  We study grassmannians associated with a linear space with a nondegenerate
hermitian form. The geometry of these grassmannians allows us to explain the
relation between a (pseudo-)riemannian projective geometry and the conformal
structure on its ideal boundary (absolute). Such relation encompasses, for
instance, the usual conformal structure on the absolute of real hyperbolic
space, the usual conformal structure on the absolute of de Sitter space, the
conformal contact structure on the absolute of complex hyperbolic space, and
the causal structure on the absolute of anti-de Sitter space.
