3D cartographic visualization of a continuous time-dependent phenomenon is not an easy task. The focus of this research is motivated by the struggle to visualize such a phenomenon. Based on the current state of the art, we implemented new visualization methods to visualize continuous time-dependent phenomena. All visualizations are based on the use case of road-traffic-generated noise in outdoor urban areas. These visualizations utilize the third dimension of the map scene. The first two methods focus on the variations of the noise in the vertical dimension (i.e. height). The third method is based on the idea of space–time cube and therefore utilizes the time variable as the third dimension. For demonstration purposes, all methods were implemented in an online application. Furthermore, user testing of those applications was conducted. This paper thus describes design, implementation and user evaluation of newly proposed methods for third dimension visualization. ... Read more

Three-dimensional city models are essential to assess the impact that environmental factors will have on citizens, because they are the input to several simulation and prediction software. Examples of such environmental factors are noise (Stoter et al., 2008), wind (Garcı́a-Sánchez et al., 2014), air pollution (Ujang et al., 2013), and temperature (Hsieh et al., 2011; Lee et
al., 2013). However, those 3D models, which typically contain buildings and other man-made objects such as roads, overpasses, bridges, and trees, are in practice complex to obtain, and it is very time-consuming and tedious to reconstruct them manually. The software 3dfier addresses this issue by automating the 3D reconstruction process. It takes 2D geographical datasets (e.g., topographic datasets) that consist of polygons and “3dfies” them (as in “making them three-dimensional”). The elevation is obtained from an aerial point cloud dataset, and the semantics of the polygons is used to perform the lifting to the third dimension, so that it is realistic. The resulting 3D dataset is semantically decomposed/labelled based on the input polygons, and together they form one(many) surface(s) that aim(s) to be error-free: no self-intersections, no gaps, etc. Several output formats are supported (including
the international standards), and the 3D city models are optimised for use in different software. ... Read more

This paper presents our implementation of a harmonized data model for noise simulations in the European Union (EU). Different noise assessment methods are used by different EU member states (MS) for estimating noise at local, regional, and national scales. These methods, along with the input data extracted from the national registers and databases, as well as other open and/or commercially available data, differ in several aspects and it is difficult to obtain comparable results across the EU. To address this issue, a common framework for noise assessment methods (CNOSSOS-EU) was developed by the European Commission’s (EC) Joint Research Centre (JRC). However, apart from the software implementations for CNOSSOS, very little has been done for the practical guidelines outlining the specifications for the required input data, metadata, and the schema design to test the real-world situations with CNOSSOS. We describe our approach for modeling input and output data for noise simulations and also generate a real world dataset of an area in the Netherlands based on our data model for simulating urban noise using CNOSSOS. ... Read more

Noise is one of the main problems in urban areas. To monitor and manage noise problems, governmental organisations at all levels are obliged to regularly carry out noise studies. The simulation of noise is an important part of these studies. Currently, different organisations collect their own 3D input data as required in noise simulation in a semi-automated way, even if areas overlap. This is not efficient, but also differences in input data may lead to differences in the results of noise simulation which has a negative impact on the reliability of noise studies. To address this problem, this paper presents a methodology to automatically generate 3D input data as required in noise simulations (i.e. buildings, terrain, land coverage, bridges and noise barriers) from current 2D topographic data and point clouds. The generated data can directly be used in existing noise simulation software. A test with the generated data shows that the results of noise simulation obtained from our generated data are comparable to results obtained in a current noise study from practice. Automatically generated input data for noise simulation, as achieved in this paper, can be considered as a major step in noise studies. It does not only significantly improve the efficiency of noise studies, thus reducing their costs, but also assures consistency between different studies and therefore it improves the reliability and reproducibility. In addition, the availability of countrywide, standardised input data can help to advance noise simulation methods since the calculation method can be adopted to improved ways of 3D data acquisition and reconstruction. ... Read more

Semantically enriched 3D city models have the potential to be powerful hubs of integrated information for computer-based urban spatial analysis. This article presents the state of the art in 3D city modelling in the context of broader developments such as smart cities and digital twins, and outlines six challenges that must be overcome before 3D data as a platform becomes a reality. ... Read more

