CN110141800B - A kind of accelerator optical distance ruler equipment, calibration method and optical distance ruler generation method - Google Patents

Abstract

The invention provides an accelerator optical distance ruler equipment, a calibration method and an optical distance ruler generation method, and relates to the technical field of medical equipment. The accelerator optical distance ruler equipment comprises a projector, a camera, an optical distance ruler calibration plate and an optical distance indicator. The instrument is used to project the structured light pattern sequence pattern and the light distance ruler pattern. The camera is used to capture the structured light pattern sequence pattern projected by the projector and the pictures of the light distance ruler calibration plate. The light distance ruler calibration plate is used to calibrate the projector and camera and verify The accuracy of the optical distance ruler, the optical distance indicator is used to indicate the scale of the optical distance ruler. The accelerator optical distance ruler device of the present invention can calibrate the camera and the projector by the method of structured light to obtain calibration parameters; in addition, the obtained calibration parameters can be further used to generate an optical distance ruler pattern. The accelerator optical distance ruler device provided by the invention is easy to install, the calibration method has high calibration accuracy, and simplifies the optical distance ruler calibration process.

Description

A kind of accelerator optical distance ruler equipment, calibration method and optical distance ruler generation method

technical field

The invention relates to the technical field of medical devices, in particular to an accelerator optical distance ruler device, a calibration method and a method for generating an optical distance ruler.

Background technique

The optical distance ruler is a device that indicates the distance by projecting visible light on the scale, which is widely used in medical linear accelerators. The Accelerator Light Distance Scale device projects a graduated visible light scale onto the patient, indicating the distance from the patient's skin to the radiation source, as well as the isocenter position of the accelerator. Accelerator optical distance ruler equipment is an indispensable part of medical linear accelerators.

At present, the optical distance ruler on most linear accelerators is composed of three parts: a light source, an optical lens or a plexiglass film, and an optical distance indicator. The range indicator indicates the scale.

However, the existing optical distance ruler based on glass film has many shortcomings, for example, the scale on the film is difficult to manufacture, and the accuracy of the scale is not high; the installation is difficult, and the installation position is not good, the impact on the accuracy of the optical distance ruler is relatively large; The calibration process is cumbersome; the maintenance and repair of the optical distance ruler in the later stage is more difficult; and so on. These shortcomings limit the further application of this type of optical distance ruler.

SUMMARY OF THE INVENTION

The object of the present invention is to, in view of the deficiencies in the above-mentioned prior art, provide a kind of accelerator optical distance ruler equipment, calibration method and optical distance ruler generation method, in order to solve the problem that the calibration accuracy of the optical distance ruler on the accelerator is not high and the calibration of the optical distance ruler complex process.

To achieve the above purpose, the technical solutions adopted in the embodiments of the present invention are as follows:

In a first aspect, an embodiment of the present invention provides an accelerator optical distance ruler device, which includes: a projector, a camera, an optical distance ruler calibration plate, and an optical path indicator. The projector and the camera are fixed on the shell of the accelerator, and the projection The instrument is used to project the structured light pattern sequence pattern and the light distance ruler pattern. The structured light pattern sequence pattern is used to calibrate the projector and the camera. The camera is used to collect the structured light pattern sequence pattern projected by the projector and the picture of the light distance ruler calibration plate. The distance ruler calibration plate is set outside the exit end of the accelerator, and the center of the optical distance ruler calibration plate corresponds to the isocenter position of the accelerator. The optical distance ruler calibration plate is used to calibrate the projector and camera, and to verify the accuracy of the optical distance ruler. The indicator is arranged inside the exit end of the accelerator, and the light from the optical distance indicator is emitted from the exit end along the direction parallel to the exit direction of the accelerator, and is used to indicate the scale of the optical distance ruler;

The accelerator optical distance ruler equipment is calibrated using the following calibration methods, including:

In step 401, at least three first pictures of the optical distance ruler calibration plate are collected by a camera, and the optical distance ruler calibration plate corresponding to each picture in the at least three first pictures is in a different posture, that is, at least three first pictures are collected. Checkerboard pictures in different poses;

In step 402, according to the posture of the optical distance ruler calibration plate corresponding to each of the at least three first pictures, the second picture of the optical distance ruler calibration plate on which the structured light pattern sequence pattern is projected is collected by a camera. , the structured light pattern sequence pattern is projected by the projector, that is, a checkerboard picture corresponding to the picture collected in step 401 on which the structured light pattern sequence pattern is projected is collected;

In step 403, the position of the corner point in the first picture is extracted by using a predetermined corner point detection algorithm to obtain the position coordinates of the corner point of the first picture. The position is obtained relative to the preset actual corner position coordinates of the pattern on the optical distance ruler calibration plate, and the corner position coordinates of the first picture are marked as

