To reference these data into the real time 3D scene, the PHP page will send a command to ... This part of our system had been developed using virtools's DEV.
IADIS International Conference Computer Graphics and Visualization 2008
A REAL-TIME 3D INTERACTIVE INTERFACE FOR A SPATIAL REFERENCING SYSTEM C. Busayarat UMR CNRS/MCC 694 MAP-GAMSAU
L. De Lucaa, P. Véronb, M. Florenzanoa aUMR
CNRS/MCC 694 MAP-GAMSAU, Marseille, bUMR CNRS 6168-LSIS, Aix-en- Provence
ABSTRACT In this report we were interested in the principles of development of a method for the spatial referencing of an image in a 3D space containing metric information resulting from an architectural survey. This system could constitute as an essential tool for the documentation of the current state of historical buildings. Our research is concentrated on the analysis and the implementation of tools and techniques for the image orientation, on their storage in a database, on the different methods of interrogation of this database and, finally, on the manipulation in real time. We use these principles to define a methodological approach on image acquisition in a survey campaign and to develop a implementation model of a management and consultation system for the data gathered on Internet. KEYWORDS spatial reference, 3D interactive, historical architecture, image database, camera geometrical model
1. INTRODUCTION The ability to access historical architecture information allows to better conserve it and to appreciate its value[Blaise Jy. et al., 2004]. Today, some new tools and techniques (such as 3D laser scanner and photomodeling) allow us to create a 3D building representation. However, other than the three-dimensional data, a large quantity of heterogeneous data collected during the building analysis, is often coming in various formats and is based on different type of media. To collect architecture information is, indeed, just the beginning of a long process involving the documents that show the present state of a building or the analysis of the transformations the building underwent in time. In this research, we are interested mainly in the collection of two types of data: three-dimensional metrical data and bi-dimensional data concerning the documentary source. These data are recorded on different kinds of supports. - The three-dimensional metrical data is recorded in the form of digital models and point clouds (obtained by 3D laser scanning). - The bi-dimension data comes in the form of digital photographs or other kind of visual document. The objective of this work is to create a real-time interactive WEB interface in as a tool to reference 2D information on historical architecture in a three-dimension space containing a digital model. This tool alows the spatial query of graphic documents.The system is structured in three different modules: − A spatial Referencing for graphical documents. − A database that contains the metrical three-dimensional and bi-dimensional data from the surveyed building. − A real-time 3D interactive scene for the operation of Spatial Referencing.
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ISBN: 978-972-8924-63-8 © 2008 IADIS
2. SPATIAL REFERENCING SYSTEM We can obtain several types of the data (positional, directional and optical) from image cameras by using different spatial referencing methods and in different levels of precision. The manual spatial referencing method is the simplest method and the most understandable for the system user. In this research, we create a 3D interactive interface for the image referencing. The objective of this system is to create a tool which allows any users to add referenced images into the data base in interactive way. The system allows the users to manipulate in real-time the plan of the image in 3D space by controlling the navigation camera. The semi-automatic method : This spatial referencing method use a programmed algorithm called camera calibration which is a process that makes it possible to deduce digital values for the camera geometrical and optical parameters from corresponding point between images or between image and 3D model [Cipolla R. et al., 1999,]. This camera calibration method can be use to find the intrinsic parameters (focal distance, enlarging, distortion), the extrinsic parameters (matrix value containing information of camera rotation and translation) and the cameras pose in a three-dimensional coordinate set. The automatic method : Within the framework of our laboratory, we have created a new method of spatial referencing which allow us to automatically record the position and orientation at the moment the photograph has been taken. This method uses a capability of the total station and a peripheral called Omega. The Omega has a total station's prism target and sphere locaters attached. These sphere locaters can be used as a marker for the detection of the camera orientation. Since the total station can measure the given specific point, we can use this function to measure the distance of each 3D scanner's targets. This combination between 3D scanner, total station and Omega is able to give us a 3D point cloud with all the photo referenced into the same three-dimension virtual space. The development of our system has to solve the problem of the uncertainty of image positioning.That is to associate each image with two categories of geometrical information. - External parameter: relative position and orientation of the camera in a coordinate system. - Internal parameter: camera’s focal length In the 3D scene the camera geometrical model associated with an image will be expressed by: 1. T vector (Tx,Ty,Tz) – the camera’s position in space. 2. R vector (Rx,Ry,Rz) – the camera’s orientation in space. 3. Decimal digital value (FL) – the camera’s focal length. These informations could be stored in a database as attributes to qualifying each image. In this work, we also propose several possibilities for spatial reference for different image formats to further enrich our database, such as Perspective projection ,Orthographic projection,Panorama image and Sequence of images. Each format has its own camera geometrical model. Dynamic web page development : For the image uploading process, a dynamic page (developed in PHP) will be used as a tool of the local images selection. Another function of this part of the system is to insert images and their information in the database. The information stored for each photograph is: identification number of image, identification number of the project, method of space referencing , dimensions of the image (width and height). To reference these data into the real time 3D scene, the PHP page will send a command to the 3D scene to download the image from the database and to apply it on a 2D plan (image plan). After that, the system will place the image plan in front of the navigation camera. The user can then manipulate the camera in the 3D scene to referenc image in an interactive way. 3D interactive scene development : This part of our system had been developed using virtools's DEV language. We created a 3D virtual space that allow user to navigate and reference the image in interactive way with different methods and different formats of documents.
