Investigating the traveler experience: the use of eye-tracking for urban design purposes

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Perception

Piga, Tangredi & Signorelli

Barbara E.A. PigaCarmine TangrediValerio Signorelli

Laboratorio di Simulazione Urbana “Fausto Curti”DIAP, Politecnico di Milano, Milano, Italy.

Investigating the traveler experience: the use of eye-tracking for urban design purposes KeywordsVisual perception, Eye-tracking, Simulation, Urban Design, Landscape

AbstractThe research addresses the theme of visual perception of the landscape. Having as a reference the highway traveler, the main aim is to propose an approach that allows to highlight where the observer in motion focuses the attention on the traversed environment. The recurring and privileged viewpoint of the road user, with its speed and the fixed route, is a great occasion for reconsidering and redesigning our landscape or the urban edges. The research proposes a method and a tool for supporting the design phase focusing on the continuous and dynamic experience of the observer. This can inform the urban de-signer about the user experience, both in the actual condition and in the future (simulated) one. Working in this direction we would like to encourage design projects that take into ac-count the perceptual impact in time and space. We have experimented a technique normally used for other purposes, especially in the field of marketing and peo-ple safety, namely eye-tracking. For instance, using two syn-chronized cameras, one directed to the observed scene and another to the observer’s eye, it is possible to understand where the subject poses her/his attention on the scene. The experimentation gives an important feedback on the possibility of the tool for supporting the understanding of how people perceive urban/rural spaces.

IntroductionThe presented study is part of a wider ongoing research, named New Tools To Analyze And Manage The Linear Cul-tural Landscape. Preservation And Planning Policies, which deals with the design of linear infrastructure [1]. The research addresses the issue of the relationship between linear infra-structures and the systems of historical and environmental resources they cross. The main goal is to identify analytical

Figure 1. Eye-Tracking Process Scheme: From the On-site Record-ing to the Final Output.

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Envisioning Architecture

Proceedings EAEA 2011

tures that look for a visual synergy of the crossed landscape, or it can be useful to study new interventions on the land-scape itself to give a visual coherence to specific traversed environments. The basic idea is that the dynamic visual experience of the road user, and specifically the user of urban highways, is a great occasion to reinforce the identity of the crossed en-vironment. The traveller velocity gives a unique opportunity: the possibility to see a large area in a relative short time. This means that only few elements of the landscape will be visible to the observers, some of them will appear in a continuous way and will accompany her/him along the route (back-ground) and others will be single ones or spots (foreground). Assessing what is visible and what mainly attracts the user attention is crucial for the understanding of the visual experi-ence, and for developing a design project [Appleyard et al, 1964]. Having a method that can highlight these factors can be useful for the design phase in several stages: it can serve to study how a situation is working in the present condition, it can support the development of the design guidelines for specific projects to be developed, and it can be used to verify the efficacy of project outputs in relation to its possibility to catch the user attention. The method allows to individuate the visuals that the majority of people look at, and the ones that only few people

and planning tools for the requalification of contemporary territories. To reach this main aim, part of the research has been developed at the Laboratorio di Simulazione Urbana ‘Fausto Curti’ [2] of the Politecnico di Milano, with a specific focus on the theme of visual perception of the environment, which is the subject of this contribution. We propose a methodological approach to study the effect of landscape transformation in the road user behavior. We implement a tool that allows to record where travelers pose the gaze, and to understand how a landscape transformation changes the user visual reaction to it. This kind of analysis can give the designer a trend of the observed element in the panorama in the present condition and in the future one, allowing her/him to have data to develop a project or to test the effective output of the planned landscape projects on the final users. The research addresses the general issue of the visual experience of a person in motion. The specific focus is about the visualization of road users along linear infrastructures, i.e. highways. In studying the topic, the main attention is devoted to the possibility to scientifically analyze which ele-ments mainly catch the attention of subjects that travel in the existing condition, and how this situation could be altered by new design projects of the landscape or the highway itself. Taking into account the viewpoint of the highway users, the proposed method can support the design of new infrastruc-

Figure 2. First prototype of eye-tracking glasses for urban analysis developed by the Laboratorio di Simulazione Urbana “Fausto Curi”.

