What are the characteristics of the traditional camera calibration method

How to Understand Industrial Camera Calibration

TEO USA, a manufacturer specializing in the research, development, and production of industrial cameras, is pleased to answer your questions. Industrial camera calibration is based on the industrial camera model, from the known features of the image of the point and the world coordinates to solve the industrial camera model parameters, to establish the positional relationship between the image point and the corresponding space point. Camera calibration method can be divided into: traditional calibration method, self-calibration method. Traditional calibration method is based on the calibration object structure information for calibration, can be used for any camera model, calibration accuracy, but the shortcomings are the need for high-precision calibration object; while the self-calibration method does not rely on the calibration reference, and only use the camera in the process of movement of the surrounding environment image and the image of the correspondence between the camera to the calibration method is called the camera self-calibration method.

Camera calibration error tolerance range of 0.1 to 0.5 or so. Calibration is to rely on special standard equipment to determine the sensor's input and output conversion relationship, camera calibration is the process of solving the parameters, calibration refers to the sensor in use or storage after the performance of the retest, in the calibration process, if some of the sensor indicators have changed should be corrected.

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Why should I calibrate my sensors? How to calibrate?

The sensors will drift after a period of time, and need to be calibrated with a calibration instrument to calibrate the sensor. (That is, a comparison test to see if the difference between the actual and theoretical values of the sensor is within acceptable limits.)

For example, a 0~1MPa output for 4~20mA pressure sensor calibration. Input 0pa,200kpa,400kpa,600kpa,1MPa and measure the corresponding output current value respectively. Then calculate whether the deviation of the output current value from the theoretical 4~20mA is within the range.

Out of range, the sensor can not continue to use, need to be calibrated or replaced. Within range, it can continue to be used.

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Sensitive components directly feel the measurement, and the output and the measurement of a definite relationship between the physical quantities of the signal; conversion element will be sensitive to the output of the physical quantities of the signal converted to electrical signals; transforming the circuit is responsible for converting the output of the electrical signals of the conversion element to amplify the modulation; conversion elements and transforming the circuit generally also need auxiliary power supply Power supply.

Variable frequency power sensor through the input voltage, current signal AC sampling, and then the sampling value through the cable, fiber optic and other transmission systems and digital input secondary instrumentation connected to the digital input secondary instrumentation on the voltage, current sampling value for the operation, you can get the voltage RMS value, current RMS value, fundamental voltage, fundamental current, harmonic voltage, harmonic current, active power, fundamental power, harmonic power and other parameters.

Using the characteristic that resistance changes with temperature to measure temperature and temperature-related parameters. In the temperature detection precision requirements of the occasion, this sensor is more suitable. More widely used RTD materials for platinum, copper, nickel, etc., they have a large resistance temperature coefficient, good linearity, stable performance, wide range of use temperature, easy to process and so on. Used to measure the temperature within the range of -200 ℃ ~ +500 ℃.

The traditional camera calibration method requires the use of calibrators with known dimensions, and the internal and external parameters of the camera model are obtained by using certain algorithms through the establishment of correspondences between points with known coordinates on the calibrators and their image points. According to the different calibrators can be divided into three-dimensional calibrators and plane-type calibrators.

Three-dimensional calibrators can be calibrated from a single image, calibration accuracy is higher, but the processing and maintenance of high-precision three-dimensional calibrators is more difficult. Plane-type calibration object than three-dimensional calibration object production is simple, easy to ensure the accuracy, but calibration must use two or more images.

Traditional camera calibration method in the calibration process always need calibration object, and calibration object production accuracy will affect the calibration results. At the same time, some occasions are not suitable for placing the calibration object also limits the application of traditional camera calibration method.

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Depending on the application, calibration is required for high accuracy and distortion rate.

Industrial camera calibration is based on the industrial camera model, by the known features of the image of the point and the world coordinates to solve the parameters of the industrial camera model, to establish the positional relationship between the image point and the corresponding space point. Camera calibration method can be divided into: traditional calibration method, self-calibration method. Traditional calibration method is based on the calibration object structure information for calibration, can be used for any camera model, calibration accuracy, but the shortcomings are the need for high-precision calibration object; while the self-calibration method does not rely on the calibration reference, and only use the camera in the process of movement of the surrounding environment image and the image of the correspondence between the camera to the calibration of the camera is known as the self-calibration method of the camera. used for lightning, sand and dust, electromagnetic interference, static electricity and other harsh industrial environments, and can continue to operate unaffected in these harsh environments.

