D. Hidson Chemical fiotection Section Protective Sciences Division

DEFENCE RESEARCH ESTABLISHMENT OTTAWA TECHNICAL NOTE W 1

PCN 051 LO

July 1988 Ottawa

Best Availa

This paper contains a review of the ex2anding use of computers and computer-aided design in the f lelds of bio-engf neering, human engin-eering, medicine and anthropometry. Work done in recent years on modelling complex biological shapes and some methods of shape analysis are assessed. A bi bllography is included.

Cette note technique contient une revue ds llexpansion dans llutilisation des ordinateurs et de la conception assist4e par ordinateur dans les dmaines de la bio-ingbnierie, de l'ing6nierie humaine, de la m6decine et de 11anthropom6trie. Cn dvalue aussi le travail accompli au cours des recentes ann6es dans le but de moddliser les formes biologiques c~mplexes de m6me que quelques m6thodes dlanalyse des formes. Une bibliographic est incluse.

1.0 INTROQUCTION . . . . . . . . . . . . . . . . . . . . . . . . . 1

2.1 5X;ILY BICZ:ICINEi3INC ATTEPPTS . . . . . . . . . . . . . . 1 . . . . . . . . . . . . . . . . . . . . . 2.2 C3ASfi SIWLATICN 4 . . . . . . . . 2.3 MEDICAL APPLICATIONS OF COMPUTER MODELLING 6 . . . 2.4 COYPUTER-4IDED DESIGN AND BIONECHANICAL ENGINEERING 10 I 2.5 SHAPE ANALYSIS AND COMPUTER MODELLING . . . . . . . . . . 13 . . . . . . . . 2.6 CCMPllTER MODG'LLINC OF ANTHROPOMETRIC DATA 14

. . . . . . . . . . . . . . . . . . . . . . . . . . 3.0 COKLUSIONS 17

. . . . . . . . . . . . . . . . . . . . . . . . . . 4.0 REFERENCES 17

. . . . . . . . . . . . . . . . . . . . . . . . . ! 5.0 BISLIOCRAPHY 19

Today, almost every branch of engineering uses com t e r 3 in one

no sxception. fl -- -

P form or another and medical science, anthropometry and bid>ngineering a r e

%The use of computers aas come r e l a t i ve ly l a t e t o these d i sc ip l ines a3 largo amounts of computing power and sophisticated graphics a r e required fo r the complex data generated by the human body. I f one is using computers to generate a graphical representation of the human body ( a s i n anthropcmetric s tud i e s ) or t o determine the shape of the cockpit of a r 'igater a i r c r a 3 , large q c a n t i t i t s of data must be handled, a s r a r e ly a r e these var iables expressable as simple geometric functions. One of the reasons for the delay of computer applications has been the lack of the capab i l i t i e s of computer graphics t o render thdse data in a useable and v i s ib l e form. The recent advances in image gene~at ion and processing, i n terms of complexity and speed, have enabled workers in these f i e l d s t o adopt computers for tasks which would have seemed impss ib l e only a few years ago.

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This paper contains a short review of some oP the appl icat ions of computers i n bio-engineering and ths use of computer-aidad design in anthropanetrics, bio-engineering and medical science. L&, ( l C T )

2.0 LITERATURE REVIEW

2.1 EARLY BIOENGINEERING .iTTEMPTS

One of the ehr-lier attempts t o process human factor quant i t i es by means ot' cornp1:ters and t o use t h i s computerized process as a design aid was reported i n "Combiman - Computerized Bio-mechanical Man-Modelw by K.H. Kroemer ( 1 ) . Combiman was a11 e f f c r t t o model the s i z e , shape, mass properties and jo in t movements of a human form graphically, using cornpcter graphics. The idea was t o prodme a computerized, a n t h r o p o ~ e t r i c , biomechanical and ::.gonomic model of the human form.

Trr c o n s t r u c t t h i s ~ o d e l , t h e problem was apprcached i n thrce, f d i a t i n c t c o n c e p t u a l phases : a n t n r o p o o e t r i c , b iomechanical and ~ ? r ;>nomet r i c . Tha f ( r s t p h a s e , t h e ~ A n t h r o p o f n e t r i c a n a l o g n , was d e s i g n e d t o e n s u r e t h a t t h e model c o n t a i n e d t h e s t a n d a r d a n t h r o p o m e t r i c d a t a o f t h e w b j e c t s , t h a t d a t a was s t o r e d on s u b j e c t s wear ing s p e c i a l equ ipment , and t h a t c a l c u l a t i o n s on changes i n a n t h r o p o m e t r i c d e s c r i p t o r s (p roduced by v a r i a t i o n s i n p o s t u r e , e tc . ) c o u l u be done. The second p h a s e , t h e a b i m e c h a n i c a l a n a l o g a , was d e s i g n e d t o r e p r e s e n t body mechan ics by w>del l i . lg t h e l i n k a g e s y s t e m and mass p rope l ' t i e s of t h e human body. The combina t ion o f t h e s e two p h a s e s g e n e r a t e d t h e t h i r d p h a s e , t h e "ergonomic phasea . T h i s was t o combine t h e p h y s i c a l c h a r a c t e r i s t i c s of the human body and iho p h y s i c s of t h e workp lace i n such a way a s t o a s s e s s i n t e r a c t i o n s between v a r i a b l e s and i n d i c a t e t h a t c e r t a i n physically-def!.ned t a s k r e q u i r e m e n t s can bo met w i t b i n t h e g i v e n c o n s t r a i n t s .

The first models ( b e f o r e Combiman) were of t h e v a r i o u s n s t i c k m a n w t y p e : s t r a i g h t l l n e c o n n e c t i o n s o f two- and th ree -d imens iona l j o i n t s , b u t i n 1964, Hanavan deve loped a model o f t h e human body w i t h i n e r t i a l p r o p e r t i e s which was, i n i t s e l f , a major advance. The Combiman model was t o be a f u r t h e r advance .

The first phase o f development was t o a l l o k comple te s t o r a g e o f a n t h r o p o m e t r i c i n f o r m a t i o n . The a o d e l l i n ~ done u s i n g t h i s i n f o r m a t i o n was t o m a n i p u l a t e t h e s t o r e d d a t a t o t a k e i n t o accouqt a c t u a l changes r e p r e s e n t a t i v e o f r e a l working sf t u a t i o n s . The second phase would i n c o r p o r a t e dynamic p r o p e r t i e s , t h a t is, the model would react t o e x t e r n a l f o r c e s s u c k a s g - f i e l d s and v i b r a t i o n . The " a c t i v u n v e r s i o n would i n c o r p o r a t e i n t e r n a l f o r c e s , t o r q u e s , work and power c a p a b i l i t i e s . The t h i r d phase o f t h e model i n c l u d e d models o f t h e workplace w i t h which t h e Combiman model f r t e r a c t e d .

