Richard S. Gallagher. Computer Visualization: Graphics Techniques for Engineering and Scientific Analysis

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Computer Visualization: Graphics Techniques for Engineering and Scientific Analysis

by Richard S. Gallagher. Solomon Press

CRC Press, CRC Press LLC

ISBN: 0849390508 Pub Date: 12/22/94

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1.8 References

1. Argyris, J. and S. Kelsey, Energy Theorums And Structural Analysis, Butterworth Scientific

Publications, London, 1960.

2. Chasen, S.H., “Historical Highlights of Interactive Computer Graphics,” Mechanical Engineering,

No. 103, ASME, November 1981.

3. Christiansen, H.N., “Applications of Continuous Tone Computer-Generated Images in Structural

Mechanics,” in Structural Mechanics Computer Programs, W. Pilkey, K. Saczalski and H. Schaeffer

eds., University of Virginia Press, Charlottesville, VA, 1974.

4. Courant, R., “Variational Methods for the Solution of Problems of Equilibrium and Vibration,”

Bulletin of the American Mathematical Society, No. 49, pp. 1-43, 1943.

5. Gallagher, R. H., Finite Element Analysis Fundamentals, Prentice Hall, 1975.

6. Gallagher, R.S. et al, “Applying 3-D Visualization Techniques to Finite Element Analysis,” panel

summary in Proceedings of Visualization ’91, IEEE Computer Society Press, October 1991.

7. Greenberg, D.E, “Computer Graphics in Architecture,” Scientific American, Vol. 230, May 1974,

pp. 98–106.

8. Kaufmann, A. ed., Volume Visualization, IEEE Computer Society Press, 1990.

9. McCormick, B.H, DeFanti, T.A. and Brown, M., “Visualization In Scientific Computing,” Report of

the NSF Advisory Panel on Graphics, Image Processing and Workstations, 1987.

10. Schroeder, W. J., Volpe, C. R., and Lorensen, W. E., “The Stream Polygon: A Technique for 3-D

Vector Field Visualization,” Proceedings of IEEE Visualization ’91, IEEE Computer Society Press,

October 1991 pp 126-132.

11. Shriver, B. and G. Nielson, eds., Visualization in Scientific Computing, IEEE Computer Society

Press, 1990.

12. Sutherland, I.E., “Sketchpad: A Man-Machine Graphical Communication System,” Proc. Spring

Joint Computer Conference, No. 23, AFIPS Press, Montvale, NJ, 1963, pp. 329–346.

13. Zienkiewicz, O.C., Finite Element Fundamentals, Fourth Edition, McGraw Hill, 1989.

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Computer Visualization: Graphics Techniques for Engineering and Scientific Analysis

by Richard S. Gallagher. Solomon Press

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ISBN: 0849390508 Pub Date: 12/22/94

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Chapter 2

An Overview of Computer Graphics for Visualization

Alain Fournier

John Buchanan

COMPUTER GRAPHICS FORMS the basis for much of scientific visualization. This chapter

provides an overview of history and fundamentals of computer graphics for visualization. Topics

covered include modeling, transformations, shading, pixel and volume display techniques, and

graphics display architecture.

2.1 What is Computer Graphics?

As in every discipline, it is always interesting, if not necessarily fruitful, to ask what defines its content, and

what makes it different from other close disciplines. In our case the question is “What Is Computer

Graphics?” Another question immediately following is “Why Computer Graphics?”

The first question used to have a simple answer: Computer Graphics is making pictures with computers. This

definition has become too comprehensive to be really useful. There is hardly any aspect of picture making as

practiced these days which does not involve computers. Television shows, photos in the morning paper,

illustrations in textbooks, magazine ads: probably all have been generated, manipulated, transmitted or

touched up using computers.

Another approach is to define computer graphics as a scientific discipline, and the fact that many universities

have computer graphics groups in their midst, mostly, of course, in computer science departments, and that

PhD and other degrees are granted for work in computer graphics is a de facto existence proof. In fact, we

could use the aggregate content of theses, papers, communications in journals and conferences to define the

area. This will help, but, as with any definition, there will be “grey” areas, with work at the boundary between

computer graphics and computer vision, image processing, human factors, various engineering disciplines

especially electrical engineering), and even mathematics.

When all is carefully considered, we come back to the original simple definition, both extended and restricted:

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Computer graphics is the science and practice of producing images by mechanical means. In a brief history,

we will see that this definition has the advantage of linking the present to many pre-computer developments.

2.2 Why Computer Graphics?

It is endless to list all the areas of application of computer graphics, as indicated above, but if we make a short

list of applications where computer graphics plays an important role, it could read as follows.

Data Plotting

Cartography

Mechanical CAD

Electronic CAD

Architectural CAD

Business Graphics

Flight and Driving Simulation

Film Animation (2-D and 3-D)

Video Animation (2-D and 3-D)

Document Generation

Video Games

Display of Mathematical Objects

Process Control

Office Information Systems

Free Hand Drawing and Painting

The reader is encouraged to examine this list, and try to decide why computer graphics has value in these

applications. Reasons found or generally given include the following.

Pictures could not be made otherwise

Pictures can be made faster

Pictures can be made cheaper by computer

Pictures look different by computer

Pictures look better by computer

I have this hardware to sell you.

