sphere_direction()

double sphere_direction	(	const GEOGRAPHIC_POINT *	s,
		const GEOGRAPHIC_POINT *	e,
		double	d
	)

Given two points on a unit sphere, calculate the direction from s to e.

Definition at line 979 of file lwgeodetic.c.

{
        double heading = 0.0;
        double f;
 
        /* Starting from the poles? Special case. */
        if ( FP_IS_ZERO(cos(s->lat)) )
                return (s->lat > 0.0) ? M_PI : 0.0;
 
        f = (sin(e->lat) - sin(s->lat) * cos(d)) / (sin(d) * cos(s->lat));
        if ( FP_EQUALS(f, 1.0) )
                heading = 0.0;
        else if ( FP_EQUALS(f, -1.0) )
                heading = M_PI;
        else if ( fabs(f) > 1.0 )
        {
                LWDEBUGF(4, "f = %g", f);
                heading = acos(f);
        }
        else
                heading = acos(f);
 
        if ( sin(e->lon - s->lon) < 0.0 )
                heading = -1 * heading;
 
        return heading;
}

References FP_EQUALS, FP_IS_ZERO, GEOGRAPHIC_POINT::lat, GEOGRAPHIC_POINT::lon, LWDEBUGF, and s.

Referenced by circ_center_spherical(), interpolate_point4d_spheroid(), test_sphere_direction(), and test_sphere_project().

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