Objects in three dimensions, and their two-dimensional images, are approximated digitally by sets of voxels ("volume elements") or pixels ("picture elements"), respectively. Digital geometry is the study of geometric properties of digitized objects (or digitized images of objects); it deals both with the definitions of such properties and with algorithms for their computation. In particular, digital topology deals with properties of a "topological" nature (particularly, properties that involve the concepts of connectedness or adjacency, but do not depend on size or shape), and with algorithms that compute or preserve such properties.