@techreport{ClasenPaarProhaska2011, author = {Malte Clasen and Philip Paar and Steffen Prohaska}, title = {Level of Detail for Trees Using Clustered Ellipsoids}, institution = {ZIB}, address = {Takustr. 7, 14195 Berlin}, number = {11-41}, language = {eng}, year = {2011} }