Urban space simulation by computer Graphics

Prof. Dr. Gerhard Schmitt
Florian Wenz, Fabio Gramazio

Chair for Architecture and CAAD
ETH Zürich
Switzerland

Introduction

The art of computer graphics has transformed our ability to experience and to design urban space. The new technique is more than merely another abstraction and representation tool for buildings or cities. Computer graphics works in conjunction with previous representations of urban space, such as verbal descriptions, drawings, or physical models. As a medium, its use is not restricted to the reconstruction of ancient cities or existing projects, but it offers entirely new possibilities for the design of future cities.

Computer graphics simulations of urban space have found three major applications. One of them is the reconstruction of the past, in that ancient cities or projects are re-created as realistically as possible. The second application is the simulation of projects before they are actually built in order to optimise the design of new physical urban centres. The third application is the creation of a new kind of reality and urban space in the rapidly evolving information territory.

Urban Space and the physical city

Urban space, as opposed to rural space, always had a strong artificial component. Urban space is almost entirely man made, whereas rural space still shows the influence of nature. Urban space can only be experienced in physical cities, which today still are the most complex artefacts that societies have created. Because physical spaces and urban spaces are designed and created by man and his instruments, they lend themselves to simulation with artificial means. In the past those means were paper-based abstractions and physical models, today the computer model takes on this role.

We experience and recognise urban spaces with all our senses. We can easily differentiate an Italian Renaissance city from a post-industrial urban centre such as Los Angeles, or a town on a Swiss lake from a city on the coast of China. Once we have been there, we can even recognise them with only one or two of our senses. Important features of these physical urban spaces are the spatial definitions, the movement patterns, light and shadow, materials, colours, illumination of buildings, temperature differences, and vegetation. Also important are acoustical and olfactory sense phenomena to experience, understand and remember urban space. Besides the eye and recently the ear, the computer addresses few of our senses, which so far has limited its use as a convincing modelling tool. But as society has used physical tools to build physical cities and urban space in the past, the use of computer tools will help to create virtual spaces and cities in the future.

Computer graphics

Computer graphics describes the ability of programs and computing equipment to display and operate on graphical elements. Graphical elements appear as two-dimensional representations on computer screens or as images that appear three-dimensionally in virtual reality (VR) environments. The use of computer graphics dates back to the late 1950's and early 1960's. Ian Sutherland's program Sketchpad is often considered as the first computer graphics application which explored advanced features of modelling physical objects.

The display of graphic primitives was an initial goal of computer graphics. A second goal was the manipulation of these elements through techniques including translation, rotation, and scaling. A third goal was the introduction of realism which requires orders of magnitude more computing power than abstract representations. Over time, colour presentations replaced the originally black and white or two colour computer graphics images. This was only possible after significant advances in the speed of the computer graphics hardware. Animations or moving images require even more memory. Today, personal computer displays offer a resolution of up to 1200 by 1600 pixels with 24 bit colour depth, which means that realistically rendered objects can be displayed and interactively manipulated on the screen without loosing performance.

Computer models of buildings

Over time, buildings have been represented in various ways. Starting from early depictions in Egyptian tombs to verbal descriptions of buildings in the classical Greek period, to the Roman architectural treaties of Vitruvius, to the detailed written and pictorial description of buildings in the Renaissance treaties by architects such as Alberti and later by Palladio, a multitude of methods to record and describe buildings have been developed. Written and pictorial descriptions of buildings can also be found in all other cultures throughout the world. Common to all descriptions of buildings is the fact that they only show those aspects of buildings that are important to the artist or to society at large at the particular time.

Once researchers had solved the most important questions in representing and manipulating objects in computer models, the logical next step was to search for representations of buildings that only the computer could support. Virtual reality is one of these applications. VR systems allow the interaction with data objects in immersive environments. In a VR environment, the designer can, for example, read and manipulate text floating in space, view two-dimensional images in three-dimensional space, or directly generate and interact with objects while being immersed in the scene. In the early days of VR, its main applications were in navigation through complex scenes and worlds, accessing databases and images. VR has rapidly developed into a world of its own, enabling participants to be virtually present in other places or operate equipment remotely. Architectural VR applications include walk-throughs of projects, or the virtual visit of ancient cities.

