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The Digital Twin of the City of Zurich for Urban Planning

The Digital Twin of the City of Zurich for Urban Planning Population growth will confront the City of Zurich with a variety of challenges in the coming years, as the increase in the number of inhabitants and jobs will lead to densification and competing land uses. The tasks for the city administration have become more complex, whereas tools and methods are often based on traditional, static approaches while involving a limited number of citizens and stakeholders in relevant decisions. The digital transformation of more and more pieces of the planning and decision-making process will make both increasingly more illustrative, easier to understand and more comprehensible. An important data basis for these processes is the digital twin of the City of Zurich. 3D spatial data and their models trans- form themes of the city, such as buildings, bridges, vegetation, etc., to the digital world, are being updated when required, and create advantages in digital space. These benefits need to be highlighted and published. An important step in public awareness is the release of 3D spatial data under Open Government Data. This allows the development of applications, the promotion of understanding, and the simplification of the creation of different collaborative platforms. By visualization and analysis of digital prototypes and the demonstration of interactions with the built environment, scenarios can be digitally developed and discussed in decision-making bodies. Questions about the urban climate can be simulated with the help of the digital twin and results can be linked to the existing 3D spatial data. Thus, the 3D spatial data set, the models and their descriptions through metadata become the reference and must be updated according to the requirements. Depending on requirements and questions, further 3D spatial data must be added. The description of the 3D spatial data and their models or the lifecycle management of the digital twin must be carried out with great care. Only in this way, decision processes can be supported in a comprehensible way. Keywords Digital twin · Digital transformation in urban planning · Densification · Urban climate · Architectural competition · Participation Zusammenfassung Das Bevölkerungswachstum stellt die Stadt Zürich in den kommenden Jahren vor vielfältige Herausforderungen, denn die Zunahme von Einwohnerinnen und Einwohnern sowie von Arbeitsplätzen führt unter anderem zu einer Verdichtung und konkurrierenden Nutzungen. Die Aufgaben für die Stadtverwaltung sind komplexer geworden, wohingegen die Werkzeuge und Methoden oft auf traditionellen, statischen Ansätzen beruhen und eine begrenzte Anzahl von Bürgern und Interessen- gruppen in relevante Entscheidungen einbeziehen. Durch Digitalisierung von Schritten in der Planung wird der planerische Prozess inklusive der Entscheidungsfindung ins Digitale transformiert und damit immer anschaulicher, verständlicher und nachvollziehbarer. Eine wichtige Datengrundlage für diese Prozesse ist der Digitale Zwilling der Stadt Zürich. Er bildet durch 3D Geodaten und deren Modelle Themen der Stadt, wie Gebäude, Brücken, Vegetation, usw., räumlich in der digitalen Welt ab, wird je nach Bedarf mit unterschiedlicher Frequenz nachgeführt und schafft Vorteile im digitalen Raum. Diese Vorteile müssen aufgezeigt und bekannt gemacht werden. Ein wichtiger Schritt dazu ist die Veröffentlichung von 3D Geo- daten unter Open Government Data. Damit können Anwendungen kreiert werden und das Verständnis gefördert bzw. der Aufbau von unterschiedlichen Kollaborationsplattformen wird vereinfacht. Mit der Visualisierung und Analyse von Digitalen Prototypen und Aufzeigen von Wechselwirkungen mit dem bebauten Umfeld können Szenarien digital entwickelt und in * Gerhard Schrotter gerhard.schrotter@zuerich.ch Public Administration, City of Zurich, Zurich, Switzerland Vol.:(0123456789) 1 3 100 PFG (2020) 88:99–112 Entscheidungsgremien diskutiert werden. Fragestellungen zum Thema Stadtklima können mithilfe des Digitalen Zwillings simuliert werden und Ergebnisse wiederum an die bestehenden 3D Geodaten angeknüpft werden. Damit wird der 3D Geoda- tensatz, die Modelle und deren Beschreibungen in Form von Metadaten zur Referenz und diese müssen, den Anforderungen entsprechend, nachgeführt werden. Je nach Bedarf und Fragestellung müssen weitere 3D Geodaten hinzugefügt werden. Die Beschreibung der 3D Geodaten und derer Modelle bzw. das Lifecycle-Management des Digitalen Zwillings müssen mit hoher Sorgfalt vorgenommen werden. Nur so können Entscheidungsprozesse nachvollziehbar unterstützt werden. Schlüsselwörter Digitaler Zwilling · Digitale Transformation in der Stadtplanung · Verdichtung · Stadtklima · Architekturwettbewerb · Partizipation One of the six sub-programmes of the Digital City (Fig. 1), an important lighthouse project of the Smart City Zurich, is the so-called digital twin of the City of Zurich: 1 Environment and Strategies the digital, spatial image. The City of Zurich, like Helsinki (2019), Munich (München 2018) and Rotterdam (2019), has The Canton of Zurich expects an increase of the population opted for this terminology. Other cities such as Singapore by 280,000 people by the year 2040. According to the can- are striving for a digitalization of reality and platforms for ton’s guidelines, 80% of this growth shall take place in urban accessing and designing applications with the name Virtual regions to conserve the scarce resource of land. Accord- Singapore (2018). The term digital twin creates a proximity ing to those scenarios, around 520,000 people could live to the construction and real estate industry and thus builds within the city limits of Zurich in 2040, and the number of a bridge to the new developments in the field of Building jobs will increase accordingly. This growth will confront the Information Modelling (BIM; BauenDigital 2019) and digi- City of Zurich with many challenges in the coming years, tal transformation in the construction industry. Although the as the increase in the number of inhabitants and jobs will term is used there for a single building only, the mental bow have positive and negative effects. The city benefits from the can be made to further infrastructure and to the urban space increase in importance and diversity, from more economic itself. The ultimate goal is a digital representation of the and cultural innovations. At the same time, the competition city to simulate issues such as urban planning in climate of land uses will increase more and more. The densifica- change. For this purpose, components of the digital twin tion of the existing residential areas under consideration of must be updated with different intervals and, where appro- quality standards is, therefore, the main task. The grown priate, enriched with real-time data. In the triangle of the identity and individuality of the urban quarters should be real (physical), social and digital world, the digital twin con- preserved. In addition, noise and usage conflicts must be nects the real world with the digital world or, more precisely, minimized. In the context of sustainable growth, the chal- its space. Thus, in addition to the “traditional” link between lenges and strategic objectives have been described and set social and physical space and the link between social and out in the Strategies Zurich 2035 (2015). With the strategy focus Digital City (2019), the city coun- cil strengthens and accelerates the digital transformation in the city administration. The focus Digital City supports the strategy Smart City Zurich (2018). It uses the opportunities of digitisation to the benefit of the population, the companies and the city administration. For the City of Zurich, smart means networking people, organisations and infrastructures in such a way that social, ecological, and economic benefit will be created. The networking of data, sensors and applica- tions allows new and more efficient solutions for the users of urban infrastructures as well as for their operators. The good networking strengthens participation opportunities for the citizens and their contact with the administration. Numerous projects in various areas have already been imple- mented or are being planned. Smart City Zurich provides a common framework for these ongoing activities and planned measures. Fig. 1 Strategic focus Digital City with the six sub-programmes (source: City of Zurich) 1 3 PFG (2020) 88:99–112 101 digital space—supported by e.g. social media—this new link Thus, the digital terrain model, over 50,000 buildings is emerging (Rotterdam 2019). The digital twin opens up in various levels of detail as well as walls and bridges are new perspectives for urban planning. The new applications available. The 3D spatial data are mainly used in the city bring more understanding, more targeted questions and thus administration in the fields of environmental and urban comprehensible answers to future-relevant topics. planning or submitted as a subset to third parties for visu- alization of planned construction projects. The require- ments for content, accuracy, tracking and reliability have 2 History: The 3D City Model been developed in collaboration with various service departments of the City of Zurich. This collection of 3D The first experiments with spatial data  were carried spatial data is summarized under the term 3D city model out with ETH Zurich as early as the 1990s. The defini- (Stadtmodell 2019) (Fig. 2). tive, so-called 3D city model was created in 2011. ETH Zurich, Fachhochschule Nordwestschweiz and TU Munich were involved in the development. Vari- 3 Digital Twin for the City of Zurich ous agencies  of  the public  administration have bun- dled their forces. The GIS Competence Centre of the The digital twin is a spatial, digital model of the City of Department of Building and Planning  and  the GIS Zurich for different themes. It extends the existing spatial Centre for Geomatics + Surveying have launched the data infrastructure with 3D spatial data and their models and first draft. The digital ter rain model (LoD0), the block describes it. The focus is on 3D spatial data and it becomes model (LoD1), and the roof model (LoD2) are avail- the reference to consequently link spatial and other data. able in the reference system CH1903 + (reference frame The processes, the data acquisition and update, are fully LV95/EPSG 2056). described for the 3D spatial data, the models and the meta- The terrain model is based on the grid file of the Canton data. As a consequence, the processes in cadastral and engi- of Zurich, generated from LIDAR images from 2014 with neering surveying must also be adapted, meaning that the a resolution of 50 cm. In bridge areas, additional break third dimension must be taken into account when digitizing lines were recorded. Manual adjustments were made in space and performing further processing. areas of Lake Zurich and the Limmat. The road geom- Spatial data, spatial data models, and spatial metadata etries of the official cadastral