COLOR JET PLOTTER.

Mikael Jern Lund U n i v e r s i t y Computing C e n t r e , Sweden .

I n~o_du_~t ~o ~.

From the beg inn ing of the d e v e l o p m e n t of c o m p u t e r s , communica t ion b e t w e e n man and mach ine was domina ted by numer ica l or a l p h a b e t i c a l ways of e x p r e s - s ion . Typed l e t t e r s and numbers were p r e s e n t e d c o n s t i t u t i n g the r e s u l t s of da ta p rgrams , which were l a b o r i o u s l y wr i t t en in compute r a s s e m b l y l anguages more i n t ended for compute rs wi th the i r l imi ta t ions than for the imag ina t ion and power of a p p r e h e n s i o n of man.

Peop le not on l y u se l e t t e r s and d ig i t s but u s u a l l y a l so o t h e r c o n c e p t i o n s l ike f i g u r e s , p i c tu re s and g r aphs . A compu te r , h o w e v e r , o p e r a t e s with o the r con- c e p t i o n s l ike b i t s , b y t e s and r e g i s t e r s . This makes the communica t ion wi th a computer more d i f f i cu l t . Ear l ier man had to ca r ry the b u r d e n . One had to t ransform though t s and i dea s into l e t t e r s , d ig i t s and f r e q u e n t l y a l so into com- puter l anguage . The da ta computer p r o c e s s i n g o f t en p r o d u c e d r e su l t s of mi les of paper f i l led wi th d a t a , which the u se r p i led up in a corner and la te r perhaps threw away a f t e r s tudy ing on ly a small share of a l l in fo rmat ion .

Computer graphics enable man to start using the computer in a more appropri- ate way. The computer keeps on using digital technique and registers. The graphical external units act like interpreters between man and computer to produce pictures.

h rapid t e c h n i c a l d e v e l o p m e n t during the pas t f ive yea r s has g iven us a lcrge v a r i e t y of p o s s i b i l i t i e s of computer g raph ics pa r t ly by new high l eve l compu- te r l anguages , ' ,part ly by new t y p e s of au tomat i c drawing equ ipmen t .

Today d o t s , l i n e s , s u r f a c e s , l e t t e r s and f igures in b l a c k - a n d - w h i t e or colour can be drawn on pape r , film s t r ips and e l e c t r o n i c s c r e e n s . A number of appl i - c a t i on f i e lds are obv ious in v e r y d i f f e ren t f i e ld s l ike s h i p b u i l d i n g , c a r t og ra - phy , communi ty p l ann ing , na ture c o n s e r v a t i o n , r e s e a r c h and e d u c a t i o n .

There are s e v e r a l t ypes of equ ipment for p r e s e n t a t i o n of g r aph ica l in forma- t i o n , s ee examples in Fig. 1 and 2. None of t h e s e , h o w e v e r , can q u i c k l y draw a p ic tu re wi th co lou red s u r f a c e s and a c c u r a t e c o n t o u r s . There was a c h a n c e to so lve the p rob l em in the new ink je t t e c h n i q u e , d e v e l o p e d at the Depar tmen t of E lec t r i ca l M e a s u r e m e n t s , Lund In s t i t u t e o f T e c h n o l o g y .

18

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000

Fig. I. Part of map of the south part of Lund printed by a line printer controlled by a computer. Printing time about 10 seconds. The population density of the particu- lar block is indicated by using different characters.

/ 7

Pig . 2. Same map a s in F ig . 1 d rawn b y a CALCOMP p lo t - t e r , w h e r e s h a d i n g is u s e d to i n d i c a t e the p o p u l a t i o n d e n - s i t y . P lo t t ing t ime a b o u t 1S m i n u t e s . The p l o t t e r i s c o n - t r o l l e d b y a t a p e g e n e r a t e d b y a c o m p u t e r b a s e d on in fo r - m a t i o n from Lund" s P e r s o n and Real E s t a t e R e g i s t e r .

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P r i n c i p l e .