I n t h e l a t e 1 9 6 0 ' s and e a r l y 1970 '3 , s e v e r a l a t t e m p t s were made t o model t h e human form. B e c a u o ~ computer g r a p h i c s i n t h o s e d a y s was a n i n f a n t t e c h n o l o g y , most o f t h e computer models r e l l e d h e a v i l y o n c e r t a i n a l g o r i t h m s t o compute t h e & > i t i o n and motion o f t h e mode l led form w i t h a v e r y limited CRT d i s p l a y . Some models (Bulgar (1 967) deve loped by Popodimi t rov (21 , D y n a s t i c k (1970) deve loped by W a r t l u f t (31, Torque Man (1968) deve loped by C h a f f i n ( d l and M T M Man (1970) deve loped by K i r p a t r i c k (5)) c o n t a i n e d o n l y i n f o r r n a t i c n on t h e body's l i n k s and j o i n t s . Only t h e s h a p e and s t r e n g t h o f v a r i o u s j o i n t s wdre inc luded as o t h e r v a r i a b l e s . Torque Man was o n l y a two-dimensional model. Some o t n e r models , Boeman (deve loped by Boeing A i r c r a f t Company i n 1971 ( 6 ) c o n t a i n e d some mechan ica l o r e r g o n o m e t r i c v a r i a b l e s . Dynas t i ck , a1 though a st1 c k model, d i d c o n t a i n some mass p r o p e r t i e s a s de te rmined by Clawer, HcConvi l l e and Young ( 1 969) .

These models d i d n o t a l l perform t h a same t a s k b u t p r o v i d e d a v a r i e t y o f o u t p u t s d e w n d i n g o n t h e i n p u t . For example, :he Boeing "Boatmann model r e q u i r e d a n t h r o p o m e t r i c d a t a , c o c k p i t d e s c r i p t o r s and a d e f i n e d p a t h of t h e hand a s i n p u t and would o u t p u t t h e j o i n t a n g l e s and a

:.?;w3/fal1 decision a s t o wnether or n s t certair , controls could be reached. ?!ost of those !nodal3 were programs that output cer ta in data and d i d not consist of an array of iinpressive grsphics.

As the Combiman model u33 going t o bs a dynamic model, the aathematlcal s t ruc ture of i t had t o be formulated t o allow e f f i c i en t computer1 handling. Apart f:om performing calculat ions, the model had t o s t o r e large amounts of anthropometric data for s t a t i c configuration displays and to be abla t o handle complex algorithms describing the variou:, motions and ;inkages of the l i m b s and torso. r 'urther, the model had t o be useful while st:ll incoaplete, in other words the algorithms would have t o have the capabi l i ty of being amplified and expanded while remaining functional.

This was an ambitious project , and fouii years l a t e r , in 1376, i t was s t i l l not complete. I t was repopted by F.J. Bates e t a l . ( 7 ) t h a t , a t t ha t time, the model s t ruc ture consisted of 33 l inks , 19 f lex ib le j o in t s , 6 fixed par t s and 9 peripheral par ts . The model s t ruc ture , the number of j o in t s and l inks and the i r arrangement could be changed easily. In t h i s work, the authors developed a programmable, msthematical version of the Combiman model. The hip j o in t was taken as the base point of the l inkages and from t h i s bas3 point a chaln of l inks could be traced t o any peripheral point.

Several ways of describing the man-model were examined, beginning w i t h the simple spec i f ica t ion of jo in t locations. For a r e a l i s t i c man-mode:, the angular l imi ta t ions of the f l ex ib l e j o in t s had t o be represented. This was done by using the Euler angles that a r e commonly used in r ig id body dynamics. Thcse anglen define the three ro ta t ions with respect t o the coordinate axes. Since the l inks were a l l known quant i t ies , a matrix equation could he s e t up representing the transformations a t the pivot points. With a knowledge ox' the approximate maximum, minimum and optimum values of t he Euler angles fo r spec i f ic human jo in t s , the solut ion of a var ie ty of matrix equations w i l l allow the configuration of the Combiman model t o be deduced in normal three-dimen.sior,al space. During the execution or' a task, the paths of peripheral points and ext?emities of the body were known, so the major computing problem iras t o f lnd the values and d is t r ibb t ion of the Eulc? angles of the other jo in t s and so t o generate thc configuration of the model. A couple oi differeRt techniques wepe used for t h i s such a3 multi-dimensional optim1za;ion techniques but suf f ice :t t o say here Chat the Cmbfman project was one of the f i r s t t o address the prcblem of humhn body motions being represented in a computer image. The image here is, of course, a mathematical image and not a sophisticated graphtcs display.

The need f o r knowledge o f how t h e human body behavzs i n t r a u m a t i c s i t u a t i o n s l i k e a u t o m o b i l e a c c i d e n t s is r e a d i l y a p p a r e n t . T h i s , t o o , h a s ?con t h e s u b j e c t o f computer m o d e l l i n g t e c h n i q u e s f o r o b v i o u s r e a s o n s .

Yhen a a t h e m a t i c a l n o d e l l i n g is u s e d , its e f f e c t i v e n e s s is a lways open t o q u e s t i o n . T h i s v e r y problem was examined i n some d e t a i l by G. F r i s c h and J. OIRourke (8 ) . T h e i r papor was e n t i t l e d "The E f f e c t i v e n e s s o f ? t i t h e m a t i c a l Models a s a Human Analogn. Here t h e y c o n s i d e r e d t h r e e b i c m c c h a n i c a l m o d e l l i n g programs, "Three-D Computer S i m u l a t o r o f Motor V e h i c l e C r a s h Vic t imsn (9,101 by Ca lapan C o r p o r a t i o n ; "Crash Victim S i m u l a t o r - L i g h t A i r c r a f t n ( 1 1 1 and "PrometheusN by Boeing ( 1 2 . 1 3 ) . T h i s t y p e of m o d e l l i n g program was deve loped by v a r i o u s companies a s tes ts w i t h human s u b j e c t s were t o o dangerous and e x p e r i m e n t s w i t h m a n i k i n s v e r y v a r i a b l e . A t t h a t time t h e r e had been v e r y l i t t l e s u c c e s s w i t h m o d e l l i n g because o f t h e c m p 1 e x l t i e . s o f t h e human body i tself and t h e l i m i t a t i o n s o f e a r l i e r computers .

A set o f t es t s was d e s i g n e d and carried o u t on human s u b j e c t s . These were c e s t s d e s i g n e d t o m e t s u r e t h o r e s p o n s e o f t h e s u b j e c t t o -Gx a c c e l e r a t i o n s 1.e. s t o p p i n g q u i c k l y . E x t e r n a l a n t h r o p o m e t r i c d a t a was o b t a i n e d f o r t h e body and X-ray d a t a f o r t h e head. The X-ray d a t a was n e c e s s a r y t o a l l o w t h e f i x i n g o f t r a n s d u c e r mounts t o w e l l d e f i n e d a I a t o m i c a 1 s y s t e m s . A l l o f t h e s e programs were v a r i a n t s o f t h e D y n a s t i c k c o n c e p t , t h a t is, a l i n k a g e and p i v o t r e p r e s e n t a t i o n o f t h e human body. Tbese , however, c o n t a i n e d i n f o r m a t i o n on mass, moments o f i n e r t i a , l i n k l e n g t h s and l o c a t i o n s o f va r - ious s e g m e n t s t c e n t e r o f g r a v i t y . O t h e r a t t r i b u t e s oi t h o mode l s were b a l l and s o c k e t j o i n t r e p r e s e n t a t i o n ( e x c e p t f o r e lbows and knees which were consider-ed h inged) . Head-neck and neck- t o r s o movements were i n c l u d e d i n t h e head motion a n a l y s i s ; f r i c t i o n and v i s c o u s r e t a r d i n g f o r c e s were i n c l u d e d i n t h e j o i n t d e s c r i p t o r s .

