CityGML Data Research Articles

Automatic 3D Model Registration for Global Localization based on Publicly Available Georeferenced CityGML Data

Automatic 3D Model Registration for Global Localization based on Publicly Available Georeferenced CityGML Data

Integrating 3D city data through knowledge graphs

ABSTRACT CityGML is a widely adopted standard for representing and exchanging 3D city models. The representation of semantic and topological properties in CityGML makes it possible to query such 3D city data for analysis in various applications. Nevertheless, the potential of querying CityGML data has not been fully exploited. The official GML encoding of CityGML is mainly an information model used for data storage and exchange, but not suitable for performing complex queries. The most common way of dealing with CityGML data is to store them as tables in the 3DCityDB system. However, it remains a challenging task for end users to formulate SQL queries over 3DCityDB directly for their ad-hoc analytical tasks because of the gap between the semantics of CityGML and the relational schema adopted in 3DCityDB. The technology of Knowledge Graphs (KGs), where an ontology is at the core, is a good solution to bridge such a gap. Moreover, embracing KGs makes it easier to integrate with other spatial data sources, e.g. OpenStreetMap, and to perform queries combining information from multiple data sources. In this work, we describe a CityGML-KG framework to expose the CityGML data in 3DCityDB as a KG. To evaluate our approach, we use CityGML data from the city of Munich as a test area and integrate OpenStreetMap data.

”CITYJSON2RDF” A CONVERTER FOR PRODUCING 3D CITY KNOWLEDGE GRAPHS

Abstract. The increasing prevalence of 3D city models (3DCMs) in various applications, such as mixed reality and navigation, highlights the need for efficient data exchange. CityGML serves as a standard model for this purpose, encompassing geometric and semantic information in 3DCM data. To enhance interoperability, a compatible transfer mechanism is essential. This study introduces a conversion tool that transforms CityGML data into RDF, a knowledge graph (KG) format. Utilizing semantic web technologies, this conversion ensures the data’s seamless integration across applications. The RDF model facilitates linking to open ontologies, promoting data circulation without loss. The tool employs CityJSON encoding for its mappable JSON structure, enabling straight-forward conversion to RDF using Python components. While existing XML to RDF tools exist, this tool distinguishes itself by addressing accessibility and user intervention challenges. Linking is established by matching subject classes with relevant ontology definitions, a process dependent on developers’ understanding of the CityGML data model. The tool, accessible through URL-2, is still in development, offering a promising solution for achieving effective 3DCM data interoperability.

Querying CityGML Data through Virtual Knowledge Graphs

Querying CityGML Data through Virtual Knowledge Graphs

URBAN GROWTH SIMULATION USING URBAN DYNAMICS AND CITYGML: A USE CASE FROM THE CITY OF MUNICH

Abstract. Urban dynamics modelling using system dynamic (SD) approaches aims to provide an understanding of the major internal forces within an urban area, such as population development. SD models provide valuable information for decision and policy making. Urban systems are strongly related to the urban space, which is well described by geospatial data. Therefore, the connection of SD and geospatial data is advantageous, both for feeding spatial information into SD models and for further spatial analyses and for visualizing the results of SD in geographic context. This paper describes a new approach to combine an SD model with a semantic 3D city model. Our approach shows that a bidirectional data exchange between semantic city models and SD models improves the predictions generated by the SD models. Furthermore, we show that automatic modification of the semantic city model by the output of the SD model allows for 3D visualization and further analysis of future scenarios.Since semantic 3D city models and SD models have complex data structures, and since the models have evolved in very different domains, integrating the models is a complex task. In order to facilitate the integration process, we developed a conceptual model, which describes the data structures of the semantic city model and of the SD model as well as the bidirectional relations between the models using the concept of model weaving. The approach was tested using the SD tool Vensim and a CityGML data set from the city of Munich for an urban densification use case.