A c r o s s - s c i e n t i f i c c o - o p e r a t i o n g r o u p w i t h m e m b e r s from t h e D e p a r t m e n t s o f Bu i ld ing F u n c t i o n A n a l y s i s , E l e c t r i c a l M e a s u r e m e n t s a n d Lund U n i v e r s i t y C o m p u t i n g C e n t r e s t a r t e d w o r k on t h i s p r o j e c t . The g r o u p d e v e l o p e d a h a r d c o p y c o l o u r d i s p l a y s y s t e m w i t h t h r e e b a s e c o l o u r s a c c o m p a n i e d b y s o f t - w a r e to g e n e r a t e c o l o u r p i c t u r e s in a c o m p u t e r .

UNIVAC IBM computer

M o t o r

. . . . . . . . . .

plotting unit

F i g . 3. C o l o r jet plotter p r i n c i p l e .

The g e n e r a t i o n of a c o l o u r p i c t u r e i s d o n e in two s t e p s . F i r s t a p i c t u r e e n - t i r e l y c o n s i s t i n g of n u m b e r s i s d e s i g n e d . A s p e c i a l p r o g r a m for t h e c o l o u r p l o t t e r m a k e s t h e c o m p u t e r c a l c u l a t e a n u m e r i c a l m o d e l o f t h e p i c t u r e . The c o m p u t e r w o r k s w i t h l o g i c a l o n e s and z e r o s i n s t e a d of p h y s i c a l d r o p l e t s , w h e r e t h e o n e s c o r r e s p o n d to d r o p l e t s on the p a p e r . The n u m b e r c o d e p i c - t u r e i s s t o r e d on a m a g n e t i c t a p e , w h i c h in t he s e c o n d s t e p i s r e a d y b y t h e c o l o u r j e t p l o t t e r . The i n f o r m a t i o n on the t a p e i s t h e n t r a n s f o r m e d i n - t o a c o l o u r p i c t u r e .

The plotting unit is based on a drum on which the picture (20 x 30 cm) is to be drawn. The paper is fastened to the drum, which is rotated by a motor with a capacity of I000 rpm. Three ink jet systems yellow, red and blue are mounted on a carriage, which is moved along the drum surface by a lead screw. When drawing takes place the drum rotates at a high speed while the ink jets slowly are moving along the drum surface. Each ink jet then draws a large number of parallel lines 0.2 mm distant from each other. The line density will then be 5 lines per millimetre.

T o t a l l y t h e r e a r e 1450 l i n e s o f e a c h c o l o u r p r i n t e d on t h e p a p e r in o n e p i c - t u r e . In t h i s w a y t h e p i c t u r e i s g e n e r a t e d do t b y do t s i m i l a r to t h e p i c t u r e on a T V - s c r e e n . The e n t i r e p r i n t o u t o f a c o l o u r p i c t u r e t a k e s 60 s e c o n d s du r ing w h i c h t i m e 1 500 000 d o t s a r e p r i n t e d on t h e p a p e r b y e a c h of t h e t h r e e j e t s t h u s a m o u n t i n g to 4 500 000 d o t s . S i n c e t h e d o t s a r e v e r y c l o s e a r b i t r a r y c o l o u r s c a n b e o b t a i n e d b y v a r y i n g the d o t d e n s i t y for e a c h b a s e c o l o u r .

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o b c

F i g . 4 . The p r i n c i p l e for i n t e n s i t y m o d u l a t i o n o f a p l o t t i n g ink j e t .