survey were additionally are defined by the Federal Act on Geoinformation (GeoIG introduced as break lines. The irregular triangular mesh 2007), and have been described in detail. The Act is fully was calculated by FME with the tolerances of 1 m and “Infrastructure for Spatial Information in the European 0.1 m. The mean height error is 30–40 cm. The basic data Community” (INSPIRE) compliant and even goes beyond set dates back to 2014. the INSPIRE Directive, although it is not an actual transpo- The block model is based on the real and planned sition of the Directive, since Switzerland is not an EU Mem- building floor plans of the official cadastral survey, the ber State. Compared to other European countries there was height of which is below the terrain. The heights of eaves a formal Spatial Data Infrastructure in place in Switzerland and gables determined by photogrammetry are assigned before the implementation of INSPIRE (Crompvoets et al. as attributes to the floor plans. In buildings with a high 2018) and based upon the Federal Act on Geoinformation a recognition factor and striking differences in height, the solid governance framework has been developed. f loor plans are subdivided so that the buildings are repre- The Act on Geoinformation describes 3D spatial data sented by several prisms of different heights. In addition as the extension and characteristics of certain spaces and to the buildings, the 3D block model contains striking bridges. The mean position error is within the limits of the official cadastral survey and amounts to 10–15 cm and the mean height error amounts to 50 cm. The data set is continuously updated. The roof model consists of the walls and detailed roof structures of the buildings. Analogous to the block model, the building floor plans serve as the basis for the official cadastral survey. The evaluation of the roofscape takes place by means of semi-automatic stereo aerial photo- grammetric evaluation. In addition to the buildings, the model contains striking bridges and walls. Fig. 2 3D city model with terrain, block and roof model (source: City of Zurich) 1 3 102 PFG (2020) 88:99–112 objects, in particular their location, condition, use and legal The predictive modelling and the reactive modelling, imme- relationships, with a certain reference to time. The spatial diate action in both digital and real space, are described in data models are representations of reality, which determine Wildfire (2018). In predictive modelling, a distinction is structure and content independent of a specific spatial data made between iterative feedback and sandbox testing. This system. The formal descriptions of the characteristics of means that the most diverse simulations and scenarios in spatial data are based on metadata, such as origin, content, the digital world can be enriched, created and analysed with structure, validity, timeliness, accuracy, usage rights, access empirical values from reality. This is described in Grieves options or processing methods. Metadata are an essential (2014) under the term of digital prototypes and the environ- component for establishing and operating a geodata infra- ment of the digital twin. structure. Without metadata no valid decisions and actions For the City of Zurich, the digital twin means a consistent can be derived from geodata. Even a proper search for spe- enrichment of the 3D spatial data inventory and, in addi- cific geodata cannot be done without proper metadata. Geo- tion to the modelling and description of the data, a lifecycle cat (GeoCat 2019) is the metadata catalogue for Swiss spa- management of the individual components as well as the tial data. Federal offices, cantons, municipalities and private entire data inventory. The 3D spatial data are the basis for companies record the data. linking further spatial data or other data. Where appropriate, The concept of the digital twin according to Grieves elements from reality are linked to the digital world in real (2014) originates from the product lifecycle management. If time. The processes for digitizing reality are extended by this concept is applied to spatial data, models and metadata, the third dimension. then these can be described on the basis of a product life The developments are managed by the GIS City of Zurich cycle. The product life cycle describes the sum of the indi- (GIS Stadt Zürich) and implemented together with the part- vidual phases through which a product passes along the time ners (25 service departments of the City of Zurich). Almost dimension. Therefore, in addition to the detailed description 20 years ago, the need for coordination in the field of spatial of the spatial data and the spatial data models (via meta- information in the city was recognised. As a result, com- data), their life cycle is also described. Thus, the develop- prehensive spatial information projects were jointly imple- ment of different components of the digital twin (buildings, mented, thus laying the foundation for the urban spatial data roads, etc.) can be digitally planned and updated, and can infrastructure (SDI). In 2009, the City Council approved the be renewed or maintained on the basis of a defined interval. comprehensive strategy for GIS City of Zurich (GIS Stadt Updates may happen in short intervals and this may, but Zürich). In 2019, the strategy was revised again or adapted does not have to, be related to the so-called High-Frequency to the new challenges (GISStrategie 2019). and Low-Frequency City (Batty 2018; Wildfire 2018). Even With the expansion of the geodata infrastructure and the in a Low-Frequency City, elements which in reality undergo technical platform, the digital twin can be used for location- rapid changes and contain time-critical information (e.g. by based cooperation with internal and external partners. For means of real-time sensors) are to be linked to the digital example, planned real estate projects or urban development world. scenarios can be integrated. The data also offer optimal con- Vivid examples can be observed in the construction ditions for presentation, discussion and the shaping of the and real estate sectors (DigitalTwinCMU 2019). There, public space. The basis for various analyses and calculations construction processes and then maintenance are digitally such as visibility, noise propagation and solar potential anal- mapped using 3D spatial data and a building model as a yses, shadow calculations, flood simulations, etc. is created. digital replica that shows the structure and behaviour of a building with interactive connections to the physical object. The interactive connections transmit information such as 4 Planned, Selected Extensions status, usage or analysis data as well as control commands. Depending on the level of detail and automation as well as Due to new requirements of the service departments of the the type of connections and information, this component of City of Zurich, coordinated by the GIS City of Zurich (GIS the digital twin can reach different characteristics. It thus Stadt Zürich), projects are carried out which extend the data- depicts the structural and operational conditions of a real base. These data are then made available again and enable building over time. It can depict an existing building or one new applications. under construction. It is irrelevant whether the counterpart already exists in 4.1 Street Space 3D the real world, will exist in the future (Wikipedia 2019), or perhaps will not be realized at all. The digital prototype is To capture data efficiently or simply to reduce the need built before reality and thus enables predictive modelling. for inspections, the public space of the City of Zurich is 1 3 PFG (2020) 88:99–112 103 captured in three dimensions, integrated into the digital and parametric modelling, geometrically correct façades can twin and made available via an Intranet solution. In autumn be generated and the accuracy or deviation of the models 2020, Geomatics + Surveying will make an imaging ser- from reality can be determined. The process and the detailed vice available to all municipal employees, in which the contents of the research packages can be found under Gruen street space can be re-experienced digitally. In addition, it et al. (2019). will be possible to capture further objects in 3D, to measure Other infrastructure elements such as bridges, high- objects and to visualize existing data. voltage lines, etc. are added to the digital twin as required as additional components. In cooperation with the city and 4.2 Utility Cadastre 3D underwater archaeology, also historical 3D spatial data are constructed. Thus, the history of the city can be experienced Since July 2013, 2D pipelines and cable data (utility cadas- interactively in different time periods. From the first pile tre) of the City of Zurich have been submitted by the util- dwellings through Roman Zurich and the Middle Ages to ity owners to Geomatics + Surveying. The utility owners the present day. The demand is controlled by projects from are the Electricity Service, Energy 360° AG, Disposal and service departments or based on strategic formulations from Recycling Services, Water Supply Service, Public Trans- the GIS City of Zurich (Fig. 3). port Service and telecommunication companies. Most of the utilities have been digitized from continuously updated plans. The position accuracy is in the range of ± 20 cm. Pipe- lines and cables, e.g. due to construction work are marked 5 Enabler as inaccurate. The utility cadastre of the City of Zurich is a subset of the digital documentation of the work manage- To make the digital twin known, it is necessary that the ment of the utility owners. At least once a week, the pipeline data sets are made available as Open Government Data. and cable owners automatically deliver the new data to the This results in initial visualizations and analyses as well register operator (Geomatics + Surveying). The suppliers as economically profitable applications. In addition, the remain responsible for the content of the data (punctual- large amounts of data must be visualized (Zürich virtuell) ity, completeness, position accuracy, etc.). The operator is and  have to be  easily accessible through an advanced responsible for ensuring that the uploaded data is complete, geoportal. up-to-date (as agreed) and not modified. The utility owners  of the City of Zurich are already recording 3D coordinates today. However, this information 5.1 3D Building and Terrain Data are Open is lost at the interface to the utility cadastre. This gap in the Government Data data flow will soon be closed to enable the delivery of BIM- capable utility cadastral datasets. Simple access and the free use of administrative data, with- In the Digital Underground project (van Son et al. 2018) out the need for specific protection (Open Government Data; at the Singapore-ETH-Centre, in cooperation with the Sin- OGD for short), is part of the basic infrastructure of a digital gapore Land Authority and industrial partners, various city. OGD is further developed according to the “Open by measurement methods are