The preset actual corner position coordinates of the pattern on the optical distance ruler calibration board are predefined as

The corner coordinates correspond to the corner coordinates of the checkerboard obtained by the predetermined corner detection algorithm;

In step 404, the second pictures corresponding to the horizontal structured light and the vertical structured light are respectively decoded to obtain the horizontal codeword and the vertical codeword of the second picture;

In step 405, according to the horizontal codeword and the vertical codeword, use the homography matrix to determine the position coordinates of the corner points of the projection pattern of the projector, the position coordinates of the corner points of the projection pattern correspond to the preset actual corner point position coordinates, and the angle of the projection pattern The point position coordinates are marked as

In step 406, the calibration parameters of the camera and the projector are determined according to the first picture corner position coordinates q _c , the preset actual corner position coordinates Q and the projection pattern corner position coordinates q _p , and a predetermined calibration algorithm is used. The calibration algorithm is Zhang Zhengyou's calibration algorithm. The calibration parameters include the focal length M _c of the camera lens, the distortion D _c of the camera lens, the focal length M _p of the projector lens, the distortion D _p of the projector lens, and the geometric transformation R between the camera and the projector. _cp and _Tcp ;

The Shi-Tomasi corner detection algorithm is used in the calibration process of the projector and camera, which calculates the grayscale change E(u, v) generated by the translation of the image window [u, v]

Among them, M is the autocorrelation matrix, which is defined as follows

In the formula, w(x, y) represents the window function;

I _x and T _y represent the derivatives of the image in the x and y directions;

For the two eigenvalues λ ₁ and λ ₂ of M, the Shi-Tomasi algorithm believes that the detection of corner points depends on the smallest eigenvalue, and the corner point judgment function R is as follows, when the value of R exceeds the threshold value, it is considered as a corner point:

R=min(λ ₁ , λ ₂ );

Structured light encoding uses the phase shift method, and the phase shift method encoding mode is as follows:

I _n (x, y)=I′(x, y)+I″(x, y)cos[φ(x,y)-2π/n];

Among them, I'(x, y) is the average intensity of the point in the image;

I″(x, y) is the modulated intensity of this point in the image;

I _n (x, y) is the image collected by the final camera, n ∈ 1, 2,..., N is the index of the phase shift mode, and N is the number of pictures in the phase shift mode;

φ(x, y) is the phase to be solved;

The phase shift method used is a 3-step phase shift method, that is, N in the above formula is equal to 3;

At this time, the phase φ(x, y) can be calculated by the following formula:

Through φ(x, y)/2π×W and φ(x, y)/2π×H, the code words corresponding to the width and height of the projector are solved respectively, where: W represents the width of the projector, and H represents the width of the projector. the height of the projector;

The calculation of the projection coordinates corresponding to the corners of the checkerboard needs to be solved in combination with the local homography matrix. By solving the local homography matrix, the correspondence between the pixel points of the projector and the corners of the checkerboard is found. For each checkerboard pattern, Using the code words around the pattern, calculate the local homography matrix, and finally use the homography matrix to correspond the corners of the checkerboard with the pixels on the projector. The calculation of the homography matrix minimizes the following formula:

Among them, H∈R ^3×3 , is a homography matrix;

q _c =[x, y, 1] ^T is the pixel coordinates in the chessboard image, obtained by the three steps of the calibration process;

u=[col, row, 1] ^T is the codeword obtained by decoding;

Then, the projector corresponding point can be obtained by multiplying the homography matrix with the pixel coordinates in the checkerboard image.

The accelerator optical distance ruler device provided by the embodiment of the present invention is easy to install, the projector and the camera only need to be fixed on the accelerator, and there is no specific requirement for the relative positional relationship between the projector and the camera. The accelerator optical distance ruler device can calibrate the camera and the projector by the method of structured light, and the calibration accuracy is high.

Optionally, a first predetermined number of equally spaced checkerboard patterns are respectively provided on both sides of the axis of the optical distance ruler calibration plate to determine the relative positional relationship between the optical distance ruler calibration plate, the projector and the camera.

Optionally, a second predetermined number of equally spaced line graphics are arranged on the axis of the optical distance ruler calibration plate to verify whether the optical distance ruler meets the accuracy requirements.

Optionally, the optical path indicator is arranged on the inner wall of the exit end of the accelerator, and after the light from the optical path indicator is reflected by a mirror with a predetermined angle arranged at the exit end of the accelerator, it is emitted from the light in a direction parallel to the exit direction of the accelerator. The exit end is ejected.

Optionally, the optical distance ruler calibration plate is hung below the front pointer of the accelerator.