The r e c o r d i n g h e a d in t h i s new p l o t t e r c o n s i s t s of t h r e e e l e c t r i c a l l y c o n t r o l - l ed ink j e t s w i t h s u c h b a s e c o l o u r s t h a t , b y s u i t a b l e m i x i n g , a n y c o l o u r c a n b e o b t a i n e d . A f i ne ink je t "J" (Fig . 4 a) i s f o r m e d b y f o r c i n g ink u n d e r h igh p r e s s u r e t h r o u g h t h e n o z z l e " N " . The j e t d r a w s a l i n e on the p a p e r "R" . I f t h e ink j e t p a s s e s an e l e c t r o d e " E " , w h i c h h a s a p o t e n t i a l of m o r e t h a n 100 v o l t s , t he ink d r o p l e t s w i l l r e c e i v e a n e g a t i v e c h a r g e and w i l l r e p e l e a c h o t h e r (be p u s h e d a w a y from e a c h o t h e r ) . The ink j e t i s t r a n s f o r m e d i n - to a s p r a y a n d t h e l i ne e n d s (F ig . 4 b ) . The e n t i r e p a p e r w o u l d now b e c o m e c o l e u r e d i n s t e a d , w h i c h i s p r e v e n t e d b y t h e f o l l o w i n g m e t h o d .

As t h e ink d r o p l e t s a r e e l e c t r i c a l l y c h a r g e d , t h e y c a n b e p r e v e n t e d f rom r e a c h i n g t h e p a p e r b y a p p l y i n g an e l e c t r i c f i e l d b e t w e e n t h e e l e c t r o d e s " F l " a n d "F2" Th i s i m p l i e s t h a t t h e e l e c t r i c a l l y c h a r g e d d r o p l e t s w i l l b e p u s h e d a w a y a n d the d r o p l e t s w i t h no c h a r g e w i l l t r a v e r s e t he f i e ld u n e f f e c t - e d .

I f t he v o l t a g e s o u r c e (F ig . ~4 c) i s r e p l a c e d b y a v a r i a b l e v o l t a g e , for e x a m p l e t h e o u t p u t o f an a m p l i f i e r , t h e s h a p e of t h e j e t m a y b e c o n t r o l l e d b y c o n t r o l - l ing t h e v o l t a g e , i . e . e i t h e r a s t r a i g h t j e t on to t h e p a p e r or a. s p r a y w h i c h d o e s not c o l o u r t he p a p e r , and b y t h a t t he a p p e a r a n c e o f t h e r e c o r d e d l i n e . In p r a c t i c e t h e s h a d i n g and i n t e n s i t y of t h e l i n e c a n b e c o n t r o l l e d b y t h i s v o l t a g e in a w a y s i m i l a r to t h e w a y of c o n t r o l l i n g t h e i n t e n s i t y of an e l e c t r o n b e a m in a T V - p i c t u r e t u b e . I t i s k n o w n t h a t t h i s m o d u l a t i o n c a n b e d o n e v e r y r a p i d l y a n d t h a t m o r e t h a n 100 000 d i s c r e e t d o t s c a n b e r e c o r d e d pe r s e c o n d . This f a s t m e t h o d m a k e s t h e ink j e t v e r y u s e f u l for our p u r p o s e .

All p i c t u r e s a r e s t o r e d on m a g n e t i c t a p e . By t h a t p i c t u r e s , w h i c h a r e to b e u s e d s e v e r a l t i m e s , c a n b e s a v e d and p i c t u r e s f rom d i f f e r e n t m a g n e t i c t a p e s c a n b e c o m b i n e d to a n e w p i c t u r e , for e x a m p l e a b a c k g r o u n d m a p of a h o u s - ing a r e a c o m b i n e d w i t h a m a p of a i r p o l l u t i o n .

The plotter can also separate the colours and plot each base colour in a spe- cific picture, which very much facilitates and above all makes the produc- tion of offset plates cheaper when a great number of these pictures are wanted.

21

S o f t w a r e .