In countries, where pre-fabricated buildings or building element fabrication on demand is gaining market share, such as in Germany or Japan, the use of computer models in building design is indispensable. Clients can see a demonstration of their future home on the screen or in a VR environment. They can select and assemble important features of their house. The model is then transferred to the construction factory, where the parts are assembled. The delivery to the building site can occur within weeks or even days after the clients have made their choice. The entire design and construction time of a building can thus be reduced dramatically in an order of magnitude as compared to traditional techniques. It therefore has a large impact on the financing of the building.

This development has, unfortunately, not improved the design quality. The tendency towards fast food should not be transferred to the design field. Instant Architecture or instant urban space design may serve the immediate wishes of certain clients. But urban design is too energy intensive and has too long a life span to apply the fast food metaphor. Urban space is not a material for fast consumption but one of the few remaining physical spaces for a lasting quality experience. In the long run, the design costs of a building or of urban space are negligible as compared with the personnel and environmental costs. Those can be reduced with a careful design process in which computer graphics plays an important role.

Computer models of urban spaces

Modelling urban spaces requires similar programs and equipment as modelling buildings, with a few notable exceptions. Computer modelling of urban space has a long history. For example, Cornell University's campus and the surrounding city where represented as a computer model more then a quarter of a century ago. Naturally, urban space simulation can be more complex and demanding in terms of objects and features than building simulations, if a comparable degree of detail is required. Therefore, a number of new techniques had to emerge before visually satisfactory urban space simulation was possible. Some of these developments were the introduction of level of detail in representations, which describes a technique to display objects closer to the eye in a higher level of detail than the objects further away. Other techniques to increase the realism of the simulation were the selective visualisation and de-visualisation of objects in the display database, the successful application of texture mapping to a large number of objects and the higher rate of frames that can be displayed per second.

Figure 1a/b. Computer graphics to reconstruct the past. The Roman city of Aventicum, today Avenches, in Western Switzerland. Computer reconstruction of the city with parameterized objects. In 1989, students of the CAAD course at ETH Zürich reconstructed one different insula or building block each and positioned them in the three-dimensional city model. Today, the same computer model serves as a VR Roman city environment.

Figure 2a/b. Computer graphics to simulate the present situation. The old town of the Swiss city of Winterthur in an early VR computer simulation at ETH Zürich. The three-dimensional computer model served as a virtual design environment.

Urban space simulation can draw on additional development resources. Military research and applications have addressed this issue for a long time to simulate urban battle fields. Airline simulators use models of cities and landscapes to create realistic imagery for pilots. Another set of programs important for urban simulation are Geographic Information Systems (GIS), which are an instrument for cities and communities to store and represent all important properties of the built-up and natural environment. The combination of research and application results from GIS models with visualisation techniques of commercial airline simulators offers new possibilities.

Whereas building simulations often evolve from the inside out with emphasis on the interior spaces, urban simulations often evolve from the outside in. Aerial views, bird's eye views or moving through cities at high speed with trains or automobiles are important simulation techniques. All of them require significant computing power and visualisation software which became available at reasonable prices only in the last years.

Real time computer graphics and animation

Even the most realistically rendered urban scene is not as impressive when only one or two frames per second can be displayed as compared to a less accurately rendered urban scene that can be walked through at 25 or 30 frames per second. The main difference in perception is between the feeling of being controlled in the low-frame per second walk-throughs to the feeling of being in control at the high- frame per second examples. Accordingly, computer manufacturers have developed strategies that support texture mapping in real time on geometric scenes. This technique, again developed first in military applications, is now available for a wide range of computing equipment.

