clairaut_geographic()

int clairaut_geographic	(	const GEOGRAPHIC_POINT *	start,
		const GEOGRAPHIC_POINT *	end,
		GEOGRAPHIC_POINT *	g_top,
		GEOGRAPHIC_POINT *	g_bottom
	)

Computes the pole of the great circle disk which is the intersection of the great circle with the line of maximum/minimum gradient that lies on the great circle plane.

Definition at line 1105 of file lwgeodetic.c.

{
        POINT3D t1, t2;
        GEOGRAPHIC_POINT vN1, vN2;
        LWDEBUG(4,"entering function");
        robust_cross_product(start, end, &t1);
        normalize(&t1);
        robust_cross_product(end, start, &t2);
        normalize(&t2);
        LWDEBUGF(4, "unit normal t1 == POINT(%.8g %.8g %.8g)", t1.x, t1.y, t1.z);
        LWDEBUGF(4, "unit normal t2 == POINT(%.8g %.8g %.8g)", t2.x, t2.y, t2.z);
        cart2geog(&t1, &vN1);
        cart2geog(&t2, &vN2);
        g_top->lat = z_to_latitude(t1.z,LW_TRUE);
        g_top->lon = vN2.lon;
        g_bottom->lat = z_to_latitude(t2.z,LW_FALSE);
        g_bottom->lon = vN1.lon;
        LWDEBUGF(4, "clairaut top == GPOINT(%.6g %.6g)", g_top->lat, g_top->lon);
        LWDEBUGF(4, "clairaut bottom == GPOINT(%.6g %.6g)", g_bottom->lat, g_bottom->lon);
        return LW_SUCCESS;
}

References cart2geog(), GEOGRAPHIC_POINT::lat, GEOGRAPHIC_POINT::lon, LW_FALSE, LW_SUCCESS, LW_TRUE, LWDEBUG, LWDEBUGF, normalize(), robust_cross_product(), POINT3D::x, POINT3D::y, POINT3D::z, and z_to_latitude().

Referenced by test_clairaut().

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