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Research contextThe starting point and main reference of the study is the research conducted in the Sixties at the California University (Berkeley) by D. Appleyard, K. Lynch and J.R. Myer, pub-lished as The View from the Road (1964). This research, which has prompted and anticipated the foundation of the first Environmental Simulation Laboratory[3], remains quite unique in its approach to this topic. That research is particularly interesting because it focuses on the experience of the traveller as an important refer-ence for the design of new roads. To do that the research team developed an iconographic system to describe the user visual perception of the road. They experimented the usage of different techniques, e.g. sequences of images and videos, and they developed an encoded iconographic system to describe the results of the study as a map. This was an interesting starting point, but, as the same authors declared, the method presents some limits, first of all the fact that it “is never at first intuitively obvious (…) it will take time and some practice before any such system will seem to communicate the ‘feel’ of a complicated experience of motion” [Appleyard et al. 1964, p.21]. This specific design approach did not have an important development along the years, while the studies about street views and safety are more common. In this field the usage of new technologies, i.e. simulators and simulations and eye/

consider. In doing this, this analytical method can be useful for individuating vistas that have to be emphasized, pre-served, or that need to be revised or newly created. All these aspects have to be considered in time, as a sequence of events that the user goes through. For this reason the use of videos as the base element of analysis is particularly suited. The core of this research is individuating a method that allows to scientifically analyze visual users’ behavior in the described condition. To do this we set up a prototype of an eye-tracking tool, an instrument that enables to grab on a video where the observer poses her/his attention. One of the requirements was to developed a low cost instrument; we decided to follow this approach because we needed to test the validity of the proposed method for urban design purpos-es, and because in this way it will be possible to use more than one tool, and hence more than one person, at the same time in the same place for future applications. Since our main goal was to propose a methodological ap-proach, we have just tested the equipment and the possible output on an highway called Padana Superiore, located in the northern Italy. We did not develop the survey that would allow us to have reliable results on the road user behavior in that specific context; yet, in that case we should involve sev-eral people to have a reliable statistic data. For this reason did not have yet questioned why some landscape elements or condition catch the attention more than others.

Figure 3. First prototype of eye-tracking hat for urban analysis developed by the Laboratorio di Simulazione Urbana “Fausto Curi”.

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gaze target in time and space [Fig. 1]. We experiment the usage of different typologies of web-cams on different types of support, as well as various soft-ware. We tested the usage of two different supports to hold the cameras: a pair of glasses [Fig. 2] and a hat [Fig. 3]. The main problem of the first solution was the reflection of the lenses, so we kept them out; another difficulty was the total weight of the tool, so we moved on testing the usage of a hat to hold the webcams. This solution is more efficient, because after a while the observer is not more aware about the tool, while having a pair of glasses is more invasive if the person is not used to wear them. On the other hand, it is more dif-ficult to calibrate the correct position of the hat compared to the glasses, because it is necessary to fix it properly in order to get a straight shot. We tested different types of webcams, starting from the low cost and low resolution ones, but the results were not satisfactory and the entire process was not accurate enough. Using 2Mb webcams is the minimum requirements that we consider the bare essential to get to an acceptable solution for our purposes. To test the usage of the tool in outdoor spaces we needed to connect the webcams to a laptop for recordings the videos [Fig. 4a-b]. We successfully used two instances of Virtual Dub, a freeware video software, on a netbook [Fig. 5]. The computer performances were enough to run the processes, and we could take advantage of its portability (small and

head tracking techniques, were important for the advancing of the research. The eye-tracking technique is particularly rel-evant for our purposes, because it allows to analyses where the subject poses her/his attention on the scene. Using this technique, employed for the researches on street safety, and the approach of the Berkeley research team, we are developing a design method that could be employed for design and evaluation purposes.