When e a c h o f t h e programs was t e s t e d , a v a r i e t y cf v a r i a b l e s was r e c o r d e d i n c l u d l ng a n w l a r a c c e l e r a t i o n o f t h e head, l a p be1 t l o a d s , head a n g u l a r v e l o c i t y and r e s u l t a n t l i n e a r a c c e l e r a t i o n .

The C a l s p a n 3-D Computer S i m u l a t o r c o n t a l n e d a s i x t e e n - s e @ n e n t , f i f t e e n - j o i n t r e p r e s e n t a t i o n o f t h e man w i t h t h e p r o v i a i o n f o r usage o f a s o p h i s t i c a t e d s h o u l d e r j o i n t model w i t h b a l l and s o c k e t c o n n e c t i o n s and musc les s i m u l a t e d by s p r i n g dampers . A s t h e s i m u l a t i o n s were r u n w i t h t h e s h o u l d e r s t r a p s ' i n p l a c e 1 , t h e t h o r a x c o u l d e x h i b i t g r e a t e r e x c u r s i o n t h a n t h e s h o u l d e r s t h e m s e l v e s .

-1.. ? , ..<. CYSLX pro;-xa '\Cr-mh ' I lc t ln Sinulator - L i q h t Ai rc ra f t ) ' ? r : ~ i ~ t < ? d of 3 ?.?ree-dizensional man-model, a i r2 ra f t seat and restrair?t

:j.;!?:tq. T h i s uas, 2f ccurse, designed t o investigate the crash io r th iness c f varicus aeats and restrai t i t systems for ccmmercial a i r c r a f t . Here, ?!;id se? is and s o f t s ea t s could be simulated as well as forced elongaLion of shoulder s t r a p webbing on an eleven-segment body. The setgent properties were reduced t o f rac t ions of t o t a l body weight and s t a tu re . These f rac t ions , along w i t h other fac tors to account for body s i z e , were used t o ca lcu la te the subject ' s antt~ropometric character is t ics . Th i s ycTrarn dlffered somewhat from the Calspan model in that the head and neck :i:?re t reated as one nass un i t .

The Prometheus program from Boeing was a two-dimensional crash victim simulator w i t h an occupant consisting of seven l inks , l ap and 3houlder be l t s and an interact ion w i t h the environment through a non-linear finite-element model of the s ea t s t ruc ture . A s many variables as possible Mere made t o match those in the Calspan program ( for instance, head-neck center of gravity posi t ion) . This was t o enable the investigators t o make 5s many cmparlsons as possible between the actual execution methods of the programs. T h i s had t o be done in order t o ensure that differences in the r e s u l t s were not due t o differences in the numerical integration procedures t u t t o differences in the aodels themselves. The programs were run t o ensure tha t they were v i r t ua l l y error-free but differences i n the numerical integrat ion packages cannot be t o t a l l y ruled out as a source of differences i n the r e su l t s .

The various man-models consisted of a variety of jo in t s and l i nks and these were modified ( for instance, the Calspan model had the head pivot and ciavicular j o in t s locked) so a s t o compare more direct ly w i t h the Prometneus model.

The cmparison of these models showed that resu l t s were f a i r l y consistent but s ign i f ican t differences were apparent, for instance, i n tka predicted be l t loads and the time tha t peak forces were attained. I t was found tha t although the r e s u l t s of simulation programs agreed w i t h one another qu i te well , t h e i r ab ' l i t i es t o rep l ica te t e s t data were generally quite poor. Because a l l the programs were very sensi t ive t o i n i t i a l conditions, the lack of precise input parameters could lead t o very d i f fe ren t ~ e s u l t s due t o only a small variation i n these parameters. Despite the agreement of the program re su l t s , the comparison of these with the r e s u l t s of actual tess ing snowed tha t the assessment of what were the relevant parameters from which t o form a man-model needed some serious revis4 on.

Some of the problems t h 9 auchors encountered are recrdily understandable. Modelling a dynamic, biological system with a simple, mechanistic schematic w i l l undoubtedly demonstrate differences and discrepancies. Bearing in mind the complexity of the hman organism, it is perhaps remarkable t ha t such gcgaod agreement was observed.

2 . 3 3EDICAL APPLICATICNS OF COYPUTER "DELLiNC

As c a a p u t e r g r a p h i c s h a s come of a g e , i t has come t 3 be a v a l u a b l c t o o l i n ths medica l u o r l d .

X o d e l i i n g geometry i t s e l f , however, 13 e a s i e r a s a l a r g e number o f aa3umptions a o o u t dynamic p r o p e r t i e s o f sys tems c m be d i s p e n s e d w i t h . The g e m e t r l c s t r u c t u r e s i n b i o l o g i c a l fo rms t h a t can be modelled v a r y i n c o m p l e x i t y f r o 3 t h e i c o s a h e d r a l s t r u c t u r e o f v i r u s e s ( 1 4 ) t o t h e s h a p e o f human bone s t r u c t u r e s . ( R e f e r e n c e 1 4 w i l l n o t be reviewed i n d e t a i l . )

With t h e a d v e n t o f c m p u t e d t m o g r a p h y (CT) i n t h e 1570's I t h c a m e p o s s i b l e t o p e r f o r n t h r a e - d i m e n s i o n a l r e c o n s t r u c t i o n and v i s u a l i z a t i o n o f t h e v e n t r i c u l a r s y s t m and b r a i n l e s i o n s ( 1 5 ) . When CT is w e d on a p a t i e n t , a b o u t t w e n t y images a r e produced and t h e s e a r e a l l t u o - d i m e n s i o n s a l images. The a u t h o r s h e r e used computer s o f t r a r e tc g e n e r a t e a r a s t e r i s a g e . They used some t e c h n i c u e s t h a t u t i l i z e d c u r r e n t tuo-d lmens iona i CT head d i s p l a y sys tems . The c m p u t e d s u r f a s e s were g e n e r a t e d by t a k i n g t h e set o f c o n t a u r l i n e s de f ined by t h e a n a t o m i c a l o b j e c t and i n t e r s e c t 1 r . g them w i t h a set of p a r a l l e l p lanes . The s o f t w a r e t h e n t o o k t h e s e and g e n e r a t e d a t r i a n g u l a r mesh ( s i m i l a r t o a f i n i t e - e l e m e n t mesh) .

