Enhanced LoD concepts for virtual 3D city models

Virtual 3D city models contain digital three dimensional representations of city objects like buildings, streets or technical infrastructure. Because size and complexity of these models continuously grow, a Level of Detail (LoD) concept effectively supporting the partitioning of a complete model into alternative models of different complexity and providing metadata, addressing informational content, complexity and quality of each alternative model is indispensable. After a short overview on various LoD concepts, this paper discusses the existing LoD concept of the CityGML standard for 3D city models and identifies a number of deficits. Based on this analysis, an alternative concept is developed and illustrated with several examples. It differentiates between first, a Geometric Level of Detail (GLoD) and a Semantic Level of Detail (SLoD), and second between the interior building and ist exterior shell. Finally, a possible implementation of the new concept is demonstrated by means of an UML model

Tools for BIM-GIS integration (IFC georeferencing and conversions): Results from the GeoBIM benchmark 2019

The integration of 3D city models with Building Information Models (BIM), coined as GeoBIM, facilitates improved data support to several applications, e.g., 3D map updates, building permits issuing, detailed city analysis, infrastructure design, context-based building design, to name a few. To solve the integration, several issues need to be tackled and solved, i.e., harmonization of features, interoperability, format conversions, integration of procedures. The GeoBIM benchmark 2019, funded by ISPRS and EuroSDR, evaluated the state of implementation of tools addressing some of those issues. In particular, in the part of the benchmark described in this paper, the application of georeferencing to Industry Foundation Classes (IFC) models and making consistent conversions between 3D city models and BIM are investigated, considering the OGC CityGML and buildingSMART IFC as reference standards. In the benchmark, sample datasets in the two reference standards were provided. External volunteers were asked to describe and test georeferencing procedures for IFC models and conversion tools between CityGML and IFC. From the analysis of the delivered answers and processed datasets, it was possible to notice that while there are tools and procedures available to support georeferencing and data conversion, comprehensive definition of the requirements, clear rules to perform such two tasks, as well as solid technological solutions implementing them, are still lacking in functionalities. Those specific issues can be a sensible starting point for planning the next GeoBIM integration agendas

Generalization of buildings within the framework of CITYGML

For a better visual impression, 3D information systems and architecture need detailed, photo-realistic visualization of 3D data-sets. However, easy accessibility with efficient rendering becomes difficult due to the detailed data associated with 3D objects. Therefore, different applications demand different levels of detail (LoD). Currently, City Geography Markup Language (CityGML), as the Open Geospatial Consortium standard, is being used to model and represent buildings in different LoDs (LoD0-LoD4), but it does not provide methods to generate different LoDs automatically. Thus, generalized (abstracted) 3D scenes of buildings need to be generated to fulfill the demands of task-specific applications by reducing data volume. This paper discusses various ways to generalize building models, within the framework of CityGML, reducing the level of detail from higher LoD to lower. The LoD4 data is parsed and analyzed. Various heuristics are applied to simplify the ground plan and the results are then aggregated. The minimum length of an edge for simplification is restricted to the CityGML generalization specifications provided and is characterized by differing accuracies and minimal dimensions of objects for LoD1 and LoD2. This could maintain the accuracy of generalized objects and avoid the elimination or merging of important features. Second, the heights of the walls of the simplified ground plans are raised with the aim to construct simplified 3D building models. Algorithms for simplification and aggregation aiming to derive LoD2 and LoD1 are implemented and tested on a number of buildings of Putrajaya, Malaysia. The experiment results show that the minimum length of edges to be simplified is inversely proportional to the size of generalized model