Methodology | techniqueThere are different typologies of eye-trackers that allow to grab ocular movement. The less invasive one, even if less precise, uses videos as analytical data [4]. Our research uses this method and, instead of buying an expensive equip-ment, we have decided to build our own low cost solution. In fact, by using simple high quality webcams and open-source software, it is possible to reach a sufficient output for urban design studies; more sophisticated and precise tools are more suitable in surveys that require high accuracy. Building our own product has the advantage to be more flexible: we can modify it according to our necessity. To develop the tool we needed a device for grabbing videos (two webcams and a netbook) and a computer with the software for data elaboration. Using two cameras, one directed to the observed scene, and the other one to the observer’s eye, it is possible to grab two synchronized videos that can be elaborated by specific software to analyze the

Figure 4a-b. Use of the eye-tracking hat in a car journey.

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a map can provide a more complete information, especially if it is seen in parallel with the analyzed panoramic video. The trace can easily be registered with a simple gps solu-tion. Even some applications for smartphone allow to record the travel in kml extension [6], or similar format, using just an internet connection; beyond the information of the route, the file contains information about the hour of the day, the speed of the travel, and the elevation for every location. The use of gps tools are preferable, but in lack of them, a simple internet connection can give the same information, even if less accurate. In both cases the data are not particularly pre-cise, but as the user is travelling on a known route, it is quite easy to adjust the trajectory in post processing, if necessary. Even with some degrees of acceptable inaccuracy, it is pos-sible to match the two previous videos with the one of the route on the map. In doing this the final observer can easily understand to which panorama the traveler was looking at in a specific location, and s/he can check where the gaze was directed. Knowing the speed it could be also possible to analyze which are the landscape elements that catch the attention at different velocity. If the aim is to analyze the today condition, this survey can be done in real settings. Alternatively it is possible to do it at the laboratory using video recordings [Fig. 7a-b]. There are different ways to do that, since different tools have already been used to simulate the travel experience. The ideal solu-tion is the one that can reproduce the environment as close

light) and its long battery capacity (8 hours). We tested this solution for a short walk too, and it worked well, even if a webcam wifi connection to a computer would be preferable. In order to elaborate the videos we conducted a study to understand which open-source eye-tracking software was more suitable for our purposes. We tested several software and we are now working with two different ones: Open Eyes and ITU Gaze Tracker [5]. These tools allow to elaborate video data and to depict the visual focus attention of the observer in movement. By synchronizing the videos of the eye and the video of the observed panorama, the software is able to elaborate the target of the eye on the scene [Fig. 6]. In doing this the software traces the eyes movement on the recorded views, and automatically produces a dynamic representation of the areas of attention. This allows to have information about the scanpath (when the gaze moves from a location to another) and fixation (when the gaze stays fixed on an element) of the observer in motion in specific contexts. Mounting the video of the observed panorama with the identification of the target (main video), together with the one of the eye (auxiliary video), it is possible to see that the movement of the eye in the auxiliary video corresponds to the different position of the point of interest (target) on the elaborated video (main video). Another useful information that can be added in the post-elaboration process is the position of the observer in space and the travel velocity. A video that shows the trajectory on

Figure 5. Eye-tracking computer video recording during a car journey.

Figure 6. Output of the elaboration of the panorama and eye videos recorded in the real environment with target indication.

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view of the observer and correct distance with the simulation) [Bosselmann, 1998; Piga 2010]. Having the simulator equipment available, this approach can result more flexible and convenient than going to the real setting, but the response equivalence between the simulated environment and the real condition should be verified for this specific type of study. Besides this, it is possible to consider it a plausible solution, as simulations are being used for sev-eral purposes in several contexts (e.g. military, automotive, ect) with reliable outputs, and some researches validated the use of accurate simulation as replacement of reality [Craik and McKechnie, 1975; Appleyard, 1976; Sheppard, 1989]. The possibility to use simulated settings is particularly relevant, because it gives the possibility to test how a design project, or its alternatives, will catch the attention of the road user. If the response equivalence between the outputs of the eye-tracking analysis of similar reality and simulated environ-ment is confirmed, this could be a very useful tool for urban design purposes. This could be a way for envisioning and study possible (future or re-created) conditions and test its compliance with the desiderata. To have reliable data on all these aspects the survey should be conducted with several users. The analysis and the comparison of the different data achieved can highlight a common trend in the users behavior. It is undoubted that even the same person who travels in two different moments on a specific route, will look at different things, but if we

