Functional and stochastic models for geometrical detection of spatial deformation in engineering: A practical approach

The objective of this study is to formulate a simple and practical but rigorous two-step analysis procedure for the geometrical detection of spatial deformation using geodetic methods. A thorough and critical study of theory and current practice of deformation monitoring has been undertaken, and a practical scheme has been developed for 3-D least squares estimation (LSE) and one-stage detection procedure (i.e. stability determination and localization of spatial deformation) via two-epoch analysis. In LSE, a simple datum definition via minimum constraints with fixed coordinates has been adopted; a strategy for rank defect analysis of normal equations by simplified eigenvalue decomposition (EVD) has been developed; an optimised computational procedure for S-transformations has been formulated; a mathematical model for additional parameters and pseudo observables (distance differences and ratios) has been extended and established for 3-D application; a procedure for handling of algebraically correlated pseudo observations via observation de-correlation has been established; a procedure for robustified LSE for multiple gross errors detection has been formulated and its effects has been derived; a simple method of variance component estimation (VCE) has been extended; and the use of global and local tests and reliability analyses in LSE has been presented. In deformation detection, a strategy for determination of common stations between epochs via S-transformations and partitioning has been developed; a flexible one-stage computational procedure for geometrical detection of spatial deformation by iterative congruency testing and S-transformations has been established; the robust method for deformation detection has been modified to allow one-stage computation; and general S-transformations equations have been applied in all cases. This developed strategy has been implemented in five computer programs (ESTIMATE, COMPS, COMON, DETECT and ROBUST). The developed programs can be executed either on an IBM based personal computer (PC) or under the UNIX environment. Links between these programs and two of the Engineering Surveying Research Centre’s (ESRC) programs (GAP and DCRE) have been established. The programs have been successfully applied and evaluated using simulated and real data. Five real photogrammetric monitoring schemes undertaken by the ESRC, with up to 169 stations, were analysed for detecting the significance of spatial deformation between epochs. The results obtained confirmed the suitability of the strategy in practical applications. Further refinement to the developed programs are suggested to make them more user friendly. Further possible research activities include a combined or integrated approach for deformation analysis and real time deformation monitoring

Improvement in measurement accuracy for hybrid scanner

The capability to provide dense three-dimensional (3D) data (point clouds) at high speed and at high accuracy has made terrestrial laser scanners (TLS) widely used for many purposes especially for documentation, management and analysis. However, similar to other 3D sensors, proper understanding regarding the error sources is necessary to ensure high quality data. A procedure known as calibration is employed to evaluate these errors. This process is crucial for TLS in order to make it suitable for accurate 3D applications (e.g. industrial measurement, reverse engineering and monitoring). Two calibration procedures available for TLS: 1) component, and 2) system calibration. The requirements of special laboratories and tools which are not affordable by most TLS users have become principle drawback for component calibration. In contrast, system calibration only requires a room with appropriate targets. By employing optimal network configuration, this study has performed system calibration through self-calibration for Leica ScanStation C10 scanner. A laboratory with dimensions of 15.5m x 9m x 3m and 138 well-distributed planar targets were used to derive four calibration parameters. Statistical analysis (e.g. t-test) has shown that only two calculated parameters, the constant rangefinder offset error (0.7mm) and the vertical circle index error (-45.4inch were significant for the calibrated scanner. Photogrammetric technique was utilised to calibrate the 3D test points at the calibration field. By using the test points, the residual pattern of raw data and self-calibration results were plotted into the graph to visually demonstrate the improvement in accuracy for Leica ScanStation C10 scanner

THREE-DIMENSIONAL RECORDING AND PHOTOREALISTIC MODEL RECONSTRUCTION FOR VIRTUAL MUSEUM APPLICATION – AN EXPERIENCE IN MALAYSIA

In recent years, museums are utilizing the ability of virtual reality (VR) technologies to visualize their collections in three-dimensional (3D) environment. The demands for 3D digitization of cultural heritage have increase greatly to facilitate the development of virtual museum. Among the available techniques, the use of laser scanning for digital recording and 3D reproduction of the heritage sites and archaeological artefacts are technically more reliable due to its rapid and high resolution data capture. However, the suitable 3D laser scanners used greatly depend on the level of details and size of an object. This research used medium and close-range type of laser scanners to digitally record the heritage objects. The aim of this research was to develop methodology framework for digital recording and 3D reproduction of archaeological artefact and heritage sites in Malaysia by using terrestrial laser scanning technology. Besides, this research focused on the reconstruction of photorealistic 3D models based on the colour information yield by close-range photogrammetry. The colour descriptions were obtained either by built-in camera or externally integrated camera on the laser scanner. For better colour descriptions, external images were captured by independent Nikon D300s digital camera. The geometric model accuracy of A’Famosa and terracotta Buddha statuette was in 5 mm and 0.41 mm respectively. 3D flythrough animation was rendered by using the coloured point clouds model. The development of 3D Virtual Walkthrough Museum (3DVWM) utilized the 3D PDF document and SCENE WebShare platform to offer realistic visualization experience to the visitors where the reality-based models could be manipulate in 3D geometric aspects and use of metric analysis. Thus, 3DVWM can facilitate the virtual museum application in Malaysia and enable wider visitors to virtually appreciate the cultural heritage in Malaysia. Thus, this indirectly stimulates the tourism industry in our country

Natural features technique for non-contact three dimensional craniofacial anthropometry using stereophotogrammetry