Rule-Based Quality Assurance Tool for 3D Buildings

Abstract. This article presents a Data Quality Assurance (DQA) tool for 3D city buildings, which is developed using the FME Workbench application. It evaluates the quality of both CityGML and CityJSON data sets against predefined rules and produces quality information in the tabular or geometrical format. All violations are categorized based on their severity, which means that the tool can automatically discard or fix some of the found errors. By doing so, the tool can play an important role in Spatial Data Infrastructures (SDI) and improve data integration processes by improving data quality and interoperability.

Photovoltaic Solar Energy from Urban Sprawl: Potential for Poland

Urban sprawl is a process that shapes contemporary urban spaces. Generally, this process is associated with negative effects due to the generation of high costs. However, not all the effects of urban sprawl should be considered in the context of the increasing costs of the use of space; some of them should be regarded as cost cutting factors, for example, the possibility of the use of roofed areas in generating energy from sunlight. Solar energy is believed to be one of the sources of clean energy that reduce pollution and greenhouse gas emissions into the atmosphere. However, solar energy generation necessitates the development of large areas for the purpose of installing photovoltaic modules and substantial funds for creating large solar farms. For this reason, a significant role in state energy policies is played by small dispersed installations mounted on the roofs of buildings. There is a gap in existing research on the assessment of urban sprawl in terms of the potential use of rooftops for solar installations in suburban areas. This research gap has not yet been filled, either conceptually and methodologically. Hence, the contribution of the research to the development of the current state of knowledge involves the identification of economic and environmental benefits of usually negatively perceived urban sprawl. The proposal of a method for the identification of suburban housing potential for solar energy generation constitutes another addition to the state of knowledge. The main objective of this article is to analyse the energy generating potential of buildings located in suburban and urban areas characterised by the confirmed occurrence of urban sprawl phenomena. CityGML data were used to conduct an analysis of the exposure of roofs to sunlight using algorithms based on vector data. The authors estimated the dynamics of changes in time and referred the existing photovoltaic installations to the total potential of a selected area. The use of the energy potential of the analysed roofs of buildings was used to evaluate the external costs and benefits of spatial planning. The discussion presented the current conditions of the energy sector and energy policies in Poland and the EU. In addition, recommendations were proposed for local spatial policies concerning the mitigation of the effects of suburbanization in the context of developing the system of PV micro-installations.

MAP GENERATION FOR RETRO GAMING ENGINES

Abstract. Current attempts to integrate gaming, geospatial and AEC technologies are driven by increased hardware capabilities and target virtual worlds as close to reality as possible. In this paper we pursue a converse destination and populate low-tech virtual worlds from geospatial data, building and city models, specifically for retro gaming engines in spatial chat tools. We consider an island, a building and a city district scenario and populate these scenarios from OSM, IFC, and CityGML data sources. The derived worlds are targeting use cases in business, educational and recreational settings. Based on a prototypical implementation, we study the feasibility and limitations of good quality retro gaming map generation with automatic means from existing data sets, but also the potential of such worlds for Green IT, accessibility and inspiration of new user groups. We describe the algorithms and processes to generate the maps and outline the concept for a user survey. Beyond that, by discussing map generation techniques from classical gaming in context of and comparison with geospatial and AEC practices, this paper contributes a retrospective of early gaming techniques that might be both entertaining and informative for current development practice.

Using 3D CityGML for the Modeling of the Food Waste and Wastewater Generation-A Case Study for the City of Montréal.

