A Remark on the Projective Geometry of Constant Curvature Spaces
  We highlight the relation between the projective geometries of $n$-dimensional Euclidean, spherical and hyperbolic spaces through the projective models of these spaces in the $n+1$-dimensional Minkowski space, using a cross ratio notion which is proper to each of the three geometries. 
Athanase Papadopoulos (IRMA), Sumio Yamada
math.MG math.GT