being evaluated for already laid Default’’ principle. Since 2012, the City of Zurich has been utilities where the location or depth is uncertain or no use- providing data from public administration free of charge, ful information is available. In addition to the measurement machine-readable and under a free licence. An OGD policy methods, new modelling approaches (Yan et al. 2019) are and guidelines have been issued, made binding city-wide also being explored. Also, an exchange platform DUCon- and put into effect. The OGD Internet Portal contains the nect has been created to share and discuss experiences Open Data Catalogue as well as information on handling worldwide. of open data, application examples and further information about Open Data. End of 2018, the terrain model, block 4.3 More Detailed Models model and roof model were also published on the OGD plat- form. This upshift was accompanied by a media conference. The FCL Virtual Singapore project investigates methods to From the media conference on 12 November 2018 until model 3D building data more realistically. The focus is on 20 September 2019, a total of 11,722 data sets were down- the efficient modelling of façades on the basis of existing loaded from the OGD portal (Fig. 4). The five data sets of roof models. Using different raw data from the latest technol- the 3D spatial data (Fig. 4) already correspond to about one- ogies and methods (such as laser scanning, photogrammetry) third of all downloads in this period. This makes 3D spatial data the most frequently used data of this portal. Geodata in 1 3 104 PFG (2020) 88:99–112 Fig. 3 Data levels and exten- sions of the digital twin: street space, trees, archaeological objects, underground, power lines, BIM model, bridges (source: City of Zurich) Fig. 4 The five most down- loaded data sets on the OGD portal of the City of Zurich are 3D spatial data (source: City of Zurich) 1 3 PFG (2020) 88:99–112 105 general were downloaded 7422 times. This corresponds to the most prominent locations such as the Grossmünster, the about 65% of the downloads. old town hall and the Fraumünster has been erected. The free access of administrative data simplifies the use After a development period of about 7 months, the team enormously. This opens up new value creation opportuni- was able to release “(re)format Z:” in November 2017. ties for private individuals and the cooperation of project Thanks to the interesting setting, 25,000 downloads have partners. In addition, reliable digital data is an indispensa- been made within 3 weeks and the first place on the “Top ble basis for new business models, such as start-ups around Free Puzzle Games” list in the App Store has been reached. the Internet of Things, Smart City solutions, location-based At the beginning of 2019, 100,000 downloads and 24,500 h gaming worlds, etc. of total playing time were reached worldwide. At the end of 2019, the game will still receive around 80,000 impressions 5.2 Open Government Data Application per week in the App Store. A first successful application of the component 3D build-5.3 Geoportal ing of the digital twin of the city was realized by the com- pany Blindflug Studios with the game “(re)format Z:”, a The Geoportal simplifies the collection and assembly of spa- game about the Reformation in Zurich (Fig. 5). The history tial data. The desired topics can be selected for certain areas of the Reformation is embedded in a dystopian cyberpunk and then automatically requested. Currently, more than 200 version of the city. In this way, people who would oth- spatial data sets are available in raster and vector format. erwise not be interested in the topic are to be addressed. The geoportal enables the systematic and automated It has been decided to create the game in 3D as this is viewing of all geodata on the Internet. Also, the automated the best choice for an immersive experience. To be able to update of data and metadata and the connection to the OGD complete the project “(re)format Z:” within a short time- portal are guaranteed. The customer can order not only urban frame and to ensure that an accurate representation of the but also canton’s data via a “Single Point of Contact”. The city is created, the 3D buildings of the City of Zurich have geoportal is online since the end of 2019 (GeoPortal 2019). been used. The model contained the external shape of the houses including the roofs and the elevation data of the 5.4 Zürich Virtuell (Virtual Zurich) ground. A high degree of detail was to be achieved. The building Virtual Zurich opens a window (viewer) on the digital twin. data have been used as a basis. The detailed version has The viewer is intended to facilitate the visualization of 3D been created directly on the model, with a newly developed components. In the future, the 3D models can be viewed and system, which allows the multiple reuse of elements such as used interactively in the Intra- and Internet via a web inter- windows and doors. With the “toolbox” of about 100 indi- face (Fig. 6). The requirements of the GIS City of Zurich are vidual components the centre of Zurich’s old town, including incorporated into the implementation. In addition to public access, there will also be exclusive rooms. These exclusive Fig. 5 Excerpts from the game “re(format) Z:” and develop- ment tools (source: Blindflug Studios) 1 3 106 PFG (2020) 88:99–112 Fig. 6 Zürich virtuell: preview of the new window on the digital twin (source: City of Zurich) rooms can be used, for example, to visualize construction 6 Applications projects and make them available to a selected group of peo- ple. At the moment the technical implementation is in pro- Over the last 10  years, 3D spatial data have become gress and the viewer will go online in Q1 of 2020. increasingly established as a solution for spatial tasks. Like many other cities, Zurich uses its virtual city model in the areas of environment (e.g. noise, air pollution and Fig. 7 Established applications: noise (upper left), air pollution (upper centre), mobile phone radiation (upper right), solar potential (lower left), visualization of construction projects (lower right) (source: City of Zurich) 1 3 PFG (2020) 88:99–112 107 mobile phone radiation modelling), energy (e.g. solar for high-quality spatial development are being met. The potential analyses), urban planning (visualization of con- planning horizon for the municipal development plan is struction projects, shadow and visibility analyses) and in 20–25 years. other areas (Fig.  7). These applications are now estab- Various basic principles such as guidelines and concepts lished and described in detail, e.g. in “Applications of were created for the development of the municipal structure 3D City Models: State of the Art Review” (Biljecki et al. plan. For the visualization of a desired spatial development 2015). In the following, therefore, novel, still little-used in the first phase of the development of the municipal struc- applications of digital twins are described using the exam- ture plan, various urban development studies were developed ple of the City of Zurich with a focus on urban planning. and presented in a digital three-dimensional model. These 3D models of different parts of the City of Zurich 6.1 Municipal Development Plan (Kommunale essentially contained the following three data levels: the Richtplanung) current building development (from the digital twin), the maximum building capacity according to the current zoning The City of Zurich is growing. According to predictions, by (from a parametric model of the Esri City Engine) and pos- 2040 about 100,000 or 25% more people could live within sible target images in the form of various compaction sce- the city limits. The demand for space not only for living narios (from urban development drafts). The visualization of and working space, but also for infrastructure as well as the 3D model in an interactive web application enabled the open spaces and green spaces is therefore increasing. With planners of the city administration to make a vivid compari- the first development of the “Municipal Structure Plan son of these levels and served as a valuable basis for discus- for Settlements, Landscape, Public Buildings and Facili- sion (Fig. 8). Thanks to the linking of the geometric data ties” (Richtplan 2018), which is binding on the authorities, with various planning parameters (e.g. building utilisation, the City of Zurich is demonstrating how the requirements floor space, number of inhabitants and workplaces), analyses could also be carried out and quantitative statements derived from the 3D models. These data subsequently formed the basis for the devel- opment of the municipal development plan. To illustrate and deepen its contents, a WebViewer was also created in which the various contents of the municipal planning can be combined. 6.2 High‑Rise Planning Zurich is growing and developing. Because of the current growth predictions, the Office for Urban Development of the City of Zurich intends to update the valid high-rise guide- lines and the high-rise areas defined in the building and Fig. 8 Urbanization study (source: City of Zurich) Fig. 9 Web-based 3D applica- tion of the high rises (source: City of Zurich) 1 3 108 PFG (2020) 88:99–112 zoning regulations. In a two-stage procedure, interdiscipli- nary project teams are investigating the future development of high-rise buildings in the City of Zurich. As part of this process, the Urban Planning Office cre- ated a 3D interactive application on the Internet (Fig.  9). It shows all existing and planned high rises of the city in a temporal-spatial model. The 3D map is based on an applica- tion from New York City, NY, U.S., whose program code is “Open Source” and could be adapted for Zurich with lit- tle effort. The most important data basis of the application is the digital twin. It provides the spatial representation of the high-rises in 3D. Thanks to intelligent linking with a building database, it was also possible to make the years of construction of all high-rise buildings available. The application is freely available on the Internet at Hochhaus-Viewer (2018). For those involved in the project, further planning-relevant data can be activated via login and planning drafts can be visualized directly in the three-dimen- sional model and checked for urban development. 