Pergamon Computers ind. Engng Voi. 33, Nos 3-4, pp. 529-532, 1997

O 1997 Elsevier Science Ltd Printed in Great Britain. All rights reserved

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Presenting Map Information on a Global Postlloning System

Byoungju Kim*, Sung H. Hen*, Keewon Nam**, Jaeho Park**, Seungah Han* *Department of Industrial Engineering

**Department of Computer Science and Engineering Pohang University of Science and Technology, Pohang Korea

Abstract

A Global Positioning System (GPS) in an automobile can provide navigational information for identifying the current location of the driver and helping him det~ndrte a desirable route to the destination. This study examined two critical factors in designing the electronic map on the GPS. The rotation and movement methods of the map were manipulated in a simulated driving environment. Three u l a b i ~ measures (arrival time, navigation inefficiency, and map reading time) were collected and analyzed. The results showed that the usability of the map was largely dependent upon the movement method in terms of the erdval time. It was akin dependent upon the rotation method and the interaction between the rotation and movement method in terms of the map reading time. Design guidelines are suggested based on the experimental results. © ]99"/Elsevier Science Ltd

Keywords: GPS, Electronic Map, Design Guidelines

I. In~oducUon

Mobile communication makes drastic changes in many aspects of our daily life due to the fast development of computer and communication satellite technology. A Global Positioning System (GPS) is one of the applications of the mobile communication, which makes it more convenient and easy to drive an automobile. The GPS is expected to be widely used in the near future as the national-wide Intelligent Transportation System (ITS) is constructed [1]. The GPS can provide the driver with useful information such as road map, road names, current position, current orientation, starting point, and target point. The GPS as an automobile navigation system helps the driver easily find the way to the destination by displaying the route of the automobile traced by a satellite.

To design a usable electronic map on the GPS, it is necessary to understand how a human recognizes cognitively the navigational information that is basically spatial. The spatial cognition process is accomplished by the comparison and conversion between the ego centered reference frame (ERF) like clock direction and the world centered reference frame (WRF) like compass heading [3]. In other words, the geometry of the ERF and W~F is established in a triangulation process. The WRF is aligned with the ERF in a mental rotation process, and then the WRF image is compared with the ERF image in a image comparison process, and finally the position of the ERF is monitored in a translation process. Throughout these complicated cognitive processes, the relation between the electronic map and the scenery from a windshield is recognized by the driver. This cognitive load in the interpretation process of the electronic map becomes a sedous ~oblem in the real ddving situation, since the human attention is limited and especially the primary task of ddving requires much more attention.

The previous human factors research on the GPS has concentrated on how to display the electronic map with more usability and less cognitive loads. Two displaying

methods were examined in most studies: the NorthUp method in which the north direction of the corresponding paper map always points to the top of the electronic map, i.e., the WRF and the HeadUp method in which the current direction of the automobile always points to the top of the electronic map, i.e., the ERF. Antin [2] suggested that the HeadUp method would be superior to the NorthUp method. However, Aratz [3] revealed through his research on a flight simulator that each of the NorthUp and HeadUp methods has both advantages and disadvantages.

A major limitation of the previous research is that the cognitive 10ad while driving the automobile was not considered. Thus, the results cannot be validated and applied to the design of the electronic map in the real driving environment. To solve this problem, this study examined two critical design factors manipulated in a simulated ddving environment.

II. Method

2.1 Subjects A total of 12 subjects participated in the experiment. They were graduate or undergraduate students and the average age was 23. They all had a driver's license.

2.2 Apparatus A prototype of the electronic map was developed by using OpenGL library, X window system, and OSF/Motif widget sets on a Silicon Graphics Indigo2 workstation. The prototype displays two major components on a single screen: a 3-dimensional scene from a windshield and a 2- dimensional electronic map (Figure 1). The location and direction of the automobile on the map is presented simultaneously in the 3-dimensional and 2-dimensional components. The two arrow keys on the keyboard were used to control the direction of the automobile. When the subject gets lost, he could refer to the global map displaying the current and target location simultaneously.

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530 Proceedings of 1996 ICC&IC

Figure 1. Screen of the driving simulator

2.3 Experimental Design When people read a map, they generally pass through three stages: translation, mental movement, and mental rotation [3]. Especially, the mental movement and rotation stages are critical factors in designing an electronic map. In the experiment two factors were manipulated: rotation method and movement method. The "rotation method" factor consisted of HeadUp and NorthUp, and the "movement method" factor consisted of Fixed-Car and Moving-Car (Table 1).

Tab. 1 Expedmental factors

Factom

Rotation

Movement

Levels Definitions HeadUp

(Map rotates

NorthUp (Car rotates)

Fixed-Car (Map moves)

Moving-Car (Car moves)

Advance direction always indicates upside on the electronic map. North direction always indicates upside on the electronic map. An automobile icon is fixed at the center of the electronic map. The Map is fixed on the screen and the automobile is moving on the map.

The experiment employed a within-subjects design in which each and every subject went through the expedmental conditions listed in Table 1. Figure 2 presents the screen of the electronic maps corresponding to the experimental conditions. The triangle icon represents the location and direct on of the automobile. Each experimental condition was replicated with three different tasks in which a different departure and destination was used.

