URBAN CITY PLANNING INSEMI-IMMERSIVE VIRTUAL REALITY SYSTEMS

Frank Steinicke, Timo Ropinski, Klaus Hinrichs and Jorg MensmannInstitut fur Informatik, WWU Munster

Einsteinstraße 62, 48149 Munster, Germany{fsteini, ropinski, khh, mensmann}@math.uni-muenster.de

Keywords: Urban planning, virtual reality, user interfaces, interaction metaphors

Abstract: Virtual reality based geographic information systems (VRGIS) have been successfully employed for urbanplanning and architectural design in recent years. Tracking technologies and stereoscopic visualization ofthree-dimensional structures allow a better insight into complex datasets. Unfortunately, these systems oftenlack intuitive interaction concepts and therefore reduce VRGIS to advanced visualization environments, sincemanipulation of the content is not or only rudimentarily possible. In this paper, we present a geographic infor-mation system for urban planning tasks in semi-immersive virtual reality (VR) systems. The objective of thisapproach is to provide professional city planners with an enhanced VR interface, which enables comfortableinteraction concepts similar to the interactions of the real-world planning task. To assure the usability andrelevance of the developed system, urban planners have cooperated closely in the development process. In thispaper both the hard- and software architecture of the entire system as well as VR related interaction metaphorsand their evaluation are discussed.

1 INTRODUCTION

Urban planning tasks are of major importance for civilworks since both the environment and the inhabitantsof a city are affected. The cityscape as well as thequality of life of the residents essentially depend onthe appearance of buildings, road networks, planting,green spaces, and recreation areas such as parks andplaygrounds. To facilitate a realistic impression ofhow a building area would visually integrate into theenvironment and to enable communication regardingdevelopment proposals, it is important to present in-termediate results of the planning process properly aswell as comprehensible.

Therefore, by using two-dimensional CAD con-cepts urban planners design development plans for acertain area based on existing cadastral data, which isavailable for every town in Germany. As depicted inFigure 1 (left) cadastral data usually contains build-ing footprints, number of floors and floor’s height foreach building, parcel boundaries, and other informa-tion. Within such a development plan, urban plannersdefine entities, for example buildings and recreationareas, associated with a set of constraints, which spec-ify what types of geobjects are allowed and what re-

quirements have to be incorporated. After urban plan-ners have agreed to a certain development plan, twodifferent procedures are commonly used.

One approach is to deliver the development plan toan architectural office. On the basis of this plan archi-tects generate virtual 3D models and return exemplarythree-dimensional visualizations of these planned ar-eas to the urban planner. This procedure has the fol-lowing two major shortcomings. First, the returnedvisualizations are static insofar as the 3D models can-not be explored interactively by the urban planners.Second, modifications to the 3D models, which, forinstance, have been proposed after reviewing the 3Dvisualization, cannot be performed by urban planners.Instead, the architectural office has to be asked againto incorporate these modifications into the 3D model.During a planning task, this usually takes several iter-ations resulting in inefficiency as well as unnecessaryexpense.

The second common alternative to communicateurban development proposals is to build a physicalblock model usually made of wood, plastic or pa-per. Figure 1 (right) illustrates such a physical blockmodel for the development plan in Figure 1 (left).After a physical block model has been finished, per-

1

Figure 1: Example section of an urban development plan within cadastral information (left) and a corresponding physicalblock model made of wood downscaled to 1:1000 (right).

forming modifications is often awkward, since mostelements are inflexible and fixated to the model, sothat they have to be removed and replaced by new el-ements. Furthermore, the creation of these models isa very time consuming task, which requires high ef-forts in terms of money and manpower. Thus, simplersolutions to visualize planned development areas aredesired.

In cooperation with the urban development, cityplanning and transport planning office as well as theland surveying and land registry office of the city ofMunster in Germany, we have developed solutions forthese problems. An objective of this cooperation isto develop computer-aided concepts, which serve theneeds of professional urban planners and provide aconvenient alternative to current planning tasks. Ur-ban planners demand that the developed strategiesshould be based on their current processes resulting inphysical block models as well as computer generated3D visualizations. However, the city planners desireto have more independent and sophisticated controlover both approaches; they want to be able to generatevirtual 3D city models and create three-dimensionalvisualizations autonomously. Furthermore, the intu-itive comprehension when viewing a physical blockmodel should be obtained.