By hanging the optical distance ruler calibration plate under the front pointer, since linear accelerators usually have front pointers, additional fabrication is not required, thereby simplifying the device structure and saving costs.

In a second aspect, an embodiment of the present invention provides a method for calibrating an accelerator optical distance ruler device. The accelerator optical distance ruler device includes a camera, a projector, and an optical distance ruler calibration plate, and the method includes:

At least three first pictures of the optical distance ruler calibration plate are collected by the camera, and the optical distance ruler calibration plate corresponding to each picture in the at least three first pictures is in a different posture;

According to the posture of the optical distance ruler calibration plate corresponding to each of the at least three first pictures, the second picture of the optical distance ruler calibration plate on which the structured light pattern sequence pattern is projected is collected by the camera, respectively. The pattern is projected through a projector;

Use a predetermined corner detection algorithm to extract the position of the corner point in the first picture to obtain the position coordinate of the corner point of the first picture. Obtained from the preset actual corner position coordinates of the pattern on the ruler calibration board;

Decoding the second picture corresponding to the horizontal structured light and the vertical structured light respectively to obtain the horizontal codeword and the vertical codeword of the second picture;

According to the horizontal codeword and the vertical codeword, use the homography matrix to determine the position coordinates of the corner points of the projection pattern of the projector, and the position coordinates of the corner points of the projection pattern correspond to the preset actual corner point position coordinates;

The calibration parameters of the camera and the projector are determined according to the position coordinates of the corner points of the first picture, the preset actual position coordinates of the corner points and the position coordinates of the corner points of the projection pattern, and using a predetermined calibration algorithm.

The calibration process proposed by the embodiment of the present invention is simple and convenient, and the system can be calibrated only by a calibration plate (eg, a checkerboard) and a projector projecting a sequence pattern of a structured light mode, and the calibration accuracy is high.

Optionally, according to the horizontal codeword and the vertical codeword, use a homography matrix to determine the position coordinates of the corner points of the projection pattern of the projector, including:

Calculate the local homography matrix according to the horizontal codeword and the vertical codeword;

Based on the local homography matrix, the corner points of the projection pattern of the projector correspond to the actual corner points on the calibration plate of the optical distance ruler;

The corresponding corner position coordinates of the projection pattern are determined based on the preset actual corner position coordinates.

Optionally, a first predetermined number of checkerboard patterns distributed at equal intervals are respectively provided on both sides of the axis of the optical distance ruler calibration plate.

Optionally, the calibration parameters include the focal length of the camera lens, the distortion of the camera lens, the focal length of the projector lens, the distortion of the projector lens, and the geometric transformation between the camera and the projector.

In a third aspect, an embodiment of the present invention provides a method for generating an optical distance ruler, which is used for an accelerator optical distance ruler device to generate an optical distance ruler. The accelerator optical distance ruler device includes a camera, a projector, and an optical distance ruler calibration plate, and the method includes:

Hang the calibration plate of the optical distance ruler under the front pointer of the accelerator, so that the midpoint of the calibration plate of the optical distance ruler corresponds to the isocenter of the accelerator;

The picture of the light distance ruler calibration board is collected by the camera, and the position of the corner point in the picture is extracted by the preset corner point detection algorithm to obtain the corresponding position coordinates;

Determine the first transformation matrix of the camera relative to the optical distance ruler calibration plate by using the position coordinates and the calibration parameters of the camera and the projector obtained according to the calibration method described in the second aspect;

According to the first transformation matrix, determine the second transformation matrix of the projector relative to the optical distance ruler calibration plate;

Determine the coordinates of all scale points on the optical distance ruler calibration plate based on the preset coordinates of the preset points on the optical distance ruler calibration plate;

Based on the calibration parameters of the projector and the second transformation matrix, determine the position point corresponding to the scale point on the calibration plate of the optical distance ruler in the projected image of the projector;

Based on the corresponding position points, a light distance ruler pattern is generated in the negative of the projector.

The optical distance ruler generation method proposed in the embodiment of the present invention is convenient for later maintenance. If the positions of the camera and the projector are not changed and the focal length is not adjusted, the camera and the projector do not need to be calibrated again, and only the pre-calibrated calibration parameters need to be obtained. Optical distance ruler can be generated.

Description of drawings

In order to illustrate the technical solutions of the embodiments of the present invention more clearly, the following briefly introduces the accompanying drawings used in the embodiments. It should be understood that the following drawings only show some embodiments of the present invention, and therefore do not It should be regarded as a limitation of the scope, and for those of ordinary skill in the art, other related drawings can also be obtained according to these drawings without any creative effort.