Due to the complexity of urban models, real time movement through these environments is a challenge. For real time walk-throughs and drive-throughs, detail and accuracy must be sacrificed in favour of speed. Probably the most important improvement in the simulation of a real time walk through and fly-over for buildings or urban spaces is the ability to display textures. Textures are an essential addition to model objects. By applying textures, a large number of geometric details can be omitted. The use of appropriate texture maps reduces the necessity for highly detailed geometric models. In animations, the inaccuracies in light, detail and perspective distortion that go along with the application of textures to objects, are rarely perceivable.

A typical application is the three-dimensional extrusion of different two-dimensional features found in aerial photographs or in two-dimensional GIS representations which results in a landscape of simple volumes on the ground. These volumes are then completed by applying texture maps to their individual faces. The texture maps can be derived by walking through the streets and taking photographs, or from procedural textures applied to the individual faces. Trees and other vegetation can be mapped on simple geometric primitives, resulting in a realistic scenery while walking through the city. Lighting conditions as an indication for the time of day can be globally changed. In addition, streets and other geometric objects that show repetitive patterns are mapped with the same texture or with procedural textures, resulting in very efficient computer models.

To successfully navigate urban spaces with computer graphics programs, a number of constraints need to be introduced. Different modes of movement should be pre-programmed for walking, driving or flying. Walking will normally happen at a certain speed which cannot be exceeded, it can be constrained to sidewalks or crossings, and buildings can be entered through their entrances. Driving could be constrained to streets and parking lots. Flying has more degrees of freedom but could be constrained to certain heights except for airfields. Thus choosing the mode of navigation through the city, a visitor can be guided appropriately. Impressive demonstrations of these state-of-the-art techniques are available with all commercial visualisation and hardware systems.

Computer Graphics as a communication language

All languages have developed from specific communication needs. Spoken words eventually materialised in written language which expresses itself with a vocabulary of varying size in the different cultures. It is a major effort to learn a foreign language and few people master more than two languages perfectly. The symbolic languages of the past took another direction. They often preceded written language but were powerful in their own right. The drawings in the caves of Lascaux in France or in Altamira in Spain depict creatures that would be difficult to describe with words. But persons, who have seen these drawings will probably be able to recall them immediately in their memory when reading these lines. Thus, the written and the pictorial language cooperate and supplement each other.

Although the total number of languages is decreasing world wide, the individual is exposed to more languages through the increased mobility and telecommunication. On the other hand, understanding a map or a three-dimensional scene is made easier with every advance in computer graphics. VR models offer additional opportunities. Computer graphics simplifies the standardised, pictorial description of objects, functions and conditions. Computer networks such as the Internet make them accessible world-wide. In this respect, computer graphics representations which are similar in all cultures have the potential of becoming a new common world language in which people of all cultures can communicate.

Simulation of the future city based on physical precedents

In thinking about the future city, it is very attractive to design a new urban space which combines all the advantages of existing physical spaces and omits all its disadvantages, such as crime, traffic congestions, noise and other pollution. The oversight that can easily occur is that we base our assumptions on the existing physical properties of the city. Even today, the physical character of the city includes a very sophisticated non-physical, almost virtual quality. We hardly understand the totality of the different networks and services which are hidden under the city or inside buildings. TV, radio, and other media have little physical presence in the city but they contribute an important part of urban live. Those early generators of virtual worlds increasingly influence the perceived reality of the physical city. The boundary with predominantly virtual environments of the future has already been crossed. This demonstrates that the physical precedent of the existing city should not be taken as the only starting point for simulating and designing the future city.

The information territory

Most of the territories that are known today such as private territories, military territories, or national territories, have lost their original meaning in the age of information. Therefore, the name information territory in itself is somehow a contradiction of terms. We want to use it, because it describes a new type of territory which has in many respects similar properties as the existing territories, but it is open for a different kind of citizens. The information territory is settled by people who have access to computer networks. Different forms of access control exist, different privileges, and new rules. Access is increasingly effortless with the proliferation of computer networks even to remote parts of the earth. Privileges do exist because access and bandwidth are available only to those who can afford them financially. Rules are emerging slowly but there is definitively already an etiquette. Increasingly, commercial and political sources attempt to take control of the new territory. The reach of the Internet defines the limits of the information territory.

