| 1 | #include "slalib.h"
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| 2 | #include "slamac.h"
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| 3 | void slaGeoc ( double p, double h, double *r, double *z )
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| 4 | /*
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| 5 | ** - - - - - - - -
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| 6 | ** s l a G e o c
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| 7 | ** - - - - - - - -
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| 8 | **
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| 9 | ** Convert geodetic position to geocentric.
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| 10 | **
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| 11 | ** (double precision)
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| 12 | **
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| 13 | ** Given:
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| 14 | ** p double latitude (geodetic, radians)
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| 15 | ** h double height above reference spheroid (geodetic, metres)
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| 16 | **
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| 17 | ** Returned:
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| 18 | ** *r double distance from Earth axis (AU)
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| 19 | ** *z double distance from plane of Earth equator (AU)
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| 20 | **
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| 21 | ** Notes:
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| 22 | **
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| 23 | ** 1) Geocentric latitude can be obtained by evaluating atan2(z,r).
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| 24 | **
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| 25 | ** 2) IAU 1976 constants are used.
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| 26 | **
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| 27 | ** Reference:
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| 28 | ** Green,R.M., Spherical Astronomy, CUP 1985, p98.
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| 29 | **
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| 30 | ** Last revision: 25 July 1993
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| 31 | **
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| 32 | ** Copyright P.T.Wallace. All rights reserved.
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| 33 | */
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| 34 | {
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| 35 | double sp, cp, c, s;
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| 36 |
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| 37 | /* Earth equatorial radius (metres) */
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| 38 | static double a0 = 6378140.0;
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| 39 |
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| 40 | /* Reference spheroid flattening factor and useful function thereof */
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| 41 | static double f = 1.0 / 298.257;
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| 42 | double b = ( 1.0 - f ) * ( 1.0 - f );
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| 43 |
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| 44 | /* Astronomical unit in metres */
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| 45 | static double au = 1.49597870e11;
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| 46 |
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| 47 | /* Geodetic to geocentric conversion */
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| 48 | sp = sin ( p );
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| 49 | cp = cos ( p );
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| 50 | c = 1.0 / sqrt ( cp * cp + b * sp * sp );
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| 51 | s = b * c;
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| 52 | *r = ( a0 * c + h ) * cp / au;
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| 53 | *z = ( a0 * s + h ) * sp / au;
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| 54 | }
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