Name

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      WCS_GETPOLE

Purpose

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      Compute the coordinates of the native pole

Explanation

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      WCS_GETPOLE is used to determine the celestial position of the
      native pole. See section 2.4 of the paper
      "Representation of Celestial Coordinates in FITS" by Calabretta
      Greisen (2002, A&A, 395, 1077, also available at
      http://fits.gsfc.nasa.gov/fits_wcs.html Called by WCS_ROTATE

Calling Sequence

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      WCS_GETPOLE, crval, lonpole, theta0, alpha_p, delta_p, [LATPOLE= AT_POLE=]

Input Parameters

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      crval - 2 element vector containing standard system coordinates (the
              longitude and latitude) of the reference point in degrees
      lonpole - native longitude of the celestial North Pole (degrees)
                *unless* the fiducial point is at non-zero native longitude
                (phi_0 =/ 0), in which case phi_0 should have been subtracted,
                i.e. lonpole = phi_p - phi_0.
      theta0 - native latitude of the fiducial point (degrees)

Output Parameters

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      alpha_p, delta_p - celestial longitude and latitude of the native pole
              (Radians)

Optional Keyword Input Parameters

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      LATPOLE - native latitude of the celestial North Pole (degrees)
                NB only used to resolve ambiguity. Final value is the one
                nearest to input value of LATPOLE. Can be set outside range
                [-90,90]
  OPTIONAL KEYWORD OUTPUT PARAMETERS
      AT_POLE (byte) true if delta_p = pi/2 (avoiding some round-off errors)

Revision History

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      Written W. Landsman June, 2003
      Fix calculation when theta0 is not 0 or 90 February 2004
      E. Hivon: alpha_p, delta_p consistenly in Radians May 2010
      J. P. Leahy introduced AT_POLE, more traps for special cases to
      avoid rounding errors July 2013