Figure 3. In Dataspace, interactive data structures are represented by three-dimensional geometric descriptions and information mapping. A random access structure and a data array are connected by a sequential strip and the interior bounding surfaces of the data array are entirely covered by mapped information. Online information at http://caad.arch.ethz.ch/~wenz/babylon. Florian Wenz, 1993.

The Internet

The Internet is one of the most used terms in research, in education, and in the media since the middle of the 1990's. The Internet is a network of interconnected networks. It is accessible to anyone with a computer and at least a modem. The number of people connected to the Internet is growing rapidly and will reach probably 50 million by the end of 1996. This number is equivalent to the population of a medium sized country. The Internet connects people from all cultures, all nations, across the world. In other, more primitive forms it has existed for a long time. It underwent the same development as the telephone networks. It started with two machines sending data to each other, but evolved quickly into a world wide web. In a telephone network it is possible to call anyone anytime in the world with a single number. In the Internet it is possible to reach everyone with a unique address. But in addition, the Internet is a giant database. Given enough bandwidth, it also allows person to person communication through voice, video ore exchange of models.

It has become popular only after the first usable browsers were developed by scientists at CERN, the European research centre near Geneva. It is remarkable that an individual designed an instrument that revolutionised global communication to a degree that now influences all aspects of daily life in post-industrial countries. Internet browsers such as Mosaic or Netscape are based on a language that was developed more then two decades ago. It allows the easy exchange of information in a standardised format, independent from the platform from or to which it displays the information. This HTML or Hyper Text Markup Language is the first in a series of languages which will transform the way we read and write and eventually communicate in the cities of the future.

Space in the Internet

In addition to displaying text and images on net browsers, it is possible to display three-dimensional models on each node of the network. These models can be sent and distributed world-wide by using the Internet. Models are described in the virtual reality modelling language or VRML, a second evolving international description language that will transform the way we experience three and more-dimensional space. With VRML models, anyone is able to define space on the Internet. It is possible to combine an urban database with building models that come from another part of the world and to display both models together through VRML on the Internet.

With this development, the notion of space has received a new meaning. The urban space as we know it from physical environments is being supplemented by a virtual space. They have in common, that, once on a computer display or in a virtual environment, the simulation of a real space becomes indistinguishable from the simulation of an abstract space on the Internet. In VRML models, the boundary between the representation of physical cities and imaginary cities is vanishing rapidly. The result is a new reality.

Communication in the Internet

From the very beginning of the Internet, communication was its main purpose. Starting with researchers who wanted to transmit results, the potential for communication via computer networks was recognised quickly with the emergence of a workable browser. Since then, communication has been the main point of interest in using the net. As could be expected, the Internet is beginning to fundamentally change communication itself. Written and spoken communication have not lost their value, but they are now supplemented by the crucial capability of the Internet to access information and people world-wide and to communicate on different channels.

The only type of communication that does not require technical and artificial infrastructure is personal communication. But even this type of communication requires the knowledge of a common language. All other forms of communication are based on technical media for transmission and reception. The main difference between the Internet and traditional media such as Television, Radio or Newspapers is that no longer a few organisations provide information. Instead, all members of the Internet are potential content providers. This may lead to a situation where there are as many listeners as there are producers of information. Therefore, the Internet is the first technical medium that actually enables communication rather then transmitting filtered observations and opinions from few information providers to millions of listeners of viewers. It will take a few years until this difference is generally recognised and appreciated. But it is the main advantage of the Internet over all other existing means of technical communication. It has direct impact on urban space, as mass gatherings of people will be rare in the information society. Mass communication demonstrations to decision makers could be one means to replace them. The mailing demonstrations to keep the Internet free from censorship or domination by commercial companies are a first example pointing in this direction.