I have this software to sell you.

This book contains many elaborations of these basic reasons (excepting the last two, which are nevertheless

very powerful). At the outset it is important to note that the most “obvious” reason—pictures can be made

faster by computer—is often the least true in practice. It is only recently that producing 2-D and 3-D diagrams

and figures actually became easier and faster with computers, and still now many CAD and modelling tasks

take longer with a computer (especially if quality is taken into account). The real power of computer graphics

is in the ability to repeat at little human cost, and the ability to manipulate and reuse.

2.3 Traditional Picture Making

It will prove instructive to consider some pictures from non-computer media, and to analyze the processes

which created them. Let us consider a classical drawing, a photograph (Figure 2.1), a television frame, or a

technical drawing. What they have in common, beyond the variety of intent, talent and media, can be summed

in four characteristics:

an intent to communicate through images

a model, either real or imaginary, to provide the form underlying the image

a medium to output the picture

a process to go from the model to the output medium.

Figure 2.1 A photograph

This can directly involve highly human skills, as in a woodcut, be totally mechanical as in the television

frame, or can involve elaborate transformations, as with a photograph, which is imaged on a negative,

possibly framed, cropped, enlarged and/or contrast-enhanced before it is printed. All of this is shared with

images produced with computer graphics. The intent remains the same, the model has to be storable and

manipulable in the machine, the output medium must be controllable by computer, and the progression from

the model to the image, often called rendering in computer graphics, is the core of the discipline.

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Computer Visualization: Graphics Techniques for Engineering and Scientific Analysis

by Richard S. Gallagher. Solomon Press

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ISBN: 0849390508 Pub Date: 12/22/94

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2.4 The Graphics Process

Using this analysis of the graphics process (a more thorough analysis is necessary to validate our conclusions,

but these are essentially correct), we can now put into a diagram the basic components of the graphics system

(Figure 2.2).

This diagram is clearly connected to traditional picture making, containing a model, an imaging process and

an output medium, as well as to the computer graphics process, although different people within computer

graphics will have a different view of the same components. To programmers, each module is a piece of

software, to be written or acquired; to system designers, each is software or hardware to be selected and

matched; to users they will be functional blocks, seen for their uses, but not for their specific

implementations. In fact, the middle module, which is the most important for the programmers and designers

of the graphics system will be the least “visible” for the users, since they will take it for granted if it works

well. Still it is important for user to understand what it includes and how it works, so that one can know what

to expect and what to demand. In this book the interest and attention shifts from modelling to display or the

reverse, but one must realize that the two can be decoupled.

Figure 2.2 The graphics system

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Plate 1.1 (a, b, c). Contour, isosurface and particle gradient displays of the equivalent stress from a structural

analysis. (Courtesy Swanson Analysis Systems, Inc.)

Plate 1.2 A stream polygon describing the air flow through a room. The streamline itself represents the path

of an air particle, with color and thickness used to represent other solution variables. (From Schroeder et al.,

Plate 2.6 Face modeled with patches. (Courtesy David Forsey, University of British Columbia.)

Plate 2.13 Ray-traced scene.

Plate 4.6 (a, b). Carpet plot. (Courtesy Swanson Analysis Systems, Inc.)

Plate 4.15 Isosurfaces of stress within a comprehensive seal. (Courtesy Dedo Sistemi-Italcae SRL, Italy.)

Machinery, Inc. Reprinted by permission.)

for Computing Machinery, Inc. Reprinted by permission.)

Plate 4.28 Sampling planes, with continuous tonal and particle results displayed across the slice planes.

(Courtesy Wavefront Technologies—Data Visualizer.)

Plate 4.29 Isosurface used as a clipping and capping surface. (Courtesy Visual Kinematics, Inc.)

Plate 5.5 Streamlines of the steady flow in Figure 5.4. Color maps kinetic energy density according to the

scale in Plate 5.21.

Plate 5.6 Anisotropic texture representing the 2-D flow tangent to the cylinder in Figure 5.4. The cylinder

surface is shown unfolded. Blue, green, yellow, and red correspond to increasing velocity magnitude.

Plate 5.11 Local characterization of the velocity field in Figure 5.4. (From Hellman & Hesselink, reference

Plate 5.15 Topological surfaces depicting the time evolution of the 2-D flow past a circular cylinder. Time

Plate 5.18 Contour lines of helicity density H

(red/white = right-handed vortices; blue/ black = left-handed

vortices) together with skin-friction topology (blue and yellow lines) and vortex cores (magenta lines).

Plate 5.20 Stress tensor induced by two compressive forces. Minor tubes, medium and major helices. Color

Plate 5.21 Four different stages of a minor tube in an elastic stress tensor field. (From Delmarcelle &

Plate 5.22 Reversible momentum flux density tensor in the flow past a hemisphere cylinder. Color scale is

Plate 5.23 Global icon of the stress tensor of Figures 5.19 and 5.20.

Plate 5.24 Stress tensor (top) and viscous stress tensor (bottom) in the flow past a hemisphere cylinder. Color

scale is shown in Plate 5.21.

Plate 6.12 (a) A surface projection of a nerve cell. (b) A maximum projection of a nerve cell.

Plate 6.18 (a) VolVis polyhedral representation of a complex scene. (b) VolVis PARC rendering of the

scene.