From map to model: the development of an urban information system
Post on 21-Jun-2016
From map to model: the development of an urban information system Alan Day, Centre for Advanced Studies in Architecture, University of Bath, Bath BA2 7AY, UK The use of three-dimensional computer models for urban planning and design is discussed with particular reference to a recently completed model of the City of Bath. Problems in making such models generally available are identified and a solution, which is particularly appropriate for nonexpert users, is proposed. Keywords: planning, computer-aided design, urban models 1 Enlot, d The City in Maps: Urban Mapping to 1900, The Brit- ish Library, London (1987) 1 The utility of maps T he characteristics of the contemporary map are so familiar that they can easily be taken for granted. The map is a symbolic representation of the world drawn to an accurate scale, using a set of uniform symbols. A high degree of abstraction is employed in order to reduce the amount of information to manageable proportions and this is then presented in a structured way which allows the map to be read easily. However, maps, and in particular urban maps, were not always presented in this way. Early maps, particularly during the medieval period, were aerial views which showed the geometric form and appearance of the city as well as its street layout (Figure 1). Accuracy was often sacrificed in order to ensure that all the finest buildings and monuments were shown and the artistic and symbolic qualities of the work were at least as important as its objective status 1. The introduction of improved surveying techniques in the Renaissance facilitated the production of increasingly accurate maps and these new maps, which presented the city as a plan projection, superseded the aerial views. As they were increasingly used for military purposes and to record land transactions, accuracy became 366 0142-694X/94/030366-19 1994 Butterworth-Heinemann Ltd "r. I Urban information system 367 critical and by 1739 the move to accurate plans of cities was so well advanced that Louis Bretez's stunning plan of Paris, covering 20 sheets, (Figure 2) was not particularly well received by the Parisian press 2. Although aerial views continued to be fairly common in Europe through- out the 18th century their use was restricted to recording picturesque towns or presenting new developments, as in Baumeister's views of Karlsruhe in 1739. Accurate surveying, standardized sets of symbols, and, from the late 19th century, cheap offset lithographic printing resulted in the 2D map becoming the standard way of representing cities. There is no denying the usefulness of these maps, be it for navigation, planning new develop- ments, or mapping spatially related data, but the paradigm of the map is now so powerful that it tends to blind us to other forms of representation. The map is a product of the printing press and its cheapness and portability have been central to its success. With the advent of computers, new technology has been brought to bear on the map and the resulting geographic information systems (GIS) have taken the map and added analytic tools. These systems accept the existing paradigm and have linked it with database technology in order to give the map intelligence. Sophisticated though these systems are they have simply accepted the map as the way of representing urban form without fully considering its strengths and weaknesses. Accuracy, consistency and portability are all strengths but consistency has been achieved by reducing the complexities of the real world through the exclusion of information, and in particular by eliminating three-dimensional form. Contours have been developed to overcome this problem when representing landscape, but there is no equivalent in the urban context. 2 Ibid. p 56 This 18th century trade-off between accuracy and representation is no longer relevant as it is now possible to have the best of both worlds through the use of three-dimensional computer modelling. This preserves the accuracy of an original survey while representing land and building form realistically. Over the past 30 years computer-aided design (CAD) systems have been developed which allow the user to create three- dimensional models of buildings which can be as accurate as necessary and, once created, can be viewed from any position. As hardware and software have become increasingly powerful the scale of these 3D models has increased, from individual buildings to urban blocks and now to whole cities. There are clearly advantages in bringing GIS and CAD technology together in order to shift GIS from being map-based to being model- based. The map was the result of a need married to a particular 368 Design Studies Voi 15 No 3 July 1994 Figure 2 Plan of Paris by Michel Etienne Turgot, 1739 (Copyright - British Library Maps C.11.d.lO) Urban information system 369 technology; now that the technology has changed the map can take its place as just one level of representation within a much richer environ- ment. 2 Existing urban models Early examples, such as the Skidmore Owings and Merrill model of Chicago, 3 were just an assembly of simple blocks but increasingly sophisticated urban models have been built since. The Architecture and Building Aids Computer Unit at Strathclyde University (ABACUS) have two, an extensive model of Glasgow and a smaller, more detailed model of Edinburgh Old Town. This is intended to assist the Old Town Trust with the conservation and economic regeneration of the historic core of the city, while the Glasgow model is designed to provide GIS functionality and offer a way of integrating various types of urban information 4. The most direct use for urban models is as part of the planning process. Hall 5 reports on tests carried out on the use of computer visualization in development control where three projects were modelled and the results used for discussions between the applicant and planners. He comments on the advantages to lay people of this kind of visualization and on its usefulness to professionals engaged in the design process. The objective status of the computer material was thought to be particularly advan- tageous. As Hall puts it, 'It is suggested that a central component of the argument for the use of computer visualisation in planning control is that it can be seen to be independent of the positions of all the negotiating parties '6. 