code: public static Point2d get2DCenter(IRingSet ringSet) {
          double centerX = 0;
          double centerY = 0;
          for (int i = 0; i < ringSet.getAtomContainerCount(); i++) {
              Point2d centerPoint = get2DCenter((IRing) ringSet.getAtomContainer(i));
              centerX += centerPoint.x;
              centerY += centerPoint.y;
          }
          return new Point2d(centerX / ((double) ringSet.getAtomContainerCount()), centerY
                  / ((double) ringSet.getAtomContainerCount()));
      }
docs: Returns the geometric center of all the rings in this ringset.
  See comment for center(IAtomContainer atomCon, Dimension areaDim, HashMap renderingCoordinates) for details on coordinate sets
  
  @param  ringSet  Description of the Parameter
  @return          the geometric center of the rings in this ringset