A 3D city model is a digital representation of the spatial features in an urban environment. Buildings, terrain, vegetation, water bodies, etc. all form an integral part of a 3D city model. The possibility to enrich these city models with additional application-specific information, whether new semantics or geometry, further increases their usability. However, in practice, the applications of 3D city models are mainly focused on buildings. The majority of standards available for representing 3D city models, such as IFC and CityGML, have well-defined specifications for modelling buildings, but often none for other city features. In addition, there are several other issues associated with the development and use of 3D city models of large cities, such as massive size of 3D city models, interoperability issues for 3D data from heterogeneous sources, harmonisation of different 3D standards, etc. In this thesis, I investigate how to better model these massive and semantically enriched 3D city models, and I focus on their use in different applications. I make five contributions. First, I explain how CityGML, the international standard for semantic 3D city modelling, is not efficient for storing massive TIN terrains, and present an improved solution to compactly store massive terrains in CityGML. Second, I describe how to model terrains at different LODs in CityGML, since the current CityGML data model lacks the specifications for modelling different terrain LODs at geometric and semantic level. Third, I explain how CityGML lacks precise specifications for modelling metadata of 3D city models and present an ISO 19115 compliant solution to add metadata. Fourth, I describe in this thesis how the development of the new standards LandInfra and InfraGML and their integration with the existing popular standards (IFC and CityGML) can contribute to the BIM and 3D GIS interoperability and bring the two domains to a common footing. Fifth, I demonstrate my approach for the development of a harmonised semantic 3D city model based on CityGML for use in urban noise simulations. In addition, I have developed open source prototypes to help practitioners with the use of 3D city models. In this way, I also contribute to the open source community for 3D city modelling. The thesis proposes additional research for future work. For example, since this research focuses specifically on the LODs of terrain models, it would be worthwhile to extend the research to explore the LOD concept for other urban features such as vegetation and landuse. Furthermore, LandInfra is a relatively young standard with low community support. This too requires more attention. Tools such as parsers, validators, visualisers, DBMS support, APIs, and so on are still lacking for LandInfra (and InfraGML). It would be interesting to see how the standards evolve and whether it can be applied in practice when such support is available. Interoperability of LandInfra with IFC and other standards is also an area that requires further investigation. ... Read more

LandInfra is a relatively new open standard for modelling and representing land and infrastructure features. As it overlaps with other open standards in BIM (IFC) and 3D GIS (CityGML), it has been recognised as a potential candidate to bridge the gap between the two domains. However, the knowledge of this standard in both communities is low, and there are still no publications which fully explore LandInfra and its possibilities for integrated BIM-GIS applications. In this paper, we review the LandInfra conceptual model and its GML encoding InfraGML, provide a detailed comparison of it with respect to CityGML and IFC, and investigate a few potential use cases where LandInfra and InfraGML are useful for BIM-GIS applications. ... Read more

The Level of Detail (LOD) concept in CityGML 2.0 is meant to differentiate the multiple representations of semantic 3D city models. Despite the popularity and general acceptance of the concept by the practitioners and stakeholders in 3D city modelling, there are still some limitations. While the CityGML LOD concept is well defined for buildings, bridges, tunnels, and to some extent for roads, there is no clear definition of LODs for terrain/relief, vegetation, land use, water bodies, and generic city objects in CityGML. In addition, extensive research has been done to refine the LOD concept of CityGML for buildings but little is known on requirements and possibilities to model city object types as terrain at different LODs. To address this gap, we focus in this paper on the terrain of a 3D city model and propose a framework for modelling terrains at different LODs in CityGML. As a proof of concept of our framework, we implemented a software prototype to generate terrain models with other city features integrated (e.g. buildings) at different LODs in CityGML. ... Read more

GIS has become an important part of many disciplines and supports a vast range of applications. It is used everywhere, from agriculture to public health care. Furthermore, with the advances in technologies, the availability of GIS data and software support has grown exponentially. In this paper, we present the results of our international survey to investigate the adoption of geospatial data, standards, and software by the practitioners in different application domains. The results demonstrate a clear trend towards the increased use of GIS in a number of application domains including architecture, geosciences, hydrology, and so on. We also explore the expectations of the users from the GIS technologies and provide some insight into the current status of 3D GIS data and its applications. ... Read more

