Calibration Template Research Articles

Camera calibration using the dual double-contact property of circles

To mitigate the influence of the relative positional relationship between circles on camera calibration, this study explores the double contact of dual circles with dual circular points. We demonstrate that one of the generalized eigenvectors of two dual circles corresponds to the line passing through their respective centers. Moreover, we establish a methodology to identify this line from the three generalized eigenvectors and show that, regardless of the positional arrangement of the three co-planar circles, the image of the circular points can be constructed by calculating the image of this line. Consequently, the applicability of circles as calibration templates is expanded, enabling the development of a novel optimization technique for fitting circular images with enhanced calibration precision.

ОЦЕНКА СИСТЕМ КООРДИНАТНЫХ МЕТОК С ИСПОЛЬЗОВАНИЕМ БОРТОВОЙ КАМЕРЫ МОБИЛЬНОГО РОБОТА «СЕРВОСИЛА ИНЖЕНЕР» В УСЛОВИЯХ ЗАКРЫТЫХ ПОМЕЩЕНИЙ

Modern tasks of special areas of robotics, including search and rescue operations in urbanareas, face a number of obstacles to mobile robotics, where the automatic performance of various functionsby mobile robots remains a key task. One of the important requirements for the algorithms andsoftware of the robot is the possibility of autonomous decision-making and automatic performance bythe robot of various functions, both low and high levels based on the embedded algorithms and informationreceived from the on-board sensors of the robot. To date, the most common on-board robot sensorsare cameras of various types, due to their technical capabilities and lower cost relative to lidarsand other sensors that provide visual information in the form of digital images. Camera calibration is anecessary process for extracting accurate information from digital images. This process is necessary toobtain an exact correspondence between the three-dimensional object space and the pixel space of theimage, for the possibility of subsequent use of computer vision algorithms, aggregation, and informationprocessing. Calibration of digital cameras is an integral part of a number of practical tasks of machinevision such as navigation of mobile robotic systems, medicine, reconstruction of dense and sparse threedimensionalmaps of the environment, video surveillance and visual inspection, visual simultaneouslocalization and mapping, etc. The urgency of the problem of camera calibration is defined by the presenceof many different methods of calibration and calibration templates. Each individual solution issuitable only for special conditions, e.g., lack of lighting, bad weather conditions, the presence of thirdpartyobjects blocking visibility, etc. In most cases, each calibration method uses a specific calibrationpattern. Camera calibration is usually associated with the use of special calibration templates. Theyallow to achieve the most accurate results due to a previously known geometric structure. Currently, theprocedure for camera calibrating of robotic systems is carried out in laboratory conditions using theclassic “chessboard” method. In addition, there are only a few alternative approaches that are in their infancy state both in Russia and abroad. On the other hand, research into camera calibration methodscontinues and new alternatives for camera calibration are emerging. One of the new directions is theuse of fiducial marker systems as a reference object. A variety of parameters such as the size of the calibrationtemplate, the dimension of the calibration data set, the distribution of distances from the camerato objects on the stage, etc. creates a vast area for experimental testing of optimal camera calibrationparameters. This paper presents a research of automatic camera calibration using fiducial marker systems(FMS), which are located on the surface of the robot. Based on the results of virtual experimentswith FMS in the Gazebo simulation environment of the robotic operating system ROS, two differenttypes of FMS were selected that are optimal relative to other types of FMS covered by our previousstudies in terms of the resistance of FMS to systematic occlusion of the marker area and the effect ofmarker size on quality of its recognition. The selected FMS were tested using the onboard camera of theRussian mobile robot Servosila Engineer in indoor settings to assess the correlation of results in virtualand real environments.

Post-earthquake building safety evaluation using consumer-grade surveillance cameras

This paper demonstrates the possibility of evaluating the safety of a building right after an earthquake using consumergrade surveillance cameras installed in the building. Two cameras are used in each story to extract the time history of interstory drift during the earthquake based on camera calibration, stereo triangulation, and image template matching techniques. The interstory drift of several markers on the rigid floor are used to estimate the motion of the geometric center using the least square approach, then the horizontal interstory drift of any location on the floor can be estimated. A shaking table collapse test of a steel building was conducted to verify the proposed approach. The results indicate that the accuracy of the interstory drift measured by the cameras is high enough to estimate the damage state of the building based on the fragility curve of the interstory drift ratio. On the other hand, the interstory drift measured by an accelerometer tends to underestimate the damage state when residual interstory drift occurs because the low frequency content of the displacement signal is eliminated when high-pass filtering is employed for baseline correction.

