An abstract graphical data type (AGDT) is an extension of an abstract data type for computer graphics. AGDTs provide the advantages of the ADTs with facilities to build graphical objects in a structured way. Formally, an AGDT may be defined as a "class of graphical objects whose logical behavior is defined by a set of graphical characteristics and a set of graphical operations". AGDTs were introduced in 1979 by Nadia Magnenat Thalmann and Daniel Thalmann. To define a figure type, one must For example, a pyramid with four vertices can be defined as A tree can be defined by 3-D graphical types as