@Override
	public double[] get3DData(int px, int py, int pz, int sx, int sy, int sz)
    {
        double[] da = a.get3DData(px, py, pz, sx, sy, sz);
        double[] db;

        if (a == b)
            db = da;
        else
            db = b.get3DData(px, py, pz, sx, sy, sz);

        int s = sx*sy*sz;
		for(int i = 0; i < s; i++)
            da[i] = da[i] < db[i] ? da[i] : db[i];
        
        return da;
	}