circ_center_cartesian()

static int circ_center_cartesian ( const GEOGRAPHIC_POINT *  c1, const GEOGRAPHIC_POINT *  c2, double  distance, double  offset, GEOGRAPHIC_POINT *  center  )

static

Where the circ_center_spherical() function fails, we need a fall-back.

The failures happen in short arcs, where the spherical distance between two points is practically the same as the straight-line distance, so our fallback will be to use the straight-line between the two to calculate the new projected center. For proportions far from 0.5 this will be increasingly more incorrect.

Definition at line 191 of file lwgeodetic_tree.c.

{
        POINT3D p1, p2;
        POINT3D p1p2, pc;
        double proportion = offset/distance;
 
        LWDEBUG(4,"calculating cartesian center");
 
        geog2cart(c1, &p1);
        geog2cart(c2, &p2);
 
        /* Difference between p2 and p1 */
        p1p2.x = p2.x - p1.x;
        p1p2.y = p2.y - p1.y;
        p1p2.z = p2.z - p1.z;
 
        /* Scale difference to proportion */
        p1p2.x *= proportion;
        p1p2.y *= proportion;
        p1p2.z *= proportion;
 
        /* Add difference to p1 to get approximate center point */
        pc.x = p1.x + p1p2.x;
        pc.y = p1.y + p1p2.y;
        pc.z = p1.z + p1p2.z;
        normalize(&pc);
 
        /* Convert center point to geographics */
        cart2geog(&pc, center);
 
        return LW_SUCCESS;
}

References cart2geog(), distance(), geog2cart(), LW_SUCCESS, LWDEBUG, normalize(), POINT3D::x, POINT3D::y, and POINT3D::z.

Referenced by circ_node_internal_new().

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