CN115683157A - Optical axis parallelism error calibration method for multi-sensor photoelectric theodolite - Google Patents

Abstract

The invention provides a method for calibrating optical axis parallelism of a multi-sensor photoelectric theodolite, which can accurately measure the optical axis parallelism of a heterogeneous sensor of the photoelectric theodolite. The invention designs the special detection equipment for the external field of the infrared sensor and the visible light sensor and provides a method for positioning the mark points of two images, thereby realizing the calibration of the parallel difference of the optical axes of the heterogeneous sensor of the photoelectric theodolite and having greater significance for ensuring the measurement precision of the photoelectric theodolite.

Description

A multi-sensor photoelectric theodolite optical axis parallelism calibration method

technical field

The invention belongs to the field of optical measurement and image processing, in particular to a multi-sensor photoelectric theodolite optical axis parallel difference calibration method.

Background technique

The photoelectric theodolite is a kind of optical measuring equipment. When measuring small targets flying at high speed in the air, due to the long flight distance of the target, the photoelectric theodolite with both infrared and visible light sensors is generally used. When the measured target is close, the visible light is generally used. Sensors, when the distance is long, generally use infrared sensors. In order to ensure the amount of light entering the lens of each sensor, an independent optical path is generally used, that is, infrared and visible light have their own optical paths. In this way, in the actual installation process of optical devices, the two It is impossible for the two optical paths to be completely parallel, and this level difference is calibrated in the installation and calibration workshop with special calibration equipment. At present, the standard calibration methods need to be converted to optical construction and completed in the installation and calibration laboratory. However, the shooting range photoelectric The theodolite will inevitably vibrate during road transportation and installation in the field, and the parallelism of the optical axis of the heterogeneous sensor will inevitably change. The photoelectric theodolite is a precision angle measurement device that does not allow any error. Therefore, the existing technology has The working environment is extremely demanding, and the shortcomings of parallelism errors cannot be completely eliminated. Due to field transportation, installation, and climate changes in the test environment, the rigid body structure of the photoelectric theodolite cannot be guaranteed to be completely unchanged, and due to the limitations of field conditions, it is impossible to install a professional optical inspection frame. Therefore, this error is difficult to avoid.

Contents of the invention

In view of this, the present invention provides a multi-sensor photoelectric theodolite optical axis parallel difference calibration method, which can accurately measure the optical axis parallel difference value of heterogeneous sensors of the photoelectric theodolite.

To achieve the above object, the technical scheme of the present invention is as follows:

A multi-sensor photoelectric theodolite optical axis non-parallel calibration method, comprising the following steps: arranging visible light detection marks and infrared detection marks at intervals in front of the photoelectric theodolite, the marks facing the photoelectric theodolite, the height of the center of the mark pattern and the three axes of the photoelectric theodolite The center heights are the same, and the two marks form a certain angle with the three-axis center of the photoelectric theodolite;

Perform binarization processing on the visible light detection mark image collected by the photoelectric theodolite, and then perform Hought transformation processing on the binarized image to obtain the center position of the mark, and use two methods to obtain the intersection point of two straight lines in the mark and the center of the mark circle Find the center of the mark, and then take the mean value of the results of the two methods as the final value of the center position of the mark;

For the infrared detection mark, the infrared detection mark image collected by the photoelectric theodolite is binarized, and the gray center of gravity of the target area of the binarized image is taken as the infrared source center;

Interpret the infrared and visible light centers to obtain the comprehensive angle values of the two sensors respectively,

When shooting, the center of the visible light detection mark is aligned with the center of the visible light sensor image, and the center of the infrared and visible light detection mark is interpreted. The interpreted value minus the actual angle between the two optical axes is the optical axis parallelism.

Among them, the visible light detection mark is a black circle on the outer edge, and the circle is divided into four equal parts by angle. In the four equal parts, there are two black and two white, black and white; the infrared detection mark is a standard halogen lamp, and the light face is facing the photoelectric theodolite.

