An introduction to the 3D digital city model data management solution CityGRID. From Met GeoInfo, this true 3D RDBMS software provides tools for creation, management and visualisation of 3D city models.
An introduction to CityGRID and the advantages of using a relational database to manage your 3D data.
An Introduction to CityGRID
January 2009 CityGRID 2009 Intelligently Managing your 3D data
City Modelling: What is it? City modelling as a concept in Europe is well established, to the point of almost being a legal pre-requisite for any significant development project. In the UK, the use of massive 3D models is still going through a process of acceptance with only a few key examples (London, Glasgow and Manchester) with others actively investigating. So what are we really talking about? A City Model is the digital representation of an entire city in 3D…
City Modelling: What is it? <ul><li>Level of detail (LoD) 1 – LoD 3… </li></ul>...represented to any Level of Detail (LoD) from: LoD1: a simple block model to LoD3: complex structures with façade detail and texturing. Images: LoD1 – Salzburg, Austria LoD3 – Klagenfurt, Austria LoD3 – Glasgow, UK
City Modelling: What is it? ..to LoD 4 We can even handle interiors. This example is from Wiener Linien who modelled the entire sub-way network of Vienna. Most of the network was constructed before 1989, and no digital records existed. Rather than produce 2D information from hand-drawings, they opted to move straight to 3D, from which they can profile and produce 2D cross-sections at will. Being an underground structure, the exterior is not of interest. The internal layouts and interaction with the city above (shown here integrated with data from the City of Vienna) is vital.
City Modelling: Why? <ul><li>To improve decision making, and </li></ul><ul><li>To save time and money in the decision making process </li></ul><ul><li>Application areas : </li></ul><ul><ul><li>Information management </li></ul></ul><ul><ul><li>Conservation </li></ul></ul><ul><ul><li>Urban planning </li></ul></ul><ul><ul><li>Public consultation </li></ul></ul>But why? Is this nothing more than an expensive computer game? There is a real danger that this is exactly what it could become. The reasons for modelling a city need to be kept in mind and it is important not to let nice graphics distract! The main aim is to save money in the design process and in the long-term management of an asset (be it a city, a sub-way network or a single building). Our clients use the model for a range of applications – but they can be broadly grouped into the four areas listed here:
Information Management 1 Use the model as a record of the built environment. There is no better means of recording the structure and fabric of a city than in 3D. It is more intuitive than a map and certainly more interactive – and this means that it can be used as a baseline for other applications such as disaster management. These images show CityGRID being used live in an emergency command centre (exercise prior to the European Cup). Detailed information of buildings (above and below ground) were relayed to ground teams who otherwise would have been acting blind.
Information Management 2 <ul><li>Solar radiation models </li></ul><ul><li>A collaborative project between Met GeoInfo and EIFER (European Institute for Energy Research) to provide EDF with a predictive model for the: </li></ul><ul><li>Potential location of alternative energy generation units (i.e. solar) on a massive scale, and </li></ul><ul><li>Calculation of energy requirements for heating </li></ul>
Urban Planning 1 Urban Planning is obviously a massive ‘catch-all’ description that covers many issues and disciplines, but we thought we could show you some examples of CityGRID being used actively to assist the decision making process of planners. In this case it is shadow analysis. Not for a ‘right to light’ as we might expect in the UK, but for animal welfare – in particular for assessing the amount of time spent in the shade by Vienna's famous horse-drawn taxi’s. The yellow indicates the taxi-stands!
Urban Planning 2 In this example an Impact Assessment (Visual Intrusion and Line of Site analysis) study is being undertaken on the tower highlighted. This particular development was causing such controversy that it was actually threatening the World Heritage Site status of the city of Vienna. This image illustrated the visual impact of the tower, and with other data, gave the City the justification for imposing the decision that they wanted – i.e. to reduce the height of the development.
Public Consultation 1 <ul><li>Engaging with the entire stake-holder community is now an integral part of any planning process – and the public are a key component of this. They also have real power to influence a development. Therefore it is vital to: </li></ul><ul><li>Engage early in the process, and </li></ul><ul><li>Ensure understanding of what is being proposed. </li></ul><ul><li>CityGRID is used regularly within live public consultation meetings….here for OBB (Austrian State Railways) where CityGRID was used to communicate with communities affected by a new high-speed line... </li></ul>
Public Consultation 2 … or we can interact with the wider community via information booths. This example was a demonstration based on the ESRI ArcExplorer technology for the city of Oslo.
Public Consultation 3 … Or via the WWW, in this case Google Earth. While a useful tool for reaching a mass audience it is typically not preferred for consultation process which generally requires a more ‘controlled’ environment. It would however be a very useful delivery tool for Tourist focused applications.