The paper explains a workflow to simulate the food energy water (FEW) nexus for an urban district combining various data sources like 3D city models, particularly the City Geography Markup Language (CityGML) data model from the Open Geospatial Consortium, Open StreetMap and Census data. A long term vision is to extend the CityGML data model by developing a FEW Application Domain Extension (FEW ADE) to support future FEW simulation workflows such as the one explained in this paper. Together with the mentioned simulation workflow, this paper also identifies some necessary FEW related parameters for the future development of a FEW ADE. Furthermore, relevant key performance indicators are investigated, and the relevant datasets necessary to calculate these indicators are studied. Finally, different calculations are performed for the downtown borough Ville-Marie in the city of Montréal (Canada) for the domains of food waste (FW) and wastewater (WW) generation. For this study, a workflow is developed to calculate the energy generation from anaerobic digestion of FW and WW. In the first step, the data collection and preparation was done. Here relevant data for georeferencing, data for model set-up, and data for creating the required usage libraries, like food waste and wastewater generation per person, were collected. The next step was the data integration and calculation of the relevant parameters, and lastly, the results were visualized for analysis purposes. As a use case to support such calculations, the CityGML level of detail two model of Montréal is enriched with information such as building functions and building usages from OpenStreetMap. The calculation of the total residents based on the CityGML model as the main input for Ville-Marie results in a population of 72,606. The statistical value for 2016 was 89,170, which corresponds to a deviation of 15.3%. The energy recovery potential of FW is about 24,024 GJ/year, and that of wastewater is about 1,629 GJ/year, adding up to 25,653 GJ/year. Relating values to the calculated number of inhabitants in Ville-Marie results in 330.9 kWh/year for FW and 22.4 kWh/year for wastewater, respectively.

Extending CityGML for IFC-sourced 3D city models

Differences in the scope and intent of the contrasting IFC and CityGML data formats entail that converting the former to the latter results in loss of information. However, for some use cases it is beneficial to keep also particular information from IFC that is not native to CityGML, and achieving that requires mechanisms such as the CityGML Application Domain Extension (ADE). We develop an ADE to support retaining relevant information from IFC. Besides being driven by the particular source of the input data (IFC), this multi-purpose ADE is shaped after a discovery process that involved examining potentially applicable use cases in Singapore, doubling as an extension that is adapted to a set of use cases and the local geographic context. We implement the conceptual work by generating an enriched dataset (with an automatic conversion from IFC to CityGML), visualising it, and discuss its added value in a use case.

Urban Water Demand Simulation in Residential and Non-Residential Buildings Based on a CityGML Data Model

Humans’ activities in urban areas put a strain on local water resources. This paper introduces a method to accurately simulate the stress urban water demand in Germany puts on local resources on a single-building level, and scalable to regional levels without loss of detail. The method integrates building geometry, building physics, census, socio-economy and meteorological information to provide a general approach to assessing water demands that also overcome obstacles on data aggregation and processing imposed by data privacy guidelines. Three German counties were used as validation cases to prove the feasibility of the presented approach: on average, per capita water demand and aggregated water demand deviates by less than 7% from real demand data. Scenarios applied to a case region Ludwigsburg in Germany, which takes the increment of water price, aging of the population and the climate change into account, show that the residential water demand has the change of −2%, +7% and −0.4% respectively. The industrial water demand increases by 46% due to the development of economy indicated by GDP per capita. The rise of precipitation and temperature raise the water demand in non-residential buildings (excluding industry) of 1%.

CITYJSON + WEB = NINJA

Abstract. As web applications become more popular, 3D city models would greatly benefit from a proper web-based solution to visualise and manage them. CityJSON was introduced as a JSON encoding of the CityGML data model and promises, among several benefits, the ability to be integrated with modern web technologies. In order to provide an implementation of a web application for CityJSON data, that can be used as a reference for other applications, we developed ninja. It is a web application that allows the user to easily load and investigate a CityJSON model through a web browser. In addition, it offers support for a complex feature of CityJSON: the experimental versioning mechanism. In this paper, we describe the motivation, requirements, technical aspects and achieved functionality of ninja. We believe that such a web application can facilitate the adoption of 3D city models by more practitioners and decision makers.

TOWARDS INTEGRATION OF LADM AND CITYGML FOR THE CADASTRAL SYSTEM OF TURKEY

Abstract. With the rapid urbanization and the dynamics in land transactions, Turkish cadastre, as in many other countries, is facing challenges in the daily recording of sales, donations, taxations, and mortgages on land. Especially with the modern constructions and complex interrelationships of rights, restrictions, and responsibilities (RRR), the third dimension should not be forgotten. In this context, the design of a new cadastre data model for Turkey is essential. Inspired by this need, with this study, we aim in proposing a new cadastre model based on international standards such as Land Administration Data Model (LADM) and CityGML. LADM represents the legal and administrative aspects of the cadastral objects but does not show the semantic and 3D geometrical representation of physical cadastral objects which are required for the process of 3D cadastre. Therefore, in the paper, we propose an Application Domain Extension (ADE) for the cadastral objects that expands the integration of LADM and CityGML data model with the legal and administrative concepts defined in the Turkish Law. The study presents a detailed overview of the Turkish legal cadastre system and a proposal for its physical realization based on international standards. In addition, the developed ADE is also valuable for cadastral services undertaken by the General Directorate of Land Registry and Cadastre (GDLRC). It could also be used as a basis of a 3D national data standard for cadastral information systems.