In consideration of these two major demands, wedecided to develop an interactive 3D residential cityplanning software system, which runs in virtual re-ality (VR) systems as well as in desktop-based envi-ronments. To ensure the adaptation of the planningsystem into already existing systems and databases,a geographic information system (GIS) interface hasbeen integrated to import the required data. Virtualreality based geographic information systems (VR-GIS) are increasingly used for planning tasks, sinceVR technologies provide better perception and com-prehension of complex 3D structures (Beck, 2003).Unfortunately, these systems often lack intuitive inter-action concepts and therefore VRGIS are degraded to

exploration systems (Dodge et al., 1998; Beck, 2003).In order to enhance the interaction in VRGIS we havedeveloped intuitive interaction metaphors which facil-itate the efficient design of building plans in a highly-interactive way.

In this paper, we present the system architectureand setup of the 3D residential city planning sys-tem. In particular, we propose advanced concepts forgeneric interaction tasks, whose benefits have beenproven in usability studies. The paper is structuredas follows. In Section 2 the table-top-based VR sys-tem and its benefits are discussed. In Section 3 thearchitecture of the interactive 3D residential city plan-ning software is explained in detail. In Section 4 con-cepts which facilitate an intuitive interaction withinboth VR systems as well as desktop environments areproposed and their evaluation is discussed . Section 5concludes the paper and gives an overview of futureresearch directions.

2 SEMI-IMMERSIVE VIRTUALREALITY SETUP

Since professional urban planners desire to main-tain intuitive comprehension obtained when viewinga physical block model, we have chosen a semi-immersive RWB environment in combination with anoptical tracking system to visualize interactive vir-tual 3D city models. In comparison to physical blockmodels, the usage of such a VR system setup enablesan improved interaction with potential building plans,because interactive modification, e.g., texturing andaltering of building parameters, can be incorporated.The components of the VR system are explained inthe next subsections.

1020mm

left camera right camera1000mm

400mm

1360mm

Figure 2: Conceptual view of the semi-immersive RWB.Two cameras track the area in front of the RWB, wherefour users collaborate (adapted from (Dorfmuller-Ulhaas,2002)).

2.1 Responsive Workbench

A Barco BARON responsive workbench (RWB)(Kruger et al., 1995), is used to present 3D city mod-els stereoscopically in a way that enables urban plan-ners to work in an environment they are accustomedto. The horizontal or tilted workspace of the RWBis a well known table-top metaphor many profession-als are familiar with (see Figure 2). The images areprojected onto the display’s surface so that plannersperceive virtual 3D models as being attached to thesurface (see Figure 3 (right) and Figure 5). This isdue to the fact that the images are rendered stereo-scopically with negative parallax. The images are dis-played in sequence and are synchronized with activeshutter glasses the professional urban planners haveto wear. The stereo glasses are transparent, thereforereal-world objects such as the RWB and input devicescan be seen and users are semi-immersed into the vir-tual world.

The workbench is about 2m × 2m large and 1.2mhigh. The display screen measures 1.36m × 1.02mwith a maximum pixel resolution of 1280×1024. Themaximum refresh rate of 120Hz is ensured with a res-olution of 1024×768 pixels, which supports comfort-able working without flickering effects. As illustratedin Figure 2 the size and resolution of the workbenchallows several planners to view virtual 3D modelsin a stereoscopic projection. City planners can walkaround the RWB in order to view the virtual 3D citymodel from different perspectives. To enable such anexploration from multiple view positions, the systemmust be aware of the user’s current position, whichdetermines the virtual camera’s position and orienta-tion accordingly. For this purpose tracking systemsare used.

