Computer graphics for modelling

Publisher’s version / Version de l'éditeur:

Canadian Architect, 30, 3, pp. 29-31, 1985-03

READ THESE TERMS AND CONDITIONS CAREFULLY BEFORE USING THIS WEBSITE.

https://nrc-publications.canada.ca/eng/copyright

Vous avez des questions? Nous pouvons vous aider. Pour communiquer directement avec un auteur, consultez la

première page de la revue dans laquelle son article a été publié afin de trouver ses coordonnées. Si vous n’arrivez pas à les repérer, communiquez avec nous à [email protected].

Questions? Contact the NRC Publications Archive team at

[email protected]. If you wish to email the authors directly, please see the first page of the publication for their contact information.

NRC Publications Archive

Archives des publications du CNRC

This publication could be one of several versions: author’s original, accepted manuscript or the publisher’s version. / La version de cette publication peut être l’une des suivantes : la version prépublication de l’auteur, la version acceptée du manuscrit ou la version de l’éditeur.

Access and use of this website and the material on it are subject to the Terms and Conditions set forth at

Computer graphics for modelling

Vanier, D. J.

https://publications-cnrc.canada.ca/fra/droits

L’accès à ce site Web et l’utilisation de son contenu sont assujettis aux conditions présentées dans le site LISEZ CES CONDITIONS ATTENTIVEMENT AVANT D’UTILISER CE SITE WEB.

NRC Publications Record / Notice d'Archives des publications de CNRC:

https://nrc-publications.canada.ca/eng/view/object/?id=fbb2985f-f2f8-43ff-b69f-087c1c3fafd1

https://publications-cnrc.canada.ca/fra/voir/objet/?id=fbb2985f-f2f8-43ff-b69f-087c1c3fafd1

3er

1 3 ; ; .

f

a

rff3

_{National Research}

_{Conseil national}

N21d

)$I

_{Council Canada}

_{de recherche8 Canada}

3.

1293

z*

2

Division of

Division des

BZtfX3

Building Research

recherches en batiment

Computer Graphics for Modelling

by D.J. Vanier

Reprinted from

Canadian Architect

Volume 30, No. 3, March 1985

p. 29-31

ANALYZED

DBR Paper No. 1293

Price $1

.OO

ABSTRACT

A

three-dimensional computer graphic of the new Canadian Museum

of Man, presently under construction, is used to explain

current techniques for entering the building data and

manipulating the geometric model.

The final image consists of

200 sculptured surfaces used to represent the exterior

envelope, windows and roof systems.

Landscape architecture

features are electronically stippled on to the geometric model

to produce trees, bushes and building ivy.

Un dessin rgalisg par infographie en trois dimensions du

nouveau Musge

national

de l'Homme,

actuellement en

construction, sert d'exemple dans cette communication pour

expliquer les plus rgcentes techniques dtentr6e des donn6es

relatives aux bstiments et de manipulation des modsles

ggomCtriques.

L'image finale est composge de 200 surfaces en

relief qui reprssentent l'enveloppe extgrieure du b3timent, les

fenstres et le toit.

Les caractgristiques du paysage, telles

que les arbres, les arbustes et le lierre, sont pointillges

glectroniquement sur le modZle ge'odtrique.

COMPUTER GRAPHICS

FOR MODELLING

Computers: D.J. Vanier

A well-defined series of steps is required to produce a computer model of a building (the term "computer model" implies a graphic representation of the shape and form of a building and does not mean a complete computer data base of all the building

components). Unfortunately, it is not as simple as demonstrated at computer shows: "Push this button and a three-dimensional, fully shaded, colour image of your buildina will amear in

-

_.

.

The modelling of the new Museum of Man by architect Douglas

Cardinal, under construction in Hull, illustrates the process in practice. The computer model was

constructed using the architect's plans and physical model. This produces a computer replica which faithfully duplicates the building for presentation purposes. The eventual use of these techniques will use the software as a design tool, where the building model becomes r w a t l s m

in the designer's hands.

Building entry

In this example the building, information was obtained by

extracting the data from the concept plans on a digitizer. The software used allows the representation of the curvilinear form on the screen with a minimum number of control points. That is, the perimeter does not have to be traced millimetre by millimetre; only significant curve changes have to be located.