3 Mitchell, W J Computer-Aided Architectural Design Van Nos- trand Reinhold, New York (1977) pp 264-265 4 Grant, M 'Urban GIS - The application of the information technologies to urban manage- ment', in J A Pov~ll and R Day (ads) Informing Technologies for Construction, Civil engineering and Transport Brunel/SERC, Ux- bridge, UK, (1993) 10P 195-199 5 Hall, A C 'The use of computer visualisetion in planning control' Town Planning Review, Vo164 No 2 (1993) 193-211 6 Ibid. p 206 7 Merchant, A N 'Expert sys- tem: a design methodology' Computers, Environment and Urban Systems Vo116 No 1 (1992) 21-41 By combining computer modelling with expert systems new kinds of design tools can be created. Merchant 7 discusses the development of an Urban Design Expert System which was created to provide advice on the design of a public space. The system initially offers the designer assistance by offering a range of appropriate visual precedents and, when the scheme is complete, the system can be used for evaluation with evaluation criteria themselves being varied by the designer. The scheme design is carried out within a CAD package and the geometrical information it contains provides much of the data .for analysis by the expert system. At the moment such systems are fairly primitive and work best with constrained problems, but they indicate a way in which intelligence can be added to urban models which is complementary to the kind of analytical tools that GIS systems provide for maps. The issues involved in the creation and use of large 3D representations of 370 Design Studies Vol 15 No 3 July 1994 urban areas have been investigated over the past two years in Bath where a model of the entire Georgian city has recently been completed. Experience has been gained on the effectiveness of various ways of constructing such models and on the opportunities and constraints inherent in their use. 3 Development and conservation in Bath In most historic towns, including Bath, there is particular concern about how new should relate to old. The strongest feelings often have to do with the appearance of modern buildings and, in particular, how they relate to existing buildings within a historic setting. When new buildings are proposed there are often difficulties in understanding what is intended and in assessing the impact of the proposal on its surroundings. There is a desire for public debate, but that debate can very easily be stifled by difficulties in understanding what is proposed because of problems in reading traditional architectural drawings. Bitter experience has shown that slick draughtsmanship and a carefully contrived perspective view can all too easily fool a planning committee into thinking that a proposal is appropriate only to find, when the building is complete, that it intrudes on its surroundings in ways that were never anticipated. In order to address this problem two things are required, an accurate and easily understood representation of the proposal, and a presentation technique that is objective and not completely under the control of the applicant. 4 Visualizing change In order to address this problem, some 25 years ago Bath Preservation Trust commissioned a wooden model of the city as a vehicle for considering the implications of new developments. The intention was to alter the model in order to show change, but the expense and difficulty of doing this meant that it was never used in this way. However, had it been used, its scale of 1:500 would have meant that it would only have been useful for considering change at an urban scale and would not have been particularly appropriate for detailed consideration of the small-scale changes that constitute the bulk of planning applications. A computer model, on the other hand, is inherently flexible and so change can be accommodated and detail added in order to visualize even very minor alterations. As computers are being used increasingly for architectural design it is not unusual for a planning application to be accompanied by drawings derived from a CAD model. However, such presentations can be as deceptive as their hand-drawn counterparts as the views are carefully selected and the surroundings may not have been modelled particularly accurately. The Bath computer model is designed to Urban information system 371 address this problem. When planning permission for a new building is sought the design can be included in the urban model thus providing an accurate context and allowing views to be set up from any position, and by any party. Also, parts of the model can be supplied to architects who are working on sites in the city, thus giving them immediate access to an accurate representation of their buiiding's immediate context. 