CN112697112B - Method and device for measuring horizontal plane inclination angle of camera - Google Patents

Abstract

A method and device for measuring the tilt angle of a horizontal plane of a camera belong to the fields of precision measurement and image processing. The invention controls the movement of the working platform through the motor, so that the calibration plate graphic enters the camera's field of view, adjusts the appropriate position of the calibration plate graphic in the camera's field of view, and shoots an image of the calibration plate graphic, and then keeps the Y axis of the motor still, along the motor Move the X-axis by a certain step, and take another image of the calibration board graphic. Since the installation of the camera on the horizontal plane has an inclination angle, the coordinate values of the common area points in the two calibration board graphic images are different. After processing, the tilt angle of the camera in the horizontal plane can be obtained. The method has high precision in making the pattern of the calibration plate and high control precision in the movement of the working platform, so the calibration accuracy of the tilt angle of the horizontal plane of the camera is high, and for the calibration of different camera fields of view and different motion ranges, the step size can be changed, and the method can be adapted. Strong sex.

Description

A method and device for measuring the tilt angle of a horizontal plane of a camera

technical field

The invention belongs to the field of precise measurement and image processing, and relates to a method and a device for measuring the inclination angle of a horizontal plane of a camera.

Background technique

In industrial production applications, assembly accuracy is an important indicator to measure automated assembly technology, and the calibration of visual units in automated assembly systems is of great significance to assembly accuracy, and is critical to precise product positioning and reducing assembly errors.

At present, the calibration of the vision unit in the automatic assembly system mainly includes the monocular and multi-objective calibration of the camera, and the pose calibration of the camera and the manipulator. The camera's monocular and multi-objective calibration is mainly to obtain the internal and external parameters of the camera for object size measurement and 3D reconstruction. The relationship between them can be used for object recognition and localization, etc.

However, after the camera is installed, the installation process will cause the camera to tilt to a certain extent in both the vertical plane and the horizontal plane. When the camera has a tilt angle in the vertical plane, due to the limited depth of field of the camera, the acquired image may be partially clear and partially blurred. This will greatly affect the accuracy of the results. By making a high-precision camera calibration plate, moving the camera driving mechanism, the calibration graphics on the calibration plate enters the camera's field of view, moving the camera along the axis of camera movement with a certain step length, and shooting the calibration graphics on the calibration plate, due to the vertical direction of the camera. There is an inclination angle in the surface installation, so the definition of the upper left corner, upper right corner, lower right corner and lower left corner of the camera's field of view is different. After processing the captured image, the camera's vertical plane inclination angle can be obtained [a measurement of the camera's inclination angle] Methods, 2019, Application No. 201910004492.4].

When the camera has a tilt angle on the horizontal plane, especially for the positioning and measurement of large-sized objects, image stitching or coordinate transformation is generally required, and the tilt angle of the camera's horizontal plane will cause errors in stitching or transformation, and accurate results cannot be obtained. At present, there is no effective method for measuring and calibrating the tilt angle of the horizontal plane of the camera.

SUMMARY OF THE INVENTION

In order to solve the above-mentioned problems, the present invention provides a method for measuring the inclination angle of the horizontal plane of the camera, which realizes the systematic angle measurement of two different planes on different planes. Poor, get the tilt angle of the camera in the horizontal plane.

Technical scheme of the present invention:

A device for measuring the tilt angle of a horizontal plane of a camera, comprising a working platform, a Y axis of a motor, a calibration plate, an X axis of the motor, a calibration plate carrier, a light source, a lens, a camera, a bracket base and a camera bracket;

Wherein, the light source is installed on the lens, the lens is installed on the camera, the camera is fixedly installed on the camera bracket, and the camera bracket is fixedly connected with the bracket base; The middle of the platform is fixedly connected with the motor X axis, the motor X axis is slidably connected with the motor Y axis, and the calibration plate carrier is slidably connected with the motor Y axis.

A method for measuring the inclination angle of a horizontal plane of a camera, comprising the following steps:

Step 1. Place the calibration plate on the calibration plate carrier, set a part of the calibration plate as a public area, control the movement of the working platform by moving the motor, the calibration plate enters the camera's field of view, and shoot an image of the calibration plate, the image Common areas including calibration boards;

Step 2. Keep the Y-axis of the motor still, move the working platform along the X-axis of the motor by a step Δd, and take another image of the calibration plate, which includes the common area of the calibration plate; among them, the images of the two calibration plates are the same. the public area;

计算得出，其中，ΔV为公共区域点的V坐标值之差，ΔU为公共区域点的U坐标值之差。Step 3. Process the two images of the calibration board, and the tilt angle of the camera's horizontal plane is based on

It is calculated that ΔV is the difference between the V coordinate values of the points in the public area, and ΔU is the difference between the U coordinate values of the points in the public area.