2.2 Tracking System

High accuracy and wireless interaction is indispens-able for precise and comfortable urban planning,therefore an optical tracking system is used to deter-mine the position of the planners as well as their in-put devices. The accuracy of the stereo-based opti-cal tracking systems is in the range of submillimeters,and thus tracking errors are minor and precise interac-tions with objects displayed on the RWB are possible.Since lighting conditions around the RWB have to bedarkened because the brightness of the projection it-self is limited, infrared (IR) light in combination withIR-filters is used. The operation area of the track-ing system is determined by the physical measures ofthe workbench, a volume of about 3m× 3m× 1.5mhas to be scanned. To enable an optimal trackingof this area two cameras are arranged above and be-side the workbench as depicted in Figure 2. unit Be-cause of the many drawbacks of IR-LEDs, we havedecided to use passive markers to be tracked by thesystem. These markers are made of small spherescovered with reflective material, so that light emittedby an IR-spot, which is positioned close to the cam-era lens, is reflected back to the camera. Only the re-flected IR light of the markers passes through a filter,which is attached to the front of the lens. With cor-responding tracking algorithms (Dorfmuller-Ulhaas,2002) the position of each marker and thus the po-sition and orientation of unique rigid body arrange-ments of such markers can be determined.

2.3 Input Devices

Passive marker tracking provides more flexibility incomparison to other technologies, e.g., electronic ormagnetic approaches. Attaching certain devices witha unique rigid body arrangement of at least threemarkers results in arbitrary 6 degrees of freedom(DoF) input devices, i.e., devices whose position andorientation can be tracked. However, further inputevents such as button events and gestures are requiredto manipulate a development plan. For this purpose,we have equipped urban planners with Fakespacepinch data gloves, which provide a gesture-basedrecognition system. Furthermore, we use a hap-tic input device, which supports planning by vibra-tion feedback. In combination with acoustic signalsthis information can be used to give feedback aboutinvalid interactions, e.g., collisions between virtualbuildings during the planning process. This device isequipped with two input buttons, passive markers andthe vibration unit, which enables transmission of hap-tic signals with different intervals. The buttons can beused similar to the buttons of a standard mouse, e.g.,the left button for selection tasks, the right button toopen 3D context menus.

3 3D RESIDENTIAL CITYPLANNER

The objective of the 3D residential city planning ap-plication is to provide urban planners an intuitive andnatural interface to plan and modify residential areaswithin desktop- and VR-based system environments.In the following sections the architecture and maincomponents of this system are introduced.

3.1 Architecture

During the development phase of the application, cityplanners express their desire for flexible approachesfor the visualization of generated virtual 3D citymodels. Although photorealistic rendering is im-portant, it is not the only requirement; especiallynon-photorealistic rendering supports to comprehendstructures and relations similar to view physical blockmodels. Furthermore, during exploration interactiveframe rates are more important than photorealistic ap-pearance. However, realistic visualizations similar tothe renderings provided by architectural offices aredesired.

Due to these demands, we have chosen VRS,the Virtual Rendering System (Dollner and Hinrichs,2002), as core graphics library for building 3D citymodels. VRS is an object-oriented and scenegraphbased C++ graphics library. It introduces the usage oftwo different graphs. Geometry graphs, which storethe visual appearance of virtual objects collected inscene nodes, are combined with behavior graphs torepresent their behavior in terms of interaction andanimation. Different renderings are ensured with thislibrary, since VRS provides wrapping classes to pho-torealistic renderers, such as POVRay or Radiance,but also real-time renderers, e.g., OpenGL, are sup-ported. Changing the used rendering system withoutthe need for modification of an application’s sourcecode. Furthermore, VRS is extensible to a VR soft-ware system by using the Virtual Reality VRS (VR2S)component (Steinicke et al., 2005a), which handlesall VR related issues.

3.2 Main Components

The 3D residential city planner consists of four con-ceptual components:

1. Converter tool: The converter tool parses and con-verts the cadastral data into a scenegraph structure,which is used to represent the corresponding geo-data.

2. Geoobject model: The geoobject model is the col-lection of geoobjects and their properties. Thismodel is generated during the parser process of

the converter tool. Components of this model arebuildings, building and traffic areas, trees etc.

3. Visualization component: This component con-structs the scenegraph representing the topologicalstructure of the city model. Each scene node in thegeometry graph representing a collection of geoob-jects is associated with a visual appearance, e.g., byassigning colors or textures.