Symbol recognition system based on 3D stereo vision

With the continuous development of computer science and technology, symbol recognition systems may be converted from two-dimensional space to three-dimensional space. Therefore, this article mainly introduces the symbol recognition system based on 3D stereo vision. The three-dimensional image is taken by the visual coordinate measuring machine in two places on the left and right. Perform binocular stereo matching on the edge of the feature points of the two images. A corner detection algorithm combining SUSAN and Harris is used to detect the left and right camera calibration templates. The two-dimensional coordinate points of the object are determined by the image stereo matching module, and the three-dimensional discrete coordinate points of the object space can be obtained according to the transformation relationship between the image coordinates and the actual object coordinates. Then draw the three-dimensional model of the object through the three-dimensional drawing software. Experimental data shows that the logic resources and memory resources occupied by image preprocessing account for 30.4% and 27.4% of the entire system, respectively. The results show that the system can calibrate the internal and external parameters of the camera. In this way, the camera calibration result will be more accurate and the range will be wider. At the same time, it can effectively make up for the shortcomings of traditional modeling techniques to ensure the measurement accuracy of the detection system.

Camera calibration method based on Pascal’s theorem

As one of the classical theories of projective geometry, Pascal’s theorem is closely related to the conic, which is the image of a circle. A circle is the geometric element typically used as a template for camera calibration methods. In this work, we propose a calibration method based on Pascal’s theorem and its inference, in which a circle is used as the calibration template. The proposed calibration method can be applied to solve the image of the circular points via the Newton iteration method. The intrinsic parameters of the camera can then be determined based on the constraints of the images of the circular points and the image of the absolute conic. The results of simulations and experiments conducted verify the validity and feasibility of the proposed calibration method.

A problem with the analysis of type Ia supernovae

Abstract Type Ia supernovae have light curves that have widths and magnitudes that can be used for testing cosmologies and they provide one of the few direct measurements of time dilation. It is shown that the standard analysis that calibrates the light curve against a rest-frame average (such as SALT2) removes all the cosmological information from the calibrated light curves. Consequently type Ia supernovae calibrated with these methods cannot be used to investigate cosmology. The major evidence that supports the hypothesis of a static universe is that the measurements of the widths of the rawlight curves of type Ia supernovae do not show any time dilation. The intrinsicwavelength dependence shown by the SALT2 calibration templates is also consistent with no time dilation. Using a static cosmological model the peak absolute magnitudes of raw type Ia supernovae observations are also independent of redshift. These results support the hypothesis of a static universe.

A camera calibration method based on plane mirror and vanishing point constraint

In order to avoid a cumbersome calibration of camera parameters, a method of self-calibration using the imaging features of a plane mirror and the vanishing point pair constraint is proposed. A plane mirror and calibration template were placed at a certain angle and non-vertical geometric constraints were obtained from the calibration template, as well as from the virtual image of the calibration template. So all the internal parameters were calibrated at once. In order to reduce the influence on the calibration parameters of the vanishing point position, the least squares algorithm and the LM algorithm were used to optimize the parameters. Simulations and real experimental results show that the method has a high accuracy and robustness.

High-precision method of binocular camera calibration with a distortion model.

A high-precision camera calibration method for binocular stereo vision system based on a multi-view template and alternative bundle adjustment is presented in this paper. The proposed method could be achieved by taking several photos on a specially designed calibration template that has diverse encoded points in different orientations. In this paper, the method utilized the existing algorithm used for monocular camera calibration to obtain the initialization, which involves a camera model, including radial lens distortion and tangential distortion. We created a reference coordinate system based on the left camera coordinate to optimize the intrinsic parameters of left camera through alternative bundle adjustment to obtain optimal values. Then, optimal intrinsic parameters of the right camera can be obtained through alternative bundle adjustment when we create a reference coordinate system based on the right camera coordinate. We also used all intrinsic parameters that were acquired to optimize extrinsic parameters. Thus, the optimal lens distortion parameters and intrinsic and extrinsic parameters were obtained. Synthetic and real data were used to test the method. The simulation results demonstrate that the maximum mean absolute relative calibration errors are about 3.5e-6 and 1.2e-6 for the focal length and the principal point, respectively, under zero-mean Gaussian noise with 0.05 pixels standard deviation. The real result shows that the reprojection error of our model is about 0.045 pixels with the relative standard deviation of 1.0e-6 over the intrinsic parameters. The proposed method is convenient, cost-efficient, highly precise, and simple to carry out.