The a c t u a l c o n t o u r l i n e s were o b t a i n e d from t h e t m o g r a p h y Images i!i a v a r i e t y o f ways. A c o o r d i n a t e d i g i t i z e r was used t3 select p o i n t s on the two-dimensionai c u r v e s g e n z r a t a d from t h e CT scan. These p o i n t s were t h e n j o i n e d by a s t r a i g h t - l i n e segments . Also, CT s c a n s c o u l d be d i s p l a y e d o n a g r a p h i c s d i s p l a y and a s c r e e n c u r s o r used t o f l n d t h e r e q u i s i t e p o i n t s . The mesh was t h e n g e n e r a t e d and a p e r s p e c t i v e three-dimensional r e p r e s e n t a t i o n d i s p l a y e d .

From t h e s e d i s p l a y s , t h e m e d i c a l s t a f f involved o b t a i n e d a c l e a r p i c t u r e o f v a r i o u s i n t e r n a l p a r t s o f t h e body. Also, volumes c o u l d be estimated from t h e s u r f a c e c o n t o u r s d i s p l a j e d . The major d i s a d v a n t a g e o f t h i s sys tem was t h a t o b j e c t s t e n d e d t o become confused when more t h a n three o r f o u r were d i s p l a y e d a t t h e same time. P h i s is still t h e c a s e w i t h z o s t wire-f rame d i s p l a y s today .

V i s i b i l i t y was g r e a t l y enhanced by s u r f a c e shading. T h i s gave t k e image t h e ap?earance o f t h e " s o l i d modeln t y p e o f d i s p l a y and t h e d e p t h - c u e i n g r e d u c e d many o f t h e a m b i g u i t i e s i n pe rcep t ion . The * t i l e d w s u r f a c e ( c o n s t r u c t e d w i t h t h e t r i a r . f l l a r . mesh) u a s a l s o co lo r -coded t o add t o e a s e o f p e r c e p t i o n m d o n c e t h e c o n s t r u c t i o n w a s complete , t h e a n a t o m i c a l o b j e c t s c o u l d be viewed from a n y a n g l e and p a i t i o n .

,A3 expoctcd, as I c r s f ~ ? t u r e s were displayed the aurfacs tcndzd t 3 ? e r -:e confu,sed and c e r e color coding was w?ry important. To make the surlacos aors r e a l i s t i c , a shading algorithm was used on the surfaces. Tne i 7 3 t : ? n s i t y *paintedm on eacn aesh t r langie was l inear ly i n t a r p l a t e d between the ver t ices t o improve depth-cueing. The f lna l inproveaent remcved hidden surfaces from vieu.

A s it was necessary t o observe some of the hidderl surfaces, thev wtv-e rendered ~ i ~ i b l e by diplaying the obscuring surfaces as t ransparsr~t 3ur;ac~s. This was done b y flisolayf.ng each element of the surface as a ?:;.ear comhlnat:on of the occluding surface intensi ty a i d the in tens i ty of t::e surface be5ind i t . T h i s gave an excellent rendition of the surfaces.

There is considerable medical incerest in knowing the volume of various organs in the body. Once the surface had been displayed, t h s v-zlme problem could be tackled by means of a v o l u e , or t r i p l e , integral over tha t region of three-dimensional space. I f the object was regular, anC possessed of a knom geometric form, such a?, an e l l ipso id , then the t r i p l e integral could b- evaluated d i rec t ly . I f a simple and ana ly t ic form was not ava i lab le , an i t e r a t i v e integration procedure was used t o evaluate the volume.

The main purpose of a l l t h i s rnodel l i~g was pre-planning for canplex bratn surgery and rad ia t ioa treatment for tumors. Obviously, in such operations, there is l i t t l e rocm for explorbtion or error . Further, w i th radiat ion treatment, an accurate knowledge of the shape, s i z e and position of the tumor would enable exposures of healthy t i s sues t o hr kept t o a minimum. Repeated use or t h i s technique allows t h o s ize and shape of a tunor t o be monitored during and a f te? treatment.

A similar use of cmputer graphics technology w a s described by H. Aneil and others i n a paper on computerized reconstruction of anatomical s t ruc tures (16). Here the authors reconstructed the ventricular part of an adul t human heart by means of d ig i t i z ing sections. A specimen heart was frozen and cu t in to sect ions one03alf centimeter thick and each section was then phot~graphed. The data was digi t ized and sections were made up. Displays were presentea a s wire-frame sections and a s a so l id , shaded mde l . The d lg i t i z a t i on and displays were performed with an Applicon CAD sys tem. Each sect ion contour had t o contain the same nmber of points s o that a mesh could l a t e r be bu i l t for the shaded surface. The surface was created by generating multiple quadrangular polygons. The shaded and smoothed surface was created from t h i s bu t took large. amounts of computer time - about seven hours in t h i s case.

Apart from j u s t s t a t i c modelling, computer graphics are now being used t o examine and analyze kinematic problems. In a paper en t i t l ed lfComputer-Assiated Analysis of Ligament Constraints i n the Knee* ( 1 71, Langrana and Bronfeld looked a t modelling the shape and movements of some ligaments i n the knee jo in t .

Host of t n o knouledge a b o u t t h e I m z t i o n s of t h e s e j o i n t l i g a m e n t s k35 3cme frcm Luo s c u r c e s : a t u d l ~ s of n o r n a l gait and e x m i n a t i o n o f hman c a d a v e r s . The l o c a t i o n o f t h e a c t u a l l i g a a a n t s was found w i t h t h e a i d o f ccmputer-a ided tomography (CPT) which g i v e s rp.diographic dens1 t y i n f o m a t , i o n . Uos t o f t h e s x t . r a n e o ~ ! t i s s u e was removed f rcm a knee j o i n t , car?, be:r,g t a k e n t o l e a v e t h e l i y a m a n t s uncut . Thin K i r s c h n e r u i r e s u e r o i n s e r t o d l n t o t h e s u r r m n d i n g t i s s u e so t h a t *.he n t t a c P a e n t s i t e s wit!: re3r!?ct ;Q ot'le b r o c o u l d be r e c o r d e d on t h e CT scan.

A Jl g f:xed t h e spec imsn j o i n t i n t h e zero d e g r e e f1ox:on p o s i t i o n . F ixed wire f r a m e s were a t t a c h e d t o t h e j i g s o that: a r ad io -opaque g r i d vcrlld be g e n e r a t e d and show up c n t h e CT scans . Th i s a l l o u e d t h e s c a n d a t a t o 3e d i g i t i z e d and t h e g r i d d i s p l a y a l l9wed t h s s c a l e t o be f i x e d . P r o j e c t o r m a g n i f i c a t i o n e r r o r s were t h u s eliminated.

