CityGML Files Research Articles

DEVELOPMENT OF QGIS PLUGIN FOR URBAN ENERGY SIMULATION USING 3D CITY MODEL AT THE CITY DISTRICT LEVEL

Abstract. In the context of climate change, the increasing demand for energy-efficient buildings and sustainable urban development has become a pressing issue due to the significant proportion of global energy consumption and carbon dioxide (CO2) emissions attributable to the building sector. This requires a concerted effort to reduce its environmental impact, and Geographic Information System (GIS) applications are vital tools for achieving this by optimizing heat supply, calculating costs, analyzing profitability, and balancing CO2 emissions. This study aims to address the challenge of achieving energy efficiency and reducing CO2 emissions in the building sector, specifically at the district level. To this end, the research objective is to develop a QGIS plugin that can simulate urban energy demand at the district level by integrating 2D data with CityGML files and connecting QGIS to SimStadt software via API to visualize the simulated urban energy results in 3D on the Web Globe. The proposed plugin leverages the open-source QGIS tool QField to capture building conditions and connect 2D and 3D data on urban energy simulation. Supplementary to this, this plugin provides up-to-date information on energy demand, consumption, CO2 emissions, building component conditions via updating related tables in the database. Decision-makers can use this comprehensive and user-friendly tool to understand and act on the results, ultimately leading to a CO2-neutral district by 2045. The development of the QGIS plugin represents a significant step towards sustainable urban development and climate change mitigation by utilizing GIS applications for optimizing energy demand and reducing CO2 emissions in the built environment.

Combining CityGML files and data-driven models for microclimate simulations in a tropical city

This research first developed a solution to convert LOD 2 CityGML files to LOD 1 files. Then, by using LOD 1 files as geometric inputs, this study developed a python-based microclimate simulation program based on a customized machine learning algorithm to better understand the relationship between urban morphology and outdoor temperature. The integration with the 3D geometry makes this prediction model not only useful to the scientific research, but also as an urban planning tool for environmentally sustainable design. For model development, meteorological data and urban morphology features were used to predict the daily maximum temperature, daily minimum temperature, daily daytime average temperature and daily night-time average temperature. Voting regression (VOT) based on ordinary least square and random forests was used as the regression model. The average CV-R2 and the CV-RMSE predicted by VOT for the outdoor air temperature were 0.84 and 0.52°C. Compared with ordinary least squares, VOT improved R2 by an average of 18% and RMSE by an average of 24%. Sensitivity analysis indicated the daytime temperature was inversely proportional to the aspect ratio of urban canyon streets. In tropical climates, greenery can be used as a cooling measure. A negative logarithmic relationship was found between the daily maximum temperature, daily minimum temperature and green plot ratio. This shows that as the green coverage increases, the cooling effect of greenery increases, and it is more effective to adopt greenery early in areas with less vegetation.

INTERACTIVE 3D CITY VISUALIZATION FROM STRUCTURE MOTION DATA USING GAME ENGINE

Abstract. Developing a 3D city model is always a challenging task, whether on how to obtain the 3D data or how to present the model to users. Lidar is often used to produce real-world measurement, resulting in point clouds which further processed into a 3D model. However, this method possesses some limitation, e.g. tedious, expensive works and high technicalities, which limits its usability in a smaller area. Currently, there exists pipeline utilize point-clouds from Lidar data to automate the generation of 3D city model. For example, 3dfier (http://github.com/tudelft3d/3dfier) is a software capable of generating LoD 1 3D city model from lidar point cloud data. The resulting CityGML file could further be used in a 3D GIS viewer to produce an interactive 3D city model. This research proposed the use of Structure from Motion (SfM) method to obtain point cloud from UAV data. Using SfM to generate point clouds means cheaper and shorter production time, as well as more suitable for smaller area compared to LiDAR. 3Dfier could be utilized to produce 3D model from the point cloud. Subsequently, a game engine, i.e. Unity 3D, is utilized as the visualization platform. Previous works shows that a game engine could be used as an interactive environment for exploring virtual world based on real-world measurement and other data, such as parcel boundaries. This works shows that the process of generating 3D city model could be achieved using the proposed pipeline.

