Multi-camera Imaging System Research Articles

High Precision Visual Dimension Measurement Method with Large Range Based on Multi-Prism and M-Array Coding.

The visual dimension measurement method based on non-splicing single lens has the contradiction between accuracy and range of measurement, which cannot be considered simultaneously. In this paper, a multi-camera cooperative measurement method without mechanical motion is proposed for the dimension measurement of thin slice workpiece. After the calibration of the multi-camera imaging system is achieved through a simple and efficient scheme, the high-precision dimension measurement with a large field of view can be completed through a single exposure. First, the images of the edges of the workpiece are compressed and combined by splitting and merging light through the multi-prism system, and the results are distributed to multiple cameras by changing the light path. Then, the mapping relationship between the global measurement coordinates and the image coordinates of each camera is established based on the globally unique M-array coding, and the image distortion is corrected by the coding unit composed of black and white blocks. Finally, the edge is located accurately by edge point detection at the sub-pixel level and curve fitting. The results of measuring a test workpiece with the dimension of 24 mm × 12 mm × 2 mm through a single exposure show that the repeated measurement accuracy can reach 0.2 µm and the absolute accuracy can reach 0.5 µm. Compared with other methods, our method can achieve the large-field measurement through only one exposure and without the mechanical movement of cameras. The measurement precision is higher and the speed is faster.

A Low-Cost and Ultralight Unmanned Aerial Vehicle-Borne Multicamera Imaging System Based on Smartphones

Newly developed oblique photogrammetry (OP) techniques based on unmanned aerial vehicles (UAVs) equipped with multicamera imaging systems are widely used in many fields. Smartphones cost less than the cameras commonly used in the existing UAV OP system, providing high-resolution images from a built-in imaging sensor. In this paper, we design and implement a novel low-cost and ultralight UAV OP system based on smartphones. Firstly, five digital cameras and their accessories detached from the smartphones are then fitted into a very small device to synchronously shoot images at five different perspective angles. An independent automatic capture control system is also developed to realize this function. The proposed smartphone-based multicamera imaging system is then mounted on a modified version of an existing lightweight UAV platform to form a UAV OP system. Three typical application examples are then considered to evaluate the performance of this system through practical experiments. Our results indicate that both horizontal and vertical location accuracy of the generated 3D models in all three test applications achieve centimeter-level accuracy with respect to different ground sampling distances (GSDs) of 1.2 cm, 2.3 cm, and 3.1 cm. The accuracy of the two types of vector maps derived from the corresponding 3D models also meet the requirements set by the surveying and mapping standards. The textural quality reflected by the 3D models and digital ortho maps (DOMs) are also distinguishable and clearly represent the actual color of different ground objects. Our experimental results confirm the quality and accuracy of our system. Although flight efficiency and the accuracy of our designed UAV OP system are lower than that of the commercial versions, it provides several unique features including very low-cost, ultralightweight, and significantly easier operation and maintenance.

Investigation of turbulent boundary layer flows with adverse pressure gradient by means of 3D Lagrangian particle tracking with Shake-The-Box

A large-scale 3D Lagrangian particle tracking (LPT) investigation of a turbulent boundary layer (TBL) flow developing across different pressure gradient regions is presented in this study. Three high-speed multi-camera imaging systems, LED illumination and helium-filled soap bubbles (HFSB) tracers have been adopted to produce time-resolved sequences of particle images over a large volume encompassing approximately 3 m in the streamwise direction, 0:8 m in the spanwise direction and 0:25 m in the wall-normal direction. Individual tracers have been reconstructed and tracked within the imaged volume by means of the Shake-The-Box algorithm (STB, Schanz et al. (2016)); the FlowFit data assimilation algorithm (Gesemann et al. (2016)) has been used to evaluate the spatial velocity gradients and to interpolate the scattered LPT results onto a regular grid. Thanks to the large size of the investigated volume and to the time-resolved nature of the recorded images, the entire spatial extent of the large-scale coherent motions within the logarithmic region of the TBL (i.e. superstructures) could be captured and their dynamics investigated during their development over several boundary layer thickness in the streamwise direction, from the zero pressure gradient region (ZPG) to the adverse pressure gradient region (APG). Two free-stream velocities were investigated, namely 7 and 14m=s, corresponding to Ret ~ 3,000 and 5,000 respectively. The results confirm the location and scale of the elongated high- and low-momentum structures in the logarithmic region, as well as their meandering in the spanwise direction. Two-point correlation statistics show that the width and spacing of the superstructures are not affected by the transition from the ZPG to the APG region. The analysis of the instantaneous flow realizations from both a Lagrangian and Eulerian perspective indicates the presence of significant fluid particle elements exchange across the interfaces of the large-scale structures.

