Stereo vision calibration procedure for 3D surface measurements

In reverse engineering, rapid prototyping or quality control with complex 3D object surfaces, there is often the need to scan a complete 3D model using laser digitizers. Those systems usually use one camera and one laser,- using triangulation techniques; complex 3D objects can cause information gaps in the model obtained. To overcome this problem, another camera can be used. Traditional calibration procedures for those systems normally result in a full 3D camera calibration, involving individual implicit camera parameters, a rigid motion equation relating the explicit cameras parameters of each camera and the intersection with the laser line. This paper presents a new stereo vision laser strip calibration procedure for 3D surface measurements. In this calibration procedure the laser plane is the one that matters, only one set of laser-coplanar calibration points for camera calibration is needed, and a dead zone scan area is considered, since the digitalization arm is mounted in a 3 degree freedom machine PC-based Motion Control with multiple scan paths.Fundação para a Ciência e a Tecnologia (FCT

Calibration procedure for 3D surface measurements using stereo vision and laser stripe

This paper proposes a new stereo vision calibration procedure and laser strip detection for 3D surface measurements. In this calibration procedure the laser plane is the one that matters, only one set of laser-coplanar calibration points is needed for image cameras calibration; and a dead- zone scan area is considered, since the igitalization arm is assembled in a 3 degree-freedom machine PC-based Motion Control with multiple scan paths. It is also presented some algorithms for 3D surface treatment.Fundação para a Ciência e a Tecnologia (FCT

3D laser scanner for demonstrational purpose

Bakalářská práce se zabývá konstrukcí demonstračního 3-D skeneru a programu pro zpracování dat, pracujícího s metodou triangulace. Obsahem práce je seznámení se se základními principy skenování, popisem triangulace a teoretickým základem kalibrace optických zařízení jako jsou fotoaparáty a kamery. Následně jsou uvedeny koncepční řešení, konečná konstrukce a popis programu v MatLabu. V příloze lze najít výkres sestavy skeneru a návod pro práci se zařízením.Bachelor's thesis contains construction of demonstration 3-D scanner and scanning programme, based on triangulation method. It involves basic principes of scanning, description of triangulation and basic theory of camera calibration. Thesis solves conception and final construction, also MatLab programme is described. Assembly drawing and operating instructions are included in attachement.

Escáneres ópticos 3D de mano en ingeniería inversa

Data acquisition is a key part in any reverse engineering process. When measuring mechanical components, or any physical object, there are numerous methods to perform this phase, but handheld 3D scanners are among the most popular. Compared to static scanners, handheld scanners have the advantage of being easier to transport and use. The present article contains a brief description of reverse engineering and an analysis of the three technologies that make handheld 3D scanners possible. Examples of the most innovative devices within each category are included and the positioning methods of optical 3D scanners are discussed.This article aims to bring together the latest information on handheld optical scanners and their technologies in order to facilitate the choice of the most suitable method for each application.Una parte fundamental en cualquier proceso de ingeniería inversa es la adquisición de datos.En el caso de componentes mecánicos o, en general, de cualquier objeto físico, existen numerosos métodos y herramientas para abordar dicha fase, entre los que destacan los escáneres ópticos 3D de mano. En comparación con los escáneres estáticos, los escáneres de mano tienen la ventaja de ser más fáciles tanto de transportar como de utilizar. En este documento, tras una breve descripción del proceso de ingeniería inversa, se profundiza en la fase de adquisición de datos y, concretamente, en las tres tecnologías en las que basan su funcionamiento los escáneres ópticos 3D de mano. Además, se incluyen ejemplos de los dispositivos más innovadores dentro de cada categoría y se abordan los métodos de posicionamiento de los escáneres ópticos 3D

Sistemas automáticos para la adquisición de datos enfocados a examinar pavimentos flexibles.

This paper is a review of the main methods of data collection for pavement condition survey. The context in which this kind of data acquires its relevance is shown, as well as the description of each methodology outlined in the literature. Methods are primarily classified as manual and automated. Technological development has made possible to implement automated systems that meet the requirements for this task. However, the manual methodology currently remains as the most common.En este documento se hace una revisión de los principales métodos de recolección de datos para inspección de condición de pavimentos. Se muestra el contexto en el que surge la importancia de este tipo de datos, seguido de la descripción de cada metodología destacada en la literatura. Los métodos se clasifican fundamentalmente en manuales y automáticos. El desarrollo tecnológico ha permitido implementar sistemas automáticos que cumplen las características para realizar esta tarea. Sin embargo, actualmente la metodología manual sigue siendo la más común.

