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<ul><li><p>ARTICLE IN PRESS</p><p>1071-5819/$ - se</p><p>doi:10.1016/j.ijh</p><p>CorrespondE-mail addr</p><p>mourouzi@ics.</p><p>Int. J. Human-Computer Studies 64 (2006) 221239</p><p>www.elsevier.com/locate/ijhcs</p><p>Virtual prints: Augmenting virtual environments with interactivepersonal marks</p><p>Dimitris Grammenosa,, Alexandros Mourouzisa, Constantine Stephanidisa,b</p><p>aFoundation for Research and TechnologyHellas (FORTH), Institute of Computer Science, GR-70013 Heraklion, Crete, GreecebDepartment of Computer Science, University of Crete, Greece</p><p>Available online 4 October 2005</p><p>Abstract</p><p>This paper introduces the concept of Virtual Prints (ViPs) as an intuitive metaphor for supporting interaction and navigation, as well</p><p>as a number of additional tasks in virtual environments (VEs). Three types of ViPs are described: Virtual Footprints, which are used for</p><p>tracking user navigation (position, orientation and movement), Virtual Handprints, which are used for tracing user interaction with the</p><p>VE, and Virtual Markers, which are special marks (usually coupled with information) that can be created upon user request. In a VE,</p><p>the ViPs concept is instantiated and supported through a software mechanism (the ViPs mechanism) that allows users to create, manage</p><p>and interact with their personal ViPs, as well as other users ViPs.</p><p>The paper presents the background and related work upon which the suggested concept builds, as well as the distinctive properties that</p><p>differentiate ViPs from other related efforts. An account of how users can interact with ViPs is provided and related issues and challenges</p><p>are discussed along with techniques and methods for addressing them. The paper also describes the process followed towards defining</p><p>and experimenting with the concept of ViPs by means of iterative design and evaluation of an interactive prototype. This process</p><p>involved exploratory studies, as well as several inspections and formal tests with both experts and potential end-users, in order to assess</p><p>the usefulness of the concept and identify possible shortcomings, and also to evaluate and improve the usability of the proposed designs</p><p>and software prototypes. In general, the findings of the studies reinforce the initial hypothesis that ViPs are an intuitive and powerful</p><p>concept, and show that the related software is easy to learn and use. Overall, the results of the studies support strong evidence that an</p><p>appropriately designed and implemented, fully functional ViPs mechanism can significantly increase the usability of VEs.</p><p>r 2005 Elsevier Ltd. All rights reserved.</p><p>1. Introduction</p><p>In the real world, every living organism constantly leavestraces of its existence and its interaction with the physicalenvironment: deer leave their paw marks on the soft forestsoil, dolphins carve foam traces on the surface of the sea,flies leave annoying black spots on windows, and youngchildren imprint their dirty handprints on freshly paintedhouse walls.</p><p>Since the early years of their presence on earth, humansobserved this inherent property of the environment andlearned to use it in various ways in order to make their liveseasier. For example they learned to recognize the pawprints of animals to track down their prey or to avoid</p><p>e front matter r 2005 Elsevier Ltd. All rights reserved.</p><p>cs.2005.08.011</p><p>ing author. Tel.: +302810 391755; fax: +30 2810 391740.</p><p>esses: gramenos@ics.forth.gr (D. Grammenos),</p><p>forth.gr (A. Mourouzis), cs@ics.forth.gr (C. Stephanidis).</p><p>ferocious creatures, they used footprints to exploreunknown territories or find their colleagues in search andrescue operations (Kearney, 1999), they examined fossils tostudy human history and evolution (Tattersall, 1995), andthey revealed and analysed fingerprints to solve crimes(Beavan, 2001).In contrast to real environments, Virtual Environments</p><p>(VEs) do not allow their inhabitants to leave any tracebehind, thus suffering from an extreme cleanness syn-drome. Walk into your house after leaving your childrenalone for the weekend and you can instantly realize that awild party took place while you were away. Walk into avirtual chat room seconds after a meeting of 200 people hasfinished and it will be exactly as if no one has ever beenthere before.Inspired by these observations, the concept of Virtual</p><p>Prints (ViPs) is proposed (Grammenos et al., 2002) as thedigital, interactive counterparts of real-life tracks. The</p><p>www.elsevier.com/locater/ijhcs</p></li><li><p>ARTICLE IN PRESSD. Grammenos et al. / Int. J. Human-Computer Studies 64 (2006) 221239222</p><p>basic idea is that while a user is moving in a VE, VirtualFootprints (FootViPs) are left behind, whereas each timean interaction with an object occurs, the users VirtualHandprints1 (HandViPs) are imprinted on it. BothFootViPs and HandViPs can be time-sensitive andgradually fade, as realor virtualtime goes by. VirtualMarkers2 (MarkerViPs) are permanent marks coupled withuser-defined data (e.g. a textual or audio message) whichcan be left in the environment, or pined on any virtualobject, and can act as personal landmarks, annotations oranchors.