A Method to Measure the Bracelet Based on Feature Energy

To measure the bracelet automatically, a novel method based on feature energy is proposed. Firstly, the morphological method is utilized to preprocess the image, and the contour consisting of a concentric circle is extracted. Then, a feature energy function, which is relevant to the distances from one pixel to the edge points, is defined taking into account the geometric properties of the concentric circle. The input image is subsequently transformed to the feature energy distribution map (FEDM) by computing the feature energy of each pixel. The center of the concentric circle is thus located by detecting the maximum on the FEDM; meanwhile, the radii of the concentric circle are determined according to the feature energy function of the center pixel. Finally, with the use of a calibration template, the internal diameter and thickness of the bracelet are measured. The experimental results show that the proposed method can measure the true sizes of the bracelet accurately with the simplicity, directness and robustness compared to the existing methods.

Unified optical distortion correction method for imaging systems using a concise geometrical transformation model

Since optical distortion has been a big trouble for various kinds of imaging systems, finding a simple correction method with wide applications is of significant importance. In this paper, we propose a unified and simple correction method, performing well for both photographic and projective imaging systems. The basic idea is regarding the optical distortion as geometrical deformation between the object and image, without considering the specific features of an optical system. First of all, a calibration template is employed to establish the geometrical transformation model (GTM) for the distortion of a built optical system. Two alternative algorithms are given to estimate the GTM in algebraic form. The computation is very simple because no intrinsic parameters of the optical system are needed to establish the GTM. Besides, the errors introduced by the fabricating and assembling process can be eliminated. Then, the corrected image of the photographic system or the pre-distorted image of the projective systems can be obtained accordingly utilizing the GTM. Experiments are conducted to demonstrate the effectiveness of our method with wide applications.

The influence of turbulence models on the accuracy of CFD analysis of a reciprocating mechanism driven heat loop

A bellows-type Reciprocating-Mechanism Driven Heat Loops (RMDHL) is a novel heat transfer device that could attain a high heat transfer rate through a reciprocating flow of the working fluid inside the heat transfer device. Although the device has been tested and validated experimentally, analytical or numerical study has not been undertaken to understand its working mechanism and provide guidance for the device design. In an effort to improve earlier numerical models of the RMDHL, different turbulence models for the RMDHL design have been studied and compared with prior experimental results to select the most suitable turbulence modeling techniques. The governing equations have been numerically solved using a CFD solver. For the three-dimensional fluid flow, several turbulence models have been studied for the RMDHL, including Standard, RNG, and Realizable k-ɛ Models, Standard and SST k-ω Models, Transition k -kL-ω Model and the Transition SST Model. The results of the simulations have been analyzed and ranked using numerical model calibration template. It was found that the standard k-ω Models provided the least accurate results while the RNG-k-ɛ Model provided the most accurate predictions. It is expected that the results will help improve the accuracy of the work on the RMDHL modeling.

Measurement and analysis of fluorescent whitening agent content in soybean milk based on image techniques

Abstract This paper presents a method for measuring and quantitatively analyzing the fluorescent whitening agent in soybean milk based on image techniques. After collecting the fluorescent images of the soybean milk samples, the top seven wavelet moment invariants are selected according to the sample training and experimental comparison. Then calculate the standard templates of the 49 classes of calibration samples with different fluorescent whitening agent content ranging from 0.02 mg/ml to 0.5 mg/ml. The minimum distance method is carried out to match the testing sample with the calibration template, which realizes the quantitative analysis. To verify the effectiveness of the presented method, the prediction experiment is carried out. Results show that the absolute errors are within 0.005 mg/ml and the relative errors are within 5%, which means this method can measure the fluorescent whitening agent in soybean milk. This research presents a new approach for detecting the illegal fluorescence additive in food production.

Apparent electrical conductivity (ECa) as a surrogate for neutron probe counts to measure soil moisture content in heavy clay soils (Vertosols)

Site-specific measurements of the apparent electrical conductivity (ECa) of soil using the EM38 were correlated with near-simultaneous neutron probe readings over periods of moisture extraction by an irrigated cotton crop. Thirty sites were monitored from three ECa zones within a 96-ha field of grey Vertosol soil 30 km west of Moree, New South Wales, Australia. This study differs from previous approaches by reporting the effect on ECa of a wetting front (irrigation) reaching a single ECa measurement point in a field and by using polyethylene neutron probe access tubes so that the EM38 could be operated directly over the same site measured by a neutron probe. We report strong correlations (r = 0.94) between neutron probe counts (CRR) averaged to a depth of 40 or 60 cm and ECa from an EM38 held in the vertical mode 20 cm above the soil surface. All combinations of EM sensor height (0–1.2 m) to neutron probe measurement depth (0.2–1.4 m) returned correlations >0.85. The relationship between CCR and ECa was linear for the purposes of estimating water content over a range of background ECa levels. More critical modelling suggested a slight curve (logarithmic model) fitted best. The range of surface-surveyed ECa from the start of irrigation (refill point) to fully irrigated (full point) was ~27 mS m–1 for this Vertosol, where surface ECa readings typically ranged from 50 to 200 mS m–1. We suggest that the calibration of ECa to CRR might be effected by a two-point measurement of the soil, namely at both upper (field capacity) and lower (wilting point) ECa values, and a site-specific calibration template generated by extending these point measures to whole-field surveys.