1 shows a schematic structural diagram of an accelerator optical distance ruler device provided by an embodiment of the present invention;

2 shows a schematic structural diagram of an optical distance ruler calibration plate provided by an embodiment of the present invention;

3 and 4 show schematic flowcharts of a method for calibrating an accelerator optical distance ruler device provided by an embodiment of the present invention;

5 shows a schematic flowchart of a method for generating an optical distance ruler provided by an embodiment of the present invention;

FIG. 6 shows a schematic diagram of an optical distance ruler for projection generated by the optical distance ruler generation method of the present invention.

Reference numerals: 101-projector; 102-camera; 103-optical distance scale calibration plate; 104-optical distance indicator; 105-reflector; 106-front pointer.

Detailed ways

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, but not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

The structured light measurement method is a method of projecting a series of optical fringes (that is, structured light pattern sequence patterns) onto the object, and then using a camera to collect the optical fringe information to obtain the three-dimensional coordinates of the object. At present, the structured light measurement system has high precision in stereo measurement, which can fully meet the precision requirements of the optical distance ruler.

An embodiment of the present invention provides a medical linear accelerator optical distance ruler device based on structured light. As shown in FIG. 1 , the device mainly includes: a projector 101 , a camera 102 , an optical distance ruler calibration plate 103 and an optical distance indicator 104 , the projector 101 and the camera 102 are fixed in the box and mounted on the casing of the accelerator, the projector 101 is used for projecting the structured light pattern sequence pattern and the finally generated light distance ruler pattern, and the structured light pattern sequence pattern is used for calibrating the projector 101 and a camera 102, the camera 102 is used to collect the structured light pattern sequence pattern projected by the projector 101 and the picture of the optical distance ruler calibration plate 103, the optical distance ruler calibration plate 103 is arranged outside the exit end of the accelerator, and the optical distance ruler calibration plate 103 The center of 103 corresponds to the isocenter position of the accelerator, the optical distance ruler calibration plate 103 is used to calibrate the projector 101 and the camera 102 and to verify the accuracy of the generated optical distance ruler, and the optical distance indicator 104 is arranged inside the exit end of the accelerator, The light from the optical distance indicator 104 exits from the exit end in a direction parallel to the exit direction of the accelerator, and is used to indicate the graduation of the optical distance ruler.

Camera 102 may be a CCD (Charge Coupled Device) camera. As shown in FIG. 1 , the optical path indicator 104 can be disposed on the inner wall of the exit end of the accelerator, so that the light from the optical path indicator 104 is reflected by the reflector 105 with a predetermined angle disposed at the exit end of the accelerator, and then travels along the same direction as the accelerator. The outgoing direction is parallel to the outgoing end. For example, when the exit direction of the optical distance indicator 104 is perpendicular to the exit direction of the accelerator, the mirror 105 is placed at an angle of 45° relative to the exit direction of the optical distance indicator 104 so that the light from the optical distance indicator 104 is reflected After the mirror 105 is reflected, it is parallel to the exit direction of the accelerator. The optical distance ruler calibration plate 103 can be hung below the front pointer 106 of the accelerator, so that the center of the optical distance ruler calibration plate 103 corresponds to the isocenter position of the accelerator.

The accelerator optical distance ruler device provided by the embodiment of the present invention is easy to install, the projector and the camera only need to be fixed on the accelerator, and there is no specific requirement for the relative positional relationship between the projector and the camera. The accelerator optical distance ruler device can calibrate the camera and the projector by the method of structured light, and the calibration accuracy is high. By hanging the optical distance ruler calibration plate under the front pointer, since linear accelerators usually have front pointers, additional fabrication is not required, thereby simplifying the device structure and saving costs.

FIG. 2 shows a schematic structural diagram of an optical distance ruler calibration plate provided by an embodiment of the present invention. As shown in FIG. 2 , a predetermined number (for example, five) of A checkerboard pattern distributed at equal intervals. During the calibration process, the checkerboard pattern is used to determine the relative positional relationship between the optical distance ruler calibration plate 103 , the projector 101 and the camera 102 . In addition, a predetermined number of line patterns distributed at equal intervals (for example, at intervals of 2 mm) are provided on the axis of the optical distance ruler calibration plate 103. After the optical distance ruler is generated, the line graphics can be used to verify whether the optical distance ruler meets the accuracy requirements. .

The embodiment of the present invention also provides a method for calibrating an accelerator optical distance ruler device, and the method can be used for calibrating a camera and a projector in the accelerator optical distance ruler device. The calibration method provided by the embodiment of the present invention can be used to calibrate the camera and the projector in the accelerator optical distance ruler device provided in the foregoing embodiment of the present invention.

The method for calibrating the projector and the camera will be described below in conjunction with the accelerator optical distance ruler device provided in the above-mentioned embodiments of the present invention and referring to FIG. 3 and FIG. 4 . It should be understood that the calibration pattern on the optical distance ruler calibration plate 103 may be a checkerboard pattern, but is not limited thereto. For the sake of simplicity, a checkerboard pattern will be used as an example for description hereinafter.