Preferably, the pattern on the calibration plate is a circle, the radius of the standard circle is r1, there are two positioning circles with a radius of r2 on the calibration plate, the positioning circles are in different columns, and the column where the positioning circles are located The area between the and columns is the common area of the calibration board, and the common area point is the center of the circle in the common area, where r2>r1.

Preferably, in the step 1, the public area of the calibration plate is moved to the right side of the camera's field of view, and the captured image of the calibration plate is recorded as the Left image; in the step 2, the Y axis of the motor is kept still, and the working platform is moved along the motor. The X-axis moves in the negative direction or to the left by Δd steps, so that the common area of the calibration plate is moved to the left side of the camera's field of view, and the captured image of the calibration plate is recorded as the Right image.

Further preferably, in the Left image, the center A in the public area is (U _l , V _l ); when the working platform moves Δd steps along the negative direction of the motor X-axis, the center A in the original public area is in the Right image. A'(U _r , V _r ), convert the center A' in the Right image to the Left image coordinate system, namely:

So,

That is, the tilt angle of the camera's horizontal plane

Further preferably, the method for calculating the inclination angle of the horizontal plane of the camera by processing the two calibration plate images captured in the step 3 is as follows:

Step 3.1. According to the Left image obtained in step 1 and the Right image obtained in step 2, use the circle Hough transform method to calculate all circle parameters C(r, U, V) in the two images; wherein, r represents the radius of the circle;

Right图像中的圆心为

其中，k为圆心的下标，N表示公共区域内的所有圆心；Step 3.2. Sort the circle parameters in each image according to the radius from small to large. The first two circles with the largest radius are the positioning circles. Divide the common area according to the two positioning circles in each image, and calculate the value within the common area. The coordinates of the center of all circles, remember the center in the Left image as

The center of the circle in the Right image is

Among them, k is the subscript of the center of the circle, and N represents all the centers of the circles in the public area;

Step 3.3. Calculate the tilt angle of the horizontal plane of the camera through the coordinates corresponding to the center of the circle in the public area in the Left image and the Right image respectively.

Step 3.4. According to the θ _k obtained in step 3.3, the average value of the tilt angle of the horizontal plane of the camera can be calculated as:

beneficial effect

The graphic production accuracy of the calibration plate of the invention can reach 1 micron, and the movement accuracy of the working platform can be less than 1 micron, so the calibration accuracy is high; for the calibration of different camera fields of view and different motion ranges, the step size can be changed, and the adaptability of the invention The invention is non-contact measurement and does not damage the calibration plate; the horizontal plane inclination angle obtained after calibration has a very important role in the establishment of a high-precision assembly system error model, the positioning of large-sized objects, image stitching and coordinate transformation; the invention The measurement process is simple and easy to operate, the design of the calibration board is simple and easy to use, and the measurement result is highly accurate, which can meet the requirements of image acquisition path planning and coordinate calculation.

Description of drawings

1 is a schematic diagram of a camera horizontal plane inclination angle measuring device according to the present invention;

2 is a schematic diagram of a calibration plate of the present invention;

3 is a schematic diagram of obtaining a graphic image of a calibration plate of the present invention;

FIG. 4 is a schematic diagram of the tilt angle of the horizontal plane of the camera for calculating the common area point according to the present invention.

FIG. 5 is an image of Left and Right of the calibration plate of this embodiment.

In the figure, 1 working platform, 2 motor Y axis, 3 calibration plate, 4 motor X axis, 5 calibration plate carrier, 6 light source, 7 lens, 8 camera, 9 bracket base and 10 camera bracket.

Detailed ways

Below in conjunction with accompanying drawing, the present invention is described in further detail:

The invention provides a method for measuring the inclination angle of the horizontal plane of the camera. The invention controls the movement of the working platform through the motor, so that the calibration plate graphic enters the camera's field of view, adjusts the appropriate position of the calibration plate graphic in the camera's field of view, and shoots a calibration plate. Then, keep the Y axis of the motor still, move a certain step along the X axis of the motor, and take another image of the calibration board. The coordinate values of the area points are different, and by processing the two captured images, the tilt angle of the camera on the horizontal plane can be obtained.