4.1 The construction of the Bath computer model The 3D computer model includes the whole of the Georgian city, most commercial and business activities and a considerable portion of the city's residential fabric (Figure 3). The model was constructed using aerial photogrammetry, a technique which uses pairs of photographs which are viewed in stereo, allowing the operator to see the subject in three dimensions. A photogrammetric plotter connected to a personal compu- ter is used, and when the operator digitizes a point on a building its x, y and z co-ordinates are entered directly into a CAD package running on the PC. In Bath, survey photographs taken by Ordnance Survey in 1991 were used with any buildings constructed since that date being entered manually from the architects' drawings. One of the great benefits of employing aerial photogrammetry is that fieldwork can be kept to a minimum thus allowing the construction of the model to proceed rapidly. Also, as the photographs are taken looking vertically downwards, build- ings that are difficult to get to, or are on private land, can easily be surveyed. The external form of any building can be determined accurately and the roof geometry and details, such as parapets and chimney stacks, fully represented. The result is a model which is particularly convincing from above and which accurately represents the grain of the city (Figure 4). The weakness of the system is the capital cost of the equipment, upwards of 30 000 for a basic stereo plotter, and the paucity of elevational information, something that is inevitable when the photo- graphs are taken from above. However, this deficiency can easily be rectified by taking additional photographs where more detail is required, either as single images, or as stereo pairs to facilitate the modelling of a facade in depth. In order to introduce a precise scale when constructing a photogrammetric model actual dimensions between known points on the photograph are required. These control points can be surveyed conventionally but, as this is expensive and time-consuming, spot heights on 1:1250 Ordnance Survey maps were used. Each city block was treated as a separate CAD model and these were located relative to one another using their National Grid co-ordinates. Depending on size and complexity, each block took between three and ten days for a skilled operator to construct and no 372 Design Studies Vol 15 No 3 July 1994 ,. .', ..~ Figure 3 Plan showing the extent of the Bath computer model significant inaccuracies were experienced when the blocks were assembled into the complete urban model. The whole model comprises some 150 urban blocks, occupies 60 Mb of disk space in AutoCAD .dwg format. and cost about 100 000 to produce over an 18 month period. A 3D terrain model was also constructed to show the countryside for 10 km around Bath to ensure that any views taken from the city centre include the rural skyline which is so important to Bath's setting. As it was important for architects' CAD models to be incorporated into the urban Urban information system 373 ~t 374 Design Studies Vol 15 No 3 July 1994 model it was decided to use industry-standard CAD software with well developed data exchange procedures and so AutoCAD Release 12 running on 486-based personal computers was used to construct the urban blocks with the renderings and animation sequences being carded out in Autodesk 3D Studio running on a PC, or in Wavefront Advanced Visualiser running on a Silicon Graphics workstation. 4.2 Using the model To date, the main use of the model has been for development control. In one example a school wanted to build a new sports hall on a sensitive sloping site in front of one of Bath's most elegant crescents. Planning permission had been refused previously and the city council planners recommended that the model be used by newly appointed architects to test a number of different strategies on the site. Three different schemes were modelled and a series of views and animations set up for each. In Bath the planning committee is especially concerned about the impact of new developments on long distance views and so views of the site were set up from precise locations on the other side of the valley for each of the proposed schemes. Two meetings, each lasting about 90 minutes, were held with the planners and client's architects to consider the results of the computer visualiza- tion. All parties agreed how helpful the technique was and it emerged that the long distance views were deemed to be of little importance when compared with close-up views and the impact of the new building on its immediate neighbours. The result of the meetings was that all those present agreed that one of the solutions showed particular promise and this was then developed to a full planning application. 4.3 Issues in use At the moment the Bath model comprises some 150 submodels which can each be accessed separately or combined as required. This process is carried out via a reference drawing which shows the outline of each block as a single polyline with the AutoCAD drawing name indicated. Indi- vidual urban blocks can be loaded by clicking on the area within the appropriate polyline, or the whole model assembled automatically. Currently, when the model is being used for development control and a view or animation sequence is required, the planners have to contact the university and ask for the proposed building to be modelled and the images created. Although this system works well enough it constrains the use of the model by placing it at one remove from the end-user. The reasons for this are both economic and technical. The quantity of data Urban information system 375 contained in an urban model is large and a considerable amount of computer power is required for its manipulation. This is expensive for an organization where computer-aided design is a luxury rather than an essential working tool and where staff lack training and experience in its use. Even a planner with considerable enthusiasm for computing would find it difficult to gain sufficient experience in the range of CAD and visualization software that is used to create views of the Bath model. If one wants the end-user to have access to the system then their needs have to be addressed directly and, assuming that the model is going to be maintained and updated by experts, these needs are relatively simple. They want to be able to navigate around the model, set up views and animation sequences, print out the results, and import and export urban blocks for use by designers. To be economic such a facility should be capable of being delivered on a standard personal computer using a graphical user interface, such as Microsoft Windows. 