Real-time and ultrahigh accuracy image synthesis algorithm for full field of view imaging system

In this paper, we propose a real time, ultrahigh accuracy and full-field-of-view (RUF) algorithm for full field of view (FOV) imaging system. The proposed algorithm combines rough matching and precise matching method to stitch multiple images with the whole FOV in short time and high imaging quality. In order to verify real-time imaging effect of RUF algorithm, we also fabricate a multi-camera imaging system which includes 19 independent cameras. And the experiment result practically illustrates that full-FOV system can achieve good performances under a near-limiting FOV of 360° × 240° with low distortion, meanwhile, optical resolution reaches up to 95 megapixels. 100% registration-accuracy RUF algorithm for imaging in one second can be widely applied to any optical imaging engineering field with large FOV, such as remote sensing imaging, microscopy imaging, monitoring system engineering fields and so on.

Group geometric calibration and rectification for circular multi-camera imaging system

Calibration on multi-camera imaging system in circular arrangement is a challenge task, because the preliminary shared feature points are absent among opposite viewpoints in the calibration procedure. In this paper, we propose a scheme of group geometric calibration and ideal rectification for circular multi-camera imaging system. In this scheme, a three-dimensional (3D) calibration object with new patterns is firstly designed to extract the extrinsic parameters. After that, the ideal camera projection matrix is estimated based on these parameters. Finally, we extend our scheme from static to dynamic scenario. In the experiments, our method has a superior performance over state-of-the-art calibration methods. Furthermore, we verify our scheme by application of 3D modeling and improvements can also be found. These results demonstrate that our method performance on such imaging system is applicable for future interactive visual applications.

Kinematic analysis on sliding shot put

In this paper, a comprehensive three-dimensional kinematic quantitative analysis has been applied to analyse the movement and biomechanics of throwing technology of a Chinese excellent women's shot. The filming is conducted with a multi-camera 3D imaging system during the championship. A star high titanium 3D signal TEC V1.0C three-dimensional video analysis software system is used for parsing with the RBI web parsing resolution. The human body model applied is Japan Matsui (16, 22 key parameters). The throwing movement is divided into five main stages: the oscillating acceleration phase, the sliding stage, the transition phase and the last stage of throwing. Research analysis for each phase has focused on different biomechanical characteristics and parameters. The key parameters for the throwing movement of the subject in this work is critically compared to other data of related parameters of the domestic and foreign excellent athletes with reference to the general rule of shot put techniques. The key issues associated with the throwing and future biomechanical training is discussed.

Position Based Single Particle Tracking (P-SPT) for High-Resolution Deformation and Motion Capture

Our recently developed Position based Single Particle Tracking (P-SPT) algorithm utilizes a novel approach to track particles at high seeding density in 2D and 3D at very fast computational speeds. Traditional kinematic measurement technique like single particle tracking (SPT) struggle at accurately reconstructing large, nonlinear material deformation fields, and high spatial frequency content as they are computationally very expensive for high particle seeding densities, especially in 3D. Despite recent advances, approaches like image correlation are also computationally expensive and are limited in the recovery of high spatial frequency information due to their intrinsic correlation nature. P-SPT tracks particles by creating unique feature identifiers for each particle using the relative geometric position of neighboring particles. This unique feature identifier, or descriptor, is used for particle linking between two successive time frames. The nature of feature descriptor along with a deformation warping function enables P-SPT to capture large, nonlinear material deformation fields. Validation of P-SPT performed on synthetically generated 3D volumetric images show that P-SPT is computationally efficient equipping it to track particles at high seeding densities far exceeding the typical bead densities used in traditional SPT methodologies thus enabling it to reconstruct high spatial frequency information. Since P-SPT only requires the particle position for tracking, it can be employed for tracking motion fields in 2D images, 3D volumetric images or multi-camera imaging system. This flexibility of P-SPT along with its computational efficiency means that it can be executed reliably on a simple personal computers in variety of biological applications that require reconstruction of high frequency and high spatial motion content, like quantifying cell deformations for 2D and 3D traction force microscopy, subcellular dynamics or particle dynamics in granular and cellular media.

