Dieter Hildebrandt

Service-oriented, standards-based 3D geovisualization: Potential and challenges

The application of the architectural concept of service-oriented architectures (SOA) in combination with open standards when building distributed, 3D geovisualization systems offers the potential to cover and take advantage of the opportunities and demands created by the rise of ubiquitous computer networks and the Internet as well as to overcome prevalent interoperability barriers. In this paper, based on a literature study and our own experiences, we discuss the potential and challenges that arise when building standards-based, distributed systems according to the SOA paradigm for 3D geovisualization, with a particular focus on 3D geovirtual environments and virtual 3D city models. First, we briefly introduce fundamentals of the SOA paradigm, identify requirements for service-oriented 3D geovisualization systems, and present an architectural framework that relates SOA concepts, geovisualization concepts, and standardization proposals by the Open Geospatial Consortium in a common frame of reference. Next, we discuss the potential and challenges driven by the SOA paradigm on four different levels of abstraction, namely service fundamentals, service composition, interaction services, performance, and overarching aspects, and we discuss those driven by standardization. We further exemplify and substantiate the discussion in the scope of a case study and the image-based provisioning of and interaction with visual representations of remote virtual 3D city models.

Service-oriented interactive 3D visualization of massive 3D city models on thin clients

Virtual 3D city models serve as integration platforms for complex geospatial and georeferenced information and as medium for effective communication of spatial information. In this paper, we present a system architecture for service-oriented, interactive 3D visualization of massive 3D city models on thin clients such as mobile phones and tablets. It is based on high performance, server-side 3D rendering of extended cube maps, which are interactively visualized by corresponding 3D thin clients. As key property, the complexity of the cube map data transmitted between server and client does not depend on the models complexity. In addition, the system allows the integration of thematic raster and vector geodata into the visualization process. Users have extensive control over the contents and styling of the visual representations. The approach provides a solution for safely, robustly distributing and interactively presenting massive 3D city models. A case study related to city marketing based on our prototype implementation shows the potentials of both server-side 3D rendering and fully interactive 3D thin clients on mobile phones.

RealPeer--A Framework for Simulation-Based Development of Peer-to-Peer Systems

In the process of developing P2P systems simulation has proved to be an essential tool for the evaluation of existing and conceived P2P systems. So far, in practice there has been a clear separation between a simulation model of a P2P system and a real P2P system that operates on a real physical network. This separation hinders the transition of models to real systems and the evaluation of already deployed systems by means of simulation. This work tries to bridge this gap by proposing a methodology and a framework for the simulation-based development of P2P systems. In this approach, an initial model of a P2P system is iteratively transformed into the intended real P2P system. The presented framework effectively supports a developer in modelling, simulating and ultimately developing P2P systems. The authors demonstrate the validity of the approach and the framework by constructing an example P2P application. This application is simulated in a series of experiments as well as deployed in a large-scale Internet based P2P system

Towards Advanced and Interactive Web Perspective View Services

The Web Perspective View Service (WPVS) generates 2D images of perspective views of 3D geovirtual environments (e.g., virtual 3D city models) and represents one fundamental class of portrayal services. As key advantage, this image-based approach can be deployed across arbitrary networks due to server-side 3D rendering and 3D model management. However, restricted visualization and interaction capabilities of WPVS-based applications represent its main weaknesses. To overcome these limitations, we present the concept and an implementation of the WPVS++, a WPVS extension, which provides A) additional thematic information layers for generated images and B) additional service operations for requesting spatial and thematic information. Based on these functional extensions, WPVS++ clients can implement various 3D visualization and interaction features without changing the underlying working principle, which leads to an increased degree of interactivity and is demonstrated by prototypic web-based client applications.

An assisting, constrained 3D navigation technique for multiscale virtual 3D city models

Virtual 3D city models serve as integration platforms for complex geospatial and georeferenced information and as medium for effective communication of spatial information. In order to explore these information spaces, navigation techniques for controlling the virtual camera are required to facilitate wayfinding and movement. However, navigation is not a trivial task and many available navigation techniques do not support users effectively and efficiently with their respective skills and tasks. In this article, we present an assisting, constrained navigation technique for multiscale virtual 3D city models that is based on three basic principles: users point to navigate, users are lead by suggestions, and the exploitation of semantic, multiscale, hierarchical structurings of city models. The technique particularly supports users with low navigation and virtual camera control skills but is also valuable for experienced users. It supports exploration, search, inspection, and presentation tasks, is easy to learn and use, supports orientation, is efficient, and yields effective view properties. In particular, the technique is suitable for interactive kiosks and mobile devices with a touch display and low computing resources and for use in mobile situations where users only have restricted resources for operating the application. We demonstrate the validity of the proposed navigation technique by presenting an implementation and evaluation results. The implementation is based on service-oriented architectures, standards, and image-based representations and allows exploring massive virtual 3D city models particularly on mobile devices with limited computing resources. Results of a user study comparing the proposed navigation technique with standard techniques suggest that the proposed technique provides the targeted properties, and that it is more advantageous to novice than to expert users.