The international standard CityGML is both a data model and an exchange format to store digital 3D models of cities. While the data model is used by several cities, companies, and governments, in this paper we argue that its XML-based exchange format has several drawbacks. These drawbacks mean that it is difficult for developers to implement parsers for CityGML, and that practitioners have, as a consequence, to convert their data to other formats if they want to exchange them with others. We present CityJSON, a new JSON-based exchange format for the CityGML data model (version 2.0.0). CityJSON was designed with programmers in mind, so that software and APIs supporting it can be quickly built. It was also designed to be compact (a compression factor of around six with real-world datasets), and to be friendly for web and mobile development. We argue that it is considerably easier to use than the CityGML format, both for reading and for creating datasets. We discuss in this paper the main features of CityJSON, briefly present the different software packages to parse/view/edit/create files (including one to automatically convert between the JSON and GML encodings), analyse how real-world datasets compare to those of CityGML, and we also introduce Extensions, which allow us to extend the core data model in a documented manner. ... Read more

The relatively new Open Geospatial Consortium (OGC) standard LandInfra documents in its data model land and civil engineering infrastructure features. It has a Geography Markup Language (GML) implementation, OGC InfraGML, which has essentially no software support and is rarely used in practice. In order to share the benefits of LandInfra (and InfraGML) with a wider public, we have created the Infra Application Domain Extension (ADE), a CityGML ADE that allows us to store LandInfra features in CityGML. In this paper, we semantically map LandInfra to CityGML, describe our ADE, and discuss a few used cases where our ADE can be useful for applications for the built environment. We also provide software to automatically convert datasets from InfraGML to CityGML (and our ADE), and vice versa, as well as to validate them, which will help practitioners generate real-world InfraGML datasets. ... Read more

In this paper, we review state of the art 3D visualization technologies for floods and we focus on the Netherlands since it has a long history of dealing with floods and developing information technology solutions to prevent and predict them. We discuss the most recent advances in using 3D city models for modelling floods and discuss future directions. We argue that 3D city models provide a more realistic interpretation and assessment of floods e.g. information about the height of the water level and the number of floors that will be flooded. We present our framework to dynamically visualize floods in 3D using the Cesium 3D webglobe. An open platform using 3D city models for interactive visualization of different flood simulations can serve as a hub to involve all relevant parties such as water experts, policy developers, decision makers, and general public. We created a 3D terrain model with buildings of a study area in the Netherlands in CityJSON format. We implemented a software prototypes for converting 3D city models from CityJSON to Cesium specific glTF format for rendering over Cesium. We propose using CZML (Cesium Language) to represent time dynamic properties, water levels in our case. The developed framework which uses only open data and open-source software can be supportive in real applications such as planning for a city or municipal corporation, or for decision making. ... Read more

While there exist international standards for geospatial metadata (ISO 19115), these are rarely used in practice for 3D datasets, and one of the OGC standards for 3D city models, CityGML, does not offer a mechanism to store metadata in a structured way. Having metadata in CityGML files, which are in practice often very large and complex, would provide us with the ability to quickly understand the nature of a dataset and to determine if it is relevant for a specific task. Alack of metadata introduces uncertainty into models that are already full of assumptions and estimations. In this paper, we first examine the metadata needs that are specific for 3D geographical datasets and propose ISO 19115compliant categories. We then describe how these can be used within CityGML by defining an Application DomainExtension (ADE), which allows us to store metadata for existing city objects of CityGML, as well as objects in other domain-specific ADEs. Our ADE, its schema in both UML and XSD, and sample datasets is openly accessible, and it can be easily extended to support application specific metadata. In addition the metadata elements have been added to the core of CityJSON. We also offer software to generate automatically many of the metadata categories and we propose coupling it with the source 3D dataset. ... Read more

The Application Domain Extension (ADE) is a built-in mechanism of CityGML to augment its data model with additional concepts required by particular use cases. The goal of this paper is to provide an overview of the ADE mechanism and a literature review of developments since its introduction a decade ago. The discovery of publications found that currently there are 44 ADEs supporting a wide range of applications, but also application-agnostic purposes such as harmonisation with national geographic information standards. We hope this paper to double as a reference material for the developers of new ADEs. ... Read more

