3D modeling and Visualization

Prof. Dr. Volker Coors

Introduction Due to improved tools for the design and acquisition of 3D models, to the wider acceptance of 3D technology,

and 3D spatial databases the creation and management of urban information spaces representing entire cities

in the virtual world is feasible nowadays. The urban information space is not limited to 3D building geometry

but includes building semantics as well providing necessary information for urban planning, construction and

management.

However, sharing information between professionals from various disciplines and non-professional users such

as citizens affected by planning proposals is a big challenge for the future. Currently, traditional disciplines such

as architecture, civil engineering and GIS create classic information islands with different foci. Usually GIS is

used to represent the current status of a whole city for administrative purposes. In contrast, planning and

construction professionals focus on the future shape and status of a relatively small part city or just individual

buildings in very high detail. In general, three categories of urban geo-information can be distinguished:

GIS: two-dimensional maps, digital terrain model, 3D buildings with simple geometry of the entire city

CAAD: detailed building models including interior

BIM: building information model including information about structure and usage of individual buildings and their interior up to urban quartiers.

To achieve the integration of these different data sources 3D spatial data infrastructure (SDI) has to be built in

order to connect the existing information islands creating a distributed urban information space as a backbone

for a variety of applications including navigation, urban planning, simulation, facility management, energy

efficient cities, emergency response, homeland security, and other.

3D Spatial Data Infrastructure

The general system architecture of a 3D Spatial Data Infrastructure (3D-SDI) is shown below in

Figure 1. The core component is the 3D spatial database for managing the 3D city models, including quality

management and administration tools. This database generally consists of several distributed physical

databases. The Google Earth database is a good example of a very large database for city models from all over

the world wide. The disadvantage of such a solution is that only one company has control of the data access,

not the several owners / data providers. In contrast, in distributed 3D-SDI the 3D city models the owner of the

data, municipality or national agency is managing the data and offers standard interfaces to allow access to the

city model from several different applications. These applications could be network-connected desktop

applications, web-based applications as well as mobile applications. On top of the 3D spatial database, a 3D

geodata server is build on top of the 3D spatial database to grant access to the city model and to integrate

other data sources. An example for such a combined 3D spatial database and a 3D geodata server is the

CityServer3D developed at Fraunhofer Institute for Computer Graphics.

Figure 1: system architecture for a 3D spatial data infrastructure

In order to achieve interoperability between distributed 3D city model databases it is essential to define a

standard interface to access these data sources. These interfaces will enable individual access to the relevant

information sources for a specific task. The OGC working group 3D Information Management (3DIM) is

developing such interfaces to support a framework of data interoperability for the lifecycle of building and

infrastructure investment: planning, design, construction, operation, and decommissioning. One candidate of

such an interface specification is the OGC Web 3D Service. ‘The W3DS delivers a 3D scene graph instead of pre-

rendered images [...]. These scene graphs are rendered by the client application, e.g. by a 3D plug-in in case of

a web-browser, and enable the user to navigate a 3-dimensional world’ (Quadt/Kolbe, 2005). This principle is

shown in Figure 2. Figure 3 shows an urban planning application using the 3D-SDI.

Figure 2: Web3D Service (W3DS) interface to access the 3D city model.

Figure 3: real and future Rosensteinviertel Stuttgart, © Stadtmessungsamt Stuttgart and University of Applied Science Stuttgart

Domain specific ontology To achieve interoperability between existing information “islands”, a domain specific ontology that specifies

the knowledge stored in the overall city information model has to be developed for lossless data exchange.

CityGML (Gröger et al. 2008) is a candidate for such an ontology. It was accepted as an OGC standard for the

representation, storage and exchange of virtual 3D city and landscape models. CityGML is based on a rich,

general purpose information model in addition to geometry and appearance information. For specific domain

areas, CityGML also provides an extension mechanism to enrich the data with identifiable features under

preservation of semantic interoperability. This extension mechanism is essential to make use of CityGML in

other applications such as flood simulation (Schulte and Coors, 2008) and energy management. From BIM, the

industrial foundation classes (IFC) developed by the International Alliance for Interoperability (IAI 2007) is a

well defined data model for data interchange of building information models. The definition of a mapping of

both CityGML and IFC is a future challenge that would result into a city information model at all levels from city

wide models to high detailed building information model.

Figure 4: digital 3D city model of Stuttgart using CItyGML © Stadtmessungsamt Stuttgart

Figure 5: Semantic modelling in CItyGML, © Stadtmessungsamt Stuttgart

The Open Geospatial Consortium (OGC) is making particular efforts to promote interoperability and sharing of

geospatial resources and services through the development of consensus-based implementation specifications.

For specifying the spatial information of environments, (including areas surrounding buildings) OGC’s GML

provides a variety of objects for describing geography including features, coordinate reference systems,

geometry, topology, time, units of measurement and generalised values. GML was developed as a data

exchange standards interface to achieve data interoperability and reduce costly geographic data conversions

between different systems. It is becoming the dominant standard for spatial data modelling and exchange

(Halfawy 2004).

CityGML, an extension of GML, not only represents the graphical appearance of city models but especially takes

care of semantic representation, thematic properties, taxonomies and aggregations of digital terrain models,

sites (including buildings, bridges, tunnels), vegetation, water bodies, transportation facilities and city furniture.

Figure 6: CityGML modules, OGC CityGML Implementation Specification 1.0,20.08.2008

For a 3D geospatial data infrastructure, the fusion of data is required to provide a unified data service in order

to access the 3D urban information, building model, and other application specific information. For geospatial

data, the OGC’s data service can be employed as a wrapper. The burden of developing wrappers is greatly

reduced since the OWS is strongly supported by many commercial and open source GIS software packages.

