_lwt_EdgeRingSignedArea()

static double _lwt_EdgeRingSignedArea ( LWT_EDGERING_POINT_ITERATOR *  it )

static

Definition at line 6561 of file lwgeom_topo.c.

{
        POINT2D P1;
        POINT2D P2;
        POINT2D P3;
        double sum = 0.0;
        double x0, x, y1, y2;
 
  if ( ! _lwt_EdgeRingIterator_next(it, &P1) ) return 0.0;
  if ( ! _lwt_EdgeRingIterator_next(it, &P2) ) return 0.0;
 
  LWDEBUG(2, "_lwt_EdgeRingSignedArea");
 
  x0 = P1.x;
  while ( _lwt_EdgeRingIterator_next(it, &P3)  )
  {
    x = P2.x - x0;
    y1 = P3.y;
    y2 = P1.y;
    sum += x * (y2-y1);
 
    /* Move forwards! */
    P1 = P2;
    P2 = P3;
  }
 
        return sum / 2.0;
}

References _lwt_EdgeRingIterator_next(), LWDEBUG, POINT2D::x, pixval::x, and POINT2D::y.

Referenced by _lwt_EdgeRingIsCCW().

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