5 Theproblem ofsize With a model of the size being discussed here, such simple requirements can be problematic. Even navigation around the Bath model is difficult. In AutoCAD, with the whole model loaded, it takes about 20 minutes to regenerate the screen after moving the viewing position, and rendering a single view of the entire city in 3D Studio can take over 50 hours. Even using Wavefront Advanced Visualiser on a powerful Silicon Graphics workstation a single view can take several hours to render. There are, of course, strategies that can be adopted to reduce the amount of data that has to be manipulated, for example, by excluding all the information that is outside the view and structuring the data so that the level of detail present in any part of the model is related to its distance from the viewing position. For fast rendering it also makes sense to reduce the number of faces in the model and increase the amount of texture mapping, but such a strategy results in a model that is unsatisfactory for design purposes. The Bath model is intended to be used as a design aid and therefore must be accurate and have sufficient geometric detail to be realistic. A simple rectangular prism with scanned photographs applied to its faces to represent a building may be quite satisfactory for an interactive computer demonstration but is of limited use as a design tool, particularly when dealing with the intricacies of a historic city. Although the power of computers is increasing rapidly in relation to cost, the amount of information that makes up an urban model also tends to increase as detail is added over time. So, it is unlikely that it will be practical to 'run' a large urban model with anything approaching interac- tive navigation on a personal computer within the next five years at least. 376 Design Studies Vol 15 No 3 July 1994 8 The terms hypertext and hypermedia were coined by Ted Nelson in the 1970s and refer to a new media form in which material from a variety of sources is linked together in a flexible and open- ended way. One of the first hyperlext applications, was Ap- ple's Hypercard. If one simplifies the model, for example by having a number of different versions of each urban block, then one can navigate by using the simplest level of detail and only switch to the more complex level when the viewing position is established. In the Bath model there are currently three levels of detail: the outline polyline, a simple block model and the fully detailed geometric model. Although such a strategy works well enough, it is a device to overcome a technical deficiency and can be awkward for the user. What they want is to have the full model presented on the computer screen and to be able to move around it interactively. Clearly this is very difficult to achieve while maintaining realistic modelling and rendering and, even if one adopts strategies such as automatic scene culling and level-of-detail selection, interactive navigation will only be possible on the most powerful computers. However, by being selective in terms of what one renders one can bring rendering times down to minutes rather than hours and it is therefore possible to build up multiple views of the model in a relatively short time. If sufficient views are rendered, from known positions then one can move between these views quite quickly and thus simulate a form of interactive navigation. Although there are constraints to this approach, if sufficient views are rendered a reasonable degree of interaction can be achieved without the need to switch between various levels of detail. The disadvan- tage of using views of the model, in the form of bitmapped pictures, is that the pictures lose all the intelligence that is available in the CAD model where attribute data can be assigned to any object. This allows the user to select an object on the screen and, as the system knows what it is, a link can be made to an external application, such as a database. This is a core feature of geographic information systems, and if one can bring this kind of intelligence back into bitmapped pictures then both navigation and object selection can be achieved through the pictures without the need to run the CAD model at all. With the Bath model this has been achieved by programming AutoCAD to export a data file along with each bitmapped picture which identifies each object in the view by specifying the area it occupies in the picture. When this area, or 'button', is selected on the picture a link can be made to another picture, or to an external application, thus re-introducing some of the intelligence that existed in the original model. The urban model should not be thought of as a single entity but rather a collection of computer files which need to be browsed and selected according to the needs of the user. As one has pictures with object buttons already identified there are advantages in using a hypermedia system 8 to make the necessary links as the very essence of hypermedia is the ability Urban information system 377 9 Davis, H C, Hall, W, Heath, I, Hill, G and Wilklns, R 'Towards an integrated information en- vironment with open hypermedia systems' in D Lucarella, J Nanard, M Nanard, and P Paoli- nl (eds) The Proceedir~gs of the ACM Conference on Hypertext ECHT '92, ACM, Milano (1992) pp 181-190 to move between various kinds of data in a seamless and interactive way. In order to achieve this, use is being made of some recently developed software, Microcosm, from the Department of Electronics and Computer Science at the University of Southampton. 