distance_sphere_method()

double distance_sphere_method	(	double	lat1,
		double	long1,
		double	lat2,
		double	long2,
		SPHEROID *	sphere
	)

Definition at line 452 of file lwgeom_spheroid.c.

References SPHEROID::a, distance(), SPHEROID::e_sq, geometry_distance_spheroid(), and PG_FUNCTION_INFO_V1().

Referenced by distance_ellipse().

{
        double R,S,X,Y,deltaX,deltaY;

        double  distance        = 0.0;
        double  sin_lat         = sin(lat1);
        double  sin2_lat        = sin_lat * sin_lat;

        double  Geocent_a       = sphere->a;
        double  Geocent_e2      = sphere->e_sq;

        R       = Geocent_a / (sqrt(1.0e0 - Geocent_e2 * sin2_lat));
        /* 90 - lat1, but in radians */
        S       = R * sin(M_PI_2 - lat1) ;

        deltaX = long2 - long1;  /* in rads */
        deltaY = lat2 - lat1;    /* in rads */

        /* think: a % of 2*pi*S */
        X = deltaX/(2.0*M_PI) * 2 * M_PI * S;
        Y = deltaY/(2.0*M_PI) * 2 * M_PI * R;

        distance = sqrt((X * X + Y * Y));

        return distance;
}

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