A three-dimensional image is obtained by creating a similar (or dissimilar) outline at a different height. These two curves, when connected, form a module that can be manipulated graphically by the designer. In this case the module is a complete storey of the building. A number of modules would comprise the computer model. These can all be translated, rotated, or scaled individually or collectively.

Module manipulation

Rotation and translation are used to

orient or to position modules or groups of modules, while scaling permits a change in dimensions in the X, Y or Z directions of modules or groups of modules.

Transformation implies a combination of any or all of the above.

A module can be rotated around the X, Y or Z axis. This type of rotation is required to place modules with respect to a background or other modules. In some computer graphics systems the rotation of the wire frame module occurs in real time; that is, the network of lines and nodes can be moved intera&ivW&-m the screen by the user. This must not be confused with a method for viewing the modules. In this case, the object does not move but the user changes his eye point by changing position and distance from the object. The computer software will then calculate the new location and display the resulting image. This position change may help the designer find a better vantage point for module placement.

A translation or move can be carried out along the X, Y, or Z axis. The same is true for scaling an object. The first feature allows the designer to locate a module or group of modules on a site or in relation to each other. Scaling offers the ability to quickly alter the aspect ratio of a module.

The three-dimensional module can then be transformed, that is,

translated, scaled or rotated to the desired angle and location by the user. An extremely useful

transformation is the ability to move from orthographic to perspective with ease. Although this is a lengthy

manual procedure, computer processing speeds enable users to view one-, two- or three-point perspectives in a matter of seconds, depending on the complexity of the wire frame image.

Module placement

The user can select a portion of the total image, the "active module(s)," to rotate, scale and translate, leaving the remaining "passive modules" in their relative locations. The entire set of modules can also be manipulated together. The use of different coloured meshes allows the designer to distinguish different modules on the complicated image.

Colour shading

When all modules are in place, the three-dimensional mesh image can be enhanced by hidden line suppression, final shading and lighting manipulation. Hidden line suppression is carried out by specialty software packages; depending on the complexity of the wire frame and speed of the computer, this may take from one minute to one hour. Hidden line suppression is normally not required for colour representation, as the colour infill will eliminate the hidden back lines. Textbooks on computer graphics explain several methods for this procedure.

The three-dimensional shading of the mesh model is the most computer-intensive portion of the work. The mesh is divided into triangles automatically by the software package for the calculation of the colour. The colour of every triangulation patch of the grid is calculated by the computer depending on the location of the viewer with respect to the location of the light sources. The software must take into account viewer location, location of the light source, the red, green and blue components of the colour, and the opacity of the object itself, to calculate the colour of each patch of the grid. The individual modules are then shaded on the screen one at a time. This software package uses a Z-buffer technique for recording the Z-depth (depth into the screen) of each triangulation

COMPUTER GRAPHICS

patch of every module. This allows noncomplex shaded objects in real 1

the superimposing of modules, time, but in most cases fhese are Architect's model of the Museum of Man,

regardless of their depth in the final specially designed, dedcated currently under construction in Hull.

model. systems. The type of equipment

Colour shading should not be currently available is not powerful 2

The operator has placed the building

confused with shadowing. A portion enough to take a complex _{plan on a digitizer and has entered a} of the module facing away from the three-dimensional shaded object _{number of points graphically on the} light source will appear darker than such as the Museum of Man and _{screen. The curve on the screen is only} one facing the source. Most rotate it on the screen in front of the one half of the building perimeter.

graphics modelling systems offer designer. This will be available in the this shading capability. To cast future with the advent of faster 3

shadows, however, extra equipment and special graphics The example is shown as a 3 0

~ a l ~ ~ l a t i ~ n ~ are required by the processors for handling large data orthographic wire frame. It is quick to computer to determine which bases of graphics information. display and a module can be rotated modules will block the light source, Film and video clips have easily in seconds.

thus putting other modules in their presented 'dynamic walk throughs

shadow. These techniques use ray or fly throughs of computer House rotated around the Y axis.

tracing methods which are not graphics models of buildings. These available on most commercial are currently produced by manually 5

systems. _{or semiautomatically splicing large} The user changes his viewing position to

numbers of computer generated still the right (shown by the white angle on

Final image images. the horizontal plane) and alters vertical

At times it becomes too costly to Computer graphics can display position as depicted by the blue angle.

represent specific objects in design information to the architect _{defined (cyan circle).} The distance from the object can also be three-dimensional space. Various and present a realistic

landscaping and landscape representation of a building. It will 6

architectural effects can be be some time before designers House translated along the X axis.