Among them, the specific implementation method of obtaining the center of the marked circle is as follows:

Establish the circle equation in the image space: (xa) ² +(yb) ² =r ² , where (a, b) is the center of the circle, r is the radius, (x, y) is a point on the circumference; any edge in the image space The point ( _xi , y _i ) corresponds to a conical surface on the parameter space (a, b, r) after the Hough transformation; the conical surfaces of the parameter space corresponding to all points on the same circle in the image space intersect at A point (a ₀ , b ₀ , c ₀ ), which exactly corresponds to the center of the circle (a ₀ , b ₀ ) and radius r ₀ , the above formula can be transformed into a parameter equation as follows:

Where θ∈[0, 2π), r∈[R _min , R _max ]; quantize the parameter space to obtain a 3-dimensional accumulator array A(a, b, r), and each small cube in the array The discrete value of the parameter corresponding to (a, b, r);

When detecting the circle in the image, first calculate the gradient information of each point of the image, and then calculate the edge point according to the appropriate threshold, and then traverse the parameters θ and r in their value range with the respective quantization interval as the step size, and calculate Get all the points (a, b) whose distance from each pixel point on the edge is r, and add 1 to the accumulator A (a, b, r) corresponding to the (a, b, r) cubic small grid; for all After the edge point transformation is completed, the local peak cell of the accumulator A (a, b, r) corresponds to the circle parameter in the image space, and the center of the circle corresponding to the maximum value of the accumulator is the position of the center of the mark.

Among them, the specific implementation method of obtaining the intersection point of two straight lines in the sign is as follows:

The polar coordinate formula ρ=x cosα+y sinα is established under Cartesian coordinates, each pixel coordinate p(x, y) of the image space is known, and ρ and α are variables that need to be found. For each pixel coordinate, pass Cycle angle α to obtain a series of (ρ, α) values. If the pixels are on the same straight line, the corresponding (ρ, α) values in the parameter space are concentrated at one point, and finally find the largest two in the cumulative array by searching the peak. The group value is the intersection point of the two lines of the visible light detection mark, that is, the center position of the mark.

其中，x_i或y_i为横轴或纵轴的重心坐标，i或j为横轴或纵轴的重心坐标，其得到的(x，y)坐标即为标志中心位置。Among them, the gray center of the binarized target area is taken as the center of the infrared source as follows: the gray center of gravity of the pixels is counted in a square area with a side length of n pixels, and the formula is

Wherein, x _i or y _i is the barycentric coordinate of the horizontal or vertical axis, i or j is the barycentric coordinate of the horizontal or vertical axis, and the obtained (x, y) coordinate is the center position of the sign.

Among them, the angle measurement of the photoelectric theodolite is calculated according to the following formula: A=a+x×d _x , E=e+y×d _y ; where A is the comprehensive angle value of the azimuth angle, E is the comprehensive angle value of the elevation angle, and a is The azimuth angle of the photoelectric theodolite encoder, e is the pitch angle of the photoelectric theodolite encoder, x, y are the number of pixels of the offset image center of the target in the image, d _x , d _y are the dimensional values of the sensor.

Among them, the optical axis parallelism is as follows:

为所求平行差。Among them, θ is the angle between the infrared sensor and the visible light sensor,

is the desired parallel difference.

Among them, each visible light detection mark and infrared detection mark takes more than 30 frames of images, and the time interval between each frame of image acquisition is greater than 0.5 seconds, and each frame of image is interpreted, and the average of the interpretation results is taken as the final result.

Beneficial effect

1. The present invention realizes the optical axis parallel difference calibration of photoelectric theodolite heterogeneous sensors by designing infrared and visible light sensor special-purpose detection equipment for the field, and proposes two kinds of image marker point positioning methods, and has a great influence on ensuring the measurement accuracy of photoelectric theodolite meaning.

2. The present invention can perform parallel difference calibration on heterogeneous sensors in the field environment at any time before the test. The scheme is simple, easy to implement, and the calibration accuracy is high, which is of great significance for ensuring the measurement accuracy of the photoelectric theodolite.