6.3 Urban Climate Urban areas are considered particularly sensitive to the Fig. 10 Temperature analysis of a building study. (source: City of effects of climate change. Projects such as “Cooling Singa- Zurich) pore” (2017) try to explore holistic planning solutions and develop various strategies. According to the “Climate Sce- narios for Switzerland” (CH2018 2018), an average of 21 micro-scale climate models, the obstacle effect of planned buildings could be determined and compared with the cur- heat-days is expected for the City of Zurich in 2060; today it has an average of 6 heat-days. Those and tropical nights rent development. The analysis has shown that, depending on the spatial characteristics (length, width, height, posi- can lead to health problems, especially for sensitive groups such as the elderly, weakened people and children. Since the tion), new buildings have a provable influence on climate- ecologically relevant factors such as temperature (Fig. 10), influence of the City of Zurich on global climate change is limited, adaptation measures for the urban climate must be wind and cold air volume flow. Thanks to reliable data from the digital twin, climate implemented to counteract local overheating. Climate adap- tation is therefore one of the most important new challenges issues can now be better integrated into the planning deci- sion-making process. Together with other factors such as for urban development. Zurich is responding to the consequences of climate noise, traffic, urban planning, etc., the climate is establishing itself as an additional basis for decision-making in planning change with its considerations on climate adaptation and the “Sectoral Planning on Heat Reduction”, which will be pub- procedures. In Zurich, the results of GIS-supported climate studies will now be used, for example, for variant decisions lished in 2020. Measures to maintain and improve the cool- ing of the city are one of the focal points. Due to its location on public-sector construction projects. In addition to the cur- rent development, the City of Zurich has therefore recently on the lake and its topography, Zurich has a well-functioning cold air system. The thermal load of the bottom of the valley integrated construction planning into the digital twin, thus making it optimally usable for applications such as climate of the city is reduced at night by the influx of cool air from the surrounding hills. In areas with distinctive cold air cor- analyses. ridors, the orientation, extent and height differentiation of buildings are decisive for good ventilation of the city.6.4 Architectural Competitions As part of the “Sectoral Planning Heat Reduction”, the effects of planned buildings on the city’s cold air flows were In architecture and urban planning, competitions are held to find the optimal design for an idea or a concrete plan- analysed for selected urban areas. The analysis was carried out with a GIS-based 3D model, which was built with vari- ning task. In its long tradition, the architectural competition has contributed to a high and sustainable building culture. ous data of the digital twin (terrain, existing and planned buildings, tree locations, etc.). On the basis of meso- and The City of Zurich has been supporting and cultivating 1 3 PFG (2020) 88:99–112 109 this tradition for many years. The Office for Building Con- struction (Amt für Hochbauten) organises an average of ten competitions each year for new construction projects in the public sector and for non-profit property developers. Architectural competitions have been held in analogue form for years. Although all participating architectural firms now draw their plans digitally on the computer, they must print them out and submit them together with a model. The jury’s assessment of the entries will be based exclusively on the plans printed on paper and the physical models. With the ongoing digitization of administrative processes and the increasingly digital way of working in architectural offices, Fig. 12 Augmented reality application with design from an architec- this completely analogue process flow is being questioned ture competition (source: City of Zurich) by many participants. The Office for Building Construction is carrying out of digital design and real environment. The jury can thus pilot projects to examine the implementation of competi- tive projects with the support of digital tools. The focus of compare the volumetric of the contributions in the context of their environment and let them work on themselves. The this digitization effort is the phase of the judging process. Two new digital tools, based on the digital twin, will support use of AR in architecture and other areas of application will further expand the use of the digital twin. the evaluation of the submitted designs. In the first tool, the participants will be provided with a web-based 3D map in Digital support for further steps in the competition pro- cedure will also be examined. This includes: the digital sub- which the 3D model of the competition entry will be checked and submitted later (Fig. 11). This 3D map with integrated mission of all planning-bases in 3D from the digital twin to the participants, the submission of the digital models as a contribution is projected onto a screen during the judging process. To form an opinion, the jury can jointly view the simple BIM model, the computer-aided preliminary exami- nation of the models and the fulfilment of the volumetric individual models, change perspectives, change scales, com- pare designs synchronously in perspective and, if necessary, guidelines (Raumprogramm) by the competition organiser, the creation of simulations (e.g. the effect on the urban cli- display spatial data such as construction lines (Baulinien). The second digital tool is an Augmented Reality (AR) mate), the communication of the results with interactive web models and the integration of the winning project into the application. With the help of the HoloLens AR glasses, the designs and their extensive surroundings are projected digital twin. from the digital twin as an interactive 3D hologram into the judging room. Drafts can be compared, shadows simulated, 6.5 Digital Participation in Urban Planning Procedures spatial data switched on, scales changed and cross-sections generated. It will be examined whether this application can The digital twin opens up new opportunities for the city replace the use of physical models in the long term. The AR application also allows the visualization of the drafts on administration to win over the population for active partici- pation in planning. One of these possibilities is the block- site on a scale of 1:1 (Fig. 12). This leads to a visual fusion buster computer game “Minecraft”, where players create their own world from different “dice”. The game has already been used in other cities to attract younger people in particu- lar to participatory processes. In workshops, schools or at home, young people develop their own ideas, for example of a new neighbourhood centre, and submit them to the city as an idea. On a trial basis, the Office for Urban Development (Amt für Städtebau) has transformed parts of Zurich into a Minecraft world on the basis of the digital twin to test the applicability for future participation procedures (Fig. 13). A web-based, interactive 3D tool was used to test another form of digital participation within the city (Fig. 14). The tool shows the complete city in the browser based on the digital twin and is based on the Java Script API from Esri. Fig. 11 Web-based 3D application with design from an architecture In addition to the usual navigation functions, the application competition (source: City of Zurich) 1 3 110 PFG (2020) 88:99–112 7 Further Developments and Open Questions The following actions will be launched to improve the exist- ing digital twin of the City of Zurich: • generate more and better inter-connected 3D data faster updating of existing data • systematic recording of urban furniture better interconnection of the BIM and GIS world • detection and maintenance of the underground parts of the building • building a 3D utility cadaster. Fig. 13 Replica of the Zurich-Affoltern district in the computer game “Minecraft” (source: City of Zurich) For the modelling of the subsurface, in particular the 3D Utility Cadaster, there is no specification or a common understanding from involved stakeholders what is possible today and what representation makes sense in future? In addition, there are no corresponding jointly developed guidelines at cantonal and federal level for the modelling, recording and updating of 3D geodata. How the worlds of BIM (Building Information Model- ling) and GIS will converge? There are no practical concepts of how the two worlds will meet, where they will remain different and where they will have to interact better with each other (level of detail, automatic generalization, mutual data exchange). The amount of data (memory) and the time required for Fig. 14 Testing of the map-based participation tool by test persons preparation and processing in 3D increase. How to update (source: City of Zurich) and maintain the digital twin in the most efficient way? The “CityGML” standard, the used data model, enables offers a wide range of simple design tools. Within the plan- any modelling of urban objects. In our implementation, how- ning area, users can design their ideas by drawing, with just ever, we do not use all the possibilities of this data model. a few mouse-clicks, for instance buildings, development How to use this existing data model in a sustainable and areas, green spaces or trees, and then submitting the finished efficient way? model to the city administration. More and more point cloud data appear through mobile An use case with test persons without a planning back- mapping. How to take advantage of this data to refine the ground and without special computer affinity has shown that façade of existing block models? How to integrate point the tool is easy and intuitive to use despite its third dimen- cloud models of e.g. vegetation into the digital twin? sion and allows playful access to the topic of urban plan- ning. The offer is very low-threshold, since only a computer with Internet access and browser is needed. Participation 8 Conclusion can be convenient and time independent from home. The obstacle to active participation is thus smaller than with The digital twin is the spatial, digital model of the City of conventional participation procedures, where a presence at Zurich for different themes. The existing spatial data infra- an event organised by the city administration at a certain structure is enriched and described with 3D spatial data and time is required. With digital applications, it could be pos- their models. The processes of construction and tracking sible to encourage more citizens to actively participate and are described holistically for the spatial data, the models thus further increase the acceptance of planning projects. and the metadata. The 3D spatial data will be the reference Whether and how Minecraft or the web-based tool will be for further spatial data and data. 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The Digital Twin of the City of Zurich for Urban Planning

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Springer Journals
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Copyright © The Author(s) 2020
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2512-2789
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2512-2819
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10.1007/s41064-020-00092-2
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Abstract