Two typcrs o f e n g i n e e r i n g a n a l y s e s were performed. I n o n e , t h e W Q

d e n s i t y p r o f i l e a t d i f f e r e n t s c a n s l i c e s was i n v e s t i g a t e d and i n t h e o t h e r , t h o .oav.'-y >: t h a j o i n t w a s r e c o n s t r u c t e d and t h e r e l a t i v e role o f t h e f o u r major i t g m e n t s was s t u d i e d . The d a t a eltabled t h e knee j o i n t t.o be mode l lea w i t h t9 ree -d imens iona l c m p u t a r g r a p h i c s and a l l o w e d a n a n a l y s i s t o be p r i m e d o n how t h e l o a d s i n t h e l igament v s r e s h a r e d .

i

I 1

A c l i n i c a l s t a h i l i t y test u s i n g a d e v i c e knoun a s KT1000 was w e d t o a s s e s s t h i s and t h e p a r t i c u l a r test was a pass ive Craw t es t . T h i s t e s t w a s p o r f o r w d w i t h t h e knca i n t h e n ine ty -degree f l e x i o n p o s i t i o n . A l o a d was a p p l l e d t o t h e ?roximal end o f t h e t i b i a ( t h e t o p end o f t h e lower l e g b o n e a q l o i n i n g t h e kneecap) which pushes t h e t i b i a backwards. T h i j was Cane z g a i n w i t h t h e knee i n t h e twenty-f ive-degree f l e x i o n p o s i t i o n , and a l o a d w a s a p p l i e d t o t h e w o x i m a l end o f t h e t i b i a , t h i s time i n t h e f o r w a r d d i r e c t i o n . The XT:000 a l l o w e d b o t h t h e s e tests t c be p e ~ f o r m e d w i t k a ~ t a n d a r d l o a d o f e i g h t y - n i n e c e w t o w and a p r e c i s e measurement o f t h e i r e l a t i v e bone mot ion was o b t a i n e d . S i x t y s u b j e c t s were testee. The main i

d a t d o f t h e m s i v e d rawer tests were w e d i n t h e s i m u l a t e d test t o i d e t e r m i n e t h e l o a d s h a r i n g i n v a r i o u s l i g a m e n t s of t h e knee. T n i s was done by p l a c i n g t h e c m p u t e r i z e d knee model a t t h s proper f l e x i o n ( n i n e t y o r , t w e n t y - f i v e d e g r e e s ) f o r t h a t p a r t i c u l a r test; c a l c u l a t i n g t h e l e n g t h o f t h e l i g a m e n t s i n t h a t p o s i t i o n and tho71 super imposing t h e p a s s i v e draw S.

;a d a t a . The i n c r e a s e i n l e n g t h o f t h e l l g a m e c t s due t o t h e test c o u l d t h e n be c a l s u a t e d .

S e v e r a l a s s l m p t i o n v and a p p r o x i m a t i o n s were made i n t h e models o f l i g a m e n t t l s s u a i n r e s p e c t o f c r o s s sect1 o n a l a r e a , e l c n g a t i o n pe r u n i t f o r c e a p p l i e d and t h e 11 ke. The bone d e n s i t i e s of t h e CAT s c a n were c o n v e r t e d i n t o d i g i t a l d a t a and a th ree -d imens iona l computer model was c r e a t e d o f t h e e n t i r e knee j o i n t . Combined w i t h t h e d a t a o f t h e p a s s i v e d rawer t e s t t h e i n c r e a s e i n l i g a m e n t l e n g t h d11e t o tile tes t c o u l d be c a l c u l a t e d .

found t n a t t h e p a t t e r n of k*

e longa t ion of t h e l lgamant f l t e r s ua3 1:1 2li:se ,IwT?ernent wl", t>at. 3f t h e zede l . 'd l th c e r t a i n m s m p t l o n s a h u t the nature of t h e ;hys lca l p r o ~ o r t l e s of t h e t i s s u e s some f h i r l y a c c w ~ t e :rod!ctli.rx u e r e made or' t h e i r 3ehavlour under s t - c s s u s ing a ccmputer model.

The p o s s i b i l i t y of u i n g computer-aided des ign i n d e n t a l and r e c o n s t r u c t i v e s u r g e r y has been i n v e s t i g a t e d by Arridge e t a l . i n a paper e n t i t l e d mThree-Dimensional D i g i t i z a t i o n of t h e Face and S k u l l n 118). These new s u r g i c a l t e chn iques have l e d t o more coaplex and s o p h i s t i c a t e d mod i f i ca t i on of more p a r t s o r t h e f a c i a l ske l e ton . This su rge ry now l n c l u d e s t h e o b j e c t o f Improving o v e r a l l f 3 c i a l appearance r a t h e r than hoing l i m i t e d to c o r r e c t i n g pure ly phys ica l f u n c t l o ; ? ~ . Indeed, t h e whoie a r t of p l a s t i c s u r g e r y is devoted t o j u s t t h a t . H 3 3 t 07 t he methods a v a i l a b i e nou o b t a i n o n l y two-dimensional d a t a from photographs, X-rays and CAT-scans. The s t a n d a r d technique here was t o c u t up p r o f i l e photographs magnif ied t o t h e same s i z e a s t h e s tanCard l a t e r a l s k u l l X-ray and t o superimpose t h e s e ove r t h e hard t i s s u e rad iographs . E l e se were then moved around t o produce t h e b e s t r e s u l t s .

Attempts t o overcome t h e problems of a c q u t r i n g a c c u r a t e s u r f a c e d a t a have l e d t o t h e development of stereophotogrammetry, lwer scanning , s o n i c d i g i t f z a t i o n and a v a r i e t y 02 o t h e r techniques of shape assessment . Also, advances i n computer g r aph i c s have enabled us t3 s e e ~ o l i d model l ing and s u r f a c e shad ing brought t o a po in t where e x t r w e l y d e t a i l e d and r e a l i s t l c imaqes can be presen ted .

The approach used h e r e cons i s t ed of a s imu la t i on of t h e o l d t e chn iques . Computerized X-ray a x i a l tomography was w e d . This type of s can was *x?mful a s it could d i s t i n g u i s h beween hard and s o f t t i s s u e s . The three-d imens iona l a s p e c t o f t h e d a t a was still genera ted by t a k i n g s u c c e s s i v e two-dimensional s l i c e s through t h e s u b j e c t (about s i x t y - f o u r p a r a l l e l s l i c e s two m i l l i m e t e r s a p a r t ) and c o w t r u c t i n g t h e th ree- dimensional image. An added d isadvantage of t h i s method was t h a t it w e d i o n i z i n g r a d i a t i o n .

The exper imenta l procedure used a CT scanning system and a t e l e v i s i o n system d r i v e n by a s i n g l e shared microprocessor . Th i s enabled c m p l e t e synch ron i za t i on between p a t i e n t and TV p i c t u r e s can sequence. The d a t a was e x t r a c t e d from t h e s cene by means of two f a m e d laser beams p r o j e c t e d v e r t i c a l l y on t o t h e f a c e fraa an o b l i q u e ang l e and viewed f r a n t h e f r o n t . This method avoided t h e "b l indn s p o t s , such a s t h e s i d e s of t h e nose , t h a t are caused by extreme r e f l e c t i o n a n g l e s from t h e s u b j e c t surf ace .

