AN INTERDISCIPLINARY LABORATORY FOR GRAPHICS RESEARCH AND APPLICATIONS by Dr. Donald P. Greenberg Program of Computer Graphics Cornell University This paper describes the facilities and operation of the Program of Computer Graphics at Cornell University. A variety of graphic procedures are used for both input and output. The laboratory has the capability for producing dynamic vector displays and for generating full color images. Numerous research projects in a variety of disciplines which are actively using this multi-user graphics environment are presented. Introduction An interdisciplinary laboratory has been the objectives, operating procedures, and pro- established at Cornell University for: gress of a new interdisciplinary computer graphics facility. For more detailed information on the a) the development of computer graphics hidden surface and surface representation pro- techniques, cedures or on the animation system, the reader is b) the utilization of these techniques to referred to other papers emanating from this help solve various research problems, and laboratory and included in these proceedings.. c) the improvement of interactive design Equipment and Facilities methodology. Using primarily digitizing tablets for the graphi- The functional configuration of the graphics cal input tasks, the researcher may select any of laboratory is shown in Figure 1. The major graph- several two dimensional or three dimensional input ical components of the system are the E & S routines. These include volumetric input, serial "Picture System", the E & S frame buffer, and two sectioning, three dimensional input using two Tektronix storage tube displays. Two computers, dimensional views, and extrusion methods. Display a DEC PDP 11/50 and a PDP 11/34, are used to per- options include static or dynamic wire line draw- form all of the operations and control of the ings or full color static displays. Hidden line displays. and hidden surface algorithms, based primarily on The E & S Picture System is a pipeline system planar polygon descriptions are available. which contains a picture processor, a refresh buf- fer, picture and character generators, and a pic- The initial graphics work has provided a ture display and is capable of producing complex catalytic effect for the stimulation of joint re- dynamic vector displays. search projects. Present applications include research in structural engineering, geological The E & S frame buffer is used for the pro- sciences, water resources planning, pollution duction of the color images and has sufficient analysis, energy conservation, bio-medicine, archi- capacity to store one standard video frame (480 tecture and animation. A brief illustration of rows by 512 columns) of 8 bit pixels. For any some of these projects is presented. image, each pixel can be translated into any of 256 possible colors by means of hardware lookup The large variety of projects has enforced tables which provide 12 bit intensity levels for the need for a general, rather thpn a discipline- each of red, blue, and green. specific approach to interactive graphics. Most of the graphic inputting, editing and display Output from the frame buffer can be directed routines that have been developed can be inter- to high resolution television monitors or to a faced to either specialized applications programs large screen video projector. A 16mm motion pic- or to each other. A brief description of these ture camera has been interfaced to the support operating procedures as well as the equipment and processor for creation of stop frame motion facilities of the laboratory follows. pictures. This article is not intended to be an in- The Tektronix 4014 display terminals are depth description of any aspect of interactive standard high resolution storage tubes with the computer graphics. It is solely an overview of capability for complex static and limited dynamic The operation of the laboratory is partially sponsored by the National Science Foundation under grant number DCR-14694 entitled "Development of Computer Graphics Techniques & Applications." Permission to make digital or hard copies of part or all of this work or personal or classroom use is granted without fee provided that copies are 90 not made or distributed for profit or commercial advantage and that copies bear this notice and the full citation on the first page. To copy otherwise, to republish, to post on servers, or to redistribute to lists, requires prior specific permission and/or a fee. Siggraph ’77, July 20-22 San Jose, California image generation. A common graphics software 1) The creation of the objects to be package has been created which will drive both displayed. the dynamic and static display devices. 2) The editing of the object description. Digitizing tablets serve as the standard, general purpose graphic input devices in the 3) The generation of the displays. laboratory. Several tablets of varying sizes, ranging from a standard 11" x 11" tablet to a A typical user should be able to rapidly and large 36' x 48" digitizing tablet have been precisely describe an object in two or three interfaced either directly to the host processor, dimensions in addition to color and time. To this or through the display terminals. One transparent end, a comprehensive set of graphic input routines digitizing tablet allows for the digitizing of have been developed which can be adapted for most rear projected images. applications. Four different methods are provided for graphically inputting spatial information. The host computer is a PDP 11/50 with 96K memory. It is interfaced to Cornell's IBM 370- All of these methods rely on the availability 168 when larger memory capacity is required. A of standard interactive graphic inputting and edit- magnetic tape unit and two small disk units are ing procedures (4). also attached. The PDP 11/34 processor has been added to the laboratory equipment configuration The first graphical input approach consists primarily for the generation of color images. A of building up a complex environment from a set of large dual drive 80 megabyte Diva disk unit, predefined volumetric elements (2,6,11)(Figure 2). DD-52, has been installed to improve the effi- The three-dimensional data required for the com- ciency of the multi-user operating system and to posite object description is obtained by inter- store the large quantities of required picture actively combining a set of primitive shapes and information. forms and by utilizing their original numerical definitions. To achieve these capabilities, the Graphic Input Procedures actual three-dimensional coordinates of the primi- tive objects are separated from the transforma- In general, the characteristics of an inter- tional parameters that are applied to the data active graphics environment can be described as before display. This method permits multiple consisting of three types of graphical operations: elements to be constructed from the same set of data and displayed many times with different transformations. It also allows for individual 91 transformational parameters to be altered without Second, due to the inaccuracies of digitizing, affecting those of any other object. To separate powerful editing routines insuring planarity and the coordinate data from the transformational data, automatic joining and aligning are necessary for two files have been established. The first con- practical usage. tains the actual untransformed three-dimensional coordinate data of the original primitive objects. A third method is to define a set of serial The second file contains the transformational cross-sections of an object and automatically parameters for translation, scaling, and rotation combine these planar definitions to create the in each of the three coordinate axes. These files three-dimensional shape. All information is input are read from a mass storage device at the begin- in two-dimensional format. Normally the major ning of each work session and can be written back constraint is the large amount of data required to storage if the user makes an alteration that to accurately define amorphous shapes. For this needs to be saved for future sessions. reason, numerical procedures utilizing B-splines which can accurately represent these two-dimen- The advantage of this approach is that it sional contours with compressed data have been allows the creation of complex object descriptions implemented (1,5,12). Automatic webbing routines with a minimal amount of data input and provides or lofting procedures using Cardinal splines can dynamic visual feedback using perspective images provide the three-dimensional surface interpola- so that the researcher can work in three dimensions tion (Figure 4). Several applications, including The major restriction is that the speed of the dis- the structural engineering finite element analysis play may be limited by the referencing structure. project, are presently using this input method. This hierarchical process is particularly appli- Perhaps more important is the potential use of cable to analytical routines based on sub-elements this approach to the entire field of medicine such as structural finite element analyses or where information describing arbitrary, three- multi-zone energy simulations. dimensional objects is readily obtained in two- dimensional format. method is to A second and extremely promising The last graphical input approach can be information into the digitize three-dimensional thought of conceptually as an extrusion method. multiple sets of two-dimensional computer using A line can be generated from a point, a plane photographs (8,9). By identifying the appropriate from a line, and a solid from a plane. In each known reference points on a two-dimen- number of case, the direction of the extension can be sional drawing or photograph, it is possible to controlled and has a unique relationship to the mathematical transformation matrix determine the original two-dimensional definition. Elements that uniquely transforms the three-dimensional can be created by digitizing on any two-dimensional data the existing two-dimensional spatial to plane, transformed into a three-dimensional element, picture. If two drawings or photographs are and positioned appropriately.