In step 401, at least three first pictures of the optical distance ruler calibration plate 103 are collected by the camera 102, and the optical distance ruler calibration plate 103 corresponding to each of the at least three first pictures is in a different posture, and also That is to say, to collect checkerboard pictures in at least three different postures, and generally, it is sufficient to collect checkerboard pictures in 4 to 8 different postures.

In step 402, according to the posture of the optical distance ruler calibration plate corresponding to each of the at least three first pictures, the second picture of the optical distance ruler calibration plate on which the structured light pattern sequence pattern is projected is collected by a camera. , the structured light pattern sequence pattern is projected by the projector, that is, a checkerboard picture corresponding to the picture collected in step 401 on which the structured light pattern sequence pattern is projected is collected.

In step 403, the position of the corner point in the first picture is extracted by using a predetermined corner point detection algorithm to obtain the position coordinates of the corner point of the first picture. The position is obtained relative to the preset actual corner position coordinates of the pattern on the optical distance ruler calibration plate. The predetermined corner detection algorithm can be, for example, a Shi-Tomasi corner detection algorithm, and can The coordinates of the corner points of a picture are marked as

The preset actual corner position coordinates of the pattern on the optical distance ruler calibration board can be pre-defined as

The corner coordinates correspond to the corner coordinates of the checkerboard obtained by a predetermined corner detection algorithm.

In step 404, the second pictures corresponding to the horizontal structured light and the vertical structured light are decoded respectively to obtain the horizontal codeword and the vertical codeword of the second picture.

In step 405, according to the horizontal codeword and the vertical codeword, use the homography matrix to determine the position coordinates of the corner points of the projection pattern of the projector, the position coordinates of the corner points of the projection pattern correspond to the preset actual corner point position coordinates, and the angle of the projection pattern The coordinates of the point position can be written as

The use of the homography matrix to determine the position coordinates of the corner points of the projection pattern of the projector will be described in detail below.

In step 406 , the calibration parameters of the camera and the projector are determined according to the first picture corner position coordinates q _c , the preset actual corner position coordinates Q and the projection pattern corner position coordinates q _p , and using a predetermined calibration algorithm. The predetermined calibration algorithm here can be Zhang Zhengyou's calibration algorithm (for a detailed description of Zhang Zhengyou's calibration algorithm, please refer to the following documents: Zhang Z. AFlexible New Technique for Camera Calibration [J]. IEEE Transactions on PatternAnalysis and Machine Intelligence, 2000, 22(11): 1330-1334), the calibration parameters include the focal length M _c of the camera lens, the distortion D _c of the camera lens, the focal length M _p of the projector lens, the distortion D _p of the projector lens, and the geometric transformation between the camera and the projector R _cp and _Tcp .

The Shi-Tomasi corner detection algorithm used in the calibration process of the projector and the camera in Figures 3 and 4 is an improved algorithm of the Harris corner detection algorithm, which calculates the image window translation [u, v ] The resulting grayscale change E(u, v)

where M is the autocorrelation matrix, defined as follows

where w(x, y) represents the window function, and I _x and I _y represent the derivatives of the image in the x and y directions. For the two eigenvalues λ ₁ and λ ₂ of M, the Shi-Tomasi algorithm believes that the detection of the corner point depends on the smallest eigenvalue, and the corner point judgment function R is as follows, when the value of R exceeds a certain threshold, it is considered as a corner point:

R=min(λ ₁ , λ ₂ )

The structured light coding in Fig. 3 uses the phase shift method. Among various coding schemes, the phase shift method is a relatively common calibration method, has an extremely wide range of applications, and provides higher and higher accuracy. The phase-shift encoding mode is as follows:

I _n (x,y)=I'(x,y)+I″(x,y)cos[φ(x,y)-2π/n]

I′(x, y) is the average intensity of the point in the image, I″(x, y) is the modulated intensity of the point in the image, I _n (x, y) is the image collected by the final camera, n∈1 , 2, . N of the formula is equal to 3. At this time, the phase φ(x, y) can be calculated by the following formula:

Finally, the code words corresponding to the width and height of the projector are solved by φ(x, y)/2π×W and φ(x, y)/2π×H respectively, where W represents the width of the projector and H represents the projection. The height of the instrument.