The two d a t a sets of f a c i a l and skeletal s u r f a c e s u e r e s t o r e d i n t h e computer a s o r d i n a r y th ree-d imens iona l co-ordinates . To produce t h e imago, t h e d a t a p o i n t s were j o i n e d up i n such a uay as t o produced a :?iangular

mesh. T h i s mesh was t3en su r f aced and displayed a s a shaded s u r f a c e wi th hidden l i n e 3 and hidCen s u r f a c e s removed. This was i n terms of con;putlni?; t i a e about two minutes cln a Drrta General Nova. Par': of t h e model (tile 3k in and s o f t t i s s u e p a r t ) was d i sp l ayed a s a aemi-transparent s u r f a c e s o t h a t t h e s k e l e t a l s t r u c t u r e under i t would be c l e d r l y appa ren t .

When t3is p a r t o f t h e procedure was completed, t h e d a t a was i n t h e form r e q u i r e d , that, is, t h e model could be cu t s p t o s i m u l a t e su rge ry . The b igges t remain ing problem wrw t o ga the r da t a on t h e pos t o p w a t i v e e f f e c t s o f r eco f i s t rua t ive s u r g e r y on t h e s k e l e t a l base and t o see how t h i s a f f e c t e d a c t u a l s o f t t i s s u e r egene ra t ion . I t was found d u r i n g t h i s work t h a t t h e problems of g e t t i n g a v a r i e t y o f comouter systems t o i n t e r f a c e could be over came.

2.4 COMPUTER-AIDED D E S I G N AND BIOMECHANICAL ENGINEERING

Ailother very impor tan t p a r t of t h e use o f CAD/CAM i n medical problems is t h e use o f n u n e r i c a l c o n t r o l ( N K ) machining f o r t h e product ion of t h i n g s such a s a r t i f i c i a l j o i n t s i n t h e a r e a o f biomechanical eng inee r ing . Th i s has been desc r ibed i a some detai l by S. Dore and J. Bobyn (191. I n a paper e n t i t l e d "Unique Orthopedic Implantsw t h e a u t h o r s d e s c r i b e d t h e use o f mmputer-designed and manufactured a r t i f i c i a l j o i n t s f o r p a t i e n t s s u f f e r i n g frm v a r i o u s forms of a r t h r i t i s .

I n t h e past, v a r i o u s forms of t reatment had been a v a i l a b l e f o r a r t h r i t i c j o i n t s such a s i n s e r t i o n s of s o f t t i s s u e s between t h e a r t i c u l a t i n g j o i n t s and/or replacement of one of t h e j o i n t s . Th i s was t h e beginning o f "mold a r t h r o p l a s t y n whereby t h e shape o f a metal implant is matched t o t h e geometry o f a j o i n t . The e a r l i e r forms o f t h i s t r ea tmen t f o r arthritis involved making a copy o f t he bone geometry as c l o s e l y as p o s s i b l e t o t h e real t h i n g and f i x i n g t h i s by m a n s of a l o n g s tem i n s e r t e d i r i to t h e medul la ry cana l ( t h e bone marrow channel) . The p r e f e r r e d t y p e o f t r ea tmen t t oday i a v o l v e s t h e replacement of both a r t i c u l a t i n g s u r f a c e s o f I

t h e j o i n t and t h i s has been made p o s s i b l e by t h e development o f s e v e r a l new t echn iques i n c l u d i n g PMA - polymethyl methacry la te - a bone cement. T h i s material acted a s a g r o u t i n g agen t and f i l l ed t h e gaps between t h e

I I p r o s t h e s i s and t h e sur rounding bone t h a t allowed bone t o grow around t h e 1 implant and s e c u r e t h e p r o s t h e s i s i n place.

This process has worked r e l a t i v e l y well i n h ip - jo in t s , which, be ing bal l -and-socket j o i n t s were i n h e r e n t l y s t a b l e . However, f o r t h e knee j o i n t , t h e s t a b i l i t y w a s guaranteed by t h e surrounding muscles and n o t by

any intr insical ly stable geometry. This was an added complication as PMMA had problms as a bondlng agent. I t was weak structurally and had some bad tissue reactions.

What was needed was an implant that had exactly conforming geometry to the shape under repair. T h i s has been done for prostheses by taking an impression ( i n the case of amputee s tmps) b u t for internal joints t h i 3 w a s not possible.

So to circumvent t h i s problem, CT (computerized tmography) w a s used t o take eight scans perpendicula8 t o the lone axis of two femurs resulting i n scans that were four millimeters apart. The result of t h i s process produced a two-dimensional picture of the structure i n a plane. T h i s infomation was manually digitized to produce a three-dimensional 3et of data points. The data was then ready to be handled by an APT-basea p-ogram called SSX7 which represented the surface as an ordered se t of "m by nn points, about s i x t y in a l l .

The macMning was performed on a five-axis milling machine. This avoided problems of repeated machining on a three-axis machine as i n that case the work had t o be reposiCioned on the table so that the cutting tool would not encounter conditions of undercut. Sme surface gouging was reported and the f ina l product, machined out of "NC waxn - a polyestsr material - was compared t o the original by framing a negative of the replica wi th dental impression material and placing the negative on the bone. There was close agreement over most of the surface although erro;'s of three millimeters wers reported.

Errors were also generated by having a four-millimeter gap between

l each tomographic scan: newer devices have reduced t h i s t o one millimeter bu t the problem of excessive radiation doses to the patient may l i m i t the v1abili';y of tco many scans, The three-axis machining introduced errors because the work had to be rotzted on the table to allow a l l the surface t o be cut and be f ree of gouging.

Further work of a similar kind w a s reported by Walker, Rovick e t a1 (20). Here the authors describe the analysis of knee motion and the construction of an average knee joint for prosthesis manufacture. An a r t i f i c i a l knee joint was made up and mounted on a dynamic t e s t r i g in which the coordinate system was based on the femural geometry. b potentiometer on the axis measured the flexion angle of the knee joint and a load ce l l monitored force. Data was stored directly in data arrays in the computer. Two angles and three displacements of the femur relat ive t o the t ib ia , as well as quadriceps force, were displayed graphically as a function flexion angle (knee bend).

The three-disensional motiorr data was used in the design of external joints for a prefabricated leg brace. It was thought that i f the extsrnal joints were constructed t o mimic normal knee motion the brace

would aove synchronously u i t h tne knee and when being u e d t o provide s u o w r t f c r an 1n:wed o r pos t -ope ra t ive knee, t t would provtde nwmal 11 gc3auner.t l e n g t h p a t t e r n s .

The des ign was c a r r i e d o u t us in^ computer-aided des ign snd a des ign o p t i m i z a t i o n process was completed a l s o . The op t imiza t ion o f t h e d e s i < q would not have been p o s s i b l e a i t h o u t CAD a s a complete a n a l y t i c a l method would have been t o o cumbersme. By making small changes i n t h e des ign o f t h e brace and runn ing t h e p'ogram, immediately changes and improvements were v i s i b l e on t h e g raph ic s d i s p l a y .