Design in the Internet

Design is the art of producing a solution proposal based on incomplete descriptions of a problem or a desire. The proposal may then result in physical artefacts, or in other useful objects and functions. Design has always relied on external media and instruments to transmit the designer's ideas to the client, and in particular to the people necessary to execute the design. The influence of instruments on the designed artefact or function itself is well known. The resulting designs have been of physical nature in the past. If one takes the needs of the information society seriously, then it is not necessary anymore that design results in physical artefacts only. Instead, design will result in structures that only exist on a computer network but which can be visualised almost perfectly with computer media. To the viewer who observes a representation of a real design or a representation of a proposed design in a computer, there will be no difference, unless she or he knows the actual building or city which is represented in the first case. The Internet has therefore become the design site for all those who are interested in building in the information territory.

Figure 4. "Aquamicans", a surreal construct in VRML is made up of 51 virtual rooms, which are organised around a surrealistic text by Raymond Roussel (chapter 3 from "Locus Solus"). The rooms, which are always of the same geometry, receive their interior character through lighting and variations and are linked by 4 doors each and one elevator. The possible floor plans of the entire construct are created during interactive exploration and only exist in the user's imagination. Online information at http://caad.arch.ethz.ch/~gramazio/html/entry.html. Fabio Gramazio (etoy), 1995.

Construction in the Internet

Relatively few of the countless articles about the Internet deal with the very interesting possibility to build structures. If we assume that the future reality is influenced increasingly by the realty of the Internet and other virtual techniques, then construction in the Internet will be a real business in the near future. Writers and researchers have pointed to interesting developments in this direction over the last years. As William Mitchell from the Massachusetts Institute of Technology pointed out, the traditional building and facade of a bank in main street is increasingly replaced by automated teller machines or ATMs which can be placed anywhere where money is needed. The architectural result is the proliferation of relatively inexpensive money machines in many parts of a city and in the country side, whereas the large physically built and personnel intensive banks are slowly disappearing. The next logical step is that the entrance to a bank is not the physical facade or even the ATM machine anymore, but its three-dimensional structure or homepage on the Internet. It is foreseeable, that the corporate identity of a bank and other businesses will be increasingly influenced by their appearance in the Internet.

In many areas construction on the Internet has already begun. The variety for displaying ideas and products is striking. For example, fashion providers have invented entirely different aesthetics than universities. Car manufacturers advertise their product in another way than service providers. Newspapers reconstruct their front-pages to make it more accessible on the Internet. All cases demonstrate that the new technology, used appropriately, will change design and construction. It might in fact be much more reliable and interesting for a fashion company to build interactive, three-dimensional structures on the Internet, rather than renting expensive physical storefronts. In the past, physical materials determined urban space, later it were the constraints of style and gravity. These constraints have disappeared in the information territory. They are replaced by the human capacity to perceive.

Design and construction in the information territory are by no means easier than on physical properties. In all cases, the construction must be carefully prepared. There is nothing more disappointing than a badly designed series of pages, and it does as much damage to the owner of the pages as does a badly designed and maintained building. Construction costs in the Internet are still much lower than in physical reality, but the requests and the perfectionism are rising constantly which will in turn increase the cost of Internet design. As in the physical world, designers and contractors have opened their business in the information territory. Similar to the physical world, many commercial services are cluttered with advertisement billboards which appear in between news and other information. In the long run, it will be as difficult to keep the Internet free of commercial overcrowding as it is in the real world.

Simulation of the future city in the information territory

Simulation of future cities in the information territory offers the possibility to omit those features of cities that have been recognised as detrimental to their growth or to the comfort of the inhabitants in physical cities. We have been so accustomed to dealing with the constraints of physical territories and conditions that the disappearance of those constraints causes some real problems. For example, what does it mean when information needs no physical means to be transported? What does it mean, when people do not need to move physically to their offices during most of the week anymore? What does it mean when gravity is no issue? The answers to these questions will shape the future city.