The calculation of the projected coordinates corresponding to the corresponding checkerboard corner points in FIG. 3 needs to be solved in combination with the local homography matrix. Obtaining codewords from structured light cannot be directly used for the correspondence between projector pixels and checkerboard corners. The present invention finds this correspondence by solving a local homography matrix. For each checkerboard pattern, use the codewords around the pattern to calculate the local homography matrix, and finally use these homography matrices to correspond the checkerboard corner points to the pixels on the projector. The homography matrix is calculated by minimizing the following formula:

where H∈R ^3×3 , is the homography matrix; q _c =[x, y, 1] ^T is the pixel coordinates in the chessboard image, obtained by the three steps of the calibration process; u = [col, row, 1] ^T is the codeword obtained by decoding.

Then, the projector corresponding point can be obtained by multiplying the homography matrix with the pixel coordinates in the checkerboard image.

To sum up, the calibration process proposed by the embodiments of the present invention is simple and convenient, and the system can be calibrated only with a calibration plate (eg, a checkerboard) and a projector to project a sequence pattern of structured light patterns, and the calibration accuracy is high.

The embodiment of the present invention also provides a method for generating an optical distance ruler, which is used for an accelerator optical distance ruler device to generate an optical distance ruler, wherein the accelerator optical distance ruler device includes a camera, a projector and an optical distance ruler calibration plate. The method for generating an optical distance ruler can be applied to the accelerator optical distance ruler device provided by the foregoing embodiments of the present invention to generate an optical distance ruler.

As shown in Figure 5, the generation method of the optical distance ruler is as follows:

In step 501, preparatory work is performed, and the optical distance ruler calibration plate is hung under the front pointer of the accelerator, so that the midpoint of the optical distance ruler calibration plate corresponds to the isocenter of the accelerator.

In step 502, a picture of the optical distance ruler calibration plate is collected by the camera, and the position of the corner point in the picture is extracted by using a preset corner point detection algorithm, so as to obtain the corresponding position coordinates. When searching for the corner point, Shi- The Tomasi corner detection algorithm extracts the location of the corners in the image.

In step 503, the first transformation matrix R of the camera relative to the optical distance ruler calibration plate is determined by using the position coordinates and the calibration parameters M _c and D _c of the camera and the projector obtained according to the calibration method provided by the above-mentioned embodiments of the present invention _c and T _c . In practical applications, if the camera and projector have been calibrated before, and the positions of the camera and projector have not changed and the focal length has not been adjusted, the calibration parameters obtained in the previous calibration can be directly used without re-calibrating the camera and projector. The projector is calibrated.

In step 504, according to the first transformation matrices R _c and T _c , determine the second transformation matrices R _p and T _p of the projector relative to the optical distance ruler calibration plate, and the calculation formula is as follows:

R _p =R _cp ·R _c , T _p =R _cp ·T _c +T _cp .

In step 505, based on the preset coordinates of the preset point on the optical distance ruler calibration plate (for example, the coordinates of the center point of the optical distance ruler calibration plate may be preset to be (0, 0)), determine the optical distance ruler calibration plate The coordinates of all the tick points on it.

In step 506, based on the calibration parameters of the projector (focal length M _p and distortion D _p ) and the second transformation matrix, determine the scale points on the calibration plate of the optical distance ruler (the scale points determined in step 505 ) to project on the projector the corresponding position in the image.

In step 507, based on the corresponding position points, a light distance ruler pattern is generated in the negative of the projector. The generated light distance ruler pattern is used for projection, and an example of the light distance ruler pattern is shown in Figure 6. Optionally, after the optical distance ruler is projected, the error between it and the line pattern on the axis of the optical distance ruler calibration plate can be observed, so as to determine whether it meets the accuracy requirements.

The optical distance ruler generation method proposed in the embodiment of the present invention is convenient for later maintenance. If the positions of the camera and the projector are not changed and the focal length is not adjusted, the camera and the projector do not need to be calibrated again, and only the pre-calibrated calibration parameters need to be obtained. Optical distance ruler can be generated.

The above-mentioned embodiments are only for illustrating the technical concept and characteristics of the present invention, and their purpose is to enable those of ordinary skill in the art to understand the content of the present invention and implement them, and cannot limit the scope of protection of the present invention with this. The equivalent changes or modifications made should be covered within the protection scope of the present invention.

Claims (10)

