Display methods of laser radar data using a computer system

E l e c t r o n i c s and Communications i n Japan, Vol. 64-C, No. 4 , 1981

Display Methods of Laser Radar Data Using a Computer System

H i r o s h i Shimizu, Regular Member, Yasuhiro Sasano, Yoshihumi Yasuoka, Osamu Matsudo, Nobuo Takeuchi and Michio Okuda, Nonmembers N a t i o n a l I n s t i t u t e f o r Environmental S t u d i e s , I b a r a k i , Japan 305 SUMMARY

T h i s paper examines t h e d i s p l a y method f o r laser r a d a r d a t a . S e v e r a l d i s p l a y methods a r e s e l e c t e d [13-151 and t h e i r adv a n t a g e s and d i s a d v a n t a g e s are compared.

I n t h e computerized laser r a d a r d a t a proc e s s i n g , i t is important t o u t i l i z e e f f e c t i v e d a t a - d i s p l a y t e c h n i q u e s . T h i s paper examines two-dimensional d a t a d i s p l a y methods u s i n g t h e computer p e r i p h e r a l systems. Five methods ( c o l o r l e v e l s l i c i n g , grey l e v e l s l i c i n g , d o t d e n s i t y , contour and p e r s p e c t i v e methods) are s e l e c t e d and t h e i r advantages and d i s a d vantages are examined. According t o t h e q u a n t i t a t i v e examination on t h e o u t p u t e f f i ciency, t h e number of d a t a p e r one d i s p l a y , e t c . , t h e d e n s i t y method is t h e b e s t among a l l methods. 1.

2.

S t r u c t u r e of Laser Radar and Data C o l l e c t i o n Method

The laser r a d a r system used i n t h e experiment is composed of a l a s e r , a highspeed d a t a c o l l e c t i o n d e v i c e , and a highspeed s c a n n e r . The s i g n a l from t h e l a s e r r a d a r i s A-D converted u s i n g a t r a n s i e n t r e c o r d e r and i t s d a t a are s t o r e d i n t h e memory of a minicomputer.

Introduction

The d a t a c o l l e c t i o n i s made a u t o m a t i c a l l y a c c o r d i n g t o t h e computer program. The d a t a c a l c u l a t i o n and i t s real-time d i s p l a y a r e made by t h e minicomputer. The d a t a a n a l y s i s and i t s d i s p l a y are made by a l a r g e computer and its p e r i p h e r a l d e v i c e s .

With t h e development of i n s t r u m e n t a t i o n technology u s i n g laser r a d a r s [ l , 2 , 31, cont r o l and c o l l e c t i o n of laser r a d a r d a t a u s i n g computers become i n c r e a s i n g l y important [4-71. It is important t o p r o c e s s and a n a l y z e t h e laser r a d a r d a t a e f f e c t i v e l y and q u i c k l y . It is e q u a l l y important t o d i s p l a y t h e informat i o n c o n t e n t of t h e data on a s c r e e n .

3.

I n t h e p a s t , methods of d i s p l a y i n g remote s e n s i n g d a t a have been developed. The laser r a d a r d a t a are, however, d i f f e r e n t from t h e remote s e n s i n g d a t a . The former i s l a r g e i n q u a n t i t y and v a r i e s continuously. The d i s p l a y c o n t e n t is: (1) p l a n a r d a t a ; (2) spat i a l arrangement of t h e s t a t e s ; (3) d i s t r i b u t i o n of s t a t e s i n f i g u r e s ; (4) v a r i a t i o n of states i n f i g u r e s , e t c . Such laser r a d a r d a t a must be d i s p l a y e d q u i c k l y and images on s c r e e n s must be understood e a s i l y .

Display S u i t a b l e f o r Laser Radar Data

The conventional d i s p l a y method of p i c t u r e d a t a may be c l a s s i f i e d as follows: (1) Density method. The d i s p l a y is made a c c o r d i n g t o d e n s i t y o r grayness of p i c tures.

(2) Contour method. The p i c t u r e is d i s p l a y e d by contour l i n e s . T h i s i n c l u d e s t h e p e r s p e c t i v e method.