Several designers and researchers have dealt with this problem. John Frazer, an architect at the Architectural Association in London, has investigated alternative forms of cities and buildings for a number of years and summarised his thoughts in the book 'An Evolutionary Architecture'. William Mitchell has written extensively about the future city in the information territory in his recent book 'City of Bits'.

In practice, large numbers of people do already populate the information territory in simulated cities, and Japan is a leader in this development. Well known are Habitat or Populopolis in which Avatars navigate and meet other Avatars. In Europe, the Telepolis project in November 1995 has opened new insights into the feasibility and problems of virtual cities. And finally, thousands of copies of Sim City and related computer games have brought the idea of a virtual city to the general public. All theories on future cities and on ideal cities used traditional graphics and written text to depict and to create in the viewers' mind the best possible image of the new city. Computer graphics is therefore the medium of choice to describe the city in the information territory. It is a continuation of the use of representation to create a virtual model of the places to exist. In addition to the pictorial quality of traditional media, computer graphics and computer models of cities allow a significant depth of information associated with the graphic or written element. They also allow interactive communication with the model. The design and construction of the future city is not restricted to a few city planners and architects anymore, but taken seriously, a large portion of the population can take part in this exercise through the Internet. An example is the interactive exhibition accompanying this article, which is accessible on the Internet.

Sustainable development in the information territory

It seems much easier to guarantee the sustainability of designed structures in the information territory than in traditional physically based environments. However, sustainability has also social and ethical aspects. It will not be enough to create virtual spaces and places in cities only, but somehow they must connect with real physical places. The construction of virtual cities in the information territory must not destroy the cultural achievements of the physical cities of the past.

The design quality of the physical environment will increase in importance with the settlement of the information territory. This movement can be compared with the discovery and settlement of the 'New World' from the 15th to the 19th century. The new settlers brought some crucial ideas and techniques from Europe, but that did not stop them from developing their own culture, separated from their countries of origin. And the 'old World' did not disintegrate or deteriorate after the discovery of the 'New World'. Instead, it kept developing and producing new techniques, styles, and thoughts of its own. In today's terms, every new settler in the information territory increase the chances for a sustainable development in the traditional territories.

Quality of life in the information territory

Quality of life means access to and distribution of the most important physical and intellectual resources that we need to survive and to enjoy life. If one carefully studies the percentages of time that is spent today with information processing and information consumption, and at the same time studies the possibility that the information territory offers, then it seems indeed that the quality of life could improve dramatically when using the new technology appropriately.

The reduction of physical travel from and to places is an example how the quality of life could be improved in the information territory. Although recent studies have shown that women and men who exclusively work at home with telecommunication to their offices will not be able to socialise and move up in the career hierarchy as quickly, this type of work schedule could still mean a significant reduction in traffic pollution and other negative side effects of mobility

The most often heard critique of the new development is that personal relations will suffer from the emergence of the information territory and from information technology in general. This in turn is described as a loss in the quality of life. What is ignored in most cases is that the new information technology offers the possibility for a truly new way to communicate. It will be not a replacement of traditional communication, but a welcome expansion to traditional communication forms for several groups of a society, including children, managers, elderly people or the handicapped. Each group can and will use the new technology in their own way, but all will be based on the same common language. Breaking down traditional barriers between groups could indeed improve the quality of life for their members and for society in general.

Figure 5. "Matrix 3.0" creates spatial user representations by combining vertical and horizontal elements, logos and quotes into unique, personalised spatial fabrics. This architectural syntax machine is accessible over the Internet and uses its first global data format VRML (Virtual Reality Modelling Language). Online information at http://caad.arch.ethz.ch/~wenz/babylon. syntax by Christian Waldvogel, space by Florian Wenz, 1996.

