For further detail about the geometrical uses of Clifford algebras, see Geometric algebra. Computational geometry applies algorithms to geometrical problems. Computational geometry deals with algorithms and their implementations for manipulating geometrical objects. Symmetries in mathematics greatly simplify the study of geometrical or analytical objects. Muqarnas vaults are three-dimensional but were designed in two dimensions with drawings of geometrical cells. The many complex pictures on the sacred scrolls communicate much historical, geometrical, and mathematical knowledge. They are available in a wide variety of colors and geometrical shapes. Projections may be calculated mathematically or by various geometrical or optical techniques. A pure substance is composed of molecules with the same average geometrical structure. Above the columns are impost blocks decorated with colored geometrical designs. Various graphical methods can be easily envisaged for projecting geometrical scenes. Aberration can be analyzed with the techniques of geometrical optics. There are colourful mosaics which have geometrical forms and figures. Guards were either semicircular or straight, but always highly ornamented with geometrical patterns. He then analyzed these physical rays according to the principles of geometrical optics.