4. Interaction component: The interaction compo-nent manages required interactions with virtual 3Dcity models. A graphical user interface (GUI)based on wxWidgets allows to access certain inter-actions. Alternatively, direct interaction conceptssuch as arrangement of virtual buildings are incor-porated.

The converter tool parses the cadastral data and gen-erates a scenegraph data structure containing the cor-responding geodata. Since the cadastral data is geo-referenced, virtual 3D city models can be generatedautomatically. Because there is no overall acceptedstandard for storing cadastral information, we havedeveloped an interface which provides the requiredgenerality and flexibility to enable import of cadas-tral data from different sources. For instance, forthe city of Munster the cadastral data stores build-ing footprints, number of floors, parcel boundariesand other information in Gauß-Kruger coordinates,which are converted during the reconstruction pro-cess. Based on this information the system gen-erates a geo-referenced virtual 3D city model ofthe surrounding area, which is superimposed withaerial photographs to provide more realism and higherrecognition.

Within the geoobject model all geoobjects are ag-gregated in the class CityModel, which adminis-trates all required information for a geo-referencedcity model. Instances of type GeoObject providethe base from which all geoobjects, for example in-stances of type Building or ParcelArea, inherit.An instance of the class Building consists of one ormore BuildingParts for handling different typesof stories and roofs. The other geoobjects are orga-nized analogously.

The visualization component is separated from thegeoobject model of the virtual city. All requiredinformation to visualize the objects of an instanceof the class GeoObject is handled via the classAppearanceManager. The visual appearance ofeach geoobject can be assigned randomly, or the cityplanner can define the appearance, for example by as-signing specific textures to each geoobject. As men-tioned above VRS uses a scenegraph to represent vir-tual scenes. Since generated virtual 3D city mod-els may consist of over 50,000 complex, texturedgeoobjects, it is not recommend to store each of thesegeoobjects in corresponding scene nodes, because

Figure 3: Example photorealistic visualization of a generated 3D city model within the GUI (left) and NPR of the cadastraldata shown in Figure 1 on the workbench (right).

this would inflate memory requirements for storingthe scenegraph and decrease performance when eval-uating it. Due to the wrapping mechanism of VRS itis possible to store these enormous datasets with ren-derer specific optimization strategies.

To assist the city planners during the design processthe graphical representation of both the cadastral planas well as the building plan can be projected onto thevirtual 3D city model (see Figure 3 (right)). To furtherincrease performance, optional view-dependent level-of-detail algorithms are integrated to enable switchingbetween different levels of realism. Furthermore, itis possible to switch between non-photorealistic andphotorealistic rendering.

Besides the standard menu-based interaction con-cepts, such as creation, arrangement or deletion ofvirtual buildings, different navigation and travelingmetaphors can be chosen via menu entries. These ex-ploration metaphors as well as arrangement of geoob-jects can be performed in a direct way without us-ing the menu. These techniques include flying, glid-ing, walking and ufo-viewing metaphors, i.e., an ex-ploration with orthogonal view onto the city model.When exploring a city model, arbitrary locations canbe stored as visual bookmarks to be accessed later on,for example to generate smooth camera motions alonga resulting path.

When working in desktop-base environments, pro-fessional city planners have to handle 3D interactionswith 2D input devices, e.g., the standard mouse. Toreduce the cognitive effort for such 3D interactions,we have integrated 3D widgets (Dollner and Hinrichs,1998) into the manipulation process. 3D widgets pro-vide an easy way to manipulate objects with 6 DoFby reducing the simultaneously manipulated DoF toone degree. 3D widgets provide handles for transla-tion, rotation, and scaling of virtual geoobjects. Thus,

these manipulation tasks can be performed as easilyas in two-dimensions. However, as illustrated in Fig-ure 5, 3D widgets can also be used in VR.

4 VIRTUAL REALITYINTERACTION CONCEPTS

As mentioned above VRGIS environments lack intu-itive interaction concepts. In this section VR-basedinteraction metaphors integrated in the 3D residen-tial city planner are introduced. These generic inter-action tasks include exploration concepts for collab-orative interaction in the RWB environment and ad-vanced manipulation strategies to design, explore andcommunicate virtual 3D development plans.