This paper describes the use of stereophotogrammetry approach to measure and hence identify accurately three dimensional(3D) coordinates of important landmarks on a craniofacial surface. A “novel” technique dubbed as “natural features” technique was employed to accurately compute the 3D coordinates of selected craniofacial landmarks. The natural features technique involves the use of 3D coordinates of the natural features (such as acne, scar, corners of eyes, edge of mouth, point of chin, etc.) that appear on the craniofacial surface as an absolute stereophotogrammetric mapping control points. The 3D coordinates of the natural features were gained using digital photogrammetric bundle adjustment method. Validation of the proposed technique has firstly been carried out using mannequin and finally, it was applied on the real-life human faces. The result shows that the craniofacial landmark measurement accuracy of 0.8mm with one standard deviation can be successfully achieved by the proposed techniqu

Three dimensional modeling using close range photogrametry for historical artifact

Nowadays, historical artifacts are very valuable to our country. Most museum in Malaysia keep the high value historical artifacts in two dimensional (2D) recorded documentation and cannot give the specific measurements for reconstruction or research purposes. The main objectives of this research are to record and develop the high quality three dimensional images of historical artifact for data documentation so that, the data will be easy to access either for the reliability, accuracy, precision and ensure the originality of the shapes and textures for reconstruction purposes. The implementation of this research is using two techniques which are photograph and laser scanner. This research will focus on the preliminary stage of data recording and processing, digital reconstructions and visualization of artifacts

3D DATA ACQUISITION FOR INDOOR ASSETS USING TERRESTRIAL LASER SCANNING

The newly development of technology clearly shows an improvement of three-dimension (3D) data acquisition techniques. The requirements of 3D information and features have been obviously increased during past few years in many related fields. Generally, 3D visualization can provide more understanding and better analysis for making decision. The need of 3D GIS also pushed by the highly demand of 3D in geospatial related applications as well as the existing fast and accurate 3D data collection techniques. This paper focuses on the 3D data acquisition by using terrestrial laser scanning. In this study, Leica C10 terrestrial laser scanner was used to collect 3D data of the assets inside a computer laboratory. The laser scanner device is able to capture 3D point cloud data with high speed and high accuracy. A series of point clouds was produced from the laser scanner. However, more attention must be paid during the point clouds data processing, 3D modelling, and analysis of the laser scanned data. Hence, this paper will discuss about the data processing from 3D point clouds to 3D models. The processing of point cloud data divided into pre-processing (data registration and noise filter) and post-processing (3D modelling). During the process, Leica Cyclone 7.3 was used to process the point clouds and SketchUp was used to construct the 3D asset models. Afterward, the 3D asset models were exported to multipatch geometry format, which is a 3D GIS-ready format for displaying and storing 3D model in GIS environment. The final result of this study is a set of 3D asset models display in GIS-ready format since GIS can provides the best visual interpretation, planning and decision making process. This paper shows the 3D GIS data could be produced by laser scanning technology after further processing of point cloud data

Deformation detection for ISKANDARnet

Tragedies and disasters in the past have shown the threats that are associated with large construction projects. A timely identification of precursory movements may save lives and minimise collateral damage. An advanced global positioning system (GPS) continuously operating reference station network known as ISKANDARnet is operated continuously to detect deformations in Iskandar, State of Johor, Malaysia. In this study, three GPS continuously operating reference stations from the ISKANDARnet were used as the object stations along four nearby international GNSS service stations (NTUS, XMIS, COCO and PIMO) used as reference stations. The GPS data were streamed and processed by a GPS processing software module, Bernese processing engine. A deformation analysis module was developed using the MATLAB programming language to carry out continuous two-epoch analyses. The development also involves the implementation of the iteratively weighted similarity transformation method and a final S-transformation to analyse the GPS data. By applying these techniques, unstable object points were identified within the monitoring network and accurate displacement vectors were computed. The time-based variation of the displacements was shown in this paper. Test results showed that the system performed satisfactorily

High resolution survey for topographic surveying

In this decade, terrestrial laser scanner (TLS) is getting popular in many fields such as reconstruction, monitoring, surveying, as-built of facilities, archaeology, and topographic surveying. This is due the high speed in data collection which is about 50,000 to 1,000,000 three-dimensional (3D) points per second at high accuracy. The main advantage of 3D representation for the data is that it is more approximate to the real world. Therefore, the aim of this paper is to show the use of High-Definition Surveying (HDS), also known as 3D laser scanning for topographic survey. This research investigates the effectiveness of using terrestrial laser scanning system for topographic survey by carrying out field test in Universiti Teknologi Malaysia (UTM), Skudai, Johor. The 3D laser scanner used in this study is a Leica ScanStation C10. Data acquisition was carried out by applying the traversing method. In this study, the result for the topographic survey is under 1st class survey. At the completion of this study, a standard of procedure was proposed for topographic data acquisition using laser scanning systems. This proposed procedure serves as a guideline for users who wish to utilize laser scanning system in topographic survey fully

TLS for generating multi-LOD of 3D building model

The popularity of Terrestrial Laser Scanners (TLS) to capture three dimensional (3D) objects has been used widely for various applications. Development in 3D models has also led people to visualize the environment in 3D. Visualization of objects in a city environment in 3D can be useful for many applications. However, different applications require different kind of 3D models. Since a building is an important object, CityGML has defined a standard for 3D building models at four different levels of detail (LOD). In this research, the advantages of TLS for capturing buildings and the modelling process of the point cloud can be explored. TLS will be used to capture all the building details to generate multi-LOD. This task, in previous works, involves usually the integration of several sensors. However, in this research, point cloud from TLS will be processed to generate the LOD3 model. LOD2 and LOD1 will then be generalized from the resulting LOD3 model. Result from this research is a guiding process to generate the multi-LOD of 3D building starting from LOD3 using TLS. Lastly, the visualization for multi-LOD model will also be shown