Based on the Experimental Platform of Litchi Picking Vision Calibration

This paper constructs the picking mechanical hand binocular vision hardware system. Using an internal and external parameters calibration method of separation. In the calibration process, with calibration planar pattern translatory manner, appropriate for extracting feature points in the calibration template, through experiment and calculation to obtain the accurate parameters of camera model; external parameters calibration is a reasonable selection of reference coordinate system, through experimental analysis to obtain the two cameras outside parameter model.

3D Measurement Method Based on Binocular Vision and Linear Structured Light

To improve efficiency of industry inspection, measuring method of part shape which combines laser linear scanning and binocular vision is researched. In the system, two cameras are located at certain angle, and linear structured light is projected onto the part surface to produce distorted laser light stripe, which is used as measure feature curve. Ordinary planar plate is used as the calibration template in system calibration and images of serial parallel lines bundle are displayed on it which are acquired simultaneously by the camera to produce image series. Calibration parameters are divided into several parts, so as to calibration of them so that interference between different parts can be eliminated significantly. Based on above works, system calibration and reconstruction of 3D coordinate are implemented successfully. Experimental result shows our method’s feasibility and effectiveness, thus good prospect can be expected to it.

A New Technique for Camera Calibration Using Circle Template

In view of the poor anti-noise performance of traditional methods, the principle of camera calibration is analyzed based on calibration template with planar circles, and a new calibration technique is proposed based on pin-hole perspective model. Firstly, the edges of image ellipses are located in sub-pixel by spatial-moment operator. Then elliptic equations are obtained by the Least Square Fitting method, and common tangents of two arbitrary ellipses are also calculated. Finally, the extrinsic and intrinsic parameters are computed by the Radial Alignment Constraint (RAC) model. Experiments results indicate that proposed method has a goof performance of lower computation complexity and higher precision.

Design and Research of Camera Calibration System in Binocular Stereo Vision

Aiming at the camera calibration of binocular stereo vision system, based on Zhang’s calibration method, the specified points in the calibration template obtained by the Harris operator, a set of camera calibration system combined with VC++ and Matlab was developed. The results of the calibration system, comparing with those of four-step calibration method, was analyzed and showed that: the error of calibration data in this system was within 0~5 mm, which had a high precision calibration, providing a new reference measure for the camera calibration.

A new calibration method for linear CCD camera

The linear CCD camera which applies to micro-image measuring system must have been calibrated before working. The separate calibration method of linear CCD camera’s internal and external orientation parameters is proposed in the paper. The imaging model of the linear camera has been studied, and the equal parallel lines are used to calibrate internal parameters of camera in the experiment where the industrial environment is simulated. In addition, parallel lines and tri-forked stencil are used to calibrate external orientation parameters in the industrial field, such as the attitude angel. The separate calibration method has reduced the calibration task in the industry, and the calibration template is easy to make. The results show that the testing accuracy improves greatly by using the calibrated camera for measuring the gauge, and the calibrated camera can be easily applied to other measurement environment.

Robust metric calibration of non-linear camera lens distortion

Camera lens distortion is crucial to obtain the best performance cameral model. Up to now, different techniques exist, which try to minimize the calibration error using different lens distortion models or computing them in different ways. Some compute lens distortion camera parameters in the camera calibration process together with the intrinsic and extrinsic ones. Others isolate the lens distortion calibration without using any template and basing the calibration on the deformation in the image of some features of the objects in the scene, like straight lines or circles. These lens distortion techniques which do not use any calibration template can be unstable if a complete camera lens distortion model is computed. They are named non-metric calibration or self-calibration methods. Traditionally a camera has been always best calibrated if metric calibration is done instead of self-calibration. This paper proposes a metric calibration technique which computes the camera lens distortion isolated from the camera calibration process under stable conditions, independently of the computed lens distortion model or the number of parameters. To make it easier to resolve, this metric technique uses the same calibration template that will be used afterwards for the calibration process. Therefore, the best performance of the camera lens distortion calibration process is achieved, which is transferred directly to the camera calibration process.

Automatic determination of the position of a video camera in a system of laser optical triangulation

An automatic method of calibration of a video camera (camcorder) for the purpose of laser calibration is described. The method utilizes images taken by the camera. Different calibration templates are considered. The results of an experiment are presented and techniques for increasing calibration precision are indicated.