unit_normal()

void unit_normal	(	const POINT3D *	P1,
		const POINT3D *	P2,
		POINT3D *	normal
	)

Calculates the unit normal to two vectors, trying to avoid problems with over-narrow or over-wide cases.

Definition at line 541 of file lwgeodetic.c.

{
        double p_dot = dot_product(P1, P2);
        POINT3D P3;
 
        /* If edge is really large, calculate a narrower equivalent angle A1/A3. */
        if ( p_dot < 0 )
        {
                vector_sum(P1, P2, &P3);
                normalize(&P3);
        }
        /* If edge is narrow, calculate a wider equivalent angle A1/A3. */
        else if ( p_dot > 0.95 )
        {
                vector_difference(P2, P1, &P3);
                normalize(&P3);
        }
        /* Just keep the current angle in A1/A3. */
        else
        {
                P3 = *P2;
        }
 
        /* Normals to the A-plane and B-plane */
        cross_product(P1, &P3, normal);
        normalize(normal);
}

References cross_product(), dot_product(), normalize(), vector_difference(), and vector_sum().

Referenced by clairaut_cartesian(), edge_calculate_gbox(), edge_intersection(), edge_intersects(), and vector_rotate().

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