3DCITYDB4BIM: A SYSTEM ARCHITECTURE FOR LINKING BIM SERVER AND 3D CITYDB FOR BIM-GIS-INTEGRATION

Abstract. Nowadays, the three-dimensional visualization of cities is becoming feasible and popular. The applications serve key sectors of urban development including architecture and urban planning. The implementation of BIM in the geospatial environment will help in evaluation of the design proposals by answering questions such as “What windows have views of a particular spot?”, “How will a design proposal affect views and shadows in an urban scene?” from multiple stakeholder perspectives.This paper presents an approach that facilitates the integration of BIM and geo visualization. 3DCityDB4BIM is a concept for combining existing open source software and open specifications for efficient data management and visualization of Building Information within its broader context. 3DCityDB4BIM core components are the 3DCityDB, the BIMServer, CesiumJS viewer, and the existing standards (glTF, CityGML and IFC). The paper presents the procedure used to enable the development of this new expert system as applied to the context of 3D Web GIS. A thorough analysis of the strengths and weaknesses of these different components has been undertaken to employ their strengths and overcome their weaknesses. The system architecture is providing an extension to the 3DCityDB linking to BIMServer without violating indoor information privacy issues. The 3D visualization format glTF works as the integration medium to visualize BIM and CityGML data in web browsers without plugins or other additional software on the client side. The developed software is open source.

The Energy-Oriented Management of Public Historic Buildings: An Integrated Approach and Methodology Applications

In the European framework, there is a strong drive to develop integrated approaches aimed at understanding and improving the energy behavior of public historic buildings within urban contexts. However, the examples already provided tend to address the issue from mono-disciplinary perspectives, losing the opportunity for a coordinated view. The research suggests a methodology to reach the definition of a three-dimensional database, which incorporates spatial models and energy information, with the final goal of merging heterogeneous information that is useful to interpret the overall framework and to design sustainable development scenarios. The platform achieves GIS (Geographic Information System) and BIM (Building Information Modeling) integration by using the CityGML data model, for supporting multi-scale analyses without break of continuity, ranging from urban to building level. The discussion combines the applicative case with the theoretical background, deepening the role of a solid knowledge framework as a basis for sustainable interventions on public historic buildings. To better explain and test the methodology, a case study on the University built heritage of Pavia is presented and three possible outputs deriving from the database are discussed. The example demonstrates the strength of the approach, which is able to provide a variety of results coming from a unique source of information, ensuring coherence and unambiguousness at all levels of investigation.

Three-dimensional CityGML building models in mobile augmented reality: a smartphone-based pose tracking system

ABSTRACT Many augmented reality (AR) systems are developed for entertainment, but AR and particularly mobile AR potentially have more application possibilities in other fields. For example, in civil engineering or city planning, AR could be used in combination with CityGML building models to enhance some typical workflows in planning, execution and operation processes. A concrete example is the geo-referenced on-site visualization of planned buildings or building parts, to simplify planning processes and optimize the communication between the participating decision-makers. One of the main challenges for the visualization lies in the pose tracking, i.e. the real-time estimation of the translation and rotation of the mobile device to align the virtual objects with reality. In this paper, we introduce a proof-of-concept fine-grained mobile AR CityGML-based pose tracking system aimed at the mentioned applications. The system estimates poses by combining 3D CityGML data with information derived from 2D camera images and an inertial measurement unit and is fully self-sufficient and operates without external infrastructure. The results of our evaluation show that CityGML and low-cost off-the-shelf mobile devices, such as smartphones, already provide performant and accurate mobile pose tracking for AR in civil engineering and city planning.

