Point3f getAtomSetCenter(BitSet bs) {
		Point3f ptCenter = new Point3f(0, 0, 0);
		int nPoints = viewer.cardinalityOf(bs);
		if (nPoints == 0)
			return ptCenter;
		for (int i = atomCount; --i >= 0;) {
			if (bs.get(i))
				ptCenter.add(atoms[i]);
		}
		ptCenter.scale(1.0f / nPoints);
		return ptCenter;
	}