4.1 Collaborative Exploration

When designing a development plan, often several ur-ban planners with different background, i.e., expertiseand knowledge, are involved. Such cooperations havebeen proven to be advantageous since the bundlingof expert’s knowledge has the potential to increaseproductivity. Consequently, it is desirable to developvirtual environments simulating such shared space inwhich collaboration can be performed as easily andnaturally as in the real world.

Although the described semi-immersive RWB sys-tem provides enough space to enable several plannersto interact in a collaborative way, the teamworkingprocess is constrained due to the shortcoming thatusually only one user is head-tracked and thus per-ceives a fully perspective-correct stereoscopic image.Hardware-based solutions to this problem involve re-duction of the refresh rate (Agrawala et al., 1997).

Because of physical constraints, these approaches arehard to scale. Hence, we have developed a software-based collaboration environment that allows severalcity planners to work together in the RWB environ-ment. The only requirement to enable such a col-laboration is that each planner who wants to partic-ipate in the collaboration process has to wear trackedglasses so that the planners’ head positions can bedetermined. Therefore, all input devices and trackedglasses have to be registered by the tracking system.If this prerequisite is fulfilled, group activity can beperformed by using two different strategies:

1. Cooperative interaction mode, i.e., tasks are ac-complished consecutively. For example, one cityplanner modifies the development plan and after-wards a second planner continues the work.

2. Split-screen collaboration mode, i.e., users col-laborate simultaneously. For example, one cityplanner creates virtual buildings and provides themto another planner who arranges them on a buildingarea.

In both modes active planners, i.e., currently inter-acting urban planners, perceive a perspective-correctstereoscopic image either on the entire projectionscreen or in different viewports on a tiled screen. Be-fore any cooperative or collaborative interaction canbe started potential participants need to register. Reg-istration can be performed by miscellaneous strate-gies, e.g., posing gestures or using speech commands.When an urban planner has registered for the coop-eration and this registration has been accepted, e.g.,an active planner or administrator confirms the reg-istration by gestures, this registered planner gets ac-tive, i.e., his head and input devices are tracked andused for the interaction. In the case of the cooper-ative interaction mode, the registered urban plannerswitches the state from a passive planner, who onlyobserves the scene, to the active planner and the pre-vious active planner gets passive. When a registrationprocess of an urban planner has been accepted in thesplit-screen collaboration mode, the screen is tiled sothat the additional active collaborator is assigned hisown viewport, whereas the viewports of other activecollaborators are scaled down accordingly. Each ac-tive collaborator perceives perspective-correct stereo-scopic images in his viewport, therefore interactionscan be performed comfortably.

The introduced concepts allow city planners tocommunicate and work together in a very naturalway. A typical planning situation benefiting from thecollaborative interaction mode divides the work intotwo subprocesses. One urban planner creates virtualbuildings via the GUI by defining building footprints,heights, roof types and textures etc., while a secondcity planner arranges these buildings in the develop-ment plan. Hence, planning processes can be accel-

Figure 4: Two users collaborating in the a tiled viewportarrangement.

erated and optimized since several planners can com-bine their knowledge and abilities. In Figure 4 the 3Dresidential city planning software runs in a two-usersplit collaboration mode, in which both planners per-ceive perspective-correct stereoscopic images.

4.2 Manipulation

The concepts described in Section 4.1 enable severalurban planners to explore virtual 3D city models.The aforementioned typical situation in which twoplanners collaborate, e.g., the first urban plannercreates virtual buildings, while the second plannerarranges them, involves many problems when usingcurrent manipulation metaphors. While GUI-basedinteraction, for instance, generating buildings canbe performed very comfortably in desktop-basedenvironments or on a personal-interaction-panel inVR (Szalavari and Gervautz, 1997), 6 DoF manipula-tions of these virtual buildings are often complicated.Although VR environments provide the possibilityto manipulate virtual objects in an intuitive manner,e.g., by using a virtual hand or a virtual pointer(Mine, 1995), these concepts are often constrained,because in VR the cognitive effort for a city planner isdefinitely higher than the corresponding effort in thereal world. In addition, it is often difficult to performprecise interactions because of tracking errors andhand tremors. For example, it is hard to select smallresp. distant objects or items, e.g., the described han-dles of 3D widgets, with a virtual pointer or virtualhand in VR. Hence, generic interaction tasks need tobe enhanced. In order to achieve this goal we proposethe improved virtual pointer (IVP) metaphor, whichavoids most of the aforementioned disadvantagesof current interaction metaphors (Steinicke et al.,2005b). This approach allows the city planner to se-lect a desired geoobject or item with a virtual pointerwithout requiring an exact hit. While a straight rayis used to indicate the direction of the virtual pointer,an additionally visualized bendable ray points tothe closest selectable geoobject (see Figure 5). Theclosest selectable geoobject which would be chosen

