Visualization Of 3D City Models Research Articles

Non-photorealistic Visualization of 3D City Models using Visual Variables in Virtual Reality Environments

Visual variables are important factors for visualization in 2D maps, and the study of non-photorealistic visualization of 3D city models in virtual environments using visual variables is also necessary to represent the attributes of city such as energy consumption. This study proposed a set of visual variable mapping model based on 3D geographical environment and conducted user cognitive test. The goal of this research is to verify the applicability of visual variables in 3D space and explore the impact of disturbing visual variables on user cognition. The results show that visualization of compound visual variables in 3D space is more effective than single variable mapping, and it makes up for the shortcomings of single mapping. It is effective to study the visualization effect in three-dimensional geographical environment using virtual reality technology. The results from this case study provide guidance for 3D user-centric visualization technology and make contribute to the development of smart city.

From consistency to flexibility: A simplified database schema for the management of CityJSON 3D city models

AbstractThe use of 3D city models is now common practice; many large cities have their own digital model. Resilient and sustainable management of these models is necessary in many cases, where an application could evolve over its lifecycle. The complexity of generic modeling standardization is often a limitation for a light and user‐friendly usage and further developments. This article aims to propose an alternative, providing a simplified database schema implemented in document‐oriented storage. Thanks to the use of the NoSQL store, the focus is on flexibility of the data schemas and thus its clarification. In order to aim attention at the compactness in web development, CityJSON has been chosen for the encoding of the 3D city models. Finally, a full‐stack application (persistent storage, consistent edition, and visualization of 3D city models) has been developed to handle the simplified schema and illustrates its capabilities in two practical use cases.

Azul: A fast and efficient 3D city model viewer for macOS

Abstract3D city models are an important research topic within geographic information, but there is still a lack of good tools to work with them in practice. In an attempt to alleviate this problem and to help with our own research, we have developed azul, a free and open‐source macOS 3D viewer that was especially engineered for the visualization of 3D city models. The aim of this article is, first of all, to describe the inner workings of azul as a complete methodology to efficiently visualize 3D city models, and which can be also applied to other hierarchically structured data models, which are becoming more prevalent in geographic information. In addition, the article has three ancillary goals: (a) to present other general‐purpose methods that are useful to efficiently process 3D city models (e.g., robust error‐correcting parsers and data models that can be used with multiple formats); (b) to describe technical issues and problematic aspects related to current 3D city model formats that are known by developers but are not properly documented in the scientific literature; and (c) to foster an open discussion about the best data structures and algorithms to process 3D city models in practice.

3DCityDB - a 3D geodatabase solution for the management, analysis, and visualization of semantic 3D city models based on CityGML

Over the last decade, more and more cities and even countries worldwide are creating semantic 3D city models of their physical environment based on the international CityGML standard issued by the Open Geospatial Consortium (OGC). CityGML is an open data model and XML-based data exchange format describing the most relevant urban and landscape objects along with their spatial and non-spatial attributes, relations, and their complex hierarchical structures in five levels of detail. 3D city models, which are structured according to CityGML, are often used for various complex GIS simulation and analysis tasks, which go far beyond pure 3D visualization. Due to the large size and complexity of the sometimes country-wide 3D geospatial data, the GIS software vendors and service providers face many challenges when building 3D spatial data infrastructures for realizing the efficient storage, analysis, management, interaction, and visualization of the 3D city models based on the CityGML standard. Hence, there has been strong demand for an open and comprehensive software solution that can provide full support of the aforementioned functionalities. The ‘3D City Database’ (3DCityDB) is a free 3D geo-database solution for CityGML-based 3D city models. 3DCityDB has been developed as an Open Source and platform-independent software suite to facilitate the development and deployment of 3D city model applications. The 3DCityDB software package consists of a database schema for spatially enhanced relational database management systems (ORACLE Spatial or PostgreSQL/PostGIS) with a set of database procedures and software tools allowing to import, manage, analyze, visualize, and export virtual 3D city models according to the CityGML standard. Within this paper, the software suite is illustrated and explained in detail with respect to the related technical implementations and the underlying conceptual software design. Moreover, the utilization of 3DCityDB in different projects and practical application fields are also presented in this paper.