CityGML rakennusmallien tuottaminen ilmalaserkeilauksesta

3D city models have become an important tool in many applications across different fields. Usually these 3D city models only represent the geometrical attributes of the city, which enables easy visualization of cities. Yet, different thematic queries, analysis tasks, and spatial data mining are out of the reach of models that only offer us information about their geometry. CityGML 3D city models bring an addition of semantic information to the models. In this thesis, the process and different techniques of building reconstruction from airborne laser scanning are explained. CityGML standard will also be explained and what has to be done in order to go from 3D building models to CityGML. The main focus of this thesis was to study how well it is possible to automatically create CityGML 2.0 3D city models from data collected only by airborne laser scanning. CityGML has five different levels-of-detail indicating the level of precision of the building. LOD1 and LOD2 were the most important levels for this thesis, and so it was tested how well different software were able to export reconstructed building models in the CityGML format with these precision levels. These exports were checked against the official specification of CityGML to see how well they met the requirements. It was also explained what more would be needed for the process and data, in order to produce higher quality models in LOD3. Two different test areas were chosen with different building and roof types. One area included detached houses, some partly covered with vegetation, and another area included mainly apartment houses. The thesis shows that as of now, it is still quite challenging to automatically produce city models that are in line with the CityGML 2.0 standard. The model driven methods had problems when it came to building installations, such as chimneys. These could not be modelled with software that used model driven methods. Data driven methods on the other hand had problems when it came to the conversion from the building models to the CityGML format. Terrain and terrain intersection curve also turned out to be more difficult to model than anticipated. Most of the software used in this thesis were not able to automatically handle the addition of these elements. The elements were possible to add later on to the CityGML file but only with use of additional software tools.3D kaupunkimalleista on tullut tärkeä työkalu eri alojen käyttämissä sovelluksissa. Yleensä näitä 3D kaupunkimalleja käytetään vain kaupunkien geometristen attribuuttien mallintamiseen visualisointitarkoituksiin. Kuitenkin erilaiset temaattiset kyselyt, analyysitehtävät ja spatiaalinen tiedonlouhinta ovat pelkästään geometriaa esittävien mallien ulottumattomissa. CityGML 3D kaupunkimallit ottavat huomioon lisäksi myös semanttisen tiedon. Tässä työssä selitetään rakennusten rekonstruointiprosessi ilmalaserkeilauksesta sekä esitellään erilaisia rekonstruointitekniikoita. Myös CityGML standardi esitellään sekä se, mitä 3D rakennusmalleille pitää tehdä, jotta ne saataisiin CityGML muotoon. Tämän työn pääpiste oli, kuinka hyvin on mahdollista automaattisesti luoda CityGML 2.0 muotoisia 3D kaupunkimalleja pelkästään ilmalaserkeilaamalla kerätystä aineistosta. CityGMLssä on viisi erilaista yksityiskohtatasoa, jotka kertovat, kuinka tarkasti rakennus on mallinnettu. Näistä LOD1 ja LOD2 olivat tämän työn kannalta oleellisimmat. Tämän vuoksi sitä, kuinka hyvin ohjelmista saadaan ulos rakennusmalleja CityGML muodossa näillä tarkkuusvaatimuksilla, testattiin. Saatuja tuloksia verrattiin virallisiin CityGML vaatimuksiin, jotta saatiin selville, kuinka hyvin vaatimukset täyttyivät. Myös se käytiin läpi, mitä muutoksia tarvittaisiin, jotta malleista saataisiin korkeamman, LOD3, tason malleja. Valittiin kaksi erilaista testialuetta, joilla oli erilaisia rakennus- ja kattotyyppejä. Toisella alueella oli omakotitaloja, joista jotkut olivat osittain kasvillisuuden peittämiä ja toisella oli pääsääntöisesti kerrostaloja. Työstä käy ilmi, että vielä tällä hetkellä automaattinen CityGML 2.0 standardin mukaisten kaupunkimallien tuottaminen on haastavaa. Mallipohjaisilla menetelmillä oli vaikeuksia rakennusten pienien osien, kuten savupiippujen, suhteen. Näitä ei pystytty mallintamaan ohjelmilla, jotka pohjautuivat mallipohjaisiin menetelmiin. Toisaalta tietopohjaisilla menetelmillä oli ongelmia, kun ne muunnettiin CityGML formaattiin. Maanpinnan sekä maanpinnan ja rakennuksen leikkauksen mallintamisessa oli odotettua enemmän ongelmia. Useimmat tässä työssä käytetyt ohjelmat eivät pystyneet automaattisesti näitä mallintamaan. Kuitenkin, ne oli mahdollista lisätä jälkikäteen käyttämällä muita ohjelmia