Working and living in the information territory

Much has been written about the impact of the information technology on the future working and living conditions. The best example is to observe people who already live and work in this environment. It is indeed a danger that the information territory could become so attractive, that people of a certain age group and profession get totally drawn into it and start to neglect and ignore their physical environment, along with the people who populate it. Hopefully this will be the exception and not the norm. Today energy business and telecommunication business are two of the world wide dominating economic forces. Any increase in telecommunication will reduce the energy needed to produce the artefacts of the future. Vice versa, any reduction in prize of energy reduces the need for developing sophisticated telecommunication devices.

A new world economy has developed and is in operation already. Electronic media increasingly render the traditional transmission of documents, letters and other information obsolete. In many cases, fax and electronic mail have replaced the telegram and the written letter. But none of the previous means of communications have disappeared entirely. Therefore we can expected, that many aspects of working and living in the information territory will be similar to the present situation, but that many of the time consuming and physically straining and dangerous activities, such as driving or flying, can be reduced.

We think that the physical environment will increase in importance, once much of the office and other light industrial work can be replaced by electronic means and by simulation. The need for large office spaces and production facilities will decrease, which makes the places where people work and live during the days even more important.

Figure 6. "Hollow Planet" is a virtual urban construction site, created by remote participants over the Internet. The sectors of "Hollow Planet" are in the centre of an outlined Planet Earth, whose continents are visible from anywhere. They replace the horizontal reference plane of the horizon and express the concept of a completely self contained system, which can evolve independently of the constraints of the physical world. Online information at http://caad.arch.ethz.ch/~wenz/babylon. Florian Wenz, 1996.

Hybrid Spaces and Memescapes

It is important to understand, that scientifically motivated recording and simulating of spatial and natural systems in some cases have emancipated themselves into independent entities with their own values, mechanics and rules. The continent of Antarctica, for example, although being almost uninhabited, is one of the most intensely researched natural environments of the planet. With many of the research stations being connected to digital networks, large amounts of data is continuously being created for and by an international scientific community on the Internet. This results in a virtual cognitive model of Antarctica which resides in networks and is connected to the physical Antarctica via computer and sensor interfaces. Similar developments are on the way for large urban agglomerations where the political, geological and technological situation is favourable. In these cases, the driving force is usually not scientific research, but the marketplace with its strong economic powers. In its ambitious plan "IT 2000" from 1991, the Singapore government describes how it will transform the nation into an "Intelligent Island" within the next 15 years:

"Singaporeans will be able to tap into vast reservoirs of electronically stored information and services to improve their business, to make their working lives easier, and to enhance their personal, social, recreational and leisure options. Text, sound, pictures, video, documents, designs and other forms of media can be transferred and shared through the high capacity and high speed nationwide information infrastructure made up of fibre optic cables reaching all homes and offices, and a pervasive wireless network working in tandem. This information infrastructure will also permeate our physical infrastructure making mobile telecomputing possible, and our homes, work places, airport, seaport and surface transportation systems "smarter". (National Computer Board, "IT2000 - A Vision of an Intelligent Island", Singapore 1991)

It is obvious from the development of the Internet that such an extensively "wired" city will effectively create a networked urban system, that will coexist with the present city in close symbiosis. An existing example of such symbiosis is the "Digital City Amsterdam" which started off as a BBS mailbox system in 1994 and now counts over 50 0000 "citizens". In contrast to the Singapore model, "Digital City Amsterdam" is a non-profit organisation, is focused on communication and uses mainly modems and telephone lines for connectivity.

