The 3rd ISPRS Workshop on Dynamic and Multi-Dimensional GIS & the 10th Annual Conference of CPGIS on Geoinformatics

Chen, Jun

Bibliographic data

Monograph

Persistent identifier:: 856566209

Author:: Chen, Jun

Title:: The 3rd ISPRS Workshop on Dynamic and Multi-Dimensional GIS & the 10th Annual Conference of CPGIS on Geoinformatics

Sub title:: May 23 - 25, 2001, Bangkok, Thailand

Scope:: VI, 434 Seiten

Year of publication:: 2001

Place of publication:: Pathumthani, Thailand

Publisher of the original:: AIT

Identifier (digital):: 856566209

Illustration:: Illustrationen, Diagramme, Karten

Language:: English

Usage licence:: Attribution 4.0 International (CC BY 4.0)

Publisher of the digital copy:: Technische Informationsbibliothek Hannover

Place of publication of the digital copy:: Hannover

Year of publication of the original:: 2016

Document type:: Monograph

Collection:: Earth sciences

Chapter

Title:: 3D MODELLING FOR AUGMENTED REALITY. Siyka ZLATANOVA

Document type:: Monograph

Structure type:: Chapter

1SPRS, Vol.34, Part 2W2, “Dynamic and Multi-Dimensional GIS”, Bangkok, May 23-25, 2001 3D MODELLING FOR AUGMENTED REALITY Siyka ZLATANOVA Department of Geodesy, Delft University of Technology Thijsseweg 11,2629 JA, Delft, The Netherlands s.zlatanova@qeo.tudelft.nl KEYWORDS 3D topology, 3D model, spatial objects, 3D visualisation, 3D GIS, real-time ABSTRACT This paper addresses an approach for storing 3D spatial objects with respect to the requirements of an outdoor augmented reality application. The presented 3D data structure focuses spatial objects of urban areas, as the aim is support of 3D topology, high level of details and appropriate performance. To satisfy these contradictory requirements, only the outlines of spatial objects are organised in a 3D topological model. Details on façades (e.g. doors, windows) are modelled as line features. An explicit relationship “line on face" indicates the link between the lines and the corresponding façades. The paper concentrates on the 3D topological data structure, which a typical example of so called boundary representations. The 3D data structure is implemented in Oracle 8/ DBMS using three different approaches, i.e. relational, relational with object views and object-relational. The tests have showed that the proposed data structure can be tuned to meet the needs of real-time rendering and positioning for augmented reality. We consider our results a promising step toward extending 3D GISs to serve real-time applications. 1 INTRODUCTION Augmented reality is a mixture of reality and virtuality that allows real world to be augmented with additional information. Virtual objects (text or graphics) are visualised in the field of view via special transparent glasses. The user can observe the surrounding world and the virtual objects simultaneously (see Figure 1). Until recently, the augmented reality application were restricted to indoor applications e.g. surgery, inspection of hazardous spaces. With the advances of the computer and vision technology, augmented reality systems attempt to leave the world of indoor applications, which rises new challenging topics for research. Among them, structuring and database organisation of the 3D model required for positioning and visualisation of virtual objects is most pressing. Augmented reality aiming at outdoor urban applications (e.g. rescue operations, utility management, urban development, guided navigation) needs a 3D model of size comparable to a town, i.e. thousands of houses, streets, parking lots, etc. For example, the national 2D topographic map of The Netherlands contains about 31 million line objects (see [12]). In residential areas this number might increase three or four times for the corresponding 3D model. Such an application faces all the problems in processing and maintaining large 3D data sets. This paper presents a 3D model aiming at both maintenance of 3D topology (one of the most important features of a 3D GIS) and efficient organisation of 3D data for augmented reality applications. The paper is organised in four sections: first the requirements to the data structure are specified with respect to the tasks of the vision system, second the proposed data structure is discussed, then the 3D re-construction procedures are briefly explained and finally some initial experiments within Oracle database are reported. The research is a part of the interdisciplinary UbiCom project carried out at Delft University of Technology, The Netherlands (see [11]). Figure 1: A person with mobile equipment and the observed view 2 REQUIREMENTS Discussions related to the content and the structuring of data in 3D GIS can be found in many publications on 3D GIS (see [2], [3], [8], [13], [15]). Therefore, in this paper, we focus the specific requirements to the 3D model with respect to the vision system intended in the UbiCom project. The 3D model is to be used for two critical subsystems of the system architecture, i.e. positioning and visualisation (rendering) of virtual objects. The expected types of data retrieved from the database are different for both subsystems. • Line features. The positioning system in UbiCom relies on line features (straight lines) supplied by the database. The term positioning refers to determining the accurate location of the user (i.e. the person using the system) in the real world. The movement of the user is followed (tracked) by mobile equipment (GPS, accelerator and inertial system) that provides an approximate positioning at range of 2-10 meters. The accurate positioning is to be achieved by establishing the correspondence between lines extracted from video images (provided by the video camera that is also a part of the mobile unit) in real-time and lines retrieved from the 3D model (see [8]). The success of the line matching (and thus the accurate positioning) is closely related to the amount of details maintained in the 3D model. • 3D topology. In contract to positioning, the visualisation of virtual objects requires no details but correct shape and orientation of the real objects. Since the virtual object is “mixed” with the real world, it is very likely a real object to appear between the virtual one and the user. In this case the real object is said to be an occluder of the virtual object (see [7]). The user should not see the occluded parts of the virtual object. In other words, the rendering engine has to be able to compute which parts of the virtual object are not visible in that particular moment and remove them from the scene. The computations require the accurate location of the user (provided by the positioning system) and the 3D model of the real objects (retrieved from the 3D GIS). The 3D model has to ensure connectivity and continuity. • Performance. The mobile equipment is capable of tracking the movement in certain period of time without reference to the database. This period depends on the speed of walking and the movements of the head. The estimation is that every 6-7 sec the system has to receive new data sets from the database. Within this time (called lag of the system), a query has to be sent to the database, processed and the retrieved data has to be transmitted back to the mobile unit. The performance of the database is one of the critical issues influencing the lag of the system. • Vector representation. Since both rendering and positioning system use vector representation, we concentrate on vector data structures. . VRML. The Virtual Reality Modelling Language was chosen as a standard to exchange data between the individual subsystems. The language provides a full and flexible

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