Proposal for a new LoD and multi-representation concept for CityGML

The Open Geospatial Consortium (OGC) CityGML standard offers a Level of Detail (LoD) concept that enables the representation of CityGML features from a very detailed to a less detailed description. Due to a rising application variety, the current LoD concept seems to be too inflexible. Here, we present a multi representation concept (MRC) that enables a user-defined definition of LoDs. Because CityGML is an international standard, official profiles of the MRC are proposed. However, encoding of the defined profiles reveals many problems including mapping the conceptual model to the normative encoding, missing technologies and so on. Therefore, we propose to use the MRC as a meta model for the further definition of an LoD concept for CityGML 3.0

Interoperability of Traffic Infrastructure Planning and Geospatial Information Systems

Building Information Modelling (BIM) as a Model-based design facilitates to investigate multiple solutions in the infrastructure planning process. The most important reason for implementing model-based design is to help designers and to increase communication between different design parties. It decentralizes and coordinates team collaboration and facilitates faster and lossless project data exchange and management across extended teams and external partners in project lifecycle. Infrastructure are fundamental facilities, services, and installations needed for the functioning of a community or society, such as transportation, roads, communication systems, water and power networks, as well as power plants. Geospatial Information Systems (GIS) as the digital representation of the world are systems for maintaining, managing, modelling, analyzing, and visualizing of the world data including infrastructure. High level infrastructure suits mostly facilitate to analyze the infrastructure design based on the international or user defined standards. Called regulation1-based design, this minimizes errors, reduces costly design conflicts, increases time savings and provides consistent project quality, yet mostly in standalone solutions. Tasks of infrastructure usually require both model based and regulation based design packages. Infrastructure tasks deal with cross-domain information. However, the corresponding data is split in several domain models. Besides infrastructure projects demand a lot of decision makings on governmental as well as on private level considering different data models. Therefore lossless flow of project data as well as documents like regulations across project team, stakeholders, governmental and private level is highly important. Yet infrastructure projects have largely been absent from product modelling discourses for a long time. Thus, as will be explained in chapter 2 interoperability is needed in infrastructure processes. Multimodel (MM) is one of the interoperability methods which enable heterogeneous data models from various domains get bundled together into a container keeping their original format. Existing interoperability methods including existing MM solutions can’t satisfactorily fulfill the typical demands of infrastructure information processes like dynamic data resources and a huge amount of inter model relations. Therefore chapter 3 concept of infrastructure information modelling investigates a method for loose and rule based coupling of exchangeable heterogeneous information spaces. This hypothesis is an extension for the existing MM to a rule-based Multimodel named extended Multimodel (eMM) with semantic rules – instead of static links. The semantic rules will be used to describe relations between data elements of various models dynamically in a link-database. Most of the confusion about geospatial data models arises from their diversity. In some of these data models spatial IDs are the basic identities of entities and in some other data models there are no IDs. That is why in the geospatial data, data structure is more important than data models. There are always spatial indexes that enable accessing to the geodata. The most important unification of data models involved in infrastructure projects is the spatiality. Explained in chapter 4 the method of infrastructure information modelling for interoperation in spatial domains generate interlinks through spatial identity of entities. Match finding through spatial links enables any kind of data models sharing spatial property get interlinked. Through such spatial links each entity receives the spatial information from other data models which is related to the target entity due to sharing equivalent spatial index. This information will be the virtual properties for the object. The thesis uses Nearest Neighborhood algorithm for spatial match finding and performs filtering and refining approaches. For the abstraction of the spatial matching results hierarchical filtering techniques are used for refining the virtual properties. These approaches focus on two main application areas which are product model and Level of Detail (LoD). For the eMM suggested in this thesis a rule based interoperability method between arbitrary data models of spatial domain has been developed. The implementation of this method enables transaction of data in spatial domains run loss less. The system architecture and the implementation which has been applied on the case study of this thesis namely infrastructure and geospatial data models are described in chapter 5. Achieving afore mentioned aims results in reducing the whole project lifecycle costs, increasing reliability of the comprehensive fundamental information, and consequently in independent, cost-effective, aesthetically pleasing, and environmentally sensitive infrastructure design.:ABSTRACT 4 KEYWORDS 7 TABLE OF CONTENT 8 LIST OF FIGURES 9 LIST OF TABLES 11 LIST OF ABBREVIATION 12 INTRODUCTION 13 1.1. A GENERAL VIEW 14 1.2. PROBLEM STATEMENT 15 1.3. OBJECTIVES 17 1.4. APPROACH 18 1.5. STRUCTURE OF THESIS 18 INTEROPERABILITY IN INFRASTRUCTURE ENGINEERING 20 2.1. STATE OF INTEROPERABILITY 21 2.1.1. Interoperability of GIS and BIM 23 2.1.2. Interoperability of GIS and Infrastructure 25 2.2. MAIN CHALLENGES AND RELATED WORK 27 2.3. INFRASTRUCTURE MODELING IN GEOSPATIAL CONTEXT 29 2.3.1. LamdXML: Infrastructure Data Standards 32 2.3.2. CityGML: Geospatial Data Standards 33 2.3.3. LandXML and CityGML 36 2.4. INTEROPERABILITY AND MULTIMODEL TECHNOLOGY 39 2.5. LIMITATIONS OF EXISTING APPROACHES 41 INFRASTRUCTURE INFORMATION MODELLING 44 3.1. MULTI MODEL FOR GEOSPATIAL AND INFRASTRUCTURE DATA MODELS 45 3.2. LINKING APPROACH, QUERYING AND FILTERING 48 3.2.1. Virtual Properties via Link Model 49 3.3. MULTI MODEL AS AN INTERDISCIPLINARY METHOD 52 3.4. USING LEVEL OF DETAIL (LOD) FOR FILTERING 53 SPATIAL MODELLING AND PROCESSING 58 4.1. SPATIAL IDENTIFIERS 59 4.1.1. Spatial Indexes 60 4.1.2. Tree-Based Spatial Indexes 61 4.2. NEAREST NEIGHBORHOOD AS A BASIC LINK METHOD 63 4.3. HIERARCHICAL FILTERING 70 4.4. OTHER FUNCTIONAL LINK METHODS 75 4.5. ADVANCES AND LIMITATIONS OF FUNCTIONAL LINK METHODS 76 IMPLEMENTATION OF THE PROPOSED IIM METHOD 77 5.1. IMPLEMENTATION 78 5.2. CASE STUDY 83 CONCLUSION 89 6.1. SUMMERY 90 6.2. DISCUSSION OF RESULTS 92 6.3. FUTURE WORK 93 BIBLIOGRAPHY 94 7.1. BOOKS AND PAPERS 95 7.2. WEBSITES 10

