For a computer to automatically analyze and process geometric shapes, the objects have to be represented in a digital form.
Once the objects are given, either by modeling (computer-aided design), by scanning (3D scanner) or by extracting shape from 2D or 3D images, they have to be simplified before a comparison can be achieved.
These simplified representations try to carry most of the important information, while being easier to handle, to store and to compare than the shapes directly.
Such descriptors are commonly based on geodesic distances measures along the surface of an object or on other isometry invariant characteristics such as the Laplace–Beltrami spectrum (see also spectral shape analysis).
Therefore, depending on the application, it is necessary to analyze how well a descriptor captures the features of interest.