100

1SSN0424-8368/81/0004-0~100$7.50/0 Q

1982 S c r i p t a P u b l i s h i n g Co.

(3) Shape method. The p i c t u r e s are d i s played according t o t h e i r shapes. (4) Numerical method. The p i c t u r e s are d i s p l a y e d a c c o r d i n g t o t h e i r numerals recorded i n t h e p i c t u r e s . The former two d i s p l a y continuous d a t a , w h i l e t h e l a t t e r two d i s p l a y t h e d i s c r e t e data. The l a s e r r a d a r h a s been used f o r observ a t i o n of a e r o s o l s [ 1 6 ] , p o l l u t i o n s u r v e i l l a n c e [ 1 7 ] , o b s e r v a t i o n of weather [ 1 8 , 191, c l o u d s and r a i n [ 2 0 ] . The d a t a are d i s p l a y e d by t h e following methods. 3.1

F i g . 1. An example of grey l e v e l s l i c e ( t h e time v a r i a t i o n of s p a t i a l a e r o s o l d i s t r i b u tion).

Density method

T h i s method may be c l a s s i f i e d i n t o t h e c o l o r l e v e l s l i c e method, gray l e v e l s l i c e method and d o t d e n s i t y method. I n t h e c o l o r l e v e l s l i c i n g , t h e s i g n a l i n t e n s i t y is d i s played according t o t y p e s of c o l o r s and t h e i r b r i g h t n e s s . I n t h e gray l e v e l s l i c i n g , t h e s i g n a l i s d i s p l a y e d on t h e b l a c k and w h i t e CRT. I n t h e d o t d e n s i t y method, t h e d a r k n e s s of p i c t u r e s i s d i s p l a y e d u s i n g a l i n e p r i n t e r (LP) and X-Y p l o t t e r . 3.2

Contour method F i g . 2 . An example of d o t d e n s i t y ( t h e t i m e v a r i a t i o n of s p a t i a l a e r o s o l d i s t r i b u t i o n ) .

The same v a l u e s i n t h e d a t a are connected t o form c o n t o u r s on t h e p l a n e . The shadowing technique and l i n e width v a r i a t i o n technique may be employed t o c l a r i f y t h e obscure relat i o n among d a t a [ l l ] . 3.3

P e r s p e c t i v e method

Three c o o r d i n a t e a x e s f o r s p a c e , t i m e and d a t a are used t o d i s p l a y d a t a on a plane. I n t h i s p a p e r , we d i s c u s s t h e f i s h n e t p l o t [I11 * 3.4

Examples of laser r a d a r d a t a d i s p l a y

I n t h i s s e c t i o n a r e p r e s e n t e d two t y p e s of d i s p l a y examples o b t a i n e d by t h e c o l o r graphic p r o c e s s i n g d e v i c e [21] ( t h e 512 x 512 p i c t u r e elements and 256 l e v e l s f o r each of r e d , green and b l u e ) .

Fig. 3. An example of contour ( t h e t i m e v a r i a t i o n of s p a t i a l a e r o s o l d i s t r i b u t i o n ) .

F i g u r e s 1 t o 4 d i s p l a y d a t a f o r t h e obs e r v a t i o n of t i m e v a r i a t i o n of t h e i n v e r s e l a y e r h e i g h t . F i g u r e 1 (gray l e v e l s l i c i n g ) employs 16 p i c t u r e elements p e r one d a t a and d i s p l a y s 128 x 128 d a t a . The t e n i n t e n s i t y l e v e l s are used. Figure 2 (dot d e n s i t y ) u s e s 43 x 43 d a t a a t 9 l e v e l s . F i g u r e 3 (contour method) u s e s 128 x 128 d a t a a t 5 l e v e l s . Figure 4 ( p e r s p e c t i v e method) u s e s 32 x 32 d a t a a t 20 l e v e l s . I n t h e contour and pers p e c t i v e methods, i t i s not p o s s i b l e t o inc r e a s e t h e numbers of d a t a and l e v e l s because of overlapping of l i n e s .

