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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
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