edge_point_side()

static int edge_point_side ( const GEOGRAPHIC_EDGE *  e, const GEOGRAPHIC_POINT *  p  )

static

Returns -1 if the point is to the left of the plane formed by the edge, 1 if the point is to the right, and 0 if the point is on the plane.

Definition at line 690 of file lwgeodetic.c.

References dot_product(), GEOGRAPHIC_EDGE::end, FP_IS_ZERO, geog2cart(), LWDEBUG, LWDEBUGF, normalize(), robust_cross_product(), GEOGRAPHIC_EDGE::start, and w.

Referenced by edge_point_on_plane(), and sphere_signed_area().

{
        POINT3D normal, pt;
        double w;
        /* Normal to the plane defined by e */
        robust_cross_product(&(e->start), &(e->end), &normal);
        normalize(&normal);
        geog2cart(p, &pt);
        /* We expect the dot product of with normal with any vector in the plane to be zero */
        w = dot_product(&normal, &pt);
        LWDEBUGF(4,"dot product %.9g",w);
        if ( FP_IS_ZERO(w) )
        {
                LWDEBUG(4, "point is on plane (dot product is zero)");
                return 0;
        }

        if ( w < 0 )
                return -1;
        else
                return 1;
}

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