*************************************** World Coordinate System (`astropy.wcs`) *************************************** .. _wcslib: http://www.atnf.csiro.au/~mcalabre/WCS/ .. _Paper IV: http://www.atnf.csiro.au/people/mcalabre/WCS/index.html .. _SIP: http://irsa.ipac.caltech.edu/data/SPITZER/docs/files/spitzer/shupeADASS.pdf .. _ds9: http://hea-www.harvard.edu/RD/ds9/ Introduction ============ `astropy.wcs` contains utilities for managing World Coordinate System (WCS) transformations in FITS files. These transformations map the pixel locations in an image to their real-world units, such as their position on the sky sphere. It is at its base a wrapper around Mark Calabretta's `wcslib`_, but also adds support for the Simple Imaging Polynomial (`SIP`_) convention and table lookup distortions as defined in WCS `Paper IV`_. Each of these transformations can be used independently or together in a standard pipeline. Getting Started =============== The basic workflow is as follows: 1. ``from astropy import wcs`` 2. Call the `~astropy.wcs.wcs.WCS` constructor with an `astropy.io.fits` header and/or hdulist object. 3. Optionally, if the FITS file uses any deprecated or non-standard features, you may need to call one of the `~astropy.wcs.wcs.WCS.fix` methods on the object. 4. Use one of the following transformation methods: - `~astropy.wcs.wcs.WCS.all_pix2world`: Perform all three transformations from pixel to world coordinates. - `~astropy.wcs.wcs.WCS.wcs_pix2world`: Perform just the core WCS transformation from pixel to world coordinates. - `~astropy.wcs.wcs.WCS.wcs_world2pix`: Perform just the core WCS transformation from world to pixel coordinates. - `~astropy.wcs.wcs.WCS.sip_pix2foc`: Convert from pixel to focal plane coordinates using the `SIP`_ polynomial coefficients. - `~astropy.wcs.wcs.WCS.sip_foc2pix`: Convert from focal plane to pixel coordinates using the `SIP`_ polynomial coefficients. - `~astropy.wcs.wcs.WCS.p4_pix2foc`: Convert from pixel to focal plane coordinates using the table lookup distortion method described in `Paper IV`_. - `~astropy.wcs.wcs.WCS.det2im`: Convert from detector coordinates to image coordinates. Commonly used for narrow column correction. Using `astropy.wcs` =================== Loading WCS information from a FITS file ---------------------------------------- This example loads a FITS file (supplied on the commandline) and uses the WCS cards in its primary header to transform. .. literalinclude:: examples/from_file.py :language: python Building a WCS structure programmatically ----------------------------------------- This example, rather than starting from a FITS header, sets WCS values programmatically, uses those settings to transform some points, and then saves those settings to a new FITS header. .. literalinclude:: examples/programmatic.py :language: python Other information ================= .. toctree:: :maxdepth: 1 relax history See Also ======== - `wcslib`_ Reference/API ============= .. automodapi:: astropy.wcs Acknowledgments and Licenses ============================ wcslib is licenced under the `GNU Lesser General Public License <http://www.gnu.org/licenses/lgpl.html>`_.