1. A method for representing a shape of an object represented by a set of points, wherein the set of points include points inside, outside and a boundary of the shape, the method comprising the steps of: learning a decision function from the set of points, wherein the decision function is a hypersurface defined by support vectors of a radial basis function (RBF) support vector machine (SVM) that separates the set of points inside and outside the shape, such that the hypersurface and the support vectors represent the shape of the object; selecting feature points in the set of points using the decision function; and determining a local descriptor for each feature point, wherein the steps are performed in a processor.