Underwater 3D measurements with advanced camera modelling

A novel concept of camera modelling for underwater 3D measurements based on stereo camera utilisation is introduced. The geometrical description of the ray course subject to refraction in underwater cameras is presented under assumption of conditions, which are typically satisfied or can be achieved approximately. Possibilities of simplification are shown, which allow an approximation of the ray course by classical pinhole modelling. It is shown how the expected measurement errors can be estimated, as well as its influence on the expected 3D measurement result. Final processing of the 3D measurement data according to the requirements regarding accuracy is performed using several kinds of refinement. For example, calibration parameters can be refined, or systematic errors can be decreased by subsequent compensation by suitable error correction functions. Experimental data of simulations and real measurements obtained by two different underwater 3D scanners are presented and discussed. If inverse image magnification is larger than about one hundred, remaining errors caused by refraction effects can be usually neglected and the classical pinhole model can be used for stereo camera-based underwater 3D measurement systems

A New Sensor System for Accurate 3D Surface Measurements and Modeling of Underwater Objects

Featured Application A potential application of the work is the underwater 3D inspection of industrial structures, such as oil and gas pipelines, offshore wind turbine foundations, or anchor chains. Abstract A new underwater 3D scanning device based on structured illumination and designed for continuous capture of object data in motion for deep sea inspection applications is introduced. The sensor permanently captures 3D data of the inspected surface and generates a 3D surface model in real time. Sensor velocities up to 0.7 m/s are directly compensated while capturing camera images for the 3D reconstruction pipeline. The accuracy results of static measurements of special specimens in a water basin with clear water show the high accuracy potential of the scanner in the sub-millimeter range. Measurement examples with a moving sensor show the significance of the proposed motion compensation and the ability to generate a 3D model by merging individual scans. Future application tests in offshore environments will show the practical potential of the sensor for the desired inspection tasks

Compact handheld fringe projection based underwater 3D-scanner

A new, fringe projection based compact handheld 3D scanner for the surface reconstruction of measurement objects under water is introduced. The weight of the scanner is about 10 kg and can be used in a water depth of maximal 40 metres. A measurement field of about 250 mm x 200 mm is covered under water, and the lateral resolution of the measured object points is about 150 μm. Larger measurement objects can be digitized in a unique geometric model by merging subsequently recorded datasets. The recording time for one 3D scan is a third of a second. The projection unit for the structured illumination of the scene as well as the computer for device control and measurement data analysis are included into the scanners housing. A display on the backside of the device realizes the graphical presentation of the current measurement data. It allows the user to evaluate the quality of the measurement result in real-time already during the recording of the measurement under water. For the calibration of the underwater scanner a combined method of air- and water-calibration was developed which needs only a few recorded underwater images of a plane surface and an object with known lengths. First measurement results obtained with the new scanner are presented

Mobile 3D sensor for documenting maintenance processes of large complex structures

With the new handheld goSCOUT3D sensor system, the entire surface of complex industrial machinery spanning several meters can be captured three-dimensionally within a matter of minutes. In addition, a comprehensive photo collection is registered and precisely assigned to the corresponding 3D object points in one hybrid 2D/3D model. At the basis of the robust 3D digitization are the measuring principles of photogrammetric reconstruction using a high-resolution color camera and simultaneous localization and imaging using a tracking unit. Following image acquisition, the process leading to generation of the complete hybrid model is fully automated. Under continuous movement of the sensor head, up to six images per second and a total of up to several thousand images can be recorded. Those images are then aligned in 3D space and used to reconstruct the 3D model. Results regarding accuracy measurements are presented as well as application examples of digitized technical machinery under maintenance and inspection

Façade reconstruction of destroyed buildings using historical photographs

KEY WORDS: monocular reconstruction, camera calibration, image rectification A methodology for the metric reconstruction of the planar surface of facades of destroyed buildings using historical single-view photographs has been presented in this work. The methodology is based on using a-priori object properties like linearity, parallelism, perpendicularity, symmetry etc. in addition to information extracted from the photographs. The methodology involves the determination of line segments and vanishing points and, if necessary, intrinsic camera calibration. The methodology may be a useful tool for tasks like documentation of historical architecture, surveying, and restoration. Reconstruction examples and results of facades of destroyed buildings are presented and error estimation results are given.

The Duality of Ray-Based and Pinhole-Camera Modeling and 3D Measurement Improvements Using the Ray-Based Model

Geometrical camera modeling is the precondition for 3D-reconstruction tasks using photogrammetric sensor systems. The purpose of this study is to describe an approach for possible accuracy improvements by using the ray-based-camera model. The relations between the common pinhole and the generally valid ray-based-camera model are shown. A new approach to the implementation and calibration of the ray-based-camera model is introduced. Using a simple laboratory setup consisting of two cameras and a projector, experimental measurements were performed. The experiments and results showed the possibility of easily transforming the common pinhole model into a ray-based model and of performing calibration using the ray-based model. These initial results show the model’s potential for considerable accuracy improvements, especially for sensor systems using wide-angle lenses or with deep 3D measurements. This study presents several approaches for further improvements to and the practical usage of high-precision optical 3D measurements