3. The outer edge of the visible light detection mark of the present invention is a black circle, and the circle is divided into four equal parts by angle. Among the four equal parts, there are two black and two white, black and white, and the center point of the mark is consistent with the ground height of the three-axis center of the photoelectric theodolite. more precise.

4. In order to eliminate the influence of atmospheric disturbance, each visible light detection mark and infrared detection mark in the present invention take more than 30 frames of images, and the time interval of each frame of image acquisition is greater than 0.5 seconds, and each frame of image is interpreted to obtain the interpretation result The mean is the final result.

Description of drawings

Fig. 1 is a schematic diagram of the principle of the measurement method of the present invention.

Fig. 2 is the specific measurement schematic diagram of the embodiment of the present invention

Detailed ways

The present invention will be described in detail below with reference to the accompanying drawings and examples.

The invention provides a multi-sensor photoelectric theodolite optical axis parallel difference calibration method, adopts infrared and visible light sensor special detection equipment for the field, respectively proposes two kinds of image marker point positioning methods, specifically as follows:

Visible light detection marks and infrared detection marks are respectively set at different distances in front of the photoelectric theodolite. Since visible light is reflected by the sun, and the mark recognition is corner point recognition, it is limited by imaging conditions. Therefore, the distance between the visible light detection mark and the photoelectric theodolite should not be too far , generally 1000 meters is more suitable, and the infrared detection mark is generally an infrared source, using the centroid to identify, the distance from the photoelectric theodolite is relatively close to the photoelectric theodolite, and the image noise is large. Therefore, the general mark distance is about 3000 meters. The visible light detection mark and the infrared detection mark form a certain angle with the three-axis center of the photoelectric theodolite, and the angle ensures that the two marks are simultaneously imaged within the frame of the photoelectric theodolite.

In this embodiment, the outer edge of the visible light detection mark is a black circle with a radius of 1 meter, and the width of the circle is 0.2 meters. The circle in the circle is divided into four equal parts by angle. In the four equal parts, there are two black and two white, black and white, and the center point of the mark It is consistent with the ground height of the three-axis center of the photoelectric theodolite, and the positioning of the center of the mark is relatively accurate. The requirement for positioning accuracy is relatively high, and the central positioning of the visible light detection mark in this embodiment is relatively accurate, so this type of visible light detection mark is generally used. Extract the circle center of the visible light detection mark, which is the center of the mark. In order to improve the extraction accuracy, the image collected by the photoelectric theodolite is binarized, and then the binarized image is processed by Hough transform to extract two vertical straight lines of the mark, and the intersection of the straight lines is the center of the mark. The mean of the mark center values extracted by the two extraction methods is the final value of the mark center.

Among them, the specific implementation method of obtaining the center of the marked circle is as follows:

Establish the circle equation in the image space: (xa) ² +(yb) ² =r ² , where (a, b) is the center of the circle, r is the radius, and (x, y) is a point on the circle. Any edge point (x _i , y _i ) in the image space corresponds to a conical surface on the parameter space (a, b, r) after Hough transformation. The conical surface of the parameter space corresponding to all the points on the same circle in the image space intersects at a point (a ₀ , b ₀ , c ₀ ), which corresponds to the center of the circle (a ₀ , b ₀ ) and radius r ₀ .

The above formula can be transformed into a parametric equation as follows:

where θ∈[0, 2π), r∈[R _min , R _max ]. Properly quantize the parameter space to obtain a 3-dimensional accumulator array A(a, b, r), and each cube cell in the array corresponds to the parameter discrete value of (a, b, r). When detecting the circle in the image, first calculate the gradient information of each point of the image, and then calculate the edge point according to the appropriate threshold, and then traverse the parameters θ and r in their value range with their respective quantization intervals as the step size, and calculate Get all the points (a, b) whose distance from each pixel on the edge is r, and add 1 to the accumulator A(a, b, r) corresponding to the (a, b, r) cubic small grid. After the transformation of all edge points is completed, the local peak cell of the accumulator A(a, b, r) corresponds to the circle parameter in the image space. The center of the circle corresponding to the maximum value of the accumulator is the position of the mark center.

