  We introduce length dilatation structures on metric spaces, tempered
dilatation structures and coherent projections and explore the relations
between these objects and the Radon-Nikodym property and Gamma-convergence of
length functionals. Then we show that the main properties of sub-riemannian
spaces can be obtained from pairs of length dilatation structures, the first
being a tempered one and the second obtained via a coherent projection.
  Thus we get an intrinsic, synthetic, axiomatic description of sub-riemannian
geometry, which transforms the classical construction of a Carnot-Caratheodory
distance on a regular sub-riemannian manifold into a model for this abstract
sub-riemannian geometry.