A c o m p l e x s o f t w a r e i s n e e d e d to g e n e r a t e a c o l o u r p i c t u r e w i t h t h e c o l o u r j e t p l o t t e r . For t h a t r e a s o n a c o m p r e h e n s i v e p rog ram s y s t e m COLOR h a s b e e n d e v e l o p e d . The C O L O R - p r o g r a m h a s b e e n w r i t t e n p a r t i c u l a r l y for t h e c o l o u r j e t p l o t t e r a n d u s e s , a m o n g o t h e r t h i n g s , a s p e c i a l p a t t e r n t e c h n i q u e to p lo t f l a t c o l o u r e d s u r f a c e s , w h i c h o p e n s a n e w d i m e n s i o n o f a p p l i c a t i o n f i e l d s w i t h i n c o m p u t e r g r a p h i c s . The p r i n c i p l e u s e d b y t h e c o l o u r j e t p l o t t e r m a k e s a v a r i a b l e i n t e n s i t y i m p o s s i b l e . The n u m b e r o f d r o p l e t s h i t t i n g t h e p a p e r i s c o n s t a n t . H o w e v e r , d i f f e r e n t c o l o u r s h a d e s c a n b e o b t a i n e d i f t h e d r o p l e t s a r e p l a c e d w i t h v a r y i n g d i s t a n c e from e a c h o t h e r . The d a r k e s t s h a d e of a b a s e c o l o u r o c c u r s w h e n t h e n u m b e r o f d o t s p e r mm 2 r e a c h e s i t s m a x i m u m , 5 x 5 d o t s / m m 2. A l i g h t e r s h a d e i s o b t a i n e d i f t h e d o t s a r e p l a c e d l e s s d e n s e . The u s e r c a n c h o o s e b e t w e e n p a t t e r n s w h e r e t h e c o l o u r c h a n g e s f rom a l i g h t e r to d a r k e r s h a d e in v e r y s m a l l s t e p s .

There are two colour scales in COLOR:

The c o l o u r s c a l e w i t h p a t t e r n c o d e s (0 - 16) i s u s e d w h e n s m o o t h t r a n s i t i o n s b e t w e e n t h e s h a d e s a r e w a n t e d . Each b a s e c o l o u r ( y e l l o w , red and b lue) i s s p e c i f i e d w i t h a n u m b e r (0 - 16) , w h e r e 16 c o r r e s p o n d s to t h e d a r k e s t c o - l ou t s h a d e and 1 to t h e l i g h t e s t , i . e . t he ink d r o p l e t s a r e v e r y s p a r s e (0 = no c o l o u r ) . The t o t a l n u m b e r o f c o l o u r c o m b i n a t i o n s o b t a i n a b l e w i t h t h e s e p a t t e r n s = 17 x 17 x 17 = 4 9 1 3 .

1 2

10 11 12

4 5 6

~5 ~4 ~5

7 8

II 16

9

Fig. 5. Examples of colour pattern (0 - 16).

The colour scale with pattern codes (0 - 25) contains specific patterns like for example lines with varying density, squares etc. These patterns are used when the user wants to distinguish particular areas from each other.

22

1

iii!iiii!iii!!iiii

10

N 19

2 3

ili!il 11 1.2

4 5 6 7 8 9

1~ 14 15 16 ~7 18

20 2~t 22 23 24

n 25

Fig . 6. E x a m p l e s of c o l o u r p a t t e r n (0 - 25) .

COLOR is a v e r y f l e x i b l e prngram s y s t e m and a l s o e n a b l e s p r o g r a m m e r s wi th l i t t l e e x p e r i e n c e to g e n e r a t e c o l o u r p i c t u r e s . COLOR i s w r i t t e n in FORTRAN and h a s b e e n i m p l e m e n t e d at a n u m b e r of c o m p u t i n g c e n t r e s in S c a n d i n a v i a .

At the Lund University Computing Centre there are two colour jet plotters in- stalled at present. COLOR generates magnetic tape, which is then sent D Lund for plotting.

COLOR consists of programs on t h r e e levels:

BASIC SOFTWARE FUNCTIONAL SOFTWARE APPLICATION SOFTWARE

(basic routines, level 1} (subroutines, level 2) ( a p p l i c a t i o n r o u t i n e s , l e v e l 3)

The lowest level (level I) consists of routines for drcrW, ing

......................................................................................................... ' ......................................................................... i

l i n e ( c o n t i n u o u s , d a s h e d or do t ted) b e t w e e n two p o i n t s in a r b i t r a r y w i d t h and c o l o u r .