A virtual globe-based time-critical adaptive visualization method for 3D city models

ABSTRACT3D city models, which are important items of content on the virtual globe, are characterized by complicated structures and large amounts of data. These factors make the visualization of 3D city models highly dependent upon the performance of computer hardware. Thus, achieving the efficient rendering of 3D city models using different hardware performance levels represents one of the key problems currently facing researchers. This paper proposes a time-critical adaptive visualization method that first estimates the possible rendering time for each model according to the data structure of the model in addition to the CPU/GPU performance of the computer. It then dynamically adjusts the rendering level for each model based on the results of an estimation of the rendering time to ensure that the final scene can be completed within a given time. To verify the effectiveness and flexibility of this method, it is applied using different computers. The results show that the adaptive visualization method presented in this paper not only can adapt to computers with different levels of performances but also demonstrates an obvious improvement in the time estimation precision, visual effects, and optimization speed relative to existing adaptive visualization methods.

Real-time visualization of 3D city models at street-level based on visual saliency

Street-level visualization is an important application of 3D city models. Challenges to street-level visualization include the cluttering of buildings due to fine detail and visualization performance. In this paper, a novel method is proposed for street-level visualization based on visual saliency evaluation. The basic idea of the method is to preserve these salient buildings in a scene while removing those that are non-salient. The method can be divided into pre-processing procedures and real-time visualization. The first step in pre-processing is to convert 3D building models at higher Levels of Detail (LoDs) into LoD1 models with simplified ground plans. Then, a number of index viewpoints are created along the streets; these indices refer to both the position and the direction of each street site. A visual saliency value is computed for each building, with respect to the index site, based on a visual difference between the original model and the generalized model. We calculate and evaluate three methods for visual saliency: local difference, global difference and minimum projection area. The real-time visualization process begins by mapping the observer to its closest indices. The street view is then generated based on the building information stored in those indexes. A user study shows that the local visual saliency method performs better than do the global visual saliency, area and image-based methods and that the framework proposed in this paper may improve the performance of 3D visualization.

Automatic simplification and visualization of 3D urban building models

A high-fidelity and real-time rendering urban building model was implemented through the simplification of 3D building groups. An approach to simplify a single 3D building has been addressed for generating a levels-of-detail (LOD) building model in nearby urban regions. In farther regions, a single-chain cluster was used to collect footprints of neighboring building groups. To effectively merge footprints, the Delaunay triangulation and line simplification were employed. As a result, a coarse LOD model was created based on generalized footprints and building heights. Our approach not only preserved urban legibility (Lynch, 1960), which is effective for viewers visually navigating through an urban environment, but also implemented dynamic visualization of 3D city models.

Detection and typification of linear structures for dynamic visualization of 3D city models

Cluttering is a fundamental problem in 3D city model visualization. In this paper, a novel method for removing cluttering by typification of linear building groups is proposed. This method works in static as well as dynamic visualization of 3D city models. The method starts by converting building models in higher Levels of Details (LoDs) into LoD1 with ground plan and height. Then the Minimum Spanning Tree (MST) is generated according to the distance between the building ground plans. Based on the MST, linear building groups are detected for typification. The typification level of a building group is determined by its distance to the viewpoint as well as its viewing angle. Next, the selected buildings are removed and the remaining ones are adjusted in each group separately. To preserve the building features and their spatial distribution, Attributed Relational Graph (ARG) and Nested Earth Mover’s Distance (NEMD) are used to evaluate the difference between the original building objects and the generalized ones. The experimental results indicate that our method can reduce the number of buildings while preserving the visual similarity of the urban areas.

Online Visualization of 3D City Model Using CityGML and X3DOM

This article proposes a novel framework for online visualization of 3D city models. CityGML is used to represent the city models, based on which 3D scenes in X3D are generated, then dynamically updated to the user side with AJAX and visualized in WebGL-supported browsers with X3DOM. The experimental results show that the proposed framework can easily be implemented using widely supported major browsers and can efficiently support online visualization of 3D city models in small areas. For the visualization of large volumes of data, generalization methods and multiple-representation data structure should be studied in future research.