Population growth will confront the City of Zurich with a variety of challenges in the coming years, as the increase in the number of inhabitants and jobs will lead to densification and competing land uses. The tasks for the city administration have become more complex, whereas tools and methods are often based on traditional, static approaches while involving a limited number of citizens and stakeholders in relevant decisions. The digital transformation of more and more pieces of the planning and decision-making process will make both increasingly more illustrative, easier to understand and more comprehensible. An important data basis for these processes is the digital twin of the City of Zurich. 3D spatial data and their models trans- form themes of the city, such as buildings, bridges, vegetation, etc., to the digital world, are being updated when required, and create advantages in digital space. These benefits need to be highlighted and published. An important step in public awareness is the release of 3D spatial data under Open Government Data. This allows the development of applications, the promotion of understanding, and the simplification of the creation of different collaborative platforms. By visualization and analysis of digital prototypes and the demonstration of interactions with the built environment, scenarios can be digitally developed and discussed in decision-making bodies. Questions about the urban climate can be simulated with the help of the digital twin and results can be linked to the existing 3D spatial data. Thus, the 3D spatial data set, the models and their descriptions through metadata become the reference and must be updated according to the requirements. Depending on requirements and questions, further 3D spatial data must be added. The description of the 3D spatial data and their models or the lifecycle management of the digital twin must be carried out with great care. Only in this way, decision processes can be supported in a comprehensible way. Keywords Digital twin · Digital transformation in urban planning · Densification · Urban climate · Architectural competition · Participation Zusammenfassung Das Bevölkerungswachstum stellt die Stadt Zürich in den kommenden Jahren vor vielfältige Herausforderungen, denn die Zunahme von Einwohnerinnen und Einwohnern sowie von Arbeitsplätzen führt unter anderem zu einer Verdichtung und konkurrierenden Nutzungen. Die Aufgaben für die Stadtverwaltung sind komplexer geworden, wohingegen die Werkzeuge und Methoden oft auf traditionellen, statischen Ansätzen beruhen und eine begrenzte Anzahl von Bürgern und Interessen- gruppen in relevante Entscheidungen einbeziehen. Durch Digitalisierung von Schritten in der Planung wird der planerische Prozess inklusive der Entscheidungsfindung ins Digitale transformiert und damit immer anschaulicher, verständlicher und nachvollziehbarer. Eine wichtige Datengrundlage für diese Prozesse ist der Digitale Zwilling der Stadt Zürich. Er bildet durch 3D Geodaten und deren Modelle Themen der Stadt, wie Gebäude, Brücken, Vegetation, usw., räumlich in der digitalen Welt ab, wird je nach Bedarf mit unterschiedlicher Frequenz nachgeführt und schafft Vorteile im digitalen Raum. Diese Vorteile müssen aufgezeigt und bekannt gemacht werden. Ein wichtiger Schritt dazu ist die Veröffentlichung von 3D Geo- daten unter Open Government Data. Damit können Anwendungen kreiert werden und das Verständnis gefördert bzw. der Aufbau von unterschiedlichen Kollaborationsplattformen wird vereinfacht. Mit der Visualisierung und Analyse von Digitalen Prototypen und Aufzeigen von Wechselwirkungen mit dem bebauten Umfeld können Szenarien digital entwickelt und in * Gerhard Schrotter gerhard.schrotter@zuerich.ch Public Administration, City of Zurich, Zurich, Switzerland Vol.:(0123456789) 1 3 100 PFG (2020) 88:99–112 Entscheidungsgremien diskutiert werden. Fragestellungen zum Thema Stadtklima können mithilfe des Digitalen Zwillings simuliert werden und Ergebnisse wiederum an die bestehenden 3D Geodaten angeknüpft werden. Damit wird der 3D Geoda- tensatz, die Modelle und deren Beschreibungen in Form von Metadaten zur Referenz und diese müssen, den Anforderungen entsprechend, nachgeführt werden. Je nach Bedarf und Fragestellung müssen weitere 3D Geodaten hinzugefügt werden. Die Beschreibung der 3D Geodaten und derer Modelle bzw. das Lifecycle-Management des Digitalen Zwillings müssen mit hoher Sorgfalt vorgenommen werden. Nur so können Entscheidungsprozesse nachvollziehbar unterstützt werden. Schlüsselwörter Digitaler Zwilling · Digitale Transformation in der Stadtplanung · Verdichtung · Stadtklima · Architekturwettbewerb · Partizipation One of the six sub-programmes of the Digital City (Fig. 1), an important lighthouse project of the Smart City Zurich, is the so-called digital twin of the City of Zurich: 1 Environment and Strategies the digital, spatial image. The City of Zurich, like Helsinki (2019), Munich (München 2018) and Rotterdam (2019), has The Canton of Zurich expects an increase of the population opted for this terminology. Other cities such as Singapore by 280,000 people by the year 2040. According to the can- are striving for a digitalization of reality and platforms for ton’s guidelines, 80% of this growth shall take place in urban accessing and designing applications with the name Virtual regions to conserve the scarce resource of land. Accord- Singapore (2018). The term digital twin creates a proximity ing to those scenarios, around 520,000 people could live to the construction and real estate industry and thus builds within the city limits of Zurich in 2040, and the number of a bridge to the new developments in the field of Building jobs will increase accordingly. This growth will confront the Information Modelling (BIM; BauenDigital 2019) and digi- City of Zurich with many challenges in the coming years, tal transformation in the construction industry. Although the as the increase in the number of inhabitants and jobs will term is used there for a single building only, the mental bow have positive and negative effects. The city benefits from the can be made to further infrastructure and to the urban space increase in importance and diversity, from more economic itself. The ultimate goal is a digital representation of the and cultural innovations. At the same time, the competition city to simulate issues such as urban planning in climate of land uses will increase more and more. The densifica- change. For this purpose, components of the digital twin tion of the existing residential areas under consideration of must be updated with different intervals and, where appro- quality standards is, therefore, the main task. The grown priate, enriched with real-time data. In the triangle of the identity and individuality of the urban quarters should be real (physical), social and digital world, the digital twin con- preserved. In addition, noise and usage conflicts must be nects the real world with the digital world or, more precisely, minimized. In the context of sustainable growth, the chal- its space. Thus, in addition to the “traditional” link between lenges and strategic objectives have been described and set social and physical space and the link between social and out in the Strategies Zurich 2035 (2015). With the strategy focus Digital City (2019), the city coun- cil strengthens and accelerates the digital transformation in the city administration. The focus Digital City supports the strategy Smart City Zurich (2018). It uses the opportunities of digitisation to the benefit of the population, the companies and the city administration. For the City of Zurich, smart means networking people, organisations and infrastructures in such a way that social, ecological, and economic benefit will be created. The networking of data, sensors and applica- tions allows new and more efficient solutions for the users of urban infrastructures as well as for their operators. The good networking strengthens participation opportunities for the citizens and their contact with the administration. Numerous projects in various areas have already been imple- mented or are being planned. Smart City Zurich provides a common framework for these ongoing activities and planned measures. Fig. 1 Strategic focus Digital City with the six sub-programmes (source: City of Zurich) 1 3 PFG (2020) 88:99–112 101 digital space—supported by e.g. social media—this new link Thus, the digital terrain model, over 50,000 buildings is emerging (Rotterdam 2019). The digital twin opens up in various levels of detail as well as walls and bridges are new perspectives for urban planning. The new applications available. The 3D spatial data are mainly used in the city bring more understanding, more targeted questions and thus administration in the fields of environmental and urban comprehensible answers to future-relevant topics. planning or submitted as a subset to third parties for visu- alization of planned construction projects. The require- ments for content, accuracy, tracking and reliability have 2 History: The 3D City Model been developed in collaboration with various service departments of the City of Zurich. This collection of 3D The first experiments with spatial data  were carried spatial data is summarized under the term 3D city model out with ETH Zurich as early as the 1990s. The defini- (Stadtmodell 2019) (Fig. 2). tive, so-called 3D city model was created in 2011. ETH Zurich, Fachhochschule Nordwestschweiz and TU Munich were involved in the development. Vari- 3 Digital Twin for the City of Zurich ous agencies  of  the public  administration have bun- dled their forces. The GIS Competence Centre of the The digital twin is a spatial, digital model of the City of Department of Building and Planning  and  the GIS Zurich for different themes. It extends the existing spatial Centre for Geomatics + Surveying have launched the data infrastructure with 3D spatial data and their models and first draft. The digital ter rain model (LoD0), the block describes it. The focus is on 3D spatial data and it becomes model (LoD1), and the roof model (LoD2) are avail- the reference to consequently link spatial and other data. able in the reference system CH1903 + (reference frame The processes, the data acquisition and update, are fully LV95/EPSG 2056). described for the 3D spatial data, the models and the meta- The terrain model is based on the grid file of the Canton data. As a consequence, the processes in cadastral and engi- of Zurich, generated from LIDAR images from 2014 with neering surveying must also be adapted, meaning that the a resolution of 50 cm. In bridge areas, additional break third dimension must be taken into account when digitizing lines were recorded. Manual adjustments were made in space and performing further processing. areas of Lake Zurich and the Limmat. The road geom- Spatial data, spatial data models, and spatial metadata etries of the official cadastral survey were additionally are defined by the Federal Act on Geoinformation (GeoIG introduced as break lines. The irregular triangular mesh 2007), and have been described in detail. The Act is fully was calculated by FME with the tolerances of 1 m and “Infrastructure for Spatial Information in the European 0.1 m. The mean