The Energy Application Domain Extension for CityGML: enhancing interoperability for urban energy simulations

The road towards achievement of the climate protection goals requires, among the rest, a thorough rethinking of the energy planning tools (and policies) at all levels, from local to global. Nevertheless, it is in the cities where the largest part of energy is produced and consumed, and therefore it makes sense to focus the attention particularly on the cities as they yield great potentials in terms of energy consumption reduction and efficiency increase. As a direct consequence, a comprehensive knowledge of the demand and supply of energy resources, including their spatial distribution within urban areas, is therefore of utmost importance. Precise, integrated knowledge about 3D urban space, i.e. all urban (above and underground) features, infrastructures, their functional and semantic characteristics, and their mutual dependencies and interrelations play a relevant role for advanced simulation and analyses. As a matter of fact, what in the last years has proven to be an emerging and effective approach is the adoption of standard-based, integrated semantic 3D virtual city models, which represent an information hub for most of the abovementioned needs. In particular, being based on open standards (e.g. on the CityGML standard by the Open Geospatial Consortium), virtual city models firstly reduce the effort in terms of data preparation and provision. Secondly, they offer clear data structures, ontologies and semantics to facilitate data exchange between different domains and applications. However, a standardised and omni-comprehensive urban data model covering also the energy domain is still missing at the time of writing (January 2018). Even CityGML falls partially short when it comes to the definition of specific entities and attributes for energy-related applications. Nevertheless, and starting from the current version of CityGML (i.e. 2.0), this article describes the conception and the definition of an Energy Application Domain Extension (ADE) for CityGML. The Energy ADE is meant to offer a unique and standard-based data model to fill, on one hand, the above-mentioned gap, and, on the other hand, to allow for both detailed single-building energy simulation (based on sophisticated models for building physics and occupant behaviour) and city-wide, bottom-up energy assessments, with particular focus on the buildings sector. The overall goal is to tackle the existing data interoperability issues when dealing with energy-related applications at urban scale. The article presents the rationale behind the Energy ADE, it describes its main characteristics, the relation to other standards, and provides some examples of current applications and case studies already adopting it