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slalib/geoc.f

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+      SUBROUTINE sla_GEOC (P, H, R, Z)
+*+
+*     - - - - -
+*      G E O C
+*     - - - - -
+*
+*  Convert geodetic position to geocentric (double precision)
+*
+*  Given:
+*     P     dp     latitude (geodetic, radians)
+*     H     dp     height above reference spheroid (geodetic, metres)
+*
+*  Returned:
+*     R     dp     distance from Earth axis (AU)
+*     Z     dp     distance from plane of Earth equator (AU)
+*
+*  Notes:
+*
+*  1  Geocentric latitude can be obtained by evaluating ATAN2(Z,R).
+*
+*  2  IAU 1976 constants are used.
+*
+*  Reference:
+*
+*     Green,R.M., Spherical Astronomy, CUP 1985, p98.
+*
+*  Last revision:   22 July 2004
+*
+*  Copyright P.T.Wallace.  All rights reserved.
+*
+*  License:
+*    This program is free software; you can redistribute it and/or modify
+*    it under the terms of the GNU General Public License as published by
+*    the Free Software Foundation; either version 2 of the License, or
+*    (at your option) any later version.
+*
+*    This program is distributed in the hope that it will be useful,
+*    but WITHOUT ANY WARRANTY; without even the implied warranty of
+*    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+*    GNU General Public License for more details.
+*
+*    You should have received a copy of the GNU General Public License
+*    along with this program (see SLA_CONDITIONS); if not, write to the 
+*    Free Software Foundation, Inc., 59 Temple Place, Suite 330, 
+*    Boston, MA  02111-1307  USA
+*
+*-
+
+      IMPLICIT NONE
+
+      DOUBLE PRECISION P,H,R,Z
+
+*  Earth equatorial radius (metres)
+      DOUBLE PRECISION A0
+      PARAMETER (A0=6378140D0)
+
+*  Reference spheroid flattening factor and useful function
+      DOUBLE PRECISION F,B
+      PARAMETER (F=1D0/298.257D0,B=(1D0-F)**2)
+
+*  Astronomical unit in metres
+      DOUBLE PRECISION AU
+      PARAMETER (AU=1.49597870D11)
+
+      DOUBLE PRECISION SP,CP,C,S
+
+
+
+*  Geodetic to geocentric conversion
+      SP = SIN(P)
+      CP = COS(P)
+      C = 1D0/SQRT(CP*CP+B*SP*SP)
+      S = B*C
+      R = (A0*C+H)*CP/AU
+      Z = (A0*S+H)*SP/AU
+
+      END