gbox_pt_outside()

int gbox_pt_outside	(	const GBOX *	gbox,
		POINT2D *	pt_outside
	)

Given a unit geocentric gbox, return a lon/lat (degrees) coordinate point point that is guaranteed to be outside the box (and therefore anything it contains).

Calculate a spherical point that falls outside the geocentric gbox.

Definition at line 1552 of file lwgeodetic.c.

{
        double grow = M_PI / 180.0 / 60.0; /* one arc-minute */
        int i;
        GBOX ge;
        POINT3D corners[8];
        POINT3D pt;
        GEOGRAPHIC_POINT g;
 
        while ( grow < M_PI )
        {
                /* Assign our box and expand it slightly. */
                ge = *gbox;
                if ( ge.xmin > -1 ) ge.xmin -= grow;
                if ( ge.ymin > -1 ) ge.ymin -= grow;
                if ( ge.zmin > -1 ) ge.zmin -= grow;
                if ( ge.xmax < 1 )  ge.xmax += grow;
                if ( ge.ymax < 1 )  ge.ymax += grow;
                if ( ge.zmax < 1 )  ge.zmax += grow;
 
                /* Build our eight corner points */
                corners[0].x = ge.xmin;
                corners[0].y = ge.ymin;
                corners[0].z = ge.zmin;
 
                corners[1].x = ge.xmin;
                corners[1].y = ge.ymax;
                corners[1].z = ge.zmin;
 
                corners[2].x = ge.xmin;
                corners[2].y = ge.ymin;
                corners[2].z = ge.zmax;
 
                corners[3].x = ge.xmax;
                corners[3].y = ge.ymin;
                corners[3].z = ge.zmin;
 
                corners[4].x = ge.xmax;
                corners[4].y = ge.ymax;
                corners[4].z = ge.zmin;
 
                corners[5].x = ge.xmax;
                corners[5].y = ge.ymin;
                corners[5].z = ge.zmax;
 
                corners[6].x = ge.xmin;
                corners[6].y = ge.ymax;
                corners[6].z = ge.zmax;
 
                corners[7].x = ge.xmax;
                corners[7].y = ge.ymax;
                corners[7].z = ge.zmax;
 
                LWDEBUG(4, "trying to use a box corner point...");
                for ( i = 0; i < 8; i++ )
                {
                        normalize(&(corners[i]));
                        LWDEBUGF(4, "testing corner %d: POINT(%.8g %.8g %.8g)", i, corners[i].x, corners[i].y, corners[i].z);
                        if ( ! gbox_contains_point3d(gbox, &(corners[i])) )
                        {
                                LWDEBUGF(4, "corner %d is outside our gbox", i);
                                pt = corners[i];
                                normalize(&pt);
                                cart2geog(&pt, &g);
                                pt_outside->x = rad2deg(g.lon);
                                pt_outside->y = rad2deg(g.lat);
                                LWDEBUGF(4, "returning POINT(%.8g %.8g) as outside point", pt_outside->x, pt_outside->y);
                                return LW_SUCCESS;
                        }
                }
 
                /* Try a wider growth to push the corners outside the original box. */
                grow *= 2.0;
        }
 
        /* This should never happen! */
        // lwerror("BOOM! Could not generate outside point!");
        return LW_FAILURE;
}

References cart2geog(), gbox_contains_point3d(), GEOGRAPHIC_POINT::lat, GEOGRAPHIC_POINT::lon, LW_FAILURE, LW_SUCCESS, LWDEBUG, LWDEBUGF, normalize(), rad2deg, POINT2D::x, POINT3D::x, pixval::x, GBOX::xmax, GBOX::xmin, POINT2D::y, POINT3D::y, pixval::y, GBOX::ymax, GBOX::ymin, POINT3D::z, GBOX::zmax, and GBOX::zmin.

Referenced by CircTreePIP(), geography_point_outside(), lwpoly_pt_outside(), and test_tree_circ_pip2().

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