F i g u r e s 5 t o 8 show t h e d a t a o b t a i n e d i n t h e measurement of c r o s s s e c t i o n of p o l l u t e d c l o u d s . The numbers of d a t a and l e v e l s a r e 124 x 64 d a t a and 10 l e v e l s f o r Fig. 5 , 43 x 24 d a t a and 9 l e v e l s f o r Fig. 6 , 128 x 64 d a t a and 5 l e v e l s f o r Fig. 7, and 64 x 32 d a t a and 20 l e v e l s f o r Fig. 8 . 3.5

Ease i n understanding p i c t u r e contents

Table 1 s h o w s t h e comparison of t h e d i s p l a y e f f i c i e n c y and t h e number of d a t a which

101

T a b l e 1.

D i s p l a y e f f i c i e n c y and t h e number of d a t a t o h e d i s p l a y e d p e r one s c r e e n

\

Display

\

It e m s No. of d a t a pointslscreen 3 r a c t i c a l limit) No. of i n t e n s i t y levels A r a c t i c a l limit)

Data/screen (practical limit) No. of s t e p s i n program Computation t i m e (CPU t ime)

Color l e v e l slicing

P o i n t densi t y method

Grey l e v e l slicing

Perspect i v e method

216(256*2561 2"(128/128) 2" 212 22'

100

2n

242

10 226

p 5

2 21

9a

9a

60"

6 0"

-9 9 2In

z7

P

10 223

64

2In

2 17

2

a5 55"

154 4' 14''

132

Fig. 6 . F i g . 4 . An example of p e r s p e c t i v e ( t h e t i m e v a r i a t i o n of s p a t i a l a e r o s o l d i s t r i b u t i o n )

.

Fig. 7. F i g . 5.

Contour method

I

3'

An example of d o t d e n s i t y ( c r o s s s e c t i o n of a s t a c k plume).

An example o f c o n t o u r ( c r o s s s e c t i o n of a s t a c k plume).

An example o f grey l e v e l s l i c e ( c r o s s s e c t i o n of a s t a c k plume). method r e q u i r e a t l e a s t 2 x 2 p i c t u r e e l e ments t o p r e v e n t two l i n e s from o v e r l a p p i n g . I n t h e p e r s p e c t i v e method, however, 32 x 32 o r 6 4 x 6 4 d a t a c a n d i s c r i m i n a t e 32 l i n e s c l e a r l y w i t h i n 512 x 512 p i c t u r e e l e m e n t s .

c a n be d i s p l a y e d p e r one s c r e e n . I n t h e c o l o r and gray l e v e l s l i c i n g methods, a t l e a s t one p i c t u r e element i s r e q u i r e d t o d i s p l a y one d a t a p o i n t . The d o t d e n s i t y method req u i r e s t h e p i c t u r e e l e m e n t s o f t h e same numb e r a s t h e i n t e n s i t y l e v e l . For example w i t h 9 i n t e n s i t y levels, 9 p i c t u r e elements a r e r e q u i r e d . The c o n t o u r method and p e r s p e c t i v e

The c o l o r l e v e l s l i c i n g and g r a y l e v e l s l i c i n g must have t h e same r e s o l u t i o n a s t h e d i s p l a y d e v i c e s . I n p r a c t i c e , however, about 10 l e v e l s can r e a d i l y be d i s t i n g u i s h e d

102

Fig. 8.

programs and t h e c o m p u t a t i o n s p e e d s where t h e HITAC 8450 i s u s e d . The d e n s i t y method i s t h e most a d v a n t a g e o u s ; t h e computation i s 3-4 times f a s t e r . The r e a s o n i s a s f o l lows. I n t h e d e n s i t y method, t h e d a t a i n t e n s i t y i s d i v i d e d i n t o levels. The c o n t o u r method r e q u i r e s t h e p r o c e s s o f s e a r c h i n g t h e d a t a of t h e same v a l u e s . The p e r s p e c t i v e method r e q u i r e s t h e p r o c e s s o f c o n v e r t i n g the data t o the perspective coordinates, the p r o c e s s o f p r o j e c t i n g t h e d a t a t o the p l a n e c o o r d i n a t e s , a n d t h e p r o c e s s of t r e a t i n g h i d d e n l i n e s [ 1 2 ] . The d i s p l a y speed i s 15 s e c o n d s f o r a l l methods.

An example of p e r s p e c t i v e ( c r o s s s e c -

t i o n of a s t a c k plume).