For some c o n d i t i o n s replacement of t h e e n t i r e knee j o i n t is necessary . Host d e s i m s f o r t h i s use p lanar p ro j ec t ion of t h e h e e geometry but t o a t t empt t o g e t a b e t t e r r e p r e s e n t a t i o n of t h e geometry a procedure u a s a p p l i e d t o de te rmine an "average knee geometryu a s a b a s i s f o r j o i n t design. The s e c t i o n s of twenty knees were ob ta ined and superimposed on t h e computer s c r een where shape v a r i a t i o n s were immediately a p p w e n t . To g e n e r a t e an ave rage shape , t r ansve rae l i n e s were drawn a c r o s s

- t h e p e r i p h e r i e s around t h e p r o f i l e o f superimposed images such t h a t t h e s e l i n e s were pe rpend icu l a r t o t h e mean tangent of a l l p r o f i l e s a t t h a t po in t . I t was found t h a t once t h e s e c t i o n s on t h e main j o i n t bea r ing s u r f a c e s were normalized f o r s i z e , t h e v a r i a t i o n s i n shape were q u i t e sma l l be ing o f t h e o r d e r of one millimeter.

A model of t h e knee was b u i l t up with t h e a e t of average p r o f i l e s . The r e s u l t a n t surf a c e s i n t h e model were modelled w i n g a n a l y t i c a l s u r f a c e s e.g. s p h e r i c a l s u r f a c e s and forms f rom o t h e r g e m e t r i c s o l i d s r a t h e r t h a n us ing a t r u e s c u l p t u r e d s u r f a c e genera ted f r o o sets of s p l i n e curves . Th i s process could be used on one p a r t i c u l a r knee as key dimensions could be taken by means of CAT s cans o r from radiographs and then f e d i n t o t h e s u r f a c e g e n e r a t i n g program enab l ing ind iv idua l i zed des ign t o be performed.

After de termining t h e form of t h e bearing s u r f a c e s , t h e femoral component was designed. The femur could be f lexed on t h e t i b i a and i n any r e g i o n s where poor f i t was detected, modi f ica t ions t o t h e s u r f a c e could be made.

When des ign ing t h e t o t a l knee j o i n t , cons ide ra t i on had to be g iven t o t h e face where meta l and p l a s t i c p a r t s would be working t o g e t h e r . Design problems inc luded deg rees of freedom i n t h e J o i n t motions and how much ahoa ld be al lowed. Various ti b i a l s u r f a c e s were designed by def i n i n g motion o r s t a b i l i t y c r i t e r i a and c o n s t r u c t i n g t h e t i b i a l 3-C s u r f a c e by moving t h e femoral cmponen t through a v a r i e t y of p o s i t i o n s s o de f ined . A s u r f a c e f o r average knee motion was generated by moving t h e femoral component through t h e f l e x i o n range. The su r f ace coordfna tes were s o r t e d i n d a t a a r r a y s and a grid w a s de f ined i n t h e ho r i zon ta l plane and f o r each s q u a r e on t h e g r id t h e po in t wi th t h e maximun y-value r ep re sen ted a po in t on t h e t i b i a l s u r t a c e .

The graphics display was produced u s i n g a so l id s modelling package ca l led Movie.BYU dexloped by H . Y . Chr1ut:ansen and :olleagues a t Brigham Young Untversi t y , Utah ( 2 1 ) . A Gould Deanza Image Processor was used i n conjunction with a DEC minicomputer for the CPU. The Movie.BYU package displays so l id m ~ d e l s w i t h simulated l i g h t sourcev and t h i s combination requ-res a s ign i f ican t amount of computing power.

2.5 SHAPE ANALYSIS AND COMPUTER N D E L L I N G

The most complex part of computer-aidad design is usually the creat ion of CAD databases for complex shapes.

A recent advance in interface techniques was reported by Boulanger ( 2 2 ) . For objects w i t h regular shapes or geometric regular i ty the ana ly t ic design capab i l i t i e s of the CAD s y s t e m a re generally used. But in the case of i r regular shapes (such a s human body forms) the data for such a shape has t o be gathered by some scanning method on a point-to-point basts.

A system was deveioped a t the National Research Council of Canada consis t ing of a l i n e scanning laser and l i gh t sensor. The system can scan in a r a s t e r mode generating Gata in the form of an array of points or it can be used t o make range measurements a t randoaly selected points. The device a l so allows the scanning of an object 360 degrees around a cy l indr ica l axis .

The s y s t e m consis ts of a l a se r l i gh t source, a scan.?ing mechanism and an off-axis detector. The projection and detection of the l i g h t spot and its detection had t o be done by a synchronized system so a pyramidal mirror was constructed for t h i s . The distance from the projector t o the ob jec t ' s surface was calculated simply by means of t r iangulat ion given the known or ien ta t ions of the projector and detector. The detector is a l a t e r a l e f fec t photodiode deposited on a sens i t ive layer . Because of the s t ruc ture of t h i s camera i t was possible t o obtain ref lectance data from the object and 3D range data. The resolution avai lable i n the x- and y- dimensions was 1 mm and i n the Z-dimension 0.5 mm.

The disadvantage with the r a s t e r scan process (any r a s t e r scan process! was tha t the whole f i e l d of view had t o be d ig i t i zed before any depth information on spec i f i c data points could be extracted. To overcome tha t problem, the authors designed a new model of camera tha t dispensed with the pyramidal mirror and used a plane mirror. The scanning minors were very precisely control lable . A cyl indrical scanner, based on the same

tc?chnlque a s t h e ralrdom t c c e s s s c a n n e r , was developed and t h i s enabled an c b j , x t t a be p l a c e d dn a r B o t a t i F g t a b l e and scanned ~p and down a long t h e a x i a l dimension s o chat c a . p l e t e 300° c y l i n d r i c a l da t a could be ob t a ined .

To r e n d e r m u l t i p l e views of an ob;ect , the d a t a o b t a i n e d 'ram d i f f e r e n t p o s i t i o n s had t o be merged. For i r r e g u l a r o b j e c t s and a camera which 1s not a p o i n t t h i s can be q u i t e diff1cu:t as t h e l o c a t i o n of a r e l i a b l e o r i g i n is important,. For a c y l i n d r i c a l scan, t h e merging of d a t a was f a i r l y s t r a i g h t f o r w a r d . A s c a n was performed and t h e o b j e c t r o t a t e d th rough a known a n g l e and scanned aga i i l . The coord ina te system wa3 locat.ed by t h e a x i s o f + b e c y l i n d e r and t h e merging of a l l t h e views was done by a f a i r l y s imp le tna:lematical c a l c u l a t i o n on a l l the da ta . (Co-ol 'dinati r o t a t i o n s on a l l t h e d a t a s e t s ) . T h i s enabled the d a t a t o be c o l l e c t e d w i t h no o v e r l 2 p between t h e d a t a - s e t s .

Large q u a n t i t i e s o f d a t a here gene ra t ed ; too much f o r s u r f a c e r e n d x i n g bv means of r e g u l a r g r aph i c s . The d a t a s e t was pared down t o a 256 x 256 a r r a y of r ange d a t a po in t s . Even t h i s s i z e of o b j e c t o r model was ve ry l a r g e and cou ld no t a d e q u a t e l y be displayed by a wire-frame image. So t o overcome t h i s d i f f i c u l t y t h e d a t a was sampled eve ry i - t h p o i n t and p re sen t ed a s an a r r a y o f 20 x 20 o r 40 x 40 points . Sometimes it was r e q u i r e d t h a t d a t a p o i n t s be added f o r s a n e o f t h e s p l i n e c u r v e s i n t h e geometry t o be complated. I n a B-sp l ine r e p r e s e n t a t i o n o f t h e d a t a , t h e p o i n t s bacome t h e nodes of t h e curves . The f i n a l form of t h e d a t a p r e sen t ed a surface r e n d e r i n g and i t was a l s o i n a form that cou ld be modlf i e C f o r a CAD/CAM machining package such a 3 ?VLYHEDRAL NC.