Web Feature Service (WFS) allows a client to retrieve and update geospatial data encoded in GML from

multiple WFSs. A server that implements the OGC WFS specification can distribute geographic features to a

client application.

3D visualisation and streaming

When someone wanted to publish 3Dcity models on the Internet, until recently there were only some proprietary digital globes or special solutions of a few companies available. But as the success of the OpenGIS WMS demonstrates, distributed solutions based on standardized web services provide an attractive alternative. The benefit of transmitting real 3D scenes instead of only pictures is known from typical virtual globes: 3D city models can be experienced interactively and also enriched with further information. This includes multimedia data like images, videos or historical facts which can be used in typical end user applications for tourism and navigation. By adding more accurate data (e.g. highly detailed elevation models) and by bringing existing GIS features (e.g. intersection or buffering) into 3D space professional users can be addressed as well. Comprehensive streaming technologies are needed to allow access to large and complex data sets.

With the new generation of smartphones the access to the urban information space using the so called mobile internet becomes feasible. The combination of 3D spatial data and internet-connected smartphones enables new mobile augmented reality applications that have the potential to create new paradigm how we use and interact with computers. While browser based and internet-connected desktop applications such as Google Earth and the like open a window to a digital representation of the real world, mobile augmented reality is just adding an information layer to the reality. First prototypes such as ‘Layar’ (Layar, online 2010), Enkin, (Enkin, online 2010) and the ‘nearest tube’ application of ‘accrossair’ (accrossair, online 2010) explore the possibilities

of this emerging technology. Together with positioning and tracking technologies, streaming and visualization are key technologies to merge the urban information space and the real world.

One example of an application using a 3D spatial data infrastructure is the “Online Public Participation” (OPPA-

3D) (see Figure 7) system developed in the EU-funded project “Virtual Environment Planning System” (VEPs)

(Knapp et al 2008). It supports interactive web based applications to help people understand planning

proposals, through realistic models of existing buildings that allow for exploration and discussion. Generally

speaking, it has been developed to provide an alternative approach to planning consultation, allowing people

to view and make comments on planning developments in 2D/3D within the context of an existing landscape or

cityscape.

Figure 7: Online public participation system OPPA-3D build upon an integrated 3D spatial data infrastructure.

The following figures 8 and 9 provide a sample of a mobile navigation system for pedestrian navigation using

the 3D-SDI accessing the 3D city model from a mobile device. The client application is realized as a JavaME

application running on a Nokia E71 Smartphone.

Figure 8 Landmarks with an abstracted façade (mixture between real and abstracted representation). (c) University of Applied Science Stuttgart

Figure 9: 3D Visualization of 3D urban model on mobile device (Nokia Smartphone), (c) University of Applied Sci

First steps to a Malaysian 3D-SDI Recently, first steps towards a Malaysian 3D-SDI have been developed within a small joint research project

between3D GIS Research Lab, UTM Johor Bahru and Stuttgart University of Applied Science. The focus of the

project was to investigate a workflow for 3D modeling and integration of existing 3D-CAD models into a 3D

geospatial data infrastructure and the feasibility of CityGML for the specific Malaysian situation. The developed

workflow shown in xxx was successfully tested with buildings models in CityGML Level of detail 3 (LoD 3,

detailed façade geometry) and LoD 4 (modeling of the building interior).

Figure 10: Workflow for 3D modelling and data management

Below are some of the examples of the 3D buildings within the Putrajaya main road area that incorporated

with 3DCityServer database together with semantic information. The following Figure 11 shows the 3D building

(“Menara KBS”) in LoD3 within 3DCityServer database. Figure 12 shows a building interior model in CityGML

LoD4.

Figure 11: Putrajaya-3D: Menara KBS in CityServer3D geodata server

Figure 12: LoD 4 building interior model

Short CV

Prof. Dr. Volker Coors

Hochschule für Technik Stuttgart

Fakultät Vermessung, Informatik und Mathematik

Schellingstr. 24, 70174 Stuttgart

Tel: 0711 8926 2708

Email: volker.coors@hft-stuttgart.de

http://www.hft-stuttgart.de/

Volker Coors (* 1968) is Professor in Geoinformatics and Computer Science at University of Applied Sciences

Stuttgart (HFT Stuttgart). His research is focused on 3D Geographic Information Systems and Information

Logistics, in particular data management and visualization of large 3D urban models. He initiated an innovative

Bachelor-program in information logistics at HFT Stuttgart. He holds a Diploma degree with honours in

Computer Sciences (Subsidiary subject: civil engineering/Hydrology) and a doctoral degree in Computer

Graphics from Technical University of Darmstadt (Examiners: Prof. Dr.-Ing. Dr. h.c. mult. Dr. E.h. Hon. Prof.

Mult. J.L. Encarnacao, Prof. J. Rossignac, PhD (Georgia Tech, USA)). From 1997 to 2002 he worked as a

researcher at Fraunhofer Institute for Computer Graphics, department GIS. Volker Coors earned a DAAD

scholarship and holds a patent in the area of 3D mesh compression. He received the “Patent Awards of the INI-

GraphicsNet” in 2002 as well as the price for “Outstanding Concepts for VirtualReality” of the German Ministry

for Education and Research. He was involved in several national and European research projects on 3D urban

modelling, location based computing and augmented Reality.

Volker Coors is member of the CityGML Standard Working group at the Open Geospatial Consortium (OGC). He

represents the OGC in the Web3D consortium. The aim of the collaboration of OGC and Web3D consortia is to

develop standards-based, interoperable web-enabled geospatial content sharing, modeling and visualization.

Furthermore, he is member of the German Society of computer Science and founding member of the joint

working group “3D-City Models” of the German Society for Photogrammetry, Remote Sensing and

Geoinformatics and the German Society for Cartographie.