4. by human e y e s i n t h e g r a y l e v e l s l i c i n g . The c o l o r level s l i c i n g method must u s e two k i n d s of o r i g i n a l c o l o r s . The u s e of t h r e e k i n d s of o r i g i n a l c o l o r s makes i t d i f f i c u l t t o distinguish the intensity difference. S i n c e a b o u t 10 l e v e l s c a n be d i s t i n g u i s h e d f o r e a c h c o l o r , a t o t a l 100 l e v e l s may be r e a d i l y d i s c r i m i n a t e d . The c o n t o u r method can d i s c r i m i n a t e 256 l e v e l s which are h a l f of 512 p i c t u r e e l e m e n t s . I n p r a c t i c e , howe v e r , 10 l e v e l s are t h e p r a c t i c a l l i m i t which prevents l i n e overlapping. I n t h e perspect i v e method, 64 levels a r e t h e p r a c t i c a l l i m i t . I n s h o r t , t h e c o l o r level s l i c i n g method can d i s p l a y i n f o r m a t i o n 256 t i m e s l a r g e r t h a n t h e c o n t o u r method and 512 t i m e s l a r g e r t h a n t h e p e r s p e c t i v e method.

I n t h i s s e c t i o n , we d i s c u s s t h e performa n c e and f e a t u r e s of t h e d i s p l a y d e v i c e s ( s u c h a s , c o l o r g r a p h i c d i s p l a y , monochrome g r a p h i c d i s p l a y , LP, p l o t t e r , e t c . ) . 4.1

Performance o f d a t a d i s p l a y d e v i c e s

T a b l e 2 shows t h e p e r f o r m a n c e s of d i s p l a y d e v i c e s . I n t h e LP and p l o t t e r , t h e l i n e w i d t h depends on t h e p a p e r w i d t h . The c o l o r g r a p h i c d e v i c e c a n d i s p l a y the c o l o r and i n t e n s i t y v a r i a t i o n s and h a s maximum d i s p l a y c a p a c i t y . The p l o t t e r h a s t h e maximum s p a t i a l d e n s i t y . The c o l o r g r a p h i c d i s play device h a s r e s o l u t i o n of 8-bit l e v e l s and t h e o t h e r d e v i c e s have 2 l e v e l s .

The level s l i c i n g method c a n d i s p l a y t h e l a r g e s t number o f d a t a p e r one s c r e e n . I n g e n e r a l , we conclude:

The c o l o r g r a p h i c d i s p l a y d e v i c e i s t h e f a s t e s t i n d i s p l a y and t h e p l o t t e r is t h e s l o w e s t . The LP i s s u i t a b l e f o r w r i t i n g l e t t e r s . The p l o t t e r i s s u i t a b l e f o r drawing lines.

(1) t h e d e n s i t y method i s s u i t a b l e f o r o b s e r v a t i o n o f t e m p o r a l and s p a t i a l variat i o n s of s t a t e s , such as a e r o s o l d e n s i t y , weather, e t c . ;

4.2

(2) t h e d e n s i t y method and p e r s p e c t i v e method a r e s u i t a b l e f o r o b s e r v a t i o n of abs o l u t e v a l u e s of d a t a p o i n t s , such a s w e a t h e r s t a t e s , smoke d e n s i t y , e t c . ;

D i s p l a y example i n d a t a d i s p l a y device

F i g u r e 9 shows a n example of t h e d o t d e n s i t y u s i n g a l i n e p r i n t e r . The d a t a were t h e same a s i n F i g s . 2 and 5 . The numb e r of t h e d a t a p o i n t s w a s 132 x 398.

( 3 ) t h e c o n t o u r method i s s u i t a b l e f o r o b s e r v a t i o n of p a t t e r n s of smoke d i s t r i b u t i o n and s t a t e v a r i a t i o n , e t c . ;

F i g u r e 10 shows a n example of t h e p e r s p e c t i v e d i s p l a y u s i n g a n X-Y p l o t t e r . Bec a u s e o f h i g h - d e n s i t y d i s p l a y by u s e of t h e p l o t t e r , each l i n e i s c l e a r l y discriminated from o t h e r s . T h i s d i s p l a y r e q u i r e s 30 minutes.

