Das Titsgebaeude von Siegelschen Modulgruppen vom Geschlecht 2
  We calculate Tits buildings for certain arithmetic subgroups of Sp(4). These give information about the boundary of the corresponding moduli spaces of abelian surfaces. More pictures (in colour) and a summary of the results (in English) can be found at http://www.bath.ac.uk/~masgks/Buildings/ 
M. Friedland, G.K. Sankaran