6 Microcosm Microcosm 9 is designed to allow the user to browse through large bodies of multimedia material by following links from one place to another. It consists of an open message passing system combined with a number of viewers and filters. Viewers are programs that can display various formats of documents, including pictures, sound and video, and they communicate with the filters to establish what active areas exist in a particular document. When a selection is made, for example by clicking on a building in one of the pictures, the user activates a link which may be of a number of types. Some go directly to another piece of information, such as a picture or document, while others offers choices, perhaps based on a keyword search made through a range of documents. When linked to a palette of simple tools, this allows the user to navigate around the model by moving quickly from picture to picture and to set up views or animation sequences for subsequent rendering. As the system knows the co-ordinates of each object in three-dimensional space one can select a camera and viewing position simply by clicking on two points in a picture, or indeed across a range of pictures. These pictures need not be limited to views of the model as maps and drawings can also be included in order to aid object selection. As Microcosm offers a way of linking objects in the model with other kinds of information it opens up the possibility of using the model as a way of organizing large amounts of information about the city in order to create an urban information system in parallel with the visualization model. This could range from text and photographs recording a building's history, through social statistics derived from the census, to data gener- ated by an energy modelling package. Microcosm was originally designed to handle links between text document but it has now been developed to handle all digital media, including sound and video. It offers a number of advantages over other hypermedia systems which may be summarized as follows: No mark-up required in documents All the information concerning links is held in a linkbase and not in the document itself. This means that documents that are held on read-only media, such as a CD-ROM, can still be marked up. 378 Design Studies Vol 15 No 3 July 1994 Connectivity to other applications It is possible to make links that dispatch other programs with a given dataset as a Microcosm viewer. This means that a user can access a document that was created by another application, such as a word processor or spreadsheet, and work on it within that application. For example, one could have a link that would launch AutoCAD, read in a drawing, and allow the user to edit it directly. Wide range of link types In most hypermedia systems links have specific source and destination anchors. Microcosm supports such specific links, but also supports more general links. Links can have a fixed end point, but may be followed from any point where a given object (such as a specific text string) occurs within a document or specified set of documents. This means that it is possible to create a single link to a piece of reference material, which may then be followed wherever the specified source selection occurs without having to re-make the link at every possible source point. This results in a considerable reduction in authoring effort compared to traditional hypermedia systems. Open architecture Microcosm consists of a number of independent processes which communicate using an open message format 1. Mak- ing a viewer is simply a matter of programming an application to send these messages to the system, something which can be done with a few lines of code. Microcosm's architecture and message system are open so it is possible to distribute Microcosm functionality across different machines on a network, even where the machines themselves have differing architectures. 10 Fountain, AM, Hall, W, Heath, I and Davis, HC 'MICROCOSM: an open model for hypermedie with dynamic link- ing', in A Rlzk, N Streltz and J Andre (eds) Hypertext: Con- cepts, Systems and Applications. The Proceedings of The Euro- pean Conference on Hypertext, Cambridge University Press (1990) 11 u, z, Davis, H C and Hall, W 'Hypermedia links end in- formation retrievaJ' Proceedings of the 14th British Computer Society Research Colloquium on Information Retrieval, Lancaster University (1992) It is important to stress that Microcosm is not a database, it is a link service and multimedia navigation system n. Microcosm does not hold documents, these are simply computer files which remain in their original form. Microcosm holds attributes for these documents, and links between documents. Users may navigate by making queries from the document management system in a similar way that an SQL query is made from a relational database, but there is a much larger range of navigational techniques available. Microcosm does not make any requirement for data to be structured or formatted in any particular way, nor does it dictate the attributes that must be held for any link or document. These may be user defined in every instance. The result is a system with much greater flexibility and greater ease of navigation than is available from most hypermedia or database systems. 