226 
we want to contemplate the view point also, for the local 
reflection of very smooth surface, a better algorithm is the 
Phong model: 
I r = Ijw{i,}i)cos"a (82) 
i n 
where w(i,X) is the reflectance curve, being the ratio between 
the reflected light and the incident one. 
All the contributes can be considered with: 
/ = K a I a + Ij(K d cos0 + K s cos"a)/d (83) 
22. The animation 
The visualisation on screen of a sequence of projection 
frames, taken from points of views slightly different from 
each other, with a frequency equal or greater than 20 slides 
per second, gives the impression of animation. 
The procedure for the animation is as follows: 
select a path 
select the virtual camera focal lenght 
generation of two-dimension images along the path. 
With the type of computer we used, an image is 
generated in about 20 seconds of computation 
input of the separated images in a commercial computer 
program for the vision of the motion of the survey. In 
this stage, the computes shows 20 images per second. 
The duration of the scene is then 400 hundreds time 
shorter than the computing time. If we used a computer 
400 hundreds times faster, we could have interactivity. 
THE EXPERIENCES 
We present some examples of architectural surveys where the 
virtual reality has been applied. 
They are: 
• Notre dame du haut chapel in France by Le Corbusier 
• Passetto War Memorial, Ancona 
• Flowers Market, Pescia 
• G. A.Baxes, 1994 - Digital image processing, John 
Wiley & Sons, New York 
• J.D.Foley, A.Van Dam, S.K.,Feiner, J.F.Hughes 1990- 
Computer Graphics: Principles and Practice, Addison- 
Wesley, Readings 
• R. C. Gonzales, P.Wintz 1987 - Digital image 
processing, Addison-Wesley, Readings 
• R. Marangoni, M.Geddo 1996 - Le immagini digitali, 
Hoepli, Milano 
• W. J. Mitchell, M. McCullough, 1995 - Digital Design 
Media, Me Graw Hill, New York 
• W.K.Pratt, 1977,- Digital image processing, John 
Wiley & Sons, New York 
• D.F.Rogers, J.A.Adams 1990 - Mathematical Elements 
for Computer Graphics, McGraw-Hill International 
Editions, 
• A. Watt, 1993 - Computer Graphics, Addison-Wesley, 
Wokingham 
• A. Watt, M. Watt, 1992 - Advanced Animation and 
Rendering Techniques: Theory and Practice, Addison- 
Wesley, Wokingham 
Conclusions 
Computer graphics interests an increasing number of 
disciplines. Mechanical designers, architects use it more and 
more. Among the users of computer graphics a good place is 
taken by operators of geomatics, like surveyors, 
photogrammetrists, etc. Apart spirit levelling, any survey is 
normally full three-dimensional. By tradition we were used to 
represent it only in two dimensions in plans, front views, 
cross sections. Now, by means of computer graphics and 
virtual reality not only it is possible to represent it in more 
realistic 3D-views but also to move it or to move around it to 
achieving a better understanding and perception of it. The last 
step could be the interactivity, were the operator can chose its 
path a to walk along it. It is always possible from 3D model 
to obtain the traditional views. 
REFERENCES 
• D. Ballard, H.C. Brown, 1984 — Computer Vision, 
Prentice-Hall, Englewood