Maintaining Semantic Information across Generic 3D Model Editing Operations

Many of today’s data models for 3D applications, such as City Geography Markup Language (CityGML) or Industry Foundation Classes (IFC) encode rich semantic information in addition to the traditional geometry and materials representation. However, 3D editing techniques fall short of maintaining the semantic information across edit operations if they are not tailored to a specific data model. While semantic information is often lost during edit operations, geometry, UV mappings, and materials are usually maintained. This article presents a data model synchronization method that preserves semantic information across editing operation relying only on geometry, UV mappings, and materials. This enables easy integration of existing and future 3D editing techniques with rich data models. The method links the original data model to the edited geometry using point set registration, recovering the existing information based on spatial and UV search methods, and automatically labels the newly created geometry. An implementation of a Level of Detail 3 (LoD3) building editor for the Virtual Singapore project, based on interactive push-pull and procedural generation of façades, verified the method with 30 common editing tasks. The implementation synchronized changes in the 3D geometry with a CityGML data model and was applied to more than 100 test buildings.

Geospatial Semantic Query Engine for Urban Spatial Data Infrastructure

The research aims at design and develop a special semantic query engine “CityGML Spatial Semantic Web Client (CSSWC)” that facilitates ontology-based multicriteria queries on CityGML data in OGC standard. Presently, there is no spatial method, spatial information infrastructure or any tool to establish the spatial semantic relationship between the 3D city objects in CityGML model. The present work establishes the spatial and semantic relationships between the 3DCityObjects and facilitates ontology-driven spatial semantic query engine on 3D city objects, class with multiple attributes, spatial semantic relations like crosses, nearby, etc., with all other city objects. This is a novel and original work practically implemented generic product for any 3D CityGML model on the globe. A user-friendly form-based interface is designed to compose effective ontology based GeoSPARQL query. CSSWC enhances CityGML applications performance through effective and efficient querying system.

Incorporating Topological Representation in 3D City Models

3D city models are being extensively used in applications such as evacuation scenarios and energy consumption estimation. The main standard for 3D city models is the CityGML data model which can be encoded through the CityJSON data format. CityGML and CityJSON use polygonal modelling in order to represent geometries. True topological data structures have proven to be more computationally efficient for geometric analysis compared to polygonal modelling. In a previous study, we have introduced a method to topologically reconstruct CityGML models while maintaining the semantic information of the dataset, based solely on the combinatorial map (C-Map) data structure. As a result of the limitations of C-Map’s semantic representation mechanism, the resulting datasets could suffer either from semantic information loss or the redundant repetition of them. In this article, we propose a solution for a more efficient representation of geometry, topology and semantics by incorporating the C-Map data structure into the CityGML data model and implementing a CityJSON extension to encode the C-Map data. In addition, we provide an algorithm for the topological reconstruction of CityJSON datasets to append them according to this extension. Finally, we apply our methodology to three open datasets in order to validate our approach when applied to real-world data. Our results show that the proposed CityJSON extension can represent all geometric information of a city model in a lossless way, providing additional topological information for the objects of the model.

An indoor navigation model and its network extraction

We propose a navigation model for indoor environments that combines a 3D geometric modeling of buildings with connection properties of spaces and semantic elements such as openings and installations. The model is an extension of the IndoorGML standard navigation module with a twofold benefit: the extension facilitated the data import from the international standard CityGML and introduced the semantics of various fixtures in indoor space of buildings making the navigation model more suitable for human needs. Several experiments have been conducted by extracting networks from CityGML data and performing a comparison with other network construction techniques. The second contribution of the paper is an algorithm for the automatic extraction of the navigation network. Such an algorithm is a hybrid solution between medial axis approaches and visibility graph approaches. Normally, medial axes approaches are a good representation of human navigation in narrow corridors, especially to avoid obstacles, but introduce distortions in open space. On the other hand, visibility approaches work better in open spaces. In our extraction technique, the resulting network takes advantages of both approaches and better mimics human beings’ navigation in indoor environments.