7 Developing the Bath method Urban models of the kind discussed here are usually constructed on Urban information system 379 powerful computers but have to be delivered on more basic machines to users who may have limited computing experience. These machines, even if they are well-specified 486 PCs, will not be able to cope with the full urban model and therefore a strategy is being devised to use a networked solution where all the intensive graphics processing is carried out on a central machine with the results exported to the delivery machines for viewing. The software being developed to achieve this is based on Microcosm running under both Unix and Microsoft Windows. The expensive CAD and rendering software need only run on one machine with the client machines using delivery software which can be made available at low cost. This has the advantage of allowing an interface to be designed specifically for the unskilled user independently of the CAD software that created the model. As the model will reside on one machine it can be maintained and updated by a single skilled operator thus ensuring a high degree of data integrity. The set of pictures used for navigating the model, along with their associated Microcosm buttons, can be automatically re-rendered each week thus ensuring that users are always presented with an up-to- date representation of the model. 8 The planning information system Currently under development is a computer-based planning information system which will take the visualization capabilities that have already been developed and link them to a series of databases. One will give specific guidance to prospective planning applicants on matters which should be considered when submitting a planning application, including illustrations of current best practice selected by the development control officers. A second database will contain a comprehensive record, in text and pictures, of previous planning decisions which illustrate why particular decisions were reached, This will be useful to the public and to development control officers who aim at achieving consistency in their decision making. Built into the system will be a feedback mechanism which will allow the public to browse through current planning applications, see critical ones visual- ized in the urban model, and offer their comments for entry into the database. This will widen the range of views that are received by the officers and committee members. 9 Conclusions Large 3D computer models are becoming increasingly popular for urban planning and design. They provide a level of realism that can open up the planning process to public scrutiny and allow strategies for the future to be 380 Design Studies Vol 15 No 3 July 1994 judged more effectively. Also, once created, such models can be used in other ways as their legibility makes them ideal for accessing a database of information about a city and for co-ordinating information that is currently held separately. By linking visualization models to applications which model other kinds of data, such as social statistics, energy-use patterns or traffic flows, they can be used to present this information in ways which make it more easily communicated and hence understood. There is also the possibility of reconstructing the historical development of the city as illustrated in the model of medieval Bath shown in Figure 5. More speculative urban proposals may also be offered for public comment and discussion, such as the scheme illustrated in Figure 6, which shows a new mooring basin for the River Avon in the centre of the city. However, enthusiasm for creating large urban models is currently over- shadowing consideration of how they will actually be used in practice. They are expensive to create and strategies must be developed to ensure that their use is not unduly constrained by the current limitations of hardware and software. The great advantage of such models is that they provide a representation of the physical form of the city which everyone can understand. Maps and plans are two-dimensional projections of three-dimensional objects and that abstraction makes them much less accessible than 3D models. For the trained designer the abstraction of plan and section is helpful as it concentrates the mind on specific issues, but for those unused to the conventions of orthographic projection the synthesis of a series of two-dimensional representations into a three- dimensional form can prove impossibly difficult. Urban models offer something that has never been available before, a way of analysing the present and considering the future which is available to all. Just as the drawing is a tool used by the designer and, as such, becomes a way of thinking about a problem, so the urban model can become a way for the whole community to focus and articulate its thoughts on how urban growth and change might be accommodated. In a democracy the decisions about how a city should develop must be made by its residents, and their representatives, on the basis of informed choice. In the past too many decisions have been made by minorities simply because there was no effective public debate as little of the information necessary for making judgements was readily available. Any technique which can make this process more open is to be welcomed. Those described here do this by using new technology to bring informa- tion together and by using computers to represent change in a way that makes it intelligible to nonspecialists. Although such techniques will not, Urban information system 381 ~5 382 Design Studies Vol 15 No 3 July 1994 td Urban information system 383 of themselves, guarantee that the cities of the future will be better than those we have today they will at least ensure that the information required to facilitate a more open debate is widely available. 384 Design Studies Vol 15 No 3 July 1994
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