  We study discrete, cocompact, isometric actions of groups on Hadamard spaces,
and the induced actions on ideal boundaries. For a class of groups generalizing
fundamental groups of three-dimensional graph manifolds, we find a set of
invariants for the action which determine the boundary action up to equivariant
homeomorphism. This work was inspired by (and answers) a question of Gromov
from "Asymptotic invariants of infinite groups."
