  In this paper, we derive new shape descriptors based on a directional
characterization. The main idea is to study the behavior of the shape
neighborhood under family of transformations. We obtain a description invariant
with respect to rotation, reflection, translation and scaling. A well-defined
metric is then proposed on the associated feature space. We show the continuity
of this metric. Some results on shape retrieval are provided on two databases
to show the accuracy of the proposed shape metric.
