A compact data structure for storing, retrieving and manipulating line drawings

The field of graphical man/machine interaction is customarily split into hardware and software areas. The former can be considered to have come of age: there are over twenty-five brands of off-the-shelf consoles with all the requisite input devices, and new techniques and improvements are constantly being developed. Many consoles are also provided with primitive supporting software which allow one to draw points, lines, arcs, etc., in a symbolic language of some sort. Less well understood and developed, however, is that aspect of display software concerned with representing and manipulating the problem model from which these primitive point/line/arc pictures are derived. The "data structure" is the machine representation of the often complex and hierarchical problem model. It must be judiciously derived from the model on the one hand and, on the other, lead readily to the reduced console display file of points, lines and arcs which cause the actual visual display. Furthermore, the data structure must be efficiently stored and processed (usually contradictory requirements).