height error is 30–40 cm. The basic data Community” (INSPIRE) compliant and even goes beyond set dates back to 2014. the INSPIRE Directive, although it is not an actual transpo- The block model is based on the real and planned sition of the Directive, since Switzerland is not an EU Mem- building floor plans of the official cadastral survey, the ber State. Compared to other European countries there was height of which is below the terrain. The heights of eaves a formal Spatial Data Infrastructure in place in Switzerland and gables determined by photogrammetry are assigned before the implementation of INSPIRE (Crompvoets et al. as attributes to the floor plans. In buildings with a high 2018) and based upon the Federal Act on Geoinformation a recognition factor and striking differences in height, the solid governance framework has been developed. f loor plans are subdivided so that the buildings are repre- The Act on Geoinformation describes 3D spatial data sented by several prisms of different heights. In addition as the extension and characteristics of certain spaces and to the buildings, the 3D block model contains striking bridges. The mean position error is within the limits of the official cadastral survey and amounts to 10–15 cm and the mean height error amounts to 50 cm. The data set is continuously updated. The roof model consists of the walls and detailed roof structures of the buildings. Analogous to the block model, the building floor plans serve as the basis for the official cadastral survey. The evaluation of the roofscape takes place by means of semi-automatic stereo aerial photo- grammetric evaluation. In addition to the buildings, the model contains striking bridges and walls. Fig. 2 3D city model with terrain, block and roof model (source: City of Zurich) 1 3 102 PFG (2020) 88:99–112 objects, in particular their location, condition, use and legal The predictive modelling and the reactive modelling, imme- relationships, with a certain reference to time. The spatial diate action in both digital and real space, are described in data models are representations of reality, which determine Wildfire (2018). In predictive modelling, a distinction is structure and content independent of a specific spatial data made between iterative feedback and sandbox testing. This system. The formal descriptions of the characteristics of means that the most diverse simulations and scenarios in spatial data are based on metadata, such as origin, content, the digital world can be enriched, created and analysed with structure, validity, timeliness, accuracy, usage rights, access empirical values from reality. This is described in Grieves options or processing methods. Metadata are an essential (2014) under the term of digital prototypes and the environ- component for establishing and operating a geodata infra- ment of the digital twin. structure. Without metadata no valid decisions and actions For the City of Zurich, the digital twin means a consistent can be derived from geodata. Even a proper search for spe- enrichment of the 3D spatial data inventory and, in addi- cific geodata cannot be done without proper metadata. Geo- tion to the modelling and description of the data, a lifecycle cat (GeoCat 2019) is the metadata catalogue for Swiss spa- management of the individual components as well as the tial data. Federal offices, cantons, municipalities and private entire data inventory. The 3D spatial data are the basis for companies record the data. linking further spatial data or other data. Where appropriate, The concept of the digital twin according to Grieves elements from reality are linked to the digital world in real (2014) originates from the product lifecycle management. If time. The processes for digitizing reality are extended by this concept is applied to spatial data, models and metadata, the third dimension. then these can be described on the basis of a product life The developments are managed by the GIS City of Zurich cycle. The product life cycle describes the sum of the indi- (GIS Stadt Zürich) and implemented together with the part- vidual phases through which a product passes along the time ners (25 service departments of the City of Zurich). Almost dimension. Therefore, in addition to the detailed description 20 years ago, the need for coordination in the field of spatial of the spatial data and the spatial data models (via meta- information in the city was recognised. As a result, com- data), their life cycle is also described. Thus, the develop- prehensive spatial information projects were jointly imple- ment of different components of the digital twin (buildings, mented, thus laying the foundation for the urban spatial data roads, etc.) can be digitally planned and updated, and can infrastructure (SDI). In 2009, the City Council approved the be renewed or maintained on the basis of a defined interval. comprehensive strategy for GIS City of Zurich (GIS Stadt Updates may happen in short intervals and this may, but Zürich). In 2019, the strategy was revised again or adapted does not have to, be related to the so-called High-Frequency to the new challenges (GISStrategie 2019). and Low-Frequency City (Batty 2018; Wildfire 2018). Even With the expansion of the geodata infrastructure and the in a Low-Frequency City, elements which in reality undergo technical platform, the digital twin can be used for location- rapid changes and contain time-critical information (e.g. by based cooperation with internal and external partners. For means of real-time sensors) are to be linked to the digital example, planned real estate projects or urban development world. scenarios can be integrated. The data also offer optimal con- Vivid examples can be observed in the construction ditions for presentation, discussion and the shaping of the and real estate sectors (DigitalTwinCMU 2019). There, public space. The basis for various analyses and calculations construction processes and then maintenance are digitally such as visibility, noise propagation and solar potential anal- mapped using 3D spatial data and a building model as a yses, shadow calculations, flood simulations, etc. is created. digital replica that shows the structure and behaviour of a building with interactive connections to the physical object. The interactive connections transmit information such as 4 Planned, Selected Extensions status, usage or analysis data as well as control commands. Depending on the level of detail and automation as well as Due to new requirements of the service departments of the the type of connections and information, this component of City of Zurich, coordinated by the GIS City of Zurich (GIS the digital twin can reach different characteristics. It thus Stadt Zürich), projects are carried out which extend the data- depicts the structural and operational conditions of a real base. These data are then made available again and enable building over time. It can depict an existing building or one new applications. under construction. It is irrelevant whether the counterpart already exists in 4.1 Street Space 3D the real world, will exist in the future (Wikipedia 2019), or perhaps will not be realized at all. The digital prototype is To capture data efficiently or simply to reduce the need built before reality and thus enables predictive modelling. for inspections, the public space of the City of Zurich is 1 3 PFG (2020) 88:99–112 103 captured in three dimensions, integrated into the digital and parametric modelling, geometrically correct façades can twin and made available via an Intranet solution. In autumn be generated and the accuracy or deviation of the models 2020, Geomatics + Surveying will make an imaging ser- from reality can be determined. The process and the detailed vice available to all municipal employees, in which the contents of the research packages can be found under Gruen street space can be re-experienced digitally. In addition, it et al. (2019). will be possible to capture further objects in 3D, to measure Other infrastructure elements such as bridges, high- objects and to visualize existing data. voltage lines, etc. are added to the digital twin as required as additional components. In cooperation with the city and 4.2 Utility Cadastre 3D underwater archaeology, also historical 3D spatial data are constructed. Thus, the history of the city can be experienced Since July 2013, 2D pipelines and cable data (utility cadas- interactively in different time periods. From the first pile tre) of the City of Zurich have been submitted by the util- dwellings through Roman Zurich and the Middle Ages to ity owners to Geomatics + Surveying. The utility owners the present day. The demand is controlled by projects from are the Electricity Service, Energy 360° AG, Disposal and service departments or based on strategic formulations from Recycling Services, Water Supply Service, Public Trans- the GIS City of Zurich (Fig. 3). port Service and telecommunication companies. Most of the utilities have been digitized from continuously updated plans. The position accuracy is in the range of ± 20 cm. Pipe- lines and cables, e.g. due to construction work are marked 5 Enabler as inaccurate. The utility cadastre of the City of Zurich is a subset of the digital documentation of the work manage- To make the digital twin known, it is necessary that the ment of the utility owners. At least once a week, the pipeline data sets are made available as Open Government Data. and cable owners automatically deliver the new data to the This results in initial visualizations and analyses as well register operator (Geomatics + Surveying). The suppliers as economically profitable applications. In addition, the remain responsible for the content of the data (punctual- large amounts of data must be visualized (Zürich virtuell) ity, completeness, position accuracy, etc.). The operator is and  have to be  easily accessible through an advanced responsible for ensuring that the uploaded data is complete, geoportal. up-to-date (as agreed) and not modified. The utility owners  of the City of Zurich are already recording 3D coordinates today. However, this information 5.1 3D Building and Terrain Data are Open is lost at the interface to the utility cadastre. This gap in the Government Data data flow will soon be closed to enable the delivery of BIM- capable utility cadastral datasets. Simple access and the free use of administrative data, with- In the Digital Underground project (van Son et al. 2018) out the need for specific protection (Open Government Data; at the Singapore-ETH-Centre, in cooperation with the Sin- OGD for short), is part of the basic infrastructure of a digital gapore Land Authority and industrial partners, various city. OGD is further developed according to the “Open by measurement methods are being evaluated for already laid Default’’ principle. Since 2012, the City of Zurich has been utilities where the location or depth is uncertain or no use- providing data from public administration free of charge, ful information is available. In addition to the measurement machine-readable and under a free licence. An