- NAME
WCS_GETPOLE
- PURPOSE
Compute the coordinates of the native pole
- EXPLANATION
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
WCS_GETPOLE, crval, lonpole, theta0, alpha_p, delta_p, [LATPOLE= AT_POLE=]
- INPUT PARAMETERS
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
alpha_p, delta_p - celestial longitude and latitude of the native pole
(Radians)
- OPTIONAL KEYWORD INPUT PARAMETERS
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
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