  In this position paper we suggest a possible metric approach to shape
comparison that is based on a mathematical formalization of the concept of
observer, seen as a collection of suitable operators acting on a metric space
of functions. These functions represent the set of data that are accessible to
the observer, while the operators describe the way the observer elaborates the
data and enclose the invariance that he/she associates with them. We expose
this model and illustrate some theoretical reasons that justify its possible
use for shape comparison.