OGD policy methods, new modelling approaches (Yan et al. 2019) are and guidelines have been issued, made binding city-wide also being explored. Also, an exchange platform DUCon- and put into effect. The OGD Internet Portal contains the nect has been created to share and discuss experiences Open Data Catalogue as well as information on handling worldwide. of open data, application examples and further information about Open Data. End of 2018, the terrain model, block 4.3 More Detailed Models model and roof model were also published on the OGD plat- form. This upshift was accompanied by a media conference. The FCL Virtual Singapore project investigates methods to From the media conference on 12 November 2018 until model 3D building data more realistically. The focus is on 20 September 2019, a total of 11,722 data sets were down- the efficient modelling of façades on the basis of existing loaded from the OGD portal (Fig. 4). The five data sets of roof models. Using different raw data from the latest technol- the 3D spatial data (Fig. 4) already correspond to about one- ogies and methods (such as laser scanning, photogrammetry) third of all downloads in this period. This makes 3D spatial data the most frequently used data of this portal. Geodata in 1 3 104 PFG (2020) 88:99–112 Fig. 3 Data levels and exten- sions of the digital twin: street space, trees, archaeological objects, underground, power lines, BIM model, bridges (source: City of Zurich) Fig. 4 The five most down- loaded data sets on the OGD portal of the City of Zurich are 3D spatial data (source: City of Zurich) 1 3 PFG (2020) 88:99–112 105 general were downloaded 7422 times. This corresponds to the most prominent locations such as the Grossmünster, the about 65% of the downloads. old town hall and the Fraumünster has been erected. The free access of administrative data simplifies the use After a development period of about 7 months, the team enormously. This opens up new value creation opportuni- was able to release “(re)format Z:” in November 2017. ties for private individuals and the cooperation of project Thanks to the interesting setting, 25,000 downloads have partners. In addition, reliable digital data is an indispensa- been made within 3 weeks and the first place on the “Top ble basis for new business models, such as start-ups around Free Puzzle Games” list in the App Store has been reached. the Internet of Things, Smart City solutions, location-based At the beginning of 2019, 100,000 downloads and 24,500 h gaming worlds, etc. of total playing time were reached worldwide. At the end of 2019, the game will still receive around 80,000 impressions 5.2 Open Government Data Application per week in the App Store. A first successful application of the component 3D build-5.3 Geoportal ing of the digital twin of the city was realized by the com- pany Blindflug Studios with the game “(re)format Z:”, a The Geoportal simplifies the collection and assembly of spa- game about the Reformation in Zurich (Fig. 5). The history tial data. The desired topics can be selected for certain areas of the Reformation is embedded in a dystopian cyberpunk and then automatically requested. Currently, more than 200 version of the city. In this way, people who would oth- spatial data sets are available in raster and vector format. erwise not be interested in the topic are to be addressed. The geoportal enables the systematic and automated It has been decided to create the game in 3D as this is viewing of all geodata on the Internet. Also, the automated the best choice for an immersive experience. To be able to update of data and metadata and the connection to the OGD complete the project “(re)format Z:” within a short time- portal are guaranteed. The customer can order not only urban frame and to ensure that an accurate representation of the but also canton’s data via a “Single Point of Contact”. The city is created, the 3D buildings of the City of Zurich have geoportal is online since the end of 2019 (GeoPortal 2019). been used. The model contained the external shape of the houses including the roofs and the elevation data of the 5.4 Zürich Virtuell (Virtual Zurich) ground. A high degree of detail was to be achieved. The building Virtual Zurich opens a window (viewer) on the digital twin. data have been used as a basis. The detailed version has The viewer is intended to facilitate the visualization of 3D been created directly on the model, with a newly developed components. In the future, the 3D models can be viewed and system, which allows the multiple reuse of elements such as used interactively in the Intra- and Internet via a web inter- windows and doors. With the “toolbox” of about 100 indi- face (Fig. 6). The requirements of the GIS City of Zurich are vidual components the centre of Zurich’s old town, including incorporated into the implementation. In addition to public access, there will also be exclusive rooms. These exclusive Fig. 5 Excerpts from the game “re(format) Z:” and develop- ment tools (source: Blindflug Studios) 1 3 106 PFG (2020) 88:99–112 Fig. 6 Zürich virtuell: preview of the new window on the digital twin (source: City of Zurich) rooms can be used, for example, to visualize construction 6 Applications projects and make them available to a selected group of peo- ple. At the moment the technical implementation is in pro- Over the last 10  years, 3D spatial data have become gress and the viewer will go online in Q1 of 2020. increasingly established as a solution for spatial tasks. Like many other cities, Zurich uses its virtual city model in the areas of environment (e.g. noise, air pollution and Fig. 7 Established applications: noise (upper left), air pollution (upper centre), mobile phone radiation (upper right), solar potential (lower left), visualization of construction projects (lower right) (source: City of Zurich) 1 3 PFG (2020) 88:99–112 107 mobile phone radiation modelling), energy (e.g. solar for high-quality spatial development are being met. The potential analyses), urban planning (visualization of con- planning horizon for the municipal development plan is struction projects, shadow and visibility analyses) and in 20–25 years. other areas (Fig.  7). These applications are now estab- Various basic principles such as guidelines and concepts lished and described in detail, e.g. in “Applications of were created for the development of the municipal structure 3D City Models: State of the Art Review” (Biljecki et al. plan. For the visualization of a desired spatial development 2015). In the following, therefore, novel, still little-used in the first phase of the development of the municipal struc- applications of digital twins are described using the exam- ture plan, various urban development studies were developed ple of the City of Zurich with a focus on urban planning. and presented in a digital three-dimensional model. These 3D models of different parts of the City of Zurich 6.1 Municipal Development Plan (Kommunale essentially contained the following three data levels: the Richtplanung) current building development (from the digital twin), the maximum building capacity according to the current zoning The City of Zurich is growing. According to predictions, by (from a parametric model of the Esri City Engine) and pos- 2040 about 100,000 or 25% more people could live within sible target images in the form of various compaction sce- the city limits. The demand for space not only for living narios (from urban development drafts). The visualization of and working space, but also for infrastructure as well as the 3D model in an interactive web application enabled the open spaces and green spaces is therefore increasing. With planners of the city administration to make a vivid compari- the first development of the “Municipal Structure Plan son of these levels and served as a valuable basis for discus- for Settlements, Landscape, Public Buildings and Facili- sion (Fig. 8). Thanks to the linking of the geometric data ties” (Richtplan 2018), which is binding on the authorities, with various planning parameters (e.g. building utilisation, the City of Zurich is demonstrating how the requirements floor space, number of inhabitants and workplaces), analyses could also be carried out and quantitative statements derived from the 3D models. These data subsequently formed the basis for the devel- opment of the municipal development plan. To illustrate and deepen its contents, a WebViewer was also created in which the various contents of the municipal planning can be combined. 6.2 High‑Rise Planning Zurich is growing and developing. Because of the current growth predictions, the Office for Urban Development of the City of Zurich intends to update the valid high-rise guide- lines and the high-rise areas defined in the building and Fig. 8 Urbanization study (source: City of Zurich) Fig. 9 Web-based 3D applica- tion of the high rises (source: City of Zurich) 1 3 108 PFG (2020) 88:99–112 zoning regulations. In a two-stage procedure, interdiscipli- nary project teams are investigating the future development of high-rise buildings in the City of Zurich. As part of this process, the Urban Planning Office cre- ated a 3D interactive application on the Internet (Fig.  9). It shows all existing and planned high rises of the city in a temporal-spatial model. The 3D map is based on an applica- tion from New York City, NY, U.S., whose program code is “Open Source” and could be adapted for Zurich with lit- tle effort. The most important data basis of the application is the digital twin. It provides the spatial representation of the high-rises in 3D. Thanks to intelligent linking with a building database, it was also possible to make the years of construction of all high-rise buildings available. The application is freely available on the Internet at Hochhaus-Viewer (2018). For those involved in the project, further planning-relevant data can be activated via login and planning drafts can be visualized directly in the three-dimen- sional model and checked for urban development. 