Figure 5: Virtual 3D city model and improved virtualpointer as seen from a city planner’s view.

if the city planner would perform a selection, e.g.,by pressing a button or by pinching a glove, is calledactive geoobject. Since this geoobject is determinedin a pre-evaluation phase of the scenegraph withsimple geometric calculations, this results in almostno performance loss. After selecting the activegeoobject, manipulations can be performed similarto the manipulations of physical block models. Themovements of the virtual input device are transferredby a scaled one-to-one mapping to the selectedgeoobject, which supports also the manipulation ofdistant objects. Due to this mapping strategy virtualgeoobjects can be arranged very comfortably andintuitively.

4.3 Evaluation

In this section the evaluation of the concepts de-scribed in Section 4.1 and Section 4.2 is discussed.

The subjects chosen for the test series were fa-miliar with residential planning environments. Mostsubjects were geoinformatic students, but also land-scape ecologists, computer scientists and mathemati-cians participated in the usability study.

4.3.1 Evaluation of Exploration Concepts

We have tested both proposed cooperative and collab-orative interaction modes for usability in a prelimi-nary user study with 7 participants. The participantswere equipped with tracked shutter glasses and pinchgloves for the registration process. Registration had tobe initiated by simple gestures combined with acous-tic feedback giving an indication which user wantedto participate in the collaboration and which user wascurrently active. Up to three participants had to ex-plore virtual 3D city models simultaneously by us-ing the described concepts. Afterwards, they were

0

1

2

3

4

5

6

7

8

IVP Sticky-Ray Ray-Casting Sticky-Finger

time

in se

cond

s

local distant

(a)

1

2

3

4

5

IVP Sticky-Ray Ray-Casting Sticky-Finger

intuitive easy to use easy to learn

(b)

Figure 6: Results of the usability study.

asked to evaluate the proposed strategies in a user sur-vey. The results of this survey show that a decreasingprojection size, when splitting the screen into two orthree subviewports, has not disturbed the collabora-tors in terms of limited space or distraction of otherplanners’ viewports. Furthermore, the space in frontof the RWB has been evaluated as large enough forcollaborative interactions. The participants consid-ered the required gestures for the registration processas intuitive and easy to learn. Furthermore, the usersevaluated the usage of multimodal feedback, whichsupports the users during the interaction, in particularduring the registration process, as very helpful.

4.3.2 Evaluation of Manipulation Concepts

We have evaluated the manipulation concepts in a us-ability study with 15 participants. During the test se-ries the subjects had to accomplish several selectionand positioning tasks, i.e., randomly marked virtualbuildings had to be selected and arranged in a devel-opment plan by using different interaction metaphors.

These metaphors included the IVP metaphor and asimplification, called sticky-ray metaphor, the ray-casting technique, and the sticky-finger technique de-scribed in (Steinicke et al., 2005b; Bowman andHodges, 1997; Pierce et al., 1997). We have eval-uated the time needed for each subtask and the ac-curacy achieved with a certain metaphor. The mostsignificant result is illustrated in Figure 6 (a). Thisstate-chart shows the time needed for a selection sub-task when using the different metaphors. The resultsclearly show that the IVP metaphor improves effi-ciency and that selections are performed faster for lo-cal object selection, i.e., selection in the immediatereach of the user, as well as for distant geoobjects.Furthermore, performing manipulations was more ac-curate and precise using the described IVP metaphor.