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ABCDEFGHI JKLMNOPQRSTUVWYZO 123456789 A~C DEF GH I JKLMNOPQRSTUVWYZO 123456~89 AICI~EFCH | ~K~.MNOPQRSTUVBYZ 012345~?1~11

.texxt in a r b i t r a r y s i z e and c o l o u r .

W i t h t h e s e b a s i c r o u t i n e s a n y a r b i t r a r y p i c t u r e c an be d e s i g n e d .

The s y s t e m w h i c h is u s e d in t h i s s o f t w a r e e n a b l e s t he u s e r to " e r a s e " ( a s s i g n c e l l s in t he c o l o u r m a t r i c e s the v a l u e of z e r o ) - s u r f a c e s , l i n e s or s y m b o l s . F igu re s c a n , for e a m p l e , be d rawn on t op o f e a c h o the r and b y t he u s e of a s p e c i a l c o d e c o v e r e d s u r f a c e s c a n be " e r a s e d " . The f igu re b e l o w i l l u s t r a t e s t h i s t e c h n i q u e in p r a c t i c e . 8 s q u a r e s a re d rawn on t o p o f e a c h o t h e r . N o t e t h a t e a c h t ime a new s q u a r e is d r a w n t h e par t of t h e s q u a r e b e n e a t h , , w h i c h is c o v e r e d b y the new o n e , d i s a p p e a r s .

F ig . 7 . E x a m p l e s of the " e r a s i n g " f a c i l i t y in COLOR.

In o rder to make p rogramming for the u s e r e a s i e r t h e r e a r e a number of s u b - r o u t i n e s ( l eve l 2) for s p e c i a l f i g u r e s , among w h i c h for t h e dr a w i n g of :

c i r c l e s and r e c t a n g l e s a x e s for d i a g r a m s

c u r v e s , s t a p l e d i a g r a m s , h i s t o g r a m s and p ie c h a r t s .

24

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1921] 1 9 3 0 1'~t44) 19St ) IgSS l ' ) g l ] I 9 6 S I 9 7 0 SAKNAI~

hNDEL LAGENHETER

EFTER BYGGN PEPiOD

FORE 1901 : 701

1901-I':~Z0 : 2566

19Zi- l g s o : 8 6 4

1931- 1940 : 6527

1941-1950 : ~557

I 9 5 1 . - L955 : 5 15 1 9 5 6 - 1960 : ? t

196' l - 1965 : 6 7 0

1 9 6 6 - 1970 : 5 1 9

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25

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The h i g h e s t l e v e l w i t h a p p l i c a t i o n r o u t i n e s e n a b l e s t h e u s e r w i t h l i t t l e p rog ramming e x p e r i e n c e to d raw a p i c t u r e . T h e r e a r e , f o r i n s t a n c e , r o u - t i n e s for t h e h a n d l i n g o f t h r e e - d i m e n s i o n a l i n f o r m a t i o n :

d r a w i n g of gr id m a p s d r a w i n g o f p e r s p e c t i v e s b a s e d on gr id m ap s d r a w i n g o f c o n t o u r m ap s ( i sa r i thm maps) d r a w i n g o f t h r e e - d i m e n s i o n a l bar c h a r t s .

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Fig . 9 . P o p u l a t i o n d e n s i t y of S c a n i a p r e s e n t e d w i t h 3 d i f f e r e n t a p p l i c a t i o n p rog rams w i t h i n the COLOR a p p l i c a t i o n s o f t w a r e .

26

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P~.g. 10 . The COLOR-programs generate grid and contour maps of a func t ion Z=f (x ,y ) .

One of the larges t a p p l i c a t i o n f i e lds for the colour jet plotter i s genera t ion of GRID MAPS and CONTOUR MAPS (ISARITHM MAPS). Therefore comprehen- s i v e s p e c i a l programs (the IMAP-prgrams) have b een d e v e l o p e d for t h i s type of a p p l i c a t i o n s .