These virtual social spaces share with the existing social fabric a space which was first described by the scientist Richard Dawkins in his 1975 book "The Selfish Gene", as an ecosystem of ideas or "memescape". It is expected, that networked memescapes, like the Internet, will be main breeding grounds for cultural developments in the information age:

"This new memescape is both electronic and organic; it is a territory shared by both humans and informational machines. In this memescape, human and computer memes interact, which creates the conditions for the emergence of a different kind of phenomenology. Never before have we had to truly communicate with the machine. In the electronic memescape, however, machines become interlocutors, with whom true cognitive exchanges are made." (Oliver Dyens, "The Movement of Evolution" in: Nonlocated Online, Passagen Verlag, Vienna, 1995)

TRACE

The interactions between natural systems and virtual systems are not very well understood, because there is not yet a common descriptive language. An important function of virtual worlds is thus, to act as a mediator between these coexisting worlds. In this direction we propose a new concept for the city. The name of the installation is TRACE. TRACE generates spaces by registering activities by local and networked visitors and by interpreting and representing them. The substance and the gene code of the space is therefore formed by the history of the visitors' activities.

The energy that creates TRACE is the motivation for the individual visitor or client to represent her or himself by leaving TRACEs and to read and interpret TRACEs of other visitors. The space that can be experienced represents the state of the system at the time of the login. It emerges through a constant information exchange between a database, which stores and indexes the TRACEs through an event agent, and a geometry generator which displays them.

TRACE only shows isolated segments or sections of the entire system in very much simplified iconographic representations. Those icons depict the activities of the visitors and the resulting matrix of perception. The most important modes are always immersive (interior spaces, private) and transparent (external space, public). TRACE is therefore not a typical simulation, although it utilises many simulation techniques. It is a substitution of the real in the sense of Jean Baudrillard :

"Abstraction today is no longer that of the map, the double, the mirror or the concept. Simulation is no longer that of a territory, a referential being or a substance. It is the generation by models of a real without origin or reality: a hyperreal." (Jean Baudrillard, "Simulations", 1983)

Figure 7. (double page) TRACE - an Online Urban Process Field. Information at http://caad.arch.ethz.ch/trace. Florian Wenz, Fabio Gramazio, 1996

The technical Specifications of TRACE:

* Geometry. The geometry generator is programmed in Open Inventor and uses simple geometries, texture maps, animated objects, level of detail and hierarchical modelling. Collision detection is integrated in Open Inventor.

* Event Agent. The event agent registers activities under an Open Inventor user interface and is also programmed in Open Inventor.

* Audio Integration. Audio beacons and ambient sounds support the orientation in space and the generation of the mental maps.

* User and Space Database. The databases are in ASCII format, are updated during logout time and reflect user activities in the system.

* Interaction and user interface. User interface and interaction are simple and intuitive, and are restricted to two main modes. The user can click on objects and spatial elements which results in visible changes of processes, or he can influence the system with his movements through membranes, which results in changes in the lighting, surface or audio qualities of the space. The physical user interface is a space mouse.

* Integration into the Internet. TRACE is mirrored in VRML on the Internet and a program version that is restricted in its functionality will be accessible over the Internet.

* Hardware. TRACE will be run on an Indigo Impact workstation (Silicon Graphics Industries).

* Research Environment: Architectural Space Laboratory (ASL), Chair for CAAD and Architecture, ETH Zürich

* Concept, Programming and Support: Florian Wenz and Fabio Gramazio

* Online Information at http://caad.arch.ethz.ch/trace

Conclusions

Urban space simulation by computer graphics has transformed the way we perceive and understand existing cities and possible new cities. Space, and urban space in particular, begins to change its meaning. To understand the shape and space of today's cities, we must know the role of individual and public transportation in the 20th century. To foresee and plan the urban space of the future we must understand the role of communication which renders many of the old technologies obsolete.

In the past, computer graphics simulation was merely an instrument to represent what was conceived in the human mind and on traditional media. In the future, urban simulation by computer graphics will be a field of research in its own, because the urban space will be changed dramatically by the use of the new technology. Nothing will replace reality or the physical model, instead, the new media will be a supplement. But the difference between the traditional use of computer graphics in architecture and urban planning and the future use will be significant. We are only at the beginning of recognising the full impact of urban space simulation by computer graphics. As a consequence, the application of networked computer graphics techniques in design will result in fundamental changes of our physical environment.