( 4 ) t h e p e r s p e c t i v e method i s advantageo u s i n e v a l u a t i n g t h e i n f o r m a t i o n on t h e s c r e e n , such a s q u a n t i t i e s of smoke, p o l l u t ants, etc. 3.6

Display Devices S u i t a b l e f o r Laser Radar Data

F i g u r e 11 shows a n example of t h e p e r s p e c t i v e method u s i n g a g r a p h i c t e r m i n a l which h a s b o t h c h a r a c t e r and g r a p h i c funct i o n s . I n t h i s d i s p l a y , the o r d i n a t e r e p r e s e n t s t h e h e i g h t and t h e a b s c i s s a r e p r e s e n t s t h e i n t e n s i t y . The z e r o l e v e l w a s s h i f t e d a t e q u a l i n t e r v a l s as t i m e e l a p s e d .

Display e f f i c i e n c y

The d i s p l a y e f f i c i e n c y i s a measure of e a s i n e s s i n d i s p l a y and depends on e a s i n e s s i n programming, t h e number of s t e p s of programs, t h e computation speed and d i s p l a y speed. T a b l e 1 shows t h e number of s t e p s of

103

Line p r i n t e r

X-Y p l o t t e r

HITACHI H - 8246 - 1 2

Graphic t e r m i n a l

(

(;';,",";"_D)

TECTRONIX 4010

Color g r a p h i c

)(

GRAPHICA M-508

Display area

32.5 (cm/line)

27 (cm/line)

19.1 x 14.3 (cm/screen)

25 x 25 (cm/ screen)

Capacity

132 ( c m / l e t t e r )

2700 ( s t e p / l i n e ) 1024 x 780 ( d o t / line)

74 x 34 ( l e t t e r / screen)

512 x 512 (elements/screen)

Level r e s o l u t i o n

2

2

2

28

Display speed

10 ( l i n e / s e c )

400 ( s t e p / s e c )

1200 ( l e t t e r / sec) 400 ( d o t / s e c )

0.067 ( s c r e e n / sec)

Function

Character

Graphic

Character, graphic

Character, graphic

Advantages

Easy i n programming

High r e s o l u t i o n

Light weight

A l l functions

Disadvantages

Small d i s p l a y density

Slow d i s p l a y

Small capacity

D i f f i c u l t t o record

Table 3.

A p p l i c a b i l i t y of d i s p l a y methods Color

Grey

L P

X

X

Plotter

x

X

C G

0

0

Fig. 9.

--

dens 0

.

tour

0

I

tive

0

0

0

0

An example of d o t d e n s i t y (over p r i n t i n g )

using a l i n e p r i n t e r .

A s can be seen i n t h e s e examples, t h e choice of t h e d i s p l a y method depends on t h e t y p e of t h e d i s p l a y device. Table 3 shows t h e a p p l i c a b i l i t y of each d i s p l a y method. The mark 0 r e p r e s e n t s " a p p l i c a b l e " and t h e

mark X r e p r e s e n t s l h o t a p p l i c a b l e . " The b l a n k r e p r e s e n t s "not p r a c t i c a l . I ' The densi t y method must u t i l i z e t h e d i s p l a y device w i t h t h e c h a r a c t e r f u n c t i o n , while t h e cont o u r method and t h e p e r s p e c t i v e method must

104

F i g . 10.

An example of p e r s p e c t i v e u s i n g an X-Y plotter.

use t h e d i s p l a y d e v i c e w i t h t h e g r a p h i c funct ion. 5.

6.

Conclusion

7.

Among v a r i o u s d i s p l a y methods of laser r a d a r d a t a u s i n g a computer s y s t e m , t h e d e n s i t y method, t h e contour method and t h e p e r s p e c t i v e method were s e l e c t e d and t h e i r advantages and drawbacks were examined.

8.

The d e n s i t y method i s s u i t a b l e f o r highspeed c h a r a c t e r d i s p l a y of t h e laser r a d a r d a t a . The o t h e r two methods are s u i t a b l e f o r g r a p h i c d i s p l a y . The r e s u l t s o b t a i n e d i n t h i s r e s e a r c h are a p p l i c a b l e f o r d i s p l a y of t h e microwave r a d a r d a t a .

9.

10.

REFERENCES 11. 1.

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