superimposed on the completed abandon conventional modelling

image after the entire computer techniques and before these 7

graphic object is represented. A computer graphics tools will be cost House translated in the X direction and

"Paint" program allows the designer effective. The hardware cost for high by a Of in

to electronically stipple trees and resolution computer modelling is

bushes. Trees are created around $400,000 but these costs 8 _{House transformed in perspective view.} individually by applying colours from should soon be reduced to one-half

a "paint palette." These trees or or one-third. The current process is 9

other objects can then be stored for laborious, time intensive, costly and The building is placed on the landscape

recall and duplicated wherever repetitive. The warning, caveat (another module) and the various

desired on the shaded model. emptor, is critical when considering components are oriented for

The final view of the building is a a computer graphic system for visualization. This is only the wire frame,

complete three-dimensional model. modelling buildings. It may be not the fully shaded object; it appears One view lo~ation of this image can impressive, but man-weeks of work ''lid because the mesh grid lines are take from five minutes to five hours and hundreds of thousands of close.

for the computer to calculate. This dollars lie behind every image ₁₀

of course is entirely dependent on presented to the client at a _{Approximately half of the land has been} the size and speed of the computer computer equipment demonstration. shaded. Location and direction of the

and software. light source are selected by the designer, as is the colour of both sides of the

Notes

Dynamic images Building data entered by Dana Vanier of module.

A number of techniques can be the Division of Building Research and ₁₁

used for the real-time manipulation Jamie Worling, an architecture student _{The tree was created by pointing at}

of lighting effects or colour. employed at the Division of Building _{desired colours on the palette and}

"Look-up Tables" record the colour Research. BSP3D software developed by _{positioning these colour dots in the}

of each pixel or picture element in a Ken Evans of the Computer Graphics _{brush area. The finished tree becomes}

special fast access portion of Section, Division of Electrical _{the brush, which is then applied onto the}

computer memory. Changing the Engineering, National Research Council. shaded model.

colour reference will modify all Commercially available hardware

employed with a prototype colour

Occurrences Of that cOlOur On the _{graphics processor. This article is a} 12

screen in micro seconds, thus _{contribution of NRC's Division of} Complete 3 0 computer image. The

landscape is also 3 0 and shaded, as are

facilitating colour scheme changes. Building Research and is published with _{the sidewalks and ponds.}

T h i s p a p e r ,

w h i l e b e i n g d i s t r i b u t e d i n

r e p r i n t form by t h e D i v i s i o n of B u i l d i n g

R e s e a r c h ,

remains

t h e c o p y r i g h t of

t h e

o r i g i n a l p u b l i s h e r .

It

s h o u l d n o t be

r e p r o d u c e d i n whole o r i n p a r t w i t h o u t t h e

p e r m i s s i o n of t h e p u b l i s h e r .

A

_{l i s t}

_{of a l l p u b l i c a t i o n s a v a i l a b l e from}

t h e D i v i s i o n may be o b t a i n e d by w r i t i n g t o

t h e P u b l i c a t i o n s S e c t i o n , D i v i s i o n of

B u i l d i n g

R e s e a r c h ,

N a t i o n a l

R e s e a r c h

C o u n c i l

of

C a n a d a ,

O t t a w a ,

O n t a r i o ,

K l A

_OR6.

C e

document

est

d i s t r i b u g s o u s forme de

t i r 6 - 3 - p a r t

par l a D i v i s i o n d e s r e c h e r c h e s

e n b h t i m e n t .

Les d r o i t s d e r e p r o d u c t i o n

s o n t t o u t e f o i s l a p r o p r i C t C de 1 ' 6 d i t e u r

o r i g i n a l

.

C e

d o c u m e n t n e p e u t S t r e

r e p r o d u i t en t o t a l i t 6 ou e n p a r t i e s a n s l e

consentement de l ' g d i t e u r .

Une

l i s t e

d e s p u b l i c a t i o n s de l a D i v i s i o n

p e u t S t r e o b t e n u e en 6 c r i v a n t

3

l a

S e c t i o n

d e s p u b l i c a t i o n s , D i v i s i o n d e s r e c h e r c h e s

e n b h t i m e n t , C o n s e i l n a t i o n a l de r e c h e r c h e s

Canada, Ottawa, O n t a r i o , K I A OR6.