1. An accelerator light distance ruler device is characterized in that, comprising: a projector, a camera, a light distance ruler calibration plate and an optical path indicator, the projector and the camera are fixed on the casing of the accelerator, and the projection The projector is used to project the structured light pattern sequence pattern and the light distance ruler pattern, the structured light pattern sequence pattern is used to calibrate the projector and the camera, and the camera is used to collect the structured light pattern sequence projected by the projector The pattern and the picture of the optical distance ruler calibration plate, the optical distance ruler calibration plate is arranged outside the exit end of the accelerator, and the center of the optical distance ruler calibration plate corresponds to the isocenter position of the accelerator, the optical distance The ruler calibration plate is used for calibrating the projector and the camera and verifying the accuracy of the optical distance ruler. The direction parallel to the output direction of the accelerator is emitted from the output end to indicate the scale of the optical distance ruler; The accelerator optical distance ruler device is calibrated using the following calibration methods, specifically including: In step 401, at least three first pictures of the optical distance ruler calibration plate are collected by the camera, and the optical distance ruler calibration plate corresponding to each of the at least three first pictures is in a different posture, That is to collect checkerboard pictures in at least three different poses; In step 402, according to the posture of the optical distance ruler calibration plate corresponding to each of the at least three first pictures, respectively, the camera collects the first position of the optical distance ruler calibration plate on which the structured light pattern sequence pattern is projected. Two pictures, the structured light pattern sequence pattern is projected by the projector, that is, a checkerboard picture corresponding to the picture collected in the step 401 on which the structured light pattern sequence pattern is projected is collected; In step 403, the position of the corner point in the first picture is extracted by using a predetermined corner point detection algorithm to obtain the position coordinates of the corner point of the first picture. The position is obtained relative to the preset actual corner position coordinates of the pattern on the optical distance ruler calibration plate, and the first picture corner position coordinates are marked as

The preset actual corner position coordinates of the pattern on the optical distance ruler calibration board are predefined as

The corner coordinates correspond to the corner coordinates of the checkerboard obtained by the predetermined corner detection algorithm; In step 404, the second pictures corresponding to the horizontal structured light and the vertical structured light are respectively decoded to obtain the horizontal codeword and the vertical codeword of the second picture; In step 405, according to the horizontal codeword and the vertical codeword, the position coordinates of the corner points of the projection pattern of the projector are determined by using the homography matrix, and the position coordinates of the corner points of the projection pattern correspond to the preset actual corner point position coordinates, and the projection The coordinates of the corner points of the pattern are marked as

In step 406 , according to the first picture corner position coordinates q _c , the preset actual corner position coordinates Q and the projection pattern corner position coordinates q _p , and use a predetermined calibration algorithm, determine the camera and the projector. Calibration parameters, the predetermined calibration algorithm is Zhang Zhengyou calibration algorithm, and the calibration parameters include the focal length M _c of the camera lens, the distortion D _c of the camera lens, the focal length M _p of the projector lens, the distortion D _p of the projector lens, and the camera and geometric transformations between projectors R _cp and T _cp ; The Shi-Tomasi corner detection algorithm is used in the calibration process of the projector and the camera, which calculates the grayscale change E(u, v) generated by the translation of the image window [u, v]

Among them, M is the autocorrelation matrix, which is defined as follows

In the formula, w(x, y) represents the window function; I _x and I _y represent the derivatives of the image in the x and y directions; For the two eigenvalues λ ₁ and λ ₂ of M, the Shi-Tomasi algorithm believes that the detection of corner points depends on the smallest eigenvalue, and the corner point judgment function R is as follows, when the value of R exceeds the threshold value, it is considered as a corner point: R=min(λ ₁ , λ ₂ ); Structured light encoding uses the phase shift method, and the phase shift method encoding mode is as follows: I _n (x, y)=I′(x, y)+I″(x, y)cos[φ(x,y)-2π/n]; Among them, I'(x, y) is the average intensity of the point in the image; I″(x, y) is the modulated intensity of this point in the image; I _n (x, y) is the image collected by the final camera, n ∈ 1, 2,..., N is the index of the phase shift mode, and N is the number of pictures in the phase shift mode; φ(x, y) is the phase to be solved; The phase shift method used is a 3-step phase shift method, that is, N in the above formula is equal to 3; At this time, the phase φ(x, y) can be calculated by the following formula:

Through φ(x, y)/2π×W and φ(x, y)/2π×H, the code words corresponding to the width and height of the projector are solved respectively, where: W represents the width of the projector , and H represents the height of the projector; The calculation of the projection coordinates corresponding to the corners of the checkerboard needs to be solved in combination with the local homography matrix. By solving the local homography matrix, the correspondence between the pixel points of the projector and the corners of the checkerboard is found. For each checkerboard pattern, Using the code words around the pattern, calculate the local homography matrix, and finally use the homography matrix to correspond the corners of the checkerboard with the pixels on the projector. The calculation of the homography matrix minimizes the following formula:

Among them, H∈R ^3×3 , is a homography matrix; q _c =[x, y, 1] ^T is the pixel coordinates in the chessboard image, obtained by the three steps of the calibration process; u=[col, row, 1] ^T is the codeword obtained by decoding;