CityGML is the most important international standard used to model cities and landscapes in 3D with extensive semantics. Compared to BIM standards such as IFC, CityGML models are usually less detailed but they cover a much greater spatial extent. They are also available in any of five standardized levels of detail. CityGML serves as an exchange format and as a data source for visualizations, either in dedicated applications or in a web browser. It can also be used for a wide range of spatial analyses, such as visibility studies and solar potential. Ongoing research will improve the integration of BIM standards with CityGML, making improved data exchange possible throughout the life-cycle of urban and environmental processes. ... Read more

Terrains form an important part of 3D city models. GIS practitioners often model terrains with 2D grids. However, TINs (Triangulated Irregular networks) are also increasingly used in practice. One such example is the 3D city model of the Netherlands (3DTOP10NL), which covers the whole country as one massive triangulation with more than one billion triangles. Due to the massive size of terrain datasets, the main issue is how to efficiently store and maintain them. The international 3D GIS standard CityGML allows us to store TINs using the Simple Feature representation. However, we argue that it is not appropriate for storing massive TINs and has limitations. We focus in this article on an improved storage representation for massive terrain models as TINs. We review different data structures for compactly representing TINs and explore how they can be implemented in CityGML as an ADE (Application Domain Extension) to efficiently store massive terrains. We model our extension using UML, and XML schemas for the extension are automatically derived from these UML models. Experiments with massive real‐world terrains show that, with this approach, we can compress CityGML files up to a factor of ~20 with one billion+ triangles, and our method has the added benefit of explicitly storing the topological relationships of a TIN model ... Read more

Road traffic and industrial noise has become a major source of discomfort and annoyance among the residents in urban areas. More than 44 % of the EU population is regularly exposed to road traffic noise levels over 55 dB, which is currently the maximum accepted value prescribed by the Environmental Noise Directive for road traffic noise. With continuously increasing population and number of motor vehicles and industries, it is very unlikely to hope for noise levels to diminish in the near future. Therefore, it is necessary to monitor urban noise, so as to make mitigation plans and to deal with its adverse effects. The 2002/49/EC Environmental Noise Directive aims to determine the exposure of an individual to environmental noise through noise mapping. One of the most important steps in noise mapping is the creation of input data for simulation. At present, it is done semi-automatically (and sometimes even manually) by different companies in different ways and is very time consuming and can lead to errors in the data. In this paper, we present our approach for automatically creating input data for noise simulations. Secondly, we focus on using 3D city models for presenting the results of simulation for the noise arising from road traffic and industrial activities in urban areas. We implemented a few noise modelling standards for industrial and road traffic noise in CityGML by extending the existing Noise ADE with new objects and attributes. This research is a steping stone in the direction of standardising the input and output data for noise studies and for reconstructing the 3D data accordingly. ... Read more

Standaarden voor het beheer, de modellering, uitwisseling en ontsluiting van 3D informatie zijn essentieel bij 3D ontwikkelingen: standaarden voor 3D data bieden softwarebedrijven een solide basis voor investeringen. Bovendien maken 3D standaarden hergebruik van 3D data mogelijk. ... Read more

In addition to buildings, the terrain forms an important part of a 3D city model. Although in GIS terrains are usually represented with 2D grids, TINs are also increasingly being used in practice. One example is 3DTOP10NL, the 3D city model covering the whole of the Netherlands, which stores the relief with a constrained TIN containing more than 1 billion triangles. Due to the massive size of such datasets, the main problem that arises is: how to efficiently store and maintain them? While CityGML supports the storage of TINs, we argue in this paper that the current solution is not adequate. For instance, the 1 billion+ triangles of 3DTOP10NL require 686 GB of storage space with CityGML. Furthermore, the current solution does not store the topological relationships of the triangles, and also there are no clear mechanisms to handle several LODs. We propose in this paper a CityGML extension for the compact representation of terrains. We describe our abstract and implementation specifications (modelled in UML), and our prototype implementation to convert TINs to our CityGML structure. It increases the topological relationships that are explicitly represented, and allows us to compress up to a factor of ∼ 25 in our experiments with massive real-world terrains (more than 1 billion triangles). ... Read more