On the feasibility of tomographic-PIV with low pulse energy illumination in a lifted turbulent jet flame

Tomographic particle image velocimetry (tomographic-PIV) is a recently developed measurement technique used to acquire volumetric velocity field data in liquid and gaseous flows. The technique relies on line-of-sight reconstruction of the rays between a 3D particle distribution and a multi-camera imaging system. In a turbulent flame, however, index-of-refraction variations resulting from local heat-release may inhibit reconstruction and thereby render the technique infeasible. The objective of this study was to test the efficacy of tomographic-PIV in a turbulent flame. An additional goal was to determine the feasibility of acquiring usable tomographic-PIV measurements in a turbulent flame at multi-kHz acquisition rates with current-generation laser and camera technology. To this end, a setup consisting of four complementary metal oxide semiconductor cameras and a dual-cavity Nd:YAG laser was implemented to test the technique in a lifted turbulent jet flame. While the cameras were capable of kHz-rate image acquisition, the laser operated at a pulse repetition rate of only 10 Hz. However, use of this laser allowed exploration of the required pulse energy and thus power for a kHz-rate system. The imaged region was 29 × 28 × 2.7 mm in size. The tomographic reconstruction of the 3D particle distributions was accomplished using the multiplicative algebraic reconstruction technique. The results indicate that volumetric velocimetry via tomographic-PIV is feasible with pulse energies of 25 mJ, which is within the capability of current-generation kHz-rate diode-pumped solid-state lasers.

Fast multicamera video stitching for underwater wide field-of-view observation

Underwater robots equipped with a single forward-looking camera usually have a very limited visual range or field-of-view (FOV) due to the light absorption and scattering effects in the underwater environment, which greatly limit their applications for underwater video-based inspection, navigation, and so on. Although underwater robots using multicamera imaging systems can achieve wide FOV of surroundings, parallax distortion and time-consuming stitching computation are encountered, especially for short-distance observation. To overcome these problems, we present a fast multicamera video-stitching algorithm based on adaptive adjustment of image transformation matrix between adjacent images. The proposed method uses a fast and adaptive optimization algorithm to search the optimal parameters of transformation matrix that can minimize the parallax distortion due to short-distance imaging and maximize the matching degree between adjacent overlapping image areas. The advantage of the proposed stitching method lies in that it avoids the complex and time-consuming computations for feature-point extraction and matching. The experimental results show that the proposed method can construct multicamera-based wide FOV video effectively and meets the real-time requirement of wide FOV video observation for both indoor and underwater scenes.

Design, Implementation and Simulation of an Experimental Multi-Camera Imaging System for Terrestrial and Multi-Purpose Mobile Mapping Platforms: A Case Study

Mobile Mapping Systems (MMS’s) are powerful tools for rapidly and massively collecting imagery in various environments (e.g., rural, semi-urban, urban). In particular, the data collected at terrestrial level can be exploited to complement aerial acquisitions for extending GIS databases,visualizing and modeling urban environments and studying environment morphogenesis over time. Hence, the development of mobile mapping platforms is a topic of great interest for many mapping agencies and surveying companies. Moreover, the experimental imaging systems of mapping vehicles are equipped with varied infrastructures in part resulting from the wide range of targeted applications. Determining a detailed design procedure for such imaging systems is of critical importance, and can be both arduous and time-consuming. Although commercial imaging systems can be exploited directly they are often pre-configured for specific applications. For these reasons, we propose a case study that deals with the development of an orientable and scalable imaging system. In particular, this paper focusses on the primary stage of the mechanical implementation of a multi-camera infrastructure. To this effect, we provide a design document that includes full technical specifications and drawings for creating a roof-mounted camera mast from a vehicle platform. We also provide an inventory of resources required for creating the system. As part of the design process we analyse some well-known MMS’s paying particular attention to their imaging systems. Finally, we evaluate the proposed design by creating the complete 3D mock-up of the camera system at real-scale and by simulating camera configurations from an experimental van platform. Experimental results clearly show the usefulness of this study in the design of an experimental and multi-purpose imaging system.

Digital Imaging-Based Three-Dimensional Characterization of Flame Front Structures in a Turbulent Flame

This paper focuses on the application of a multicamera imaging system for three-dimensional (3-D) visualization and quantitative characterization of the flame front structures of a turbulent flame. The 2-D images of the flame front are captured simultaneously using identical monochromatic CCD cameras from three different directions around the flame. Dedicated computing algorithms have been developed to reconstruct the 3-D structures of the flame front using various image processing techniques such as edge detection, contour extraction, and mesh generation. A set of flame parameters, including ignition points, ignition volume, ignition surface area, and circularity, is determined from the models generated to characterize the flame front. Results obtained under a range of combustion conditions demonstrate the capability of the system for 3-D quantitative characterization of flame front structures.