_lwt_EdgeRingCrossingCount()

static int _lwt_EdgeRingCrossingCount ( const POINT2D *  p, LWT_EDGERING_POINT_ITERATOR *  it  )

static

Definition at line 6428 of file lwgeom_topo.c.

{
        int cn = 0;    /* the crossing number counter */
        POINT2D v1, v2;
#ifndef RELAX
  POINT2D v0;
#endif
 
  if ( ! _lwt_EdgeRingIterator_next(it, &v1) ) return cn;
  v0 = v1;
        while ( _lwt_EdgeRingIterator_next(it, &v2) )
        {
                double vt;
 
                /* edge from vertex i to vertex i+1 */
                if
                (
                    /* an upward crossing */
                    ((v1.y <= p->y) && (v2.y > p->y))
                    /* a downward crossing */
                    || ((v1.y > p->y) && (v2.y <= p->y))
                )
                {
 
                        vt = (double)(p->y - v1.y) / (v2.y - v1.y);
 
                        /* P->x <intersect */
                        if (p->x < v1.x + vt * (v2.x - v1.x))
                        {
                                /* a valid crossing of y=p->y right of p->x */
                                ++cn;
                        }
                }
                v1 = v2;
        }
 
        LWDEBUGF(3, "_lwt_EdgeRingCrossingCount returning %d", cn);
 
#ifndef RELAX
  if ( memcmp(&v1, &v0, sizeof(POINT2D)) )
  {
    lwerror("_lwt_EdgeRingCrossingCount: V[n] != V[0] (%g %g != %g %g)",
      v1.x, v1.y, v0.x, v0.y);
    return -1;
  }
#endif
 
  return cn;
}

References _lwt_EdgeRingIterator_next(), LWDEBUGF, lwerror(), POINT2D::x, and POINT2D::y.

Referenced by _lwt_EdgeRingContainsPoint().

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