<Binary Space Partitioning Tree>=
  public BSPTree() {
    PolygonList polylist;
    BSPTree front, back;
    if (null == polylist) { return null };
    else {
      BSPTree root = selectAndRemovePoly(polylist);
      root.front = new BSPTree();
      root.back =  new BSPTree();
      for (each p in polylist) {
         if (p is in front of root) { front.addToList(p); }
         else if (p is in back of root) { back.addToList(p); }
         else {
           p.splitPpoly(root, p, frontPoly,backPoly);
           front.addToList(frontPoly);
           back.addToList(backPoly);
         }
      }
    }
  }

• <Binary Space Partitioning Tree>: D1