Concepts for cartography-oriented visualization of virtual 3D city models

Virtual 3D city models serve as an effective medium with manifold applications in geoinformation systems and services. To date, most 3D city models are visualized using photorealistic graphics. But an effective communication of geoinformation significantly depends on how important information is designed and cognitively processed in the given application context. One possibility to visually emphasize important information is based on non-photorealistic rendering, which comprehends artistic depiction styles and is characterized by its expressiveness and communication aspects. However, a direct application of non-photorealistic rendering techniques primarily results in monotonic visualization that lacks cartographic design aspects. In this work, we present concepts for cartography-oriented visualization of virtual 3D city models. These are based on coupling non-photorealistic rendering techniques and semantics-based information for a user, context, and media-dependent representation of thematic information. This work highlights challenges for cartography-oriented visualization of 3D geovirtual environments, presents stylization techniques and discusses their applications and ideas for a standardized visualization. In particular, the presented concepts enable a real-time and dynamic visualization of thematic geoinformation.

Image-based strategies for interactive visualisation of complex 3D geovirtual environments on lightweight devices

In this article, we present strategies for service-oriented, standards and image-based 3D geovisualisation that have the potential to provide interactive visualisation of complex 3D geovirtual environments (3DGeoVE) on lightweight devices. In our approach, interactive geovisualisation clients retrieve sets of 2D images of projective views of 3DGeoVEs generated by a 3D rendering service. As the key advantage of the image-based approach, the complexity that a client is exposed for displaying a visual representation is reduced to a constant factor primarily depending on the image resolution. To provide users with a high degree of interactivity, we propose strategies that are based on additional service-side functionality and on exploiting multiple layers of information encoded into the images for the local reconstruction of visual representations of the remote 3DGeoVE. The use of service-orientation and standards facilitates designing distributed 3D geovisualisation systems that are open, interoperable and can easily be adapted to changing requirements. We demonstrate the validity of the proposed strategies by presenting proof-of-concept implementations of several image-based 3D clients for the case of virtual 3D city models.

Image-based styling

The same data can be visualized using various visual styles that each is suitable for specific requirements, e.g., 3D geodata visualized using photorealistic, cartographic, or illustrative styles. In contrast to feature-based styling, image-based styling performed in image space at image resolution allows decoupling styling from image generation and output-sensitive, expressive styling. However, leveraging image-based styling is still impeded. No previous approach allows specifying image-based styling expressively with an extensive inventory of composable operators, while providing styling functionality in a service-oriented, interoperable manner. In this article, we present an interactive system for specifying and providing the functionality of image-based styling. As key characteristics, it separates concerns of styling from image generation and facilitates specifying styling as algebraic compositions of high-level operators using a unified 3D model representation. We propose a generalized visualization model, an image-based styling algebra, two declarative DSLs, an operator taxonomy, an operational model, and a standards-based service interface. The approach facilitates expressive specifications of image-based styling for design, description, and analysis and leveraging the functionality of image-based styling in a service-oriented, interoperable, reusable, and composable manner.

Integrating 3D data in service-based visualization systems

Georeferenced data is available from a wide range of sources, e.g., Directory Services, Sensor Observation Services, Web Feature Services or even proprietary interfaces. Many of the data originating from an Internet of Things will be three-dimensional representing outdoor as well as indoor geographic features and their properties. Based on this data, its integration, and its visualization totally new applications and systems could be designed and implemented supporting various applications domains. Recent work in the area of service-based 3D visualization enables high-quality visualization of complex 3D geodata, e.g., 3D city models and 3D indoor building models, on thin clients as well as mobile devices such as smartphones and tablets. This work uses a service-based, image-based visualization approach that decouples the server-side resource-intensive management and rendering of complex, massive 3D geodata from client-side display functionalities: A Web View Service provides image representations of a 3D scene; these images, which can contain different types of information per pixel, are transmitted to a client application that can reconstruct a 3D representation of this scene. -- In this talk, we will describe how to combine 3D geodata originating from the Internet of Things with this service-based approach in a way that allows for the interactive exploration of and interaction with 3D worlds and objects of interest. In detail, this 3D geodata can be integrated into the visualization process a) at the rendering stage of a portrayal service, b) through an image post processing step or c) in the client application itself. Moreover, this data can be visually represented directly by modifying the appearance of existing features, e.g., for visualizing measurements, or indirectly by introducing additional objects, e.g., icons, into the 3D scene. We will discuss advantages and disadvantages of these different approaches for implementing visualization applications using live geodata sources.

Simulation-based development of Peer-to-Peer systems with the RealPeer methodology and framework

In the process of developing Peer-to-Peer (P2P) systems, simulation has proved to be an essential tool for the evaluation of existing and conceived P2P systems. So far, in practice, there has been a clear separation between a simulation model of a P2P system and a real P2P system that operates on a real physical network. This separation hinders the transition of models to real systems and the evaluation of already deployed systems by means of simulation. To bridge this gap, we put forward the idea of simulation-based development of P2P systems. In this approach, an initial simulation model of a P2P system is iteratively transformed into the intended real P2P system. As a concretion of this approach, we propose a methodology and a framework for the simulation-based development of P2P systems. The presented framework effectively supports a developer in modelling, simulating and ultimately developing P2P systems. We demonstrate the validity of our approach and the framework by constructing an example P2P application. This application is simulated in a series of experiments as well as deployed in a large-scale internet-based P2P system.