As shown in Figure 1, a device for measuring the tilt angle of a horizontal plane of a camera includes a working platform 1, a motor Y axis 2, a calibration plate 3, a motor X axis 4, a calibration plate carrier 5, a light source 6, a lens 7, a camera 8, The stand base 9 and the camera stand 10;

The light source 6 is installed on the lens 7, the lens 7 is installed on the camera 8, the camera 8 is fixedly installed on the camera bracket 10, and the camera bracket 10 is fixedly connected with the bracket base 9; the light source 6 There is a working platform 1 below, the middle of the working platform 1 is fixedly connected with a motor X-axis 4, the motor X-axis 4 is slidably connected with the motor Y-axis 2, and the calibration plate carrier 5 is slidably connected with the motor Y-axis 2 .

Example:

A method for measuring the inclination angle of a horizontal plane of a camera, comprising the following steps:

Step 1. Place the calibration plate on the calibration plate carrier 5, set a part of the calibration plate as a public area, control the movement of the working platform 1 by moving the motor, the calibration plate enters the camera field of view, and shoot an image of the calibration plate, The image includes the public area of the calibration board;

Step 2. Keep the motor Y-axis 2 still, move the working platform 1 along the motor X-axis 4 by a step Δd, and take another image of the calibration plate, which includes the public area of the calibration plate; The images exist in the same public area;

计算得出，其中，ΔV为公共区域点的V坐标值之差，ΔU为公共区域点的U坐标值之差。Step 3. Process the two images of the calibration board, and the tilt angle of the camera's horizontal plane is based on

It is calculated that ΔV is the difference between the V coordinate values of the points in the public area, and ΔU is the difference between the U coordinate values of the points in the public area.

As shown in Figure 2, the pattern on the calibration plate is circular, the material of the calibration plate is glass material, the pattern on the calibration plate is made by electron beam lithography, the pattern size deviation is less than ±0.5 microns, the thickness of the calibration plate is 1.6mm, The rectangular width and length of the calibration plate are 10mm*20mm, the radius of the standard circle is r1=0.5mm, and the circle spacing is 1.5mm. There are also two location circles with a radius of r2=1mm on the calibration plate, Location Circle, where the location circle is located. The column and the area between it is the common area of the calibration board is 4x4, which is used to calculate the tilt angle of the horizontal plane of the camera.

Among them, as shown in Figure 3, first move the public region of the calibration board to the right side of the camera's field of view, and record the image of the calibration board as the Left image, and then keep the motor Y-axis 2 still, along the negative direction of the motor X-axis 4 Or move Δd=5mm step to the left (equivalent to the calibration plate not moving, the camera moves along the positive X-axis direction or to the right by Δd=5mm step), so that the public area of the calibration plate is moved to the left side of the camera field of view, The captured image of the calibration plate is recorded as the Right image.

Among them, as shown in Figure 4, assuming that θ is counterclockwise (θ>0), in the Left image, the center A in the common area is (U _l , V _l ); when the working platform 1 moves along the negative direction of the motor X-axis 4 Δd=5mm step size, the center A in the original public area is A' (U _r , V _r ) in the Right image, and converting the center A' in the Right image to the Left image coordinate system is:

So,

That is, the tilt angle of the camera's horizontal plane

When θ is clockwise (θ<0), in the Left image, the center A in the common area is (U _l , V _l ); when the working platform 1 moves along the negative direction of the motor X-axis 4 with Δd=5mm steps, the original common The circle center A in the area is A'(U _r , V _r ) in the Right image. Converting the circle center A' in the Right image to the Left image coordinate system is:

So,

That is, the tilt angle of the camera's horizontal plane

Wherein, the method of calculating the inclination angle of the horizontal plane of the camera by processing the two captured images of the calibration plate in step 3 is as follows, as shown in Figure 5:

Step 3.1. According to the Left image obtained in step 1 and the Right image obtained in step 2, use the circle Hough transform method to calculate all circle parameters C(r, U, V) in the two images; wherein, r represents the radius of the circle;

i,j分别表示公共区域的行和列，将C按半径由大到小排序，取前两个元素即为两定位圆的圆参数

和

如果

则

否则，

m,n分别为两个定位圆的下标；Step 3.2. Let the public area point in the Left image be

i and j represent the rows and columns of the common area respectively, sort C according to the radius from large to small, and take the first two elements as the circle parameters of the two positioning circles

and

if

but

otherwise,

m, n are the subscripts of the two positioning circles respectively;

(T_p为圆参数的坐标差阈值)，那么如果

则得到L₁₁，如果

则得到L₃₁和L₄₁，同样地，可以得到L₁₄、L₂₄和L₄₄；Step 3.3, remove L ₂₁ and L ₃₄ in C _l , if

(T _p is the coordinate difference threshold of the circle parameter), then if

then get L ₁₁ , if

Then L ₃₁ and L ₄₁ are obtained, and similarly, L ₁₄ , L ₂₄ and L ₄₄ can be obtained;