Calibration of structured light system using unidirectional fringe patterns

3D shape measurement has a variety of applications in many areas, such as manufacturing, design, medicine and entertainment. There are many technologies that were successfully implemented in the past decades to measure three dimensional information of an object. The measurement techniques can be broadly classified into contact and non-contact measurement methods. One of the most widely used contact method is Coordinate Measuring Machine (CMM) which dates back to late 1950s. The method by far is one of the most accurate method as it can have sub-micrometer accuracy. But it becomes difficult to use this technique for soft objects as the probe might deform the surface of the object being measured. Also the scanning could be a time-consuming process. In order to address the problems in contact methods, non-contact methods such as time of flight (TOF), triangulation based laser scanner techniques, depth from defocus and stereo vision were invented. The main limitation with the time of flight laser scanner is that it does not give a high depth resolution. On the other hand, triangulation based laser scanning method scans the object line by line which might be time consuming. The depth from defocus method obtains 3D information of the object by relating depth to defocus blur analysis. However, it is difficult to capture the 3D geometry of objects that does not have a rich texture. The stereo vision system imitates human vision. It uses two cameras for capturing pictures of the object from different angles. The 3D coordinate information is obtained using triangulation. The main limitation with this technology is: when the object has a uniform texture, it becomes difficult to find corresponding pairs between the two cameras. Therefore, the structured light system (SLS) was introduced to address the above mentioned limitations. SLS is an extension of stereo vision system with one of the cameras being replaced by a projector. The pre-designed structured patterns are projected on to the object using a video projector. The main advantage with this system is that it does not use the object\u27s texture for identifying the corresponding pairs. But the patterns have to be coded in a certain way so that the camera-projector correspondence can be established. There are many codifications techniques such as pseudo-random codification, binary and N-ary codification. Pseudo-random codification uses laser speckles or structure-coded speckle patterns that vary in both the directions. However, the resolution is limited because each coded structure occupies multiple pixels in order to be unique. On the other hand, binary codifications projects a sequence of binary patterns. The main advantage with such a codification is that it is robust to noise as only two intensity levels are used (0s and 255). However, the resolution is limited because the width of the narrowest coding stripe should be more than the pixel size. Moreover, it takes many images to encode a scene that occupies a large number of pixels. To address this, N-ary codification makes use of multiple intensity levels between 0 and 255. Therefore the total number of coded patterns can be reduced. The main limitation is that the intensity-ratio analysis may be subject to noise. Digital Fringe Projection (DFP) system was developed to address the limitations of binary and N-ary codifications. In DFP computer generated sinusoidal patterns are projected on to the object and then the camera captures the distorted patterns from another angle. The main advantage of this method is that it is robust to the noise, ambient light and reflectivity as phase information is used instead of intensity. Albeit the merit of using phase, to achieve highly accurate 3D geometric reconstruction, it is also of crucial importance to calibrate the camera-projector system. Unlike the camera calibration, the projector calibration is difficult. This is mainly because the projector cannot capture images like a camera. Early attempts were made to calibrate the camera-projector system using a reference plane. The object geometry was reconstructed by comparing the phase difference between the object and the reference plane. However, the chosen reference plane needs to simultaneously possess a high planarity and a good optical property, which is typically difficult to achieve. Also, such calibration may be inaccurate if non-telecentric lenses are used. Calibration of the projector can also be done by treating it as the inverse of a camera. This method addressed the limitations of reference plane based method, as the exact intrinsic and extrinsic parameters of the imaging lenses are obtained. So a perfect reference plane is no longer required. The calibration method typically requires projecting orthogonal patterns on to the object. However, this method of calibration can be used only for structured light system with video projector. Grating slits and interferometers cannot be calibrated by this method as we cannot produce orthogonal patterns with such systems. In this research we have introduced a novel calibration method which uses patterns only in a single direction. We have theoretically proved that there exists one degree-of-freedom of redundancy in the conventional calibration methods, thus making it possible to use unidirectional patterns instead of orthogonal fringe patterns. Experiments show that under a measurement range of 200mm x 150mm x 120mm, our measurement results are comparable to the results obtained using conventional calibration method. Evaluated by repeatedly measuring a sphere with 147.726 mm diameter, our measurement accuracy on average can be as high as 0.20 mm with a standard deviation of 0.12 mm

Anomaly detection in urban drainage with stereovision

This work introduces RADIUS, a framework for anomaly detection in sewer pipes using stereovision. The framework employs three-dimensional geometry reconstruction from stereo vision, followed by statistical modeling of the geometry with a generic pipe model. The framework is designed to be compatible with existing workflows for sewer pipe defect detection, as well as to provide opportunities for machine learning implementations in the future. We test the framework on 48 image sets of 26 sewer pipes in different conditions collected in the lab. Of these 48 image sets, 5 could not be properly reconstructed in three dimensions due to insufficient stereo matching. The surface fitting and anomaly detection performed well: a human-graded defect severity score had a moderate, positive Pearson correlation of 0.65 with our calculated anomaly scores, making this a promising approach to automated defect detection in urban drainage

