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