那么如果

再根据

的大小可以得到L₁₂和L₁₃，同样地，可以得到L₂₂、L₂₃、L₃₂、L₃₃、L₄₂和L₄₃；Step 3.4, remove L ₁₁ , L ₃₁ , L ₄₁ , L ₁₄ , L ₂₄ and L ₄₄ in C _l , if

then if

Then according to

The size of L ₁₂ and L ₁₃ can be obtained, and similarly, L ₂₂ , L ₂₃ , L ₃₂ , L ₃₃ , L ₄₂ and L ₄₃ can be obtained;

Step 3.5. Similarly, from steps 3.2, 3.3, and 3.4, it can be obtained that the common area point in the Right image corresponding to the Left image is R _ij (r _rij , U _rij , V _rij );

Step 3.6. From the above step 3.5, it can be obtained that the tilt angle of the horizontal plane of the camera is:

The above are only preferred embodiments of the present invention, and are not intended to limit the present invention in any other form, and any modifications or equivalent changes made according to the technical essence of the present invention still fall within the scope of protection of the present invention. .

Claims (2)

1. The method for measuring the horizontal plane inclination angle of the camera is characterized in that the used device for measuring the horizontal plane inclination angle of the camera comprises a working platform, a motor Y axis, a calibration plate, a motor X axis, a calibration plate carrying platform, a light source, a lens, the camera, a support base and a camera support;

the camera comprises a light source, a camera support, a support base and a camera, wherein the light source is arranged on the camera, the camera is fixedly arranged on the camera support, and the camera support is fixedly connected with the support base; a working platform is arranged below the light source, a motor X shaft is fixedly connected in the middle of the working platform, the motor X shaft is in sliding connection with a motor Y shaft, and the calibration board carrying platform is in sliding connection with the motor Y shaft;

the measuring method comprises the following steps:

step 1, placing a calibration plate on a calibration plate carrying platform, setting a part of the calibration plate as a public area, controlling the movement of a working platform through a moving motor, enabling the calibration plate to enter the visual field of a camera, and shooting an image of the calibration plate, wherein the image comprises the public area of the calibration plate;

firstly, moving a public area of a calibration plate to the right side of the visual field of a camera, and recording a shot calibration plate image as a Left image;

step 2, keeping the Y axis of the motor still, moving the working platform along the X axis of the motor by a step length delta d, and shooting an image of another calibration plate, wherein the image comprises a public area of the calibration plate; wherein, the images of the two calibration plates have the same public area;

keeping the Y axis of the motor still, moving the working platform by delta d step length along the negative direction of the X axis of the motor or leftwards, moving the public area of the calibration plate to the left side of the visual field of the camera, and recording the shot image of the calibration plate as a Right image;

in the Left image, the center of a circle A in the common area is (U) _l ，V _l ) (ii) a When the working platform moves delta d step length along the negative direction of the X axis of the motor, the circle center A in the original public area is A' in the Right image (U) _r ，V _r ) And converting the circle center A' in the Right image into a Left image coordinate system, namely:

then the user can either, for example,

i.e. camera horizontal plane tilt angle

Step 3, processing the two shot calibration plate images, wherein the horizontal plane inclination angle of the camera is according to

Calculating, wherein Δ V is the difference of V coordinate values of the common region points, and Δ U is the difference of U coordinate values of the common region points;

the method comprises the following specific steps:

step 3.1, calculating all circle parameters C (r, U and V) in the two images by using a circle Hough transformation method according to the Left image obtained in the step 1 and the Right image obtained in the step 2; wherein r represents the radius of the circle;

3.2, sorting the circle parameters in each image from small to large according to the radius, wherein the first two circles with the largest radius are positioning circles, dividing a common area according to the two positioning circles in each image, calculating the coordinates of the circle centers of all circles in the common area, and recording the circle center in the Left image as the circle center

The center of a circle in the Right image is

Wherein k is a subscript of the circle center, and N represents all circle centers in the public area;

step 3.3, calculating the horizontal plane inclination angle of the camera according to the corresponding coordinates of the circle center in the Left image and the Right image in the public area

Step 3.4 θ obtained according to step 3.3 _k The average value of the camera horizontal plane tilt angle can be calculated as:

2. the method of measuring the tilt angle of the horizontal plane of a camera according to claim 1, wherein: the pattern on the calibration plate is circular, the radius of the standard circle is r1, two positioning circles with the radius of r2 exist on the calibration plate, the positioning circles are in different rows, the area where the positioning circles are located and the area between the rows are the common area of the calibration plate, the point of the common area is the center of a circle in the common area, and r2 is larger than r1.

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