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WCS_ROTATE

WCS_ROTATE

Name


      WCS_ROTATE

Purpose


      Rotate between standard (e.g. celestial) and native coordinates

Explanation


      Computes a spherical coordinate rotation between native coordinates
      and standard celestial coordinate system (celestial, Galactic, or
      ecliptic). Applies the equations in Appendix B of the paper
      "Representation of Celestial Coordinates in FITS" by Calabretta
      Greisen (2002, A&A, 395, 1077). Also see
      http://fits.gsfc.nasa.gov/fits_wcs.html

Category


      Mapping and Auxiliary FITS Routine

Calling Sequence


      WCS_ROTATE, longitude, latitude, phi, theta, crval, theta0 =
              [LONGPOLE = , LATPOLE = , PV1 = , /REVERSE, /ORIGIN ]

Input Parameters


      crval - 2 element vector containing standard system coordinates (the
              longitude and latitude) of the reference point
  INPUT OR OUTPUT PARAMETERS
      longitude - longitude of data, scalar or vector, in degrees, in the
              standard celestial coordinate system
      latitude - latitude of data, same number of elements as longitude,
              in degrees
      theta - latitude of data in the native system, in degrees, scalar or
              vector
      If the keyword(REVERSE) is set then phi and theta are input parameters
      and longitude and latitude are computed. Otherwise, longitude and
      latitude are input parameters and phi and theta are computed.

Optional Keyword Input Parameters



      THETA0 - Native latitude of the reference point (required unless PV1 set)
      PV1 - Vector giving parameters of user-defined fiducial point
      LONGPOLE - native longitude of standard system's North Pole
      LATPOLE - native latitude of the standard system's North Pole
      /REVERSE - if set then phi and theta are input parameters and longitude
                  and latitude are computed. By default, longitude and
                  latitude are input parameters and phi and theta are computed.
      /ORIGIN This keyword is obsolete and is no longer used. Replaced by
                  explicitly specifying theta0 and/or PV1

Revision History


      Written W. Landsman December, 1994
      Fixed error in finding North Pole if /ORIGIN and LONGPOLE NE 180
      Xiaoyi Wu and W. Landsman, March, 1996
      Fixed implementation of March 96 error, J. Thieler, April 1996
      Updated to IDL V5.0 W. Landsman December 1997
      Fixed determination of alpha_p if /ORIGIN and LONGPOLE EQ 180
              W. Landsman May 1998
      Ensure argument of ASIN() is -1<x<-1 after roundoff
              W. Landsman/R. Arendt June 2002
      Call WCS_GETPOLE, accept LATPOLE keyword, update cylindrical coords
              W. Landsman June 2003
      Don't attempt to rotate NaN values W. Landsman May 2004
      at some unknown time theta0 introduced
      Traps put in to detect no rotation and avoid rounding errors for
      common special cases. PV1 introduced. Comments updated & corrected.
                                            J. P. Leahy July 2013.
      Avoid roundoff error when longitude = +/- 180 W. Landsman Dec 2013
     



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