Transformation of 3D geospatial data into CityGML – a case of Prague

Abstract The 3D geoinformation is becoming important for cities and their policies. The cities are therefore exploring the possibilities of 3D virtual city models for more efficient decision making. To maximize the economic benefit of such data, the cities can provide their 3D geospatial data for further usage, and so, new applications can be created. The paper defines a way how the freely available 3D geospatial data of Prague can be transformed from the proprietary data format into the open data model. The 3D geospatial data about the buildings, bridges and digital terrain model were transformed from the 3D shapefile into the CityGML. This is an application independent information model and exchange format. This will allow for the wider use of the 3D city model by different groups of users. The generated CityGML files were further imported into the spatial database with appropriate database CityGML-based scheme. It enables more efficient management and querying of CityGML data. To enable the wider audience to explore the 3D city model, the visualization in the web environment was also explored. The paper also presents the way how the attributes from the external data sources can be connected to the 3D objects in the web environment.

A metadata ADE for CityGML

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. A lack 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 19115 compliant categories. We then describe how these can be used within CityGML by defining an Application Domain Extension (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.

Compactly representing massive terrain models as TINs in CityGML.

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.

MIGRATION OF DIGITAL CARTOGRAPHY TO CITYGML; A WEB-BASED TOOL FOR SUPPORTING SIMPLE ETL PROCEDURES

Abstract. Digital cartography is notably produced in all countries, in different scales and formats. Latest cartographic production aims at creating 3D objects with topological consistency and rich information linked by attribute tables, i.e. the principles behind data to be managed in geographic information systems (GIS) environments. These data contain all the information necessary for production of the first levels of detail (LOD) of the CityGML model. The work presented reports on the first steps for a guided workflow to upload cartographic data containing building footprints, heights and other information, and migrating it to a validated CityGML model. The steps include a web-portal for uploading the data in a compressed archive containing shapefiles, and a back-end Python script that reads coordinate vertices, attributes and other necessary information, and creates a CityGML file. The process was tested on the Italian topographic geodatabase of some of the main cities of Italy. Discussion on workflow steps and results are presented. Results show that this process is feasible and it can be used to facilitate first tests on transforming existing cartography to CityGML models, which can be then used for further analysis.

Topological information extraction from buildings in CityGML

The demand for 3D city modelling for various applications continue to grow with the capabilities of 3D city modelling. One of the uses of 3D city models is to facilitate 3D analysis which usually requires information regarding the topology of the objects within the city model. CityGML as the international standard for 3D city modelling maintains topological information with the use of a ‘topology-incidence’ where objects are referenced to each other with the condition that the objects share a common surface. This paper explains the extraction of topological information based on the data structure of the geometries in CityGML files and discusses the usability of the existing topology mechanism of CityGML. The topological information was extracted from the CityGML files using the hierarchical geometric structure of CityGML as a stand-in model to describe the topological properties of the object. The extracted information consisted of building surfaces which have been decomposed to 0D points with their respective identification and coordinates. Based on the extracted topological information and related literature, it was found that the topological information extracted from the geometric structure of CityGML was limited to the locality of the object in question and could not extend beyond the dimension of the primitive.

3D Space Shift from CityGML LoD3-Based Multiple Building Elements to a 3D Volumetric Object

In contrast with photorealistic visualizations, urban landscape applications, and building information system (BIM), 3D volumetric presentations highlight specific calculations and applications of 3D building elements for 3D city planning and 3D cadastres. Knowing the precise volumetric quantities and the 3D boundary locations of 3D building spaces is a vital index which must remain constant during data processing because the values are related to space occupation, tenure, taxes, and valuation. To meet these requirements, this paper presents a five-step algorithm for performing a 3D building space shift. This algorithm is used to convert multiple building elements into a single 3D volumetric building object while maintaining the precise volume of the 3D space and without changing the 3D locations or displacing the building boundaries. As examples, this study used input data and building elements based on City Geography Markup Language (CityGML) LoD3 models. This paper presents a method for 3D urban space and 3D property management with the goal of constructing a 3D volumetric object for an integral building using CityGML objects, by fusing the geometries of various building elements. The resulting objects possess true 3D geometry that can be represented by solid geometry and saved to a CityGML file for effective use in 3D urban planning and 3D cadastres.

3D Visualization of Urban Data Based on CityGML with WebGL

Due to the advances in computer graphics and improved network speed it is now possible to navigate in 3D virtual world in real time. Until now, technologies employed require to install standalone application or plugins on navigators. The arrival of HTML 5 brings news solutions to visualize 3D data in a browser with WebGL. Several globe projects have proven that such technologies can be employed. Unfortunately, demonstrations are often based on proprietary formats to exchange or to store data. In this work, we propose to use CityGML: a standard provided by the Open Geospatial Consortium. CityGML files are imported in our Environment Editor. With several tools that we present in this paper, data are processed and stored. A client server application is also presented to permit the visualization of geometry and semantic in a navigator.