The specific implementation method of finding the intersection point of two straight lines in the sign is as follows:

The polar coordinate formula ρ=x cosα+y sinα is established under Cartesian coordinates, each pixel coordinate p(x, y) of the image space is known, and ρ and α are variables that need to be found. For each pixel coordinate, pass Cycle angle α to obtain a series of (ρ, α) values. If the pixels are on the same straight line, the corresponding (ρ, α) values in the parameter space are concentrated at one point, and finally find the largest two in the cumulative array by searching the peak. The group value is the intersection point of the two lines of the visible light detection mark, that is, the center position of the mark.

The infrared detection mark adopts an infrared light source, and the present embodiment adopts a standard halogen lamp, and the lamp face is directly facing the photoelectric theodolite. When extracting the image collected by the photoelectric theodolite, the binarization process is firstly carried out, and secondly, the gray center of the binarization target area is taken as the center of the infrared source. The processing method is as follows: the gray center of gravity of pixels is counted in a square area with a side length of n pixels, and the formula is as follows:

Wherein, x _i or y _i is the barycentric coordinate of the horizontal or vertical axis, i or j is the barycentric coordinate of the horizontal or vertical axis, and the obtained (x, y) coordinate is the center position of the sign.

In order to eliminate the influence of atmospheric disturbance, each visible light detection mark and infrared detection mark takes more than 30 frames of images, and the time interval between each frame of image acquisition is greater than 0.5 seconds, and each frame of image is interpreted, and the average of the interpretation results is taken as the final result. Among them, the angle measurement of the photoelectric theodolite can be calculated according to the following formula:

A=a+x×d _x

E=e+y×d _y

Among them, A is the comprehensive angle value of the azimuth angle, E is the comprehensive angle value of the elevation angle, a is the azimuth angle of the photoelectric theodolite encoder, e is the elevation angle of the photoelectric theodolite encoder, x, y are the pixels in the center of the offset image of the target in the image number, d _x , d _y are the dimension values of the sensor. The infrared and visible light centers are interpreted to obtain the integrated angle values of the two sensors respectively.

The current standard flat phase difference detection method is a detection method using a collimator in the laboratory. The present invention is an on-site detection method for the actual work of the photoelectric theodolite. When shooting, the center of the visible light detection mark is aligned with the image center of the visible light sensor as much as possible, and the infrared Interpretation processing with the center of the visible light detection mark, the interpretation value minus the actual angle between the two optical axes is the optical axis parallelism, as follows:

为所求平行差。Among them, θ is the angle between the infrared sensor and the visible light sensor,

is the desired parallel difference.

To sum up, the above are only preferred embodiments of the present invention, and are not intended to limit the protection scope of the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims (8)

