  We discuss a generalisation of the Snyder model that includes all the
possible deformations of the Heisenberg algebra compatible with Lorentz
invariance, in terms of realisations of the noncommutative geometry. The
corresponding deformed addition of momenta, the twist and the $R$-matrix are
calculated to first order in the deformation parameters for all models. In the
particular case of the Snyder realisation, the exact formula for the twist is
obtained.
