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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.
*
* P.T.Wallace Starlink 4th October 1989
*
* Copyright (C) 1995 Rutherford Appleton Laboratory
*-
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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