Public Consultation 4 <ul><li>Solid models: </li></ul>A by-product almost of the model construction method means that our models are ‘water-proof’. This makes the import of the models to solid printing machines very straight-forward. This is what is being done for the City of Zagreb by GeoFoto using CityGRID.
CityGRID: What is it? <ul><li>Creation Management Visualisation </li></ul><ul><li>Input: </li></ul><ul><li>Point Cloud Data </li></ul><ul><li>Aerial Photography </li></ul><ul><li>3D Data Providers </li></ul><ul><li>Output: </li></ul><ul><li>Rendering (stills/video) </li></ul><ul><li>Interactive viewers </li></ul><ul><li>Analysis (2D/3D) </li></ul><ul><li>What is City Modelling? </li></ul><ul><li>We can regard city modelling in 3 distinct stages: </li></ul><ul><li>The creation of the data </li></ul><ul><li>The management tools for handling, manipulating and extracting the value from the data </li></ul><ul><li>The visualisation of the model – the output side of things </li></ul><ul><li>Then CityGRID is a modular suite of tools that gives you the ability to CREATE, MANAGE and OUTPUT your models. </li></ul><ul><li>But our focus is on the Manage element. This is where the value of the model can be delivered. </li></ul>
CityGRID: What is it? The CityGRID modules: CityGRID Manager, the core module that provides the true functionality of a design tool . The modules can be used in isolation. CityGRID Modeler provides fast and efficient construction tools from a number of surveyed data formats. CityGRID Planner provides planners analysis tools for the assessment of design concepts. CityGRID Viewer gives non-technical audience access to high quality, interactive virtual reality simulations as a stand-alone viewer.. CityGRID Modeler CityGRID Planner CityGRID Explorer CityGRID Manager
<ul><li>Data Structure: </li></ul><ul><ul><li>Line based </li></ul></ul><ul><li>Database </li></ul><ul><ul><li>Linkage between the model and mass storage device </li></ul></ul><ul><ul><ul><li>Data model: Persistency of objects (LoD) </li></ul></ul></ul><ul><ul><li>Data Management tools </li></ul></ul><ul><ul><ul><li>Indexing </li></ul></ul></ul><ul><ul><ul><li>Transactions </li></ul></ul></ul><ul><ul><ul><li>Replication </li></ul></ul></ul><ul><ul><ul><li>Locking </li></ul></ul></ul><ul><ul><ul><li>Security </li></ul></ul></ul>CityGRID: The advantage The CityGRID data structure: The whole things revolves around the data structure. We use LINES to store the data within the database which gives us the maximum functionality over the standard form of data structure which is based on FACES.
CityGRID: The advantage Off-the-shelf model: faces CityGRID: line model CityGRID: faces generated on the fly The CityGRID data structure: 3D city models are typically constructed using faces: independent planes without topological structure. The finished article can be impressive when presented in a viewer, but examination of the structure typically reveals problems. Without a topological structure it becomes difficult to modify a building. Multiply that problem across a city, and you have an a significant burden to address errors. In contrast CityGRID Manager uses a 3D line-structure to store building information, with the faces generated on-the-fly.
CityGRID Manager model structure Input line structure Corresponding 3D Model CityGRID: The advantage The CityGRID data structure: This structure is also very effecient in terms of data storage. The image on the left shows the information required to produce the model on the right. The data is structured with a heirarchy of element types – indicated by the different colours in this image. All this gives us the ability to maintain a city scale model using database type procedures (i.e. en mass and homogeneously)
CityGRID: The advantage CityGRID Modeler tool: The CityGRID data structure: For example we can use the structured information to ensure an accurate fit of the 3D model with a base map, using automatica database procedures. In this example a roof-protrustion is generated by having the faces conform to an external foot-print data-set. You now have a detailed model derived from aerail photogrammetry that conforms to ground plan data A common request is for data to tie in with cadastral records – which are not necessarily postionally accurate!
<ul><li>“ off-the-shelf ” models generated for a mass-market. File-based, these products in their own right are not efficiently maintainable… </li></ul>CityGRID: The advantage … .within City GRID they are. a snap-shot-in-time …. … a fully maintained digital city But CityGRID will of-course import models generated in a non-structured format – i.e. the commercially available (or off-the-shelf ) models. And once the data is in the database it becomes maintainable. The aim is to protect the massive investment made in the generation of these models by keeping them current. In all the examples viewed previously – using out of date data would have undermined the processes significantly. But clearly a database offers more…..