Investigating the reliability and reproducibility of nasal anthropometry using three-dimensional digital stereophotogrammetry

Three-dimensional Surface Imaging (3DSI) becomes an established method for anthropometric measurements and is applied in a variety of medical disciplines, for example, in the analysis of infant facial development, in the analysis of congenital conditions such as cleft lip and palate or alterations of the skull, in facial reconstructive surgery, and for aesthetic facial plastic surgery consultation. As a non-invasive technology, it plays an increasingly important role in evaluating facial morphology and is often used in support of radiation-intensive CT imaging or expensive MRI imaging. 3DSI of the face provides detailed measurements including distances, curvatures, volumes, angles, and surface areas. Previous studies have shown considerable reliability in the application of 3DSI for the planning and follow-up in rhinoplasty and craniomaxillofacial surgery. Compared to the validated data in the extensive literature on the periorbital region, there is a lack of validated data for 3D acquisition in the nose area. Therefore, more independent verification of the 3D derived measurements is necessary. The present thesis aims to lay the foundation for extensive application of the novel 3D digital nasal anthropometry by evaluating its reliability and reproducibility. In this study, standardized 3DSI of 160 volunteers (80 European Caucasian and 80 Asians) was performed using an established Vectra 3D imaging system. Two raters 3D-imaged the volunteers' facial regions in separate sessions repeatedly. 46 soft-tissue landmarks were determined, and their 138 coordinates were recorded in three spatial planes (x-y-z axis). 57 corresponding projective linear dimensions, surface distances, angles and facial ratios were evaluated for the reliability of intra-rater, inter-rater, and intra-method. Statistical analysis for the reliability was done through mean absolute difference (MAD), relative error measurement (REM), technical error of measurement (TEM), relative technical error of measurement (rTEM), and intraclass correlation coefficient (ICC). 57 corresponding projective linear dimensions, surface distances, angles and facial ratios were evaluated for the reliability of intra-rater, inter-rater, and intra-method.Statistical analysis for the reliability was done through mean absolute difference (MAD), relative error measurement (REM), technical error of measurement (TEM), relative technical error of measurement (rTEM), and intraclass correlation coefficient (ICC). Overall, the 46 landmarks and the anthropometry based on them are highly comparable in this study. The reproducibility for 138 coordinates in 160 samples distribute as follows: intra-rater: 1 mm (13%); inter-rater: 1 mm (26.8%).The reproducibility of landmarks in the nasal tip region is slightly different between Caucasians and Asians. The landmarks in the lip and chin area of males are more reproducible compared with females generally. However, there is no difference in the reproducibility ranking of landmarks by genders. Furthermore, all 57 measurements display a good reliability with ICC above 0.75. Of these, 41 measurements show excellent reliability with ICC larger than or equal to 0.9. The MAD is less than 0.3 mm for most straight-line distances. All the MAD of angles are smaller than 0.3 degree. The MAD is less than 0.01 for ratio measurements except for Nostril Aspect Ratio left (0.013). 50 measurements of estimates for the relative error magnitude were less than 1%. All of rTEM estimates were of very good reliability

Escáner 3D para control de calidad de piezas metalúrgicas

En este documento se presenta el diseño y construcción de un prototipo experimental de escáner 3D el cual puede ser utilizado para obtener las medidas y el modelo tridimensional de un producto metalúrgico con el fin de optimizar el control de calidad en las empresas que fabrican este tipo de producto, trayendo beneficios ya que se elimina la subjetividad en la medida obteniendo una confiabilidad alta y se generan las herramientas para determinar las posibles fallas en la piezas, además de poder diagnosticar en que parte de la fabricación se esta fallando. El prototipo experimental se realizó a través de una metodología estructurada, en la cual se estudiaron las diferentes técnicas de adquisición de imágenes 3D, con la información consultada se determinaron los requerimientos técnicos del sistema, para su posterior diseño y construcción. Para la construcción del dispositivo se utilizó el telémetro láser Hokuyo UTM30LX para la adquisición. Estos datos son adquiridos por medio de la herramienta ROS y procesados con la librería PCL; todo el sistema es controlado por medio de un microcontrolador PIC16F876A el cual se encarga de sincronizar el arranque del motor DC y el algoritmo de adquisición. Para evaluar el funcionamiento de la máquina se contactó a la empresa Electrigas de la ciudad de Pereira, Risaralda, la cual facilitó los cilíndros de gas que fueron escaneados los cuales son fabricados con la norma NTC 522-1 5ta actualización. La finalidad de este prototipo experimental es que entregue al usuario el modelo 3D de la pieza metalúrgica y las medidas para su posterior análisis. En el capitulo 5 se muestran las imágenes y los datos obtenidos al utilizar el escáner desarrollado