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IADIS International Conference Computer Graphics and Visualization 2008
This part of the system can manage space relations between 3D models (or point clouds) and graphic documents in 3D space in real-time. The objective is to provide the users (architects, archaeologists, historians, general public, etc.) an effective way to the access the information. The dialog between parts of the system : The Web application is based on the dialog between a SQL relational database and the 3D scene. To sends a command from the Web part to the 3D scene, we use specific programmed JavaScript functions. In the reverses direction, a Virtools DEV block makes it possible to formulate a query (URL with variables) to the database while passing through a PHP page[De Luca L. et al, 2006.]. The communication between the 3 part of the spatial reference on-line system (database, PHP page, interactive 3D scene) starts when the system user opens the image file from the client computer by using the PHP page. The system then stores the image into the database and sends a command in Javascript to the realtime 3D scene to start the image download process from the database into the scene by using a DEV block (GetWebData). After that, the user can manipulate the 3D scene to find the image point of view. This system function was programmed in Virtools DEV language. If the user of the system found the point of view (from any spatial referenc method), the user can save the camera geometrical information into the database. The 3D scene will automatically return a command in Javascript to the PHP page to modify the information of the image (to mark that this image was already referenced) and add the value of the camera geometrical model, which is a vector of translation, a vector of orientation and the focal distance
3. CONCLUSION In this report we presented our work aiming to the design and the development a system for the spatial referencing of graphic sources that use a relation between three-dimensional information (scene architectural in 3d) and two-dimensional information (graphic documentary source). This will allow us to evaluate the various levels of precision we can obtain by superposing of visual 2D element onto 3D scenes. Our system contains various functionalities that can be used directly on the Internet. This allows the enlargement of the scale of utilsation of our system and makes it possible for the general public to insert data of graphics sources in order to quickly collect and to spatially reference very large numbers of information of visual document
REFERENCES Blaise Jy. et al., 2004. Architectural Modelling and Information Interfacing: Learning from Three Case Studies, ITI 2004: 26th International Conference on Information Technology Interfaces Cavtat / Dubrovnik, 710. Kadobayashi R. et al., 2003, Integrated Presentation System for 3D Models and Image Database for Byzantine Ruins. The International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Vol. XXXIV, Part 5/W12, pp. 187192. Ioannidis C. et al, 2003. An integrated spatial information for development of the archaeological site of Mycenae, TaraspVulpera. Cipolla R. et al., 1999, Camera calibration from vanishing points in images of architectural scenes. Proc. 10th BMVC, pp. 382391, Tsai R.Y., 1987 A versatile camera calibration technique for highaccuracy 3D Machine vision metrology using offtheshelf TV cameras and lenses ,IEEE Journal of Robotics and Automation, Vol. RA3, No. 4. De Luca L. et al, 2006. Reverseengineering of architectural buildings based on a hybrid modeling approach. Special issue on Shape Reasoning and Understanding Computer&Graphics vol. 30, no. 2.
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