as possible to the real one, and that leaves the user free to move exactly as s/he could do in the real condition [Piga, 2010]. Examples of car simulators, more or less realistic, are not so unusual, and some of them can even reproduce the vibration of the vehicle itself. More sophisticated ones use directly the front part of a car, and a projected video on a large curved surface in front of it. Anyway, independently from the simulator used, a specific attention has to be paid to the modes of visualization. In fact, as several researches highlight [Craik and McKechnie, 1975; Appleyard, 1976; Sheppard, 1989], if the goal is to have a realistic feedback from the users, it is crucial that the visualizations are well founded. So, if the focus of the study is to analyze the perception of the travelers, the visualizations should be able to reproduce correctly spatial information, as the relative distance between objects as well as the relative dimension of the landscape elements or other aspects as color and texture [Appleyard, 1976; Sheppard, 1989]. The final validity of the survey depends upon the fidelity of the visualization: in any case the user will react to the simulation, but if the visualiza-tion will not be accurate enough the user reaction will not be reconnected to the real condition. To achieve this goal it is necessary to follow a precise method to simulate the virtual travel; i.e. the video has to be grabbed using the focal length of lenses similarly to the way we see, and to reproduce the video replicating the correct relationship between the observer and the elements of the landscape (correct point of

Figure 8. Output of the elaboration of the panorama and eye videos of a simulated environment with target indication.Figure 7. Eye-tracking recording of a video during a route.

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light, position of the car and similar. It is possible to auto-matically analyze the visual experience of a single user, and understand where s/he is looking at, but the software cannot compare the results of different users, as the recorded pano-rama will differ from one observer to another. For this reason analyzing a great number of users’ travels and automatically compare the results to highlight a trend is a difficult task. Of course this kind of analysis can be done manually, for instance by signing the landscape elements that are repeat-edly observed, but an automatic process would be prefer-able. At the moment we could not find a software able to do this analysis, and probably a different method for recording the videos or to reconnect it onto a unique base, i.e. a 3D model, is necessary. Anyway the analysis would be quite complex, since for each recording the car would travel at a different speed, in a different position along the route, and all the variable condition of the surrounding will differ a bit, especially traffic condition. A way to avoid this problem is to use 360° interactive video of the travel in a simulator. In this way all the circum-stance of the situation are identical for each survey, and the observer reaction to the environment could be easily recorded and compared; in this way it would be easy to sta-tistically study which are the landscape elements that largely catch the attention. This method has the main vantage that the investigation can be done in the laboratory, and that it is quite easy to superimpose a render of the landscape trans-formation to the visualization of the existing context to study its visual impact as an attractor. If the survey is conducted in a simulated environment that use a 3D digital model as a base, the automatic analysis process can be done, having a unique base as a reference. The problem of this kind of approach is that the richness of details is low compared to real video, and so the overall simulation can result less engaged to the observer. An im-portant aspect of this approach is that all the characteristic of the specific situation (light, weather condition and so on) can be replicable exactly in the same way for each user. On the contrary, the observer is not really in the landscape; this can imply a weaker user involvement and implies the need that all the surrounding elements are represented.

Conclusions | future workAt the moment we did the first test of the use of the eye-tracking technique for design purposes on a panoramic high-way. The use of simulated environments instead of real ones is one of the future developments of the research we intend

consider a wide enough case record, we can get to a statistic understanding of the situation in similar conditions. So, if we have a sufficient number of users that join the survey, we will reach a reliable output that can explain which are the landscape elements that mainly catch the user attention. In a second step some deeper analysis can be done, e.g. the du-ration of scanpath and fixation to have a better understand-ing of the dynamics of observation and its meaning. In the past the comparison of data had to be done manu-ally. Today, for some types of recordings, the technology allows to do this calculation automatically. There are several dedicated applications that can do that. They are able to analyze data and to automatically produce different kinds of visualizations that indicate the areas of major attention on a vista. Since, we are concentrating our attention on the method for the current research, we did not develop such a survey, and we studied this post-elaboration method only in theoretical terms to understand its potential applicability. The main problem to use this kind of software for land-scape analysis in real settings is that the users will look at different things, in different moments and with a different position in space, therefore an automatic post-elaboration is problematic. The software mainly used to do this kind of analysis is usually applied to researches which aim to understand the way users interact with a specific software layout or read a written digital document; in these cases the software has a reference the same bases on the monitor, i.e. software layout or the document pages, that do not change in time, whereas changes are in the user behavior. The automatic elaboration of the data can graphically produce a media of the point of interest of the different users on the same base [Fig. 8a-b]. Using the described eye-tracking process in the real condition, the video of the observed panorama differs from one user to another, as all as the contextual conditions, e.g.