CityGRID: The advantage … .by allowing the maximum level of integration with a clients decision support processes (as represented on the left hand side of the image). In the centre CityGRID Manager provides the administration for all the buildings and takes advantage of everything that the database (shown at the bottom ) has to offer…..
<ul><li>Data Structure: </li></ul><ul><ul><li>Line based </li></ul></ul><ul><li>Database </li></ul><ul><ul><li>Linkage between the model and mass storage device </li></ul></ul><ul><ul><ul><li>Data model: Persistency of objects (LoD) </li></ul></ul></ul><ul><ul><li>Data Management tools </li></ul></ul><ul><ul><ul><li>Indexing </li></ul></ul></ul><ul><ul><ul><li>Transactions </li></ul></ul></ul><ul><ul><ul><li>Replication </li></ul></ul></ul><ul><ul><ul><li>Locking </li></ul></ul></ul><ul><ul><ul><li>Security </li></ul></ul></ul>CityGRID: The advantage Some of the advantages of a database are listed here, but in particular: Transactions guarantee data consistency: every action made in creating a version of a buillding is collected and compared against a series of logical constraints. If changes are compliant the transaction is committed, if not the whole transaction is rolled back. This, combined with locking , ensures that data is not corrupted through poor editing or multiple user conflicts. Our biggest success is that not one of our clients has ever lost any of their data
LoD 1 LoD 2 LoD 3 The Logic of CityGRID Level of Detail (LoD): CityGRID is also able to manage multiple versions of buildings, which is useful both for historical ‘tracking’ and multiple representation of structures; i.e. different Levels of Detail (LoD) for use at different scales. LoD is an indication of the precision that the building has been modelled to (and independent of any positional issues). The scale goes from 1 – 3 and there is emerging acceptance of these levels. We use the CityGML definition as our basis - broadly represented in this sequence.
The Logic of CityGRID LOD: Scalable solutions according need Why is this important? Because a model needs to serves many purposes In order to represent complex realities we need to manage a building at various levels of complexity consistently (change at one LoD will be represented, where appropriate, at another) and efficiently. Note: We’ve added a LOD 1.5 to indicate that in general parlance these terms are flexible. Some models are described as having generalised roof-models. This means that they are applying a best-fit model from a library. This is typical of (semi) automated processes using LiDAR. Application: Data Source: Topographic mapping Aerial photogrammetry or airborne laser scanning LoD 1.5 Generalised Roof Model LoD 1 Block Model LoD 2 Roof Model LoD 3 Detailed Roof Model LoD 4 Interiors Aerial photogrammetry or airborne laser scanning Detailed aerial photogrammetry Façade photographs and 3D TLS of complex buildings Construction plans or surveying Noise protection, large area city planning Local area city planning, project development Project development, architectural documentation, cultural heritage. Homeland security, asset management
The Logic of CityGRID 3 Levels of hierarchy of a City GRID building CityGRID manages a building in units with a hierarchical structure extending below, made of objects , elements and then faces . As the faces are generated on the fly from the line structure, we are able to create a model at the appropriate LoD based on the defining components – and not by storing multiple current versions of the building. Unit Object 2 Object 1 Object 3 Detail element complex Main element complex facade roof
The Logic of CityGRID 4 Units, Objects and Elements: Again, you have to ask why? Well, if you think about it the definition of a building can become quite abstract. In this example (left image) the geometric unit is well defined (city block), but the number of addressed locations is harder to define. There are horizontal and vertical (flats) splits. Within CityGRID, the building (Unit) can be sub-divided into Objects, with the various Elements being used to define the form of the buildings further (balcony, dormers, etc.)
The Logic of CityGRID 5 Historical versions: Change within an urban core is rapid and needs to be represented in the model. Change in the model however can also result from operational issues – e.g. units are upgraded to higher LoD’s in line with project requirements. CityGRID enables a piece-meal approach to modelling as budgets or requirements demand. In this example an editing change has been made (new roof) that results in a new version of a building. CityGRID uses ‘partial persistency’ (i.e. only the current version is editable) to keep records of all changes to that building.
Summary <ul><li>City GRID gives you the tools to: </li></ul><ul><ul><li>keep your data safe; </li></ul></ul><ul><ul><li>Keep your data current; </li></ul></ul><ul><ul><li>Keep your data accessible; </li></ul></ul><ul><ul><li>Protect the investment made in the 3D data; </li></ul></ul><ul><ul><li>Save you money. </li></ul></ul>By utilising a database structure your 3D city model is: Safe – data security, protection from ‘error’ Current – database management tools reduce the burden of file management, and Accessible – to the widest number of applications and users