</p><p>ViPs can have a variety of uses in a VE, ranging fromsupporting navigation (i.e. travel and wayfinding), totraining and creation of tutorial sessions, conductinguser-based evaluations, etc. Furthermore, as FootViPsand HandViPs are actually a means for recording andvisualizing navigation and interaction history, respectively,they have the potential to introduce in VEs severalfunctions and concepts that are popular, if not standard,in conventional 2D user interfaces, such as shortcuts,bookmarks, undo/redo functions, collaborative review, aswell as marking/identifying (non) visited content (Mour-ouzis et al., 2003). Correspondingly, MarkerViPs can beused for content annotation and highlighting, or foroffering context-sensitive help. Although this paper focuseson using ViPs in a VE, they can also be effectively used inAugmented Reality Environments. For example a personusing an augmented reality system in a museum can followViPs that are related to a specific topic of interest, or thoseof a virtual guide.</p><p>A considerable advantage of ViPs is that they can beused in any VE and in combination with any existingnavigation and wayfinding support approach. Further-more, the fact that ViPs have real-life counterparts withwhich humans are very familiar renders them an intuitiveand potentially easy to use metaphor.</p><p>The rest of the paper is structured as follows: Section 2presents the background and related work upon which thesuggested concept builds. Section 3 describes the distinctiveproperties and characteristics of each type of ViPs, whileSection 4 provides an account of how ViPs can beinstantiated in a VE through a related software mechanism,and of how end-users can interact with them. Section 5illustrates challenges that may potentially arise whenputting ViPs to real use, along with suggestions and waysfor overcoming such challenges. Section 6 provides acomprehensive overview of possible uses of ViPs beyondnavigation, orientation and wayfinding. Section 7 describesthe process that was followed for making the transitionfrom early concept formation to a full-functioning softwareimplementation, including the exploratory studies which</p><p>1Virtual Handprints were originally named Virtual Fingerprints, but</p><p>our studies revealed that the concept of Handprints is far better both in</p><p>terms of usability and intuitiveness (e.g. fingerprints are too small to be</p><p>noticed and to interact with).2Virtual Markers were originally termed Virtual Fossils, but they were</p><p>renamed as a result of user testing.</p><p>were conducted, as well as several inspections and formalexperiments with both experts and potential end-users.Finally, Section 8 concludes the paper and offers an insightinto future work.</p><p>2. Background and related work</p><p>In the past few years, a number of industrial VEapplications have been developed and put to practicaluse. The Virtual Reality (VR) market is growing rapidly(Arrington and Staples, 2000; CYBEREDGE, 2001) andVEs have been adopted as a useful and productive tool fora variety of applications (Delaney, 1999). Nevertheless,user feedback reveals that there are still several barriersthat impede the sustainable and appropriate use of VEs inthe industry environment, including barriers concerningthe integration of technologies, barriers due to insufficientknowledge concerning the impact of such technologies onthe user, as well as usability barriers (Crosier et al., 2000;Bowman et al., 2001).</p><p>2.1. Navigation in VEs</p><p>Navigation is a key task in any type of VE. Navigationcan be considered as a combination of travel andwayfinding. Travel is the minimum interaction capabilityoffered by any VE and involves the ability of the users tocontrol the position (i.e. to move) and orientation (i.e. gazedirection) of their virtual body. Wayfinding means that theuser is aware of his/her current location and of how theycan to get to a desired destination. Although there havebeen numerous efforts in this area, navigation still remainsa major challenge, since observations from numerousstudies and usability analyses indicate that this task(especially in large-scale VEs) can be very difficult, andmay result in user disorientation and distress (Ellis et al.,1991; Darken and Sibert, 1993; McGovern, 1993; Darkenand Goerger, 1999; Vinson, 1999).The reasons why navigation can be so cumbersome in</p><p>VEs can be summarized in the following:</p><p>(a)</p> Navigation is a difficult task also in the real world.Humans may have difficulties when dealing withunfamiliar or complicated and unstructured physicalenvironments (e.g. a forest, a highway, or a modernbuilding). To overcome these difficulties, navigationsupport tools have been developed including maps,compasses, signs, and electronic global positioningsystems (GPS). Thus, even if VEs were indistinguish-able from the real ones, navigation would still be amajor challenge.