The GRID MAP is probably the s imples t form of map that can be g e n e r a t e d . Each v a l u e in a t w o - d i m e n s i o n a l matrix i s represented b y a square , th e s i z e of wh ich is determined by the u ser . The co lour of s u c h a square d e - pends on the v a l u e of the corresponding c e l l . The user makes a s u i t a b l e c l a s s i f i c a t i o n and l e t s each c l a s s be represented by a part icular c o l o u r .

The CONTOUR MAP represents a much more s o f i s t i c a t e d p resen ta t io n t e c h - n i q u e , s i n c e it e n t a i l s more or l e s s compl i ca ted methods of i n t e r p o l a t i o n .

Based on a number of known v a l u e s in a func t ion Z = ( x , y ) , where the p o in t s are: a) in a regular , rectangular pattern b) irregularly sca t tered n ew po ints are in terpolated with re spec t to surrounding known v a l u e s .

27

The transformatior~ of an i r regu la r da ta ne t to a r e g u l a r , r e c t a n g u l a r grid of po in ts is f r equen t ly needed in c a r t og raphy when i sar i thm maps (contour maps) are w a n t e d .

In m e t e o r o l o g y , for exam p l e , th is method is o f ten u sed to draw isar i thm maps of t e m p e r a t u r e , a i r p r e s s u r e and p r e c i p i t a t i o n , where input da ta come from s c a t t e r e d w e a t h e r s t a t i o n s . Also for g raph ica l p r e s e n t a t i o n of air and w a t e r po l l u t i on . A large a p p l i c a t i o n f ie ld is communi ty p l a n n i n g . Isar i thm maps are drawn of , for e x a m p l e , popu la t ion d e n s i t y on pa r i sh l e v e l , where the par i sh is o f t en c o n n e c t e d with the po in t , on which the c h u r c h is found.

28

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(PGrlsh points) to a regular grid of points. The programs for generating grid maps and contour maps can then be used.

29

:I'h.e _or_g~zn£z~tj.o~ ~o~rt¢l _the _co_louE Letplotter.

The p r i n c i p l e of c o n t r o l l i n g an ink j e t w i t h e l e c t r i c a l v o l t a g e h a s b e e n s t u d i e d for s e v e r a l y e a r s a t t h e d e p a r t m e n t of E l e c t r i c a l M e a s u r e m e n t s , Lund I n s t i t u t e of T e c h n o l o g y , w i t h t h e a im a t p r a c t i c a l u s e . One a p p l i - c a t i o n h a s b e c o m e t h e c o l o u r j e t p l o t t e r .

A p r o t o t y p e w a s b u i l t and put to w o r k in 1 9 7 2 . B a s e d o n e x p e r i e n c e f rom t h i s p r o t o t y p e two m o r e p l o t t e r s h a v e b e e n b u i l t , w h i c h t o d a y a re p l a c e d a t t he Lund U n i v e r s i t y C o m p u t i n g C e n t r e . T h e s e p l o t t e r s a r e u s e d to g i v e t h e p i c t u r e p l o t t i n g s e r v i c e o f f e r e d b y t h e C o m p u t i n g C e n t r e .

This plotting service was organized in cooperation with the department of Electrical Measurements. It has expanded and now amounts to some 20 000 pictures annually.

The s o f t w a r e for t h e c o l o u r j e t p l o t t e r w a s d e v e l o p e d a t t h e Lund U n i v e r s i - t y C o m p u t i n g C e n t r e p a r t l y g r a n t e d b y t h e S w e d i s h Board for T e c h n i c a l D e v e l o p m e n t STU. From t h e b e g i n n i n g the s o f t w a r e w a s p l a n n e d in s u c h a w a y t h a t i n s t a l l a t i o n in d i f f e r e n t t y p e s of c o m p u t e r s w o u l d b e p o s s i b l e .

