provides an flexible interface to JPG images for finding charts, cutouts for object lists, and point-and-click navigation.
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