lwpoly_pt_outside_hack()

static int lwpoly_pt_outside_hack ( const LWPOLY *  poly, POINT2D *  pt_outside  )

static

Definition at line 1487 of file lwgeodetic.c.

{
        GEOGRAPHIC_POINT g1, g2, gSum;
        POINT4D p1, p2;
        POINT3D q1, q2, qMid, qCross, qSum;
        POINTARRAY *pa;
        if (lwgeom_is_empty((LWGEOM*)poly))
                return LW_FAILURE;
        if (poly->nrings < 1)
                return LW_FAILURE;
        pa = poly->rings[0];
        if (pa->npoints < 2)
                return LW_FAILURE;
 
        /* First two points of ring */
        getPoint4d_p(pa, 0, &p1);
        getPoint4d_p(pa, 1, &p2);
        /* Convert to XYZ unit vectors */
        geographic_point_init(p1.x, p1.y, &g1);
        geographic_point_init(p2.x, p2.y, &g2);
        geog2cart(&g1, &q1);
        geog2cart(&g2, &q2);
        /* Mid-point of first two points */
        vector_sum(&q1, &q2, &qMid);
        normalize(&qMid);
        /* Cross product of first two points (perpendicular) */
        cross_product(&q1, &q2, &qCross);
        normalize(&qCross);
        /* Invert it to put it outside, and scale down */
        vector_scale(&qCross, -0.2);
        /* Project midpoint to the right */
        vector_sum(&qMid, &qCross, &qSum);
        normalize(&qSum);
        /* Convert back to lon/lat */
        cart2geog(&qSum, &gSum);
        pt_outside->x = rad2deg(gSum.lon);
        pt_outside->y = rad2deg(gSum.lat);
        return LW_SUCCESS;
}

References cart2geog(), cross_product(), geog2cart(), geographic_point_init(), getPoint4d_p(), GEOGRAPHIC_POINT::lat, GEOGRAPHIC_POINT::lon, LW_FAILURE, LW_SUCCESS, lwgeom_is_empty(), normalize(), POINTARRAY::npoints, LWPOLY::nrings, rad2deg, LWPOLY::rings, vector_scale(), vector_sum(), POINT2D::x, POINT4D::x, POINT2D::y, and POINT4D::y.

Referenced by lwpoly_pt_outside().

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