2.6 COMPUTER MODELLING OF ANTHROPOMETRIC DATA

D e s p i t e t h e fact t h a t complex s u r f a c e s can be scanned by v a r i o u s t e chn iques and model led on a computer, s e v e r a l important problems remain wit,h an th ropome t r i c model l ing t e chn iques .

Antkopometry u s u a l l y d e a l s w i th l a r g e q u a n t i t i e s o f po ln t - t o -pa in t d a t a t aken f r m a human popu la t i on sample r e p r e s e n t a t i v e o f t h e n a t i o n o r t h e l a r g e r popu la t i on t h a t t h e sample was t aken Pram e.g. t h e m i l i t a r y f o r c e s a f t h e n a t i o n . If t n e d a t a was t o s e r v e as the des ign b a s i s f o r c l o t h i n g , such as u n i f o m s , o r p r o t e c t i v e equipment, such a s ga s masks o r he lme t s , t h e n a s t h e s e form of d a t a a v e r a g i n g des ign b a s i s f o r a qas and f a c e dimensions i n

v:11 o n l y be made i n a small number of -sizes, some must be c a r r i e d o u t . For instance, t o produce a mask o r helmet, one would take va r ious c r i t i c a l head t h e su rvey and a v e r a g e them. S t a t i s t i c a l d a t a would

t h e data presentation. In the gradient s p c e , t h e surfr.,'e normals w w e plotted ant the plrns then 3ppared as pcints, and cylinders as curves. Actually becaue of various inaccuracies, ttAe @-<a appears ds "alustersn of pcr lnts , particularly as the angles were quant,~:zsd to discrete interval3 of 5 degrees. These clusters were labelled and expanded according t o the geometry they describe. Using the t i l t angles of the swface normals t h i s infornation was 'pojec ted jack' into the image plane. T2e display was cleaned by zeroing every pixel element i n a 3 x 3 4-cornected region that had the %me labdl as its four neighbors. I t wa3 found that the re-created labelled image contained some spurious small regions. These were the resxl ts of certain smoothing methods and differencing techniques that vesulted i n any 5 x 5 pixel element or smaller not being rel iable. The resul ts of t h i s analysis produced labelled images that were descriptions of the surfaces.

Once the image was classif ied, various methods were examined for obtatning object descriptions, one of which was CAD models. The model of an ~ b j e c t was stored as a se t of Pascal records corresponding to adjacent surt'aces and a s e t of variables that related the surfaces to the model cenber. Taking information from the preprocessed image, a second list of records is buil t and elements of the same type from the scene and the model were caopared. In order t o identify the object, the adjacent surfaces 'had t o t e matched and the view axes and orientations a l l compared. A l l these processes involved extensive computing but they d id manage t o extract the informat;on and identify the objects and their orientations correctly.

The recognition of objects and shapes, even fa i r ly simple shapes consisting of p.lanar sides, is not an easy job. But resolution of these types of problems are important before more complex shapes can be readily identified and manipulated.

Further work by Rioux and Boulanger reported on shape segnentation (27 ) . I n the analysis of human body shapes, there are no planes or analytical curves, sr, the segmentation of shape 'is much more complex. Segmentatlor. is a combination of data acquisition and recogaitlon. In order t o break up a shape or se t of shapes into segments, selected feature parameters have t o be used. Here s i ~ e wave coding of range images was used t o segment a collection of plane and cylindrical object surfaces.

The range imge was first taken using a He-Ne laser manner. These images had a range resolution of approxlmately 0.25 mm. The range data was stored in a I b b i t word which cont.ained the position co-ordinates and the range data. Now a Fourier transform of a planar swface would produce a single frequency grating and the cylindrical surfaces showed up as l ines in the frequency space display. The sorting, or segmentation, was done in the spectral space, by generatin? a mask t o f i l t e r the spectrum. When image reconstruction was done, various parts of the image were selectively amplified. For example, t o select the planar surfaces, certain dots were ainplified.

;{hen ihe lmage wa3 reconstructed by mans of the inverse Fourier Trnnsfsrrn of t h e f i l t e r e d pat tern, the surface Cef ini t ion was good. ?<?cause 3-D images a re invariant under t ranalat isn and ro ta t ion , the problems of scal ing (associated w i t h 4 3 1 t ion on range ax i s ) were minimized. A presentation of two human face-forms i n s ine itave coding showed the a b i l i t y of the technique t o mdify coaplex surfaces. The r e c ~ g n i t i o n , t ha t is the matchin8 af cer ta in properties tha t define the obJects, was done i n the transformed space. It may be seen that t h i s t e c h n i y e could be promising for the development of object recognition and other A 1 applications.

The techniques avai lable for computing and computer-aided design in the human and bio-engineering environment are expanding rapidly. A s i n other f i e l d s , no one knows exactlv where current developments w i l l lead, but image processing, prosthesis fabr icat ion in medicine, molecular modelling and wdesignerw drugs a l l show tha t the pos s ib i l i t i e s a r e only l imited by the Imagination. A bibliography of relevant papers is included.

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1 I

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8 e m m a ' s mewL r P r t n p . rr emuad n wmm U DEFENCE R E S m C X ESTABLISHHENT OTTAWA Department of National 9efence Ottawa, Ontario 'KIA OZA

'COKPUTER-AIDED DESIGN AND BIO-ENGINEERING: A REVIEW OF THE LITERATIIRE' (U)

HIDSON, David J.

DREO TECHNICAL NOTE NO. 88- 31

5. DATE OF PUBLICATION h m h md you of Ddltcnton of bocunmt)

JULY 1988

6a NO. OF PACES houi '6h NO. OF REFS heml ctted m cmbmg tnfrmtron lmlvdr k n r r a *O#rJIU1. nel

2 6

d#umnt

2 6

-'-b - Tk!s p a p e r c o n t a i n s a r e v i e w o f t h e e x p a n d i n g u s e o f c o m p u t e r s and

c c s p u t e r - a i d e d d e s l gn i n t h e rielOs o f b i n G n g l n e e r i n g , human e n g l n e e r i n g , n e d i c i n e a n d a n t h r o p o m e t r y . Work d o n e i n r e c e n t y e a r s cn m o d e l l i n g con?plex b i s l o g i c a l s h a p e s a n d some a e t h o d s o f s h a p e a n a l y s i s a r e a s s e s s e d . A b l S l i o g r a p h y is i n c l u d e d . / , . ,

COHPUTER-AIDED DESIGN HUMAN ENGINEERING SHAPE ANALYSIS ANTIEROPOHETRY

UNCLASSIFIED