1. A computer implemented method for generating an n dimensional vector as a shape descriptor of a non-watertight three-dimensional (3D) model, comprising: determining, as a function of three eigenvalues of a covariance matrix of the non-watertight 3D model, a type element of the vector to describe a basic shape of the model, wherein the type element is a first dimension in the vector; determining a feature of the non-watertight 3D model and a total number of features in the non-watertight 3D model; generating n−1 metric elements of the vector, each of the n−1 metric elements represents all of the feature of the non-watertight 3D model falling into one of n−1 layers divided as a function of the type element per the total number of features in the non-watertight 3D model; and performing a search for the non-watertight 3D model using the vector which can effectively process non-watertight 3D models.