@InProceedings{wurm11iros,
title =        {Hierarchies of Octrees for Efficient 3D
 Mapping},
author =        {K.M. Wurm  and D. Hennes  and D. Holz and 
R.B. Rusu and C. Stachniss and K. Konolige and W. Burgard}, 
booktitle =    IROS,
ADDRESS =      {San Francisco, CA, USA},
year =         2011
}