Figure 9a-b. Gaze analysis screenshots of the Ogama software elaboration, which highlights the users major areas of attention [www.ogama.net/node/12].

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to carry on. As it was said previously, in this case it is really important to set up a visualization that can guarantee the accuracy of the representation and the response equivalence of the users. Another important aspect will be the degree of immersion that the simulation is able to guarantee, so the intention is to test different kinds of supports for the visualiza-tion that allow different kinds of immersion. The number of people that participated to the first output is not significant for validating the outputs. Nevertheless, the experimentation gives an important feedback on the possibil-ity of the tool for supporting the understanding how people perceived urban/rural spaces. Since the applicability of the developed approach can be useful to better understand dif-ferent kinds of open spaces (i.e. urban or rural, high density or low density), related to different kinds of usage/users (i.e. leisure or commuting user), and type and velocity of travel-ling (i.e. pedestrian or cycling), we are planning to test its usefulness in understanding the perception of urban public spaces. By repeating the test on the same path a trend of the main attractors across a route is given: if the analysis is conducted on the existing condition it gives a framework to dynamically interpret the environment from an experiential point of view; if the study is conducted on a simulated environment it can give a feedback about the success of the designer desid-erata. We are now working on the existing real condition, then we will move to simulated ones and finally we will work the tool to study the impacts of different design solutions in influencing the visual experience. Since the applicability of the developed approach can be useful to better understand different kinds of open spaces (i.e. urban or rural, high density or low density), related to dif-ferent kinds of usage/users (i.e. leisure or commuting user), and type and velocity of travelling (i.e. pedestrian or cycling), we are planning to test its usefulness in understanding the perception of urban public spaces.

Notes1. This is an interdepartmental two years long research developed

at the Politecnico di Milano 2. For further information refer to: http://webdiap.diap.polimi.it/Lab/

LabSim3. http://laep.ced.berkeley.edu/simlab/4. The other two methods use sensors posed directly on the eye-

ball (e.g. contact lenses) or electrooculography (sensor around the eye)

5. We are now starting to use this software because from the re-lease 1.6 it allows the usage in space and not only on a screen.

6. This type of extension can be imported by different software, i.e. GIS, Google Earth and similar.

Relevant references• Appleyard, Donald, Lynch, Kevin, Myer, John R., [1964], The

View from the Road, Cambridge (Mass.)• Appleyard, Donald, [1976], “Understanding Professional Media.

Issues, Theory, and a Research Agenda”, IURD (Institute of Urban and Regional Development), Vol.2, No.150, (Reprint Title), pp.43-88

• Bishop, Ian, Lange, Eckart, [2005], Visualization in Landscape and Environmental Planning. Technology and Applications, Taylor & Francis, New York

• Bosselmann, Peter, [1998], Representation of Places: Reality and Realism in City Design, University of California Press, Berkeley, London

• Craik, Kenneth H., McKechnie, G.E., [1975], “Environmental Simulation Appraisal Project: Preliminary Report”, Institute of Personality Assessment and Research, Berkeley (CA)

• Piga, Barbara, [2010], La simulazione visiva per l’urbanistica. Il punto di vista percettivo nella comprensione delle trasformazi-oni urbane, PhD Thesis, Politecnico di Milano, Department of Architecture, Milan, Italy.

• Sheppard, Stephen R.J., [1989], Visual Simulation: a User’s Guide for Architects, Engineers and Planners, Van Nostrand Reinhold, New York.

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Investigating the traveler experience: the use of eye-tracking for urban design purposes