point_in_cone()

static int point_in_cone ( const POINT3D *  A1, const POINT3D *  A2, const POINT3D *  P  )

static

Utility function for checking if P is within the cone defined by A1/A2.

Definition at line 3307 of file lwgeodetic.c.

{
        POINT3D AC; /* Center point of A1/A2 */
        double min_similarity, similarity;
 
        /* Boundary case */
        if (point3d_equals(A1, P) || point3d_equals(A2, P))
                return LW_TRUE;
 
        /* The normalized sum bisects the angle between start and end. */
        vector_sum(A1, A2, &AC);
        normalize(&AC);
 
        /* The projection of start onto the center defines the minimum similarity */
        min_similarity = dot_product(A1, &AC);
 
        /* If the edge is sufficiently curved, use the dot product test */
        if (fabs(1.0 - min_similarity) > 1e-10)
        {
                /* The projection of candidate p onto the center */
                similarity = dot_product(P, &AC);
 
                /* If the projection of the candidate is larger than */
                /* the projection of the start point, the candidate */
                /* must be closer to the center than the start, so */
                /* therefore inside the cone */
                if (similarity > min_similarity)
                {
                        return LW_TRUE;
                }
                else
                {
                        return LW_FALSE;
                }
        }
        else
        {
                /* Where the edge is very narrow, the dot product test */
                /* fails, but we can use the almost-planar nature of the */
                /* problem space then to test if the vector from the */
                /* candidate to the start point in a different direction */
                /* to the vector from candidate to end point */
                /* If so, then candidate is between start and end */
                POINT3D PA1, PA2;
                vector_difference(P, A1, &PA1);
                vector_difference(P, A2, &PA2);
                normalize(&PA1);
                normalize(&PA2);
                if (dot_product(&PA1, &PA2) < 0.0)
                {
                        return LW_TRUE;
                }
                else
                {
                        return LW_FALSE;
                }
        }
        return LW_FALSE;
}

References dot_product(), LW_FALSE, LW_TRUE, normalize(), point3d_equals(), vector_difference(), and vector_sum().

Referenced by edge_intersects().

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