6.3 Urban Climate Urban areas are considered particularly sensitive to the Fig. 10 Temperature analysis of a building study. (source: City of effects of climate change. Projects such as “Cooling Singa- Zurich) pore” (2017) try to explore holistic planning solutions and develop various strategies. According to the “Climate Sce- narios for Switzerland” (CH2018 2018), an average of 21 micro-scale climate models, the obstacle effect of planned buildings could be determined and compared with the cur- heat-days is expected for the City of Zurich in 2060; today it has an average of 6 heat-days. Those and tropical nights rent development. The analysis has shown that, depending on the spatial characteristics (length, width, height, posi- can lead to health problems, especially for sensitive groups such as the elderly, weakened people and children. Since the tion), new buildings have a provable influence on climate- ecologically relevant factors such as temperature (Fig. 10), influence of the City of Zurich on global climate change is limited, adaptation measures for the urban climate must be wind and cold air volume flow. Thanks to reliable data from the digital twin, climate implemented to counteract local overheating. Climate adap- tation is therefore one of the most important new challenges issues can now be better integrated into the planning deci- sion-making process. Together with other factors such as for urban development. Zurich is responding to the consequences of climate noise, traffic, urban planning, etc., the climate is establishing itself as an additional basis for decision-making in planning change with its considerations on climate adaptation and the “Sectoral Planning on Heat Reduction”, which will be pub- procedures. In Zurich, the results of GIS-supported climate studies will now be used, for example, for variant decisions lished in 2020. Measures to maintain and improve the cool- ing of the city are one of the focal points. Due to its location on public-sector construction projects. In addition to the cur- rent development, the City of Zurich has therefore recently on the lake and its topography, Zurich has a well-functioning cold air system. The thermal load of the bottom of the valley integrated construction planning into the digital twin, thus making it optimally usable for applications such as climate of the city is reduced at night by the influx of cool air from the surrounding hills. In areas with distinctive cold air cor- analyses. ridors, the orientation, extent and height differentiation of buildings are decisive for good ventilation of the city.6.4 Architectural Competitions As part of the “Sectoral Planning Heat Reduction”, the effects of planned buildings on the city’s cold air flows were In architecture and urban planning, competitions are held to find the optimal design for an idea or a concrete plan- analysed for selected urban areas. The analysis was carried out with a GIS-based 3D model, which was built with vari- ning task. In its long tradition, the architectural competition has contributed to a high and sustainable building culture. ous data of the digital twin (terrain, existing and planned buildings, tree locations, etc.). On the basis of meso- and The City of Zurich has been supporting and cultivating 1 3 PFG (2020) 88:99–112 109 this tradition for many years. The Office for Building Con- struction (Amt für Hochbauten) organises an average of ten competitions each year for new construction projects in the public sector and for non-profit property developers. Architectural competitions have been held in analogue form for years. Although all participating architectural firms now draw their plans digitally on the computer, they must print them out and submit them together with a model. The jury’s assessment of the entries will be based exclusively on the plans printed on paper and the physical models. With the ongoing digitization of administrative processes and the increasingly digital way of working in architectural offices, Fig. 12 Augmented reality application with design from an architec- this completely analogue process flow is being questioned ture competition (source: City of Zurich) by many participants. The Office for Building Construction is carrying out of digital design and real environment. The jury can thus pilot projects to examine the implementation of competi- tive projects with the support of digital tools. The focus of compare the volumetric of the contributions in the context of their environment and let them work on themselves. The this digitization effort is the phase of the judging process. Two new digital tools, based on the digital twin, will support use of AR in architecture and other areas of application will further expand the use of the digital twin. the evaluation of the submitted designs. In the first tool, the participants will be provided with a web-based 3D map in Digital support for further steps in the competition pro- cedure will also be examined. This includes: the digital sub- which the 3D model of the competition entry will be checked and submitted later (Fig. 11). This 3D map with integrated mission of all planning-bases in 3D from the digital twin to the participants, the submission of the digital models as a contribution is projected onto a screen during the judging process. To form an opinion, the jury can jointly view the simple BIM model, the computer-aided preliminary exami- nation of the models and the fulfilment of the volumetric individual models, change perspectives, change scales, com- pare designs synchronously in perspective and, if necessary, guidelines (Raumprogramm) by the competition organiser, the creation of simulations (e.g. the effect on the urban cli- display spatial data such as construction lines (Baulinien). The second digital tool is an Augmented Reality (AR) mate), the communication of the results with interactive web models and the integration of the winning project into the application. With the help of the HoloLens AR glasses, the designs and their extensive surroundings are projected digital twin. from the digital twin as an interactive 3D hologram into the judging room. Drafts can be compared, shadows simulated, 6.5 Digital Participation in Urban Planning Procedures spatial data switched on, scales changed and cross-sections generated. It will be examined whether this application can The digital twin opens up new opportunities for the city replace the use of physical models in the long term. The AR application also allows the visualization of the drafts on administration to win over the population for active partici- pation in planning. One of these possibilities is the block- site on a scale of 1:1 (Fig. 12). This leads to a visual fusion buster computer game “Minecraft”, where players create their own world from different “dice”. The game has already been used in other cities to attract younger people in particu- lar to participatory processes. In workshops, schools or at home, young people develop their own ideas, for example of a new neighbourhood centre, and submit them to the city as an idea. On a trial basis, the Office for Urban Development (Amt für Städtebau) has transformed parts of Zurich into a Minecraft world on the basis of the digital twin to test the applicability for future participation procedures (Fig. 13). A web-based, interactive 3D tool was used to test another form of digital participation within the city (Fig. 14). The tool shows the complete city in the browser based on the digital twin and is based on the Java Script API from Esri. Fig. 11 Web-based 3D application with design from an architecture In addition to the usual navigation functions, the application competition (source: City of Zurich) 1 3 110 PFG (2020) 88:99–112 7 Further Developments and Open Questions The following actions will be launched to improve the exist- ing digital twin of the City of Zurich: • generate more and better inter-connected 3D data faster updating of existing data • systematic recording of urban furniture better interconnection of the BIM and GIS world • detection and maintenance of the underground parts of the building • building a 3D utility cadaster. Fig. 13 Replica of the Zurich-Affoltern district in the computer game “Minecraft” (source: City of Zurich) For the modelling of the subsurface, in particular the 3D Utility Cadaster, there is no specification or a common understanding from involved stakeholders what is possible today and what representation makes sense in future? In addition, there are no corresponding jointly developed guidelines at cantonal and federal level for the modelling, recording and updating of 3D geodata. How the worlds of BIM (Building Information Model- ling) and GIS will converge? There are no practical concepts of how the two worlds will meet, where they will remain different and where they will have to interact better with each other (level of detail, automatic generalization, mutual data exchange). The amount of data (memory) and the time required for Fig. 14 Testing of the map-based participation tool by test persons preparation and processing in 3D increase. How to update (source: City of Zurich) and maintain the digital twin in the most efficient way? The “CityGML” standard, the used data model, enables offers a wide range of simple design tools. Within the plan- any modelling of urban objects. In our implementation, how- ning area, users can design their ideas by drawing, with just ever, we do not use all the possibilities of this data model. a few mouse-clicks, for instance buildings, development How to use this existing data model in a sustainable and areas, green spaces or trees, and then submitting the finished efficient way? model to the city administration. More and more point cloud data appear through mobile An use case with test persons without a planning back- mapping. How to take advantage of this data to refine the ground and without special computer affinity has shown that façade of existing block models? How to integrate point the tool is easy and intuitive to use despite its third dimen- cloud models of e.g. vegetation into the digital twin? sion and allows playful access to the topic of urban plan- ning. The offer is very low-threshold, since only a computer with Internet access and browser is needed. Participation 8 Conclusion can be convenient and time independent from home. The obstacle to active participation is thus smaller than with The digital twin is the spatial, digital model of the City of conventional participation procedures, where a presence at Zurich for different themes. The existing spatial data infra- an event organised by the city administration at a certain structure is enriched and described with 3D spatial data and time is required. With digital applications, it could be pos- their models. The processes of construction and tracking sible to encourage more citizens to actively participate and are described holistically for the spatial data, the models thus further increase the acceptance of planning projects. and the metadata. The 3D spatial data will be the reference Whether and how Minecraft or the web-based tool will be for further spatial data and data. They inter-connect the data used is currently being examined by the city administration and thus the digital space approaches more and more the real within the framework of the strategy focus “Testing Smart world. By describing the data with metadata and introducing Participation” (SmartePartizipation 2018). 1 3 PFG (2020) 88:99–112 111 CS (2017) Cooling Singapore project, Future Cities Lab, Singapore lifecycle management, development and maintenance can ETH-Centre. https ://www .cooli ngsin g apor e.sg/t he-pr oje ct. be planned. The update can take place in real time and for Accessed 12 Oct 2019 certain applications the digital twin is directly connected DigitaleStadt (2019) Strategie-Schwerpunkt Digitale Stadt. Organi- to the real components, e.g. sensors in real space. 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PFG – Journal of Photogrammetry, Remote Sensing and Geoinformation ScienceSpringer Journals

Published: Feb 4, 2020

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