  In order to get a better understanding of holographic properties of
gravitational theories with a vanishing cosmological constant, we analyze in
detail the relation between asymptotically anti-de Sitter and asymptotically
flat spacetimes in three dimensions. This relation is somewhat subtle because
the limit of vanishing cosmological constant cannot be naively taken in
standard Fefferman-Graham coordinates. After reformulating the standard anti-de
Sitter results in Robinson-Trautman coordinates, a suitably modified Penrose
limit is shown to connect both asymptotic regimes.