Then, the projector corresponding point can be obtained by multiplying the homography matrix with the pixel coordinates in the checkerboard image. 2. The accelerator optical distance ruler device according to claim 1, wherein the two sides of the axis of the optical distance ruler calibration plate are respectively provided with a first predetermined number of equidistantly distributed checkerboard patterns for determining The relative positional relationship between the optical distance ruler calibration plate, the projector and the camera. 3. The accelerator optical distance ruler device according to claim 1 or 2, wherein the axis of the optical distance ruler calibration plate is provided with a second predetermined number of equidistantly distributed line graphics for verifying the optical distance Whether the ruler meets the accuracy requirements. 4 . The accelerator optical distance ruler device according to claim 1 , wherein the optical distance indicator is arranged on the inner wall of the exit end of the accelerator, and the light from the optical distance indicator is arranged on the After being reflected by a reflector with a predetermined angle at the exit end of the accelerator, it is emitted from the exit end in a direction parallel to the exit direction of the accelerator. 5. The accelerator optical distance ruler device according to any one of claims 1, 2 or 4, wherein the optical distance ruler calibration plate is hung below the front pointer of the accelerator. 6. A calibration method of an accelerator optical distance ruler device, wherein the accelerator optical distance ruler device comprises a camera, a projector and an optical distance ruler calibration plate, and the method comprises: At least three first pictures of the optical distance ruler calibration plate are collected by the camera, and the optical distance ruler calibration plate corresponding to each of the at least three first pictures is in a different posture; According to the posture of the optical distance ruler calibration plate corresponding to each of the at least three first pictures, respectively, the camera collects the second picture of the optical distance ruler calibration plate on which the structured light pattern sequence pattern is projected, the structured light pattern sequence pattern is projected by the projector; The position of the corner point in the first picture is extracted by using a predetermined corner point detection algorithm to obtain the position coordinate of the corner point of the first picture, and the position coordinate of the corner point of the first picture is based on the extracted corner point of the first picture. The position is obtained relative to the preset actual corner position coordinates of the pattern on the optical distance ruler calibration plate; Decoding the second picture corresponding to the horizontal structured light and the vertical structured light respectively to obtain the horizontal codeword and the vertical codeword of the second picture; According to the horizontal codeword and the vertical codeword, a homography matrix is used to determine the position coordinates of the corner points of the projection pattern of the projector, and the position coordinates of the corner points of the projection pattern are different from the preset actual corner point position coordinates. correspond; The calibration parameters of the camera and the projector are determined according to the position coordinates of the corner points of the first picture, the position coordinates of the preset actual corner points, and the position coordinates of the corner points of the projection pattern, and using a predetermined calibration algorithm. 7. The method for calibrating an accelerator optical distance ruler device according to claim 6, wherein the projection pattern of the projector is determined by using a homography matrix according to the horizontal codeword and the vertical codeword Corner position coordinates, including: Calculate a local homography matrix according to the horizontal codeword and the vertical codeword; Based on the local homography matrix, corresponding the corner points of the projection pattern of the projector to the actual corner points on the calibration plate of the optical distance ruler; The corresponding corner position coordinates of the projection pattern are determined based on the preset actual corner position coordinates. 8 . The method for calibrating an accelerator optical distance ruler device according to claim 6 , wherein the two sides of the axis of the optical distance ruler calibration plate are respectively provided with a first predetermined number of equally spaced checkerboard patterns. 9 . 9. The calibration method of accelerator optical distance ruler device according to claim 6, wherein the calibration parameters comprise the focal length of the camera lens, the distortion of the camera lens, the focal length of the projector lens, the distortion of the projector lens and the camera lens and the geometric transformation between the projector. 10. A method for generating an optical distance ruler, characterized in that it is used for an accelerator optical distance ruler device to generate an optical distance ruler, and the accelerator optical distance ruler device comprises a camera, a projector and an optical distance ruler calibration plate, and the method comprises: Hanging the optical distance ruler calibration plate below the front pointer of the accelerator, so that the midpoint of the optical distance ruler calibration plate corresponds to the isocenter position of the accelerator; Collect a picture of the optical distance ruler calibration board by the camera, and extract the position of the corner point in the picture by using a preset corner point detection algorithm to obtain the corresponding position coordinate coordinates; Using the position coordinates and the calibration parameters of the camera and the projector obtained by the calibration method according to any one of claims 6 to 9, the first position of the camera relative to the optical distance ruler calibration plate is determined. a transformation matrix; According to the first transformation matrix, determine a second transformation matrix of the projector relative to the optical distance ruler calibration plate; Determine the coordinates of all scale points on the optical distance ruler calibration plate based on the preset coordinates of the preset points on the optical distance ruler calibration plate; Based on the calibration parameters of the projector and the second transformation matrix, determine the position points corresponding to the scale points on the calibration plate of the optical distance ruler in the projected image of the projector; Based on the corresponding position points, a light distance ruler pattern is generated in the negative of the projector.

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