After the user study the participants have had toevaluate the metaphors in a five-point Likert scaledsurvey (from 1 to 5 associated with correspondingratings). Figure 6 (b) underlines that the participantshave evaluated the IVP metaphor as the most intuitive,ease to use and easy to learn metaphor in comparisonto the other approaches.

Furthermore, we support the interaction with mul-timodal feedback. For example, when a selection ispossible, e.g., the selection ray hits a virtual building,the users perceive a slight vibration and an acousticfeedback. The intensity of both signals depend onthe position of the virtual building with respect to theparticipant’s position. Although in several surveysparticipants have evaluated these concepts of mut-limodality as very helpful, the usage of multimodalfeedback did not increase efficiency. However, theparticipants felt convenient and confirmed during in-teraction processes when receiving multimodal feed-back.

5 CONCLUSION AND FUTUREDIRECTIONS

We have proposed a 3D residential city planning ap-plication for semi-immersive VR systems. Due tothe fact that this system has been developed with co-operation partners from the domain of urban plan-ning, their demands could be fulfilled so that they aremotivated to use the application to develop new build-ing plans. The user studies have proven the usabilityand benefits of the proposed concepts.

Currently, the land surveying and land registry of-fice evaluate a prerelease version and the urban de-velopment, city planning and transport planning of-fice will test the software system in a real planningprocess soon. When these field studies are finished,modifications of the actual application or integrationof further functions will be accomplished.

REFERENCES

Agrawala, M., Beers, A., Frohlich, B., Klimetzek, F., andBolas, M. (1997). The Two-User Responsive Work-bench: Support for Collaboration through IndividualViews of Shared Space. In ACM Proceedings of Com-puter Graphics and Interactive Techniques, pages 327– 332.

Beck, M. (2003). Real-Time Visualization of big 3D CityModels. International Archives of the Photogramme-try, Remote Sensing and Spatial Information Sciences,XXXIV(5/W10).

Bowman, D. and Hodges, L. (1997). An Evaluation ofTechniques for Grabbing and Manipulating RemoteObjects in Immersive Virtual Environments. In ACMSymposium on Interactive 3D Graphics, pages 35–38.

Dodge, M., Doyle, S., Smith, A., and Fleetwood, S. (1998).Towards the Virtual City: VR & Internet GIS for Ur-ban Planning. In Workshop on Virtual Reality and Ge-ographical Information Systems.

Dollner, J. and Hinrichs, K. (1998). Interactive, Animated3D Widgets. In Computer Graphics International1998, pages 278–286.

Dollner, J. and Hinrichs, K. (2002). A Generic RenderingSystem. IEEE Transaction on Visualization and Com-puter Graphics, 8(2):99–118.

Dorfmuller-Ulhaas, K. (2002). Optical Tracking - FromUser Motion to 3D Interaction. PhD thesis, Technis-che Universitat Wien.

Kruger, W., Bohn, C., Frohlich, B., Schuth, H., Strauss,W., and Wesche, G. (1995). The Responsive Work-bench: A Virtual Work Environment. IEEE Com-puter, 28(8):42–48.

Mine, M. (1995). Virtual Environments Interaction Techn-qiues. Technical Report TR95-018, UNC Chapel HillComputer Science.

Pierce, J., Forsberg, A., Conway, M., Hong, S., Zeleznik,R., and Mine, M. (1997). Image Plane InteractionTechniques in 3D Immersive Environments. In ACMSymposium on Interactive 3D Graphics, pages 39–44.

Steinicke, F., Ropinski, T., and Hinrichs, K. (2005a). AGeneric Virtual Reality Software System’s Architec-ture and Application. In Proceedings of the 15th In-ternational Conference on Artificial Reality and Telex-istence (ICAT05).

Steinicke, F., Ropinski, T., and Hinrichs, K. (2005b). Multi-modal Interaction Metaphors for Manipulation of Dis-tant Objects in Immersive Virtual Environments. In13th International Conference in Central Europe onComputer Graphics, Visualization and Computer Vi-sion, pages 45–48.

Szalavari, Z. and Gervautz, M. (1997). Using the PersonalInteraction Panel for 3D Interaction. In Proceedings ofthe Conference on Latest Results in Information Tech-nology, page 36.