I t h a s a l r e a d y b e e n i n s t a l l e d in m a n y c o m p u t i n g c e n t r e s in S w e d e n a n d D e n - m a r k : In t h i s w a y t h e c o l o u r p i c t u r e t e c h n i q u e c a n b e t e s t e d b e f o r e a l o c a l c o l o u r j e t p l o t t e r i s p r o c u r e d .

W h e n c a l c u l a t e d in t h e c o m p u t e r t h e p i c t u r e i s g e n e r a t e d l i k e a p a t t e r n o f o n e s a n d z e r o s . Th i s c a n b e d o n e a t e a c h c o m p u t i n g c e n t r e , w h e r e t h e s o f t w a r e i s i n s t a l l e d . The p i c t u r e i s s t o r e d on m a g n e t i c t a p e and s e n t to t h e ~und U n i v e r s i t y C o m p u t i n g C e n t r e for p l o t t i n g . The c o l o u r j e t p l o t t e r d r a w s a p i c t u r e a c c o r d i n g to t h e p a t t e r n on t h e m a g n e t i c t a p e . T a p e a n d p i c t u r e a r e r e t u r n e d to t h e c u s t o m e r .

30

The co lour jet p lo t te r t e c h n i q u e is a l r e a d y used by u s e r s in a number of app- l i c a t i on f i e l d s . The l a rges t app l i c a t i on f i e lds are in c o m m u n i t y p l ann ing . Loc a l , r eg iona l and na t iona l au tho r i t i e s have for a long per iod t e s t e d the t e c h n i q u e in p r a c t i c e wi th in the current a c t i v i t i e s of the publ ic s e c t o r . The DeparLment of Agr icu l ture , the Nat iona l Swed i sh Envi ronment P ro t ec t ion Board, the Na t iona l Board of Urban P lann ing , the Swed i sh Board for Real Es ta t e Data CFD, the Cent ra l Bureau of S t a t i s t i c s SCB, the Swedish M e t e o r o - log ica l and Hydro log i ca l I n s t i t u t e , the G e o l o g i c a l Su rvey of Sweden SGU, Hal land and Malm6 County C o u n c i l s , Go thenburg , Malta6 and Stockholm M u n i c i p a l i t i e s are some e x a m p l e s .

Examples of some cur rent p ro j ec t s are:

g raph ica l p r e s e n t a t i o n of envi ronment da ta with the c o l o u r je t p lo t te r in co - ope ra t ion wi th the envi ronment p ro t ec t ion depar tment of Malta6 County in c o n n e c t i o n wiLh the i r expe r imen ta l work for the Envi ronment Pro tec t ion In- format ion Sys tem (MI-01) ,

de ve lopmen t of sof tware for map and diagram accoun t i ng for the r e s u l t s of the c e n s u s 1975 FoB 75, c o - o p e r a t i o n b e t w e e n the Cen t r a l Bureau of S ta t i s - t i c s , Malta5 M u n i c i p l a i t y and Lund Computing C e n t r e ,

d i s p l a y of g rav ime t r i c m e a s u r e m e n t s in c o - o p e r a t i o n wi th Boliden AB, Sweden ,

g r aph ica l p r e s e n t a t i o n of popu la t ion s t a t i s t i c s , c o - o p e r a t i o n be tween Maim5 and Gothenburg M u n i c i p a l i t i e s , the Cent ra l Bureau of S t a t i s t i c s , Mun ic ipa - l i ty Data and Lund Computing Cen t r e ,

g raph ica l p r e s e n t a t i o n of air po l lu t ion , c o - o p e r a t i o n b e t w e e n SMHI, the En- v i ronment Data Project in Lund and Lund Computing C e n t r e .

References.

Hertz, C.H. and M6nsson, A. , Color Plotter for Computer Graphics using three electrically controlled ink jets. Information Processing 74 vol i, 1974, 85-88.

fern, M., Color jet software users manual.

Jem, M., IMAP-manuel, contour plotting with the color jet plotter.

Smeds, B., A 3-colour ink jet plotter for computer graphics, Bit, vol 13, No 2, 1973, 181-195.

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