code: public void removeVertex(int index) {
          this.cornerX.remove(index);
          this.cornerY.remove(index);
          this.cornerZ.remove(index);
          if (isGradation() == true) this.cornerColor.remove(index);
          setNumberOfCorner(this.cornerX.size());
          calcG();
      }
docs: Removes the corner of Polygon.
  
  @param index The index number of the corner.