<p>(b)</p><p> Lack of constraints (Chen, 2003). In the real world,several constraints exist when moving from onelocation to another. There are paths to follow, doorsto go through, insurmountable obstacles, and distanceor time restrictions that significantly decrease move-ment possibilities. In most VEs, the user has the</p></li><li><p>ARTICLE IN PRESSD. Grammenos et al. / Int. J. Human-Computer Studies 64 (2006) 221239 223</p><p>capability to fly or even instantly be transported toremote places, and often minimal actions and physicaleffort result in dislocation over very large distances.</p><p>(c)</p> Lack of cues (Vinson, 1999). Humans, in order tonavigate in large spaces of the physical world,subconsciously reconstruct an abstract mental repre-sentation of the environment, known as a cognitivemap. This representation is created through a combi-nation of spatial and proprioceptive cues. Spatial cuesmay include landmarks, the relative position ofstructures and buildings, but also sounds and smells.Proprioceptive cues are collected through the physicallocomotion of the body and its parts. VEs providesignificantly fewer spatial cues than real environments.First, there are technical and cost limitations forproducing high-fidelity visual representations. Addi-tionally, there is high reuse of 3D models in order toease the task and cost of populating and displaying thevirtual world, and thus sometimes it is difficult todifferentiate between different parts of the environ-ment. Non-visual cues are rarely integrated in VEs andproprioception is engaged only through devices andtechniques that are still in the form of researchprototypes. Finally, in non-immersive VR applications,where the VE is viewed at a small scale and through alimited, external, viewpoint, cues are hard to notice andinternalize.<p>Related work can be broadly classified in the followingcomplementary research directions:</p><p> Informing the design of VEs.</p> Development of appropriate input techniques and<p>devices for user movement in VEs.</p> Development of VE navigation and wayfinding support<p>tools.</p><p>2.1.1. Informing the design of virtual environments</p><p>This research direction is concerned with the develop-ment of appropriate guidelines (mainly by exploitingexisting environmental design principles) for the creationof well-structured spaces that inherently aid orientationand wayfinding. For example Charitos (1997) presents ataxonomy of possible objects in VEs (namely landmarks,signs, boundaries, and thresholds), as well as of the spatialelements that these objects define (places, paths, inter-sections and domains), and suggests how these elementscan be used to support wayfinding, based on architecturaldesign and on the way humans conceive and rememberspace in the real world. Along the same line of work,Darken and Sibert (1996) have studied wayfinding strate-gies and behaviours in large VEs, and suggest a set ofenvironmental design principles that can also be applied inVEs. Hunt and Waller (1999) examined the relation oforientation and wayfinding between physical and virtualworlds, and the way existing knowledge can be transferred</p><p>from the former to the latter, while Vinson (1999) offers aset of design guidelines for the placement of landmarks in aVE in order to ease navigation, based on concepts relatedto navigation in the physical world. On the other hand,research findings presented by Satalich (1995) lead to theobservation that human behaviour with regards to naviga-tion in the real world is not identical to behavioursexhibited in VEs, and thus it is likely that existing tools andprinciples may not be adequate or sufficient if directlytransferred from one domain to the other.A basic limitation of these approaches is that they</p><p>require the modification of the virtual spaces contents.This may not always be possible or desirable as, forexample in the case of VEs that are based on real-worldenvironments, thus rendering these approaches inappropri-ate for a large number of widely used VE applications suchas simulations, engineering design and architectural walk-throughs.</p><p>2.1.2. Development of appropriate input techniques and</p><p>devices for user movement in virtual environments</p><p>This research direction aims to provide easier and moreintuitive navigation in VEs through the definition anddevelopment of appropriate hardware, as well as of relatedinput techniques and metaphors that allow the user tomove more naturally in a VE. For example the Omni-Directional Treadmill (Darken et al., 1997) and the TorusTreadmill (Iwata and Yoshida, 1999) aim to offer novelhardware solutions for naturally walking or jogging in aVE. Peterson et al. (1998) propose a new input device in theform of a body-controller interface called Virtual MotionController, and compare its performance in navigating avirtual world with a joystick. Templeman et al. (1999)present Gaiter, another input device and an associatedinteraction metaphor that allows users to direct theirmovement through VEs by stepping in place. A differentapproach is followed by Razzaque et al. (2001) whointroduce a new interaction technique supporting locomo-tion in a VE, named Redirected Walking, that does notrequir...</p></li></ul>

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