1. A multi-sensor photoelectric theodolite optical axis non-parallelism calibration method is characterized in that, comprises the following steps: in the photoelectric theodolite front, visible light detection mark and infrared detection mark are arranged at intervals, the mark is positively facing the photoelectric theodolite, and the mark pattern center is earth The height is the same as the height of the three-axis center of the photoelectric theodolite, and the two marks form a certain angle with the three-axis center of the photoelectric theodolite; Binarize the image of the visible light detection mark collected by the photoelectric theodolite, and then perform Hought transformation on the binarized image to obtain the center position of the mark. Take the center of the mark, and then take the mean value of the results of the two methods as the final value of the center position of the mark; For the infrared detection mark, the infrared detection mark image collected by the photoelectric theodolite is binarized, and the gray center of gravity of the target area of the binarized image is taken as the infrared source center; Interpret the infrared and visible light centers to obtain the comprehensive angle values of the two sensors respectively, When shooting, the center of the visible light detection mark is aligned with the center of the visible light sensor image, and the center of the infrared and visible light detection mark is interpreted. The interpreted value minus the actual angle between the two optical axes is the optical axis parallelism. 2. The calibration method according to claim 1, wherein the visible light detection mark is a black circle on the outer edge, and the circle is divided into four equal parts by angle, two black and two white in the four equal parts, black and white; the infrared detection mark It is a standard halogen lamp, and the face of the lamp faces the photoelectric theodolite. 3. calibration method as claimed in claim 2, is characterized in that, the concrete implementation mode of seeking the center of circle of sign circle is as follows: Establish the circle equation in the image space: (xa) ² +(yb) ² =r ² , where (a,b) is the center of the circle, r is the radius, (x,y) is a point on the circumference; any edge in the image space Point (x _i , y _i ), after Hough transform, corresponds to a conical surface on the parameter space (a, b, r); the conical surfaces of the parameter space corresponding to all points on the same circle in the image space intersect at one point (a ₀ ,b ₀ ,c ₀ ), this point exactly corresponds to the center of the circle (a ₀ ,b ₀ ) and radius r ₀ , the above formula can be transformed into a parameter equation as follows:

Where θ∈[0,2π), r∈[R _min ,R _max ]; quantize the parameter space to obtain a 3-dimensional accumulator array A(a,b,r), each small cube in the array The discrete value of the parameter corresponding to (a,b,r); When detecting the circle in the image, first calculate the gradient information of each point of the image, and then calculate the edge point according to the appropriate threshold, and then traverse the parameters θ and r in their value range with the respective quantization interval as the step size, and calculate Get all the points (a,b) whose distance from each pixel on the edge is r, and add 1 to the accumulator A(a,b,r) corresponding to the (a,b,r) cubic small grid; for all After the edge point transformation is completed, the local peak cell of the accumulator A(a,b,r) corresponds to the circle parameter in the image space, and the center of the circle corresponding to the maximum value of the accumulator is the position of the center of the mark. 4. calibration method as claimed in claim 2 is characterized in that, the concrete implementation mode of seeking the intersection point of two straight lines in the mark is as follows: The polar coordinate formula ρ=x cosα+y sinα is established under Cartesian coordinates, each pixel coordinate p(x, y) of the image space is known, and ρ and α are variables that need to be found. For each pixel coordinate, pass Cycle angle α to obtain a series of (ρ, α) values. If the pixels are on the same straight line, the corresponding (ρ, α) values in the parameter space are concentrated at one point, and finally find the largest two in the cumulative array by searching the peak. The group value is the intersection point of the two lines of the visible light detection mark, that is, the center position of the mark. 5. calibration method as claimed in claim 2, it is characterized in that, get the gray scale center to binarization target area, as the processing method of infrared source center as follows: in the square area that side length is n pixels, count the number of pixels Gray center of gravity, the formula is

Wherein, x _i or y _i is the barycentric coordinate of the horizontal axis or the vertical axis, i or j is the barycentric coordinate of the horizontal axis or the vertical axis, and the obtained (x, y) coordinate is the center position of the sign. 6. The calibration method according to any one of claims 2-5, characterized in that, the angle measurement of the photoelectric theodolite is calculated according to the following formula: A=a+x×d _x , E=e+y×d _y ; where , A is the comprehensive angle value of the azimuth angle, E is the comprehensive angle value of the elevation angle, a is the azimuth angle of the photoelectric theodolite encoder, e is the elevation angle of the photoelectric theodolite encoder, x, y are the number of pixels of the offset image center of the target in the image , d _x , d _y are the dimension values of the sensor. 7. The calibration method according to claim 6, wherein the optical axis parallelism is as follows:

Among them, θ is the angle between the infrared sensor and the visible light sensor,

is the desired parallel difference. 8. The calibration method according to any one of claims 1-5 or 7, characterized in that each visible light detection mark and infrared detection mark takes more than 30 frames of images, and the time interval between each frame of image acquisition is greater than 0.5 seconds , interpret each frame of image, and take the average of the interpretation results as the final result.

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