(a) HeadUp and Fixed-Car condition

(b) HeadUp and Moving-Car condition

Proceedings of 1996 ICC&IC 531

(c) NorthUp and Fixed-Car condition

[ ]

r

=,

(d) NorthUp and Moving-Car condition

Figure. 2 Experimental conditions

The subjects were instructed to drive the automobile from the starting position to the destination as fast as possible. Three performance measures (arrival time, navigation inefficiency, and map reading time) were collected. The arrival time was defined as the time to reach the destination and the navigation inefficiency was defined as the difference between the actual number of crossroads passed and the optimal number of crossroads. Finally, the map reading time was defined as the total time for which the subjects referred to the global map to find the way to the destination.

2.4 Procedures The experiment consisted of three major sessions: subject training, main experiment and debriefing. After a brief introduction to the experiment, the subjects were trained to manipulate the prototype. During the main experiment, each subject went through all of the four experimental conditions in a predetermined order. Upon completion of all trials, a short debriefing session was given to the subject to collect the subjective opinion on the electronic map.

IlL Results and Discussion

3.1 Arrival Time The average arrival time was approximately 113.8 seconds in the Moving-Car condition, while it was reduced to 104.9 seconds in the Fixed-Car condition (F=5.30, p<0.05). In the Moving-Car condition, the screen scrolls instantaneously and displays the next neighbor region when the automobile icon crosses the border line on the electronic map. This sudden map changes confused the subjects and made it difficult to take the right direction at the crossroads. This contributed to the longer arrival time. On the contrary, the subjects could finish the task faster in the Fixed-Car condition than in the Moving-Car condition, since the automobile icon was fixed at the center of the electronic map and there were no sudden changes of the map. Therefore, the Fixed-Car method which shows much less display changes, is recommended where many crossroads are expected, for example, in the city environment.

3.2 Map Reading Time The subjects looked at the global map more often and for a longer time in the HeadUp condition than in the NorthUp condition. On the average, the total map reading time were 2.4 seconds and 5.2 seconds in the NorthUp method and in the HeedUp, respectively (F=9.90, p<0.05). In the HeadUp condition, the subjects were not required to conduct any mental rotations since the moving direction of the automobile in the 3-dimensional view was consistent with that on the 2-dimensional map. This method seems to be very helpful when the driver does not need to refer to the global map. However, it may be confusing when the driver loses the orientation and as a result, needs to look at the global map. This is supported by the fact that the map reading time was less in the NorthUp condition than in the HeadUp condition. This is because the subjects read the global map which is the NorthUp type and then need to convert the map image appropriate to the local map which may not be the NorthUp type. Therefore, the NorthUp type is recommended in terms of the map reading time. It is interesting to note that the interaction between the rotation and the movement methods was found significant (F=7.24, p<0.05). A post-hoc analysis (Newman-Keuls test) showed that the Moving-Car condition was not useful when it was used together with the HeadUp type (Figure 3). This result may stem from the fact that the map suddenly changed in the Moving-Car condition, and worse yet, the HeadUp type forced the subjects to go through heavy mental rotation. Other combinations were not statistically different. Based upon this result, it is not recommended the Moving-Car type be used with the HeadUp display.

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7

6

5

- 3

Moving-Car j R x ~ 7A

Y 2.9 2.3

NorthUp HeadUp

Figure 3. Interaction between the rotation and movement methods

3.3 Subjective Preference Table 2 shows the results of the subjective preference integrated with the experimental results stated above. Note that each design alternative generated by the two factors has its own advantages and disadvantages. Interestingly, no alternative turned out to be superior to the others. Thus, the designer needs to consider carefully which aitemative should be used in which condition. In addition, it may be a good design decision to make all design altamaUves available and let the driver choose the favorite one. Of course, the designer needs to make intense trade-off analyses before he/she makes a design decision.

Table. 2 Advantages and disadvantages of design aitematives

Levels of factors Characteristic NorthUp It is difficult to select the

direction at the crossroads because the direction of the outside view and the electronic map does not coincide. But the direction of the electronic map and the global

Rotation map coincides. HeadUp

Moving- Car

Movement

Fixed- Car

It is easy to select the direction at the crossroads because the direction of the outside view and the electronic map coincides. But the direction of the electronic map and the global map do not coincide. Sudden changes of the electronic map tend to make the driver lose orientation. The driver can recognize easily the movement of the automobile on the electronic map. The scrolling of the electronic map is continuous and gradual. But, the fixed image of the automobile on the map may not be realistic.

IV. Conclusion

This study examined, the usability of two factors in designing the electronic map on the GPS. Based upon the expedmantal results, the following guidelines are recommended.

• The Fixed-Car method is desirable for minimizing the arrival time, that is traveling time.

• The Moving-Car method is not recommended especially where many croesroads are expected.

• The NorthUp method is useful when the driver prefers the WRF format and needs to communicate with other persons at a different location.

• The HeadUp method is strongly recommended when many crossroads are expected in a relatively narrow region.

• The HeadUp format should never be used together with the Moving-Car method.

V. References

[1] Kwon, O. S. & Park, M. Y., 1995, The Role of Human Factors Study in ITS, Proceedings of the Ergonomics Society of Korea, 201-207

[2] Antin, J. F., 1993, Information Aspects of Car Design: Navigation, Automotive Ergonomics, 321-335

[3] Aretz, A. J., 1991, The Design of Electronic Map Displays, Human Factors, 85-101.