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Industrial camera oblique mount how to calibrate

Industrial camera calibration methods are: the traditional camera calibration method, active vision camera calibration method, the camera self-calibration method.

Traditional camera calibration methods include Tasi two-step method and Zhang's calibration method, can be used in any camera model, high accuracy. However, it needs calibrated objects and the algorithm is more complicated.

Tsai two-step method is to obtain the camera parameters linearly first, and then consider the aberration factor to get the initial parameter values, and then get the final camera parameters through nonlinear optimization.Tsai two-step method is faster, but only consider the radial aberration, when the camera aberration is serious, the method is not applicable.

The Zhang calibration method uses a calibration plate composed of two-dimensional squares for calibration, collects pictures of different positions of the calibration plate, extracts the pixel coordinates of the corner points in the pictures, calculates the initial values of the internal and external parameters of the camera through the one-shoulder matrix, estimates the coefficients of the aberrations by using the nonlinear least squares method, and finally optimizes the parameters by using the great-likelihood estimation method. The method is simple to operate and has high accuracy, which can satisfy most of the occasions.

The active vision calibration method does not need calibrators, the algorithm is simple, and the robustness is high. But the cost is high and the equipment is expensive. Active vision-based camera calibration method is to control the camera through the active system to do a specific movement, using the control platform to control the camera to occur a specific movement to shoot multiple sets of images, based on the image information and the known displacement changes to solve the internal and external parameters of the camera. This calibration method needs to be equipped with an accurate control platform, so the cost is high.

Camera self-calibration methods include hierarchical step-by-step calibration method and Kruppa-based self-calibration method, which is flexible and can be calibrated online, but has low accuracy and low robustness.

The hierarchical step-by-step calibration method is to do the projective reconstruction of the sequence of images first, and then radial calibration and Euclidean calibration are carried out on the basis of the reconstruction, and the internal and external parameters of the camera are obtained through the nonlinear optimization algorithm. Since the initial parameters are fuzzy values, the convergence of the optimization algorithm is uncertain.

The Kruppa-based self-calibration method establishes the constraint equations on the camera's internal parameter matrix through a quadratic curve, and uses at least three pairs of images to calibrate the camera. The length of the image sequence affects the stability of the calibration algorithm and does not guarantee an infinite plane in projective space.

Can anyone explain the definition and principle of backward and forward rendezvous in surveying and mapping

The coordinates of points A and B are known, and in order to compute the coordinates of the unknown point P, it is sufficient to observe ∠A and ∠B. This method of determining the plane coordinates of the unknown point P is called forward rendezvous.

The rear rendezvous refers to only set up a station on the point to be determined, to the three known control points to observe the two horizontal angles a, b, so as to calculate the coordinates of the point to be determined, known as the rear rendezvous.

The principle is to use the rear rendezvous to calculate the outer azimuth element, and use the front rendezvous to solve the coordinates of the ground point to be determined.

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The common ways of meeting point measurement are angular front meeting, side meeting, rear meeting and two-point method meeting.

1, the front of the rendezvous method is simple, reliable accuracy; when the number of points to be determined than the number of known points, can effectively save the workload, so it is widely used.

2, the side of the rendezvous application is also more. After the rendezvous only in the to be determined on the station, when the number of points to be determined when the workload can be saved, but if the point to be determined and the known points are located in or close to the same circumference (known as the hazardous circle), will lose the conditions of the solution or the point of error increases to more than the permissible limit, so the general graphic conditions are only good when used.

3, two-point method of rendezvous is usually used only in difficult conditions of individual cases. The basic characteristics of the above methods of rendezvous.

4, using edge measurement instead of angle measurement, the same can be carried out in front of the rendezvous, side rendezvous, rear rendezvous and two-point method of rendezvous, known as the side of the rendezvous_

Baidu Encyclopedia - front of the rendezvous

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