A method for locating underwater laser emission point based on binocular stereo vision

Abstract

The present invention belongs to the field of underwater positioning, and discloses a method for positioning an underwater laser emission point of binocular stereo vision, and the positioning method comprises the following steps: S1: placing a waterproof laser into water and turning it on, forming a thin laser beam underwater, and swinging the laser up and down at the same position; S2: binocular cameras capture the laser beam, obtain images of the laser beam in the left and right cameras, and obtain two frames of images containing lasers at different underwater positions; S3: performing image processing, calculating the three-dimensional coordinate straight line equation of the laser beam propagation in the two frames of images; S4: using two laser straight line equations to calculate the three-dimensional space coordinates of the laser emission point relative to the binocular camera. The method has fast positioning processing speed and high positioning accuracy, and can improve the detection range of underwater binocular stereo positioning.

Description

[0001] manual Technical Field

[0002] The invention belongs to the field of underwater positioning, and in particular relates to an underwater laser emission point positioning method based on binocular stereo vision. Background Art

[0003] With the development of modern science and technology, and in the context of accelerating the construction of a maritime power, different underwater operations have put forward different demands on underwater positioning. From the perspective of machine vision positioning technology, the development direction of underwater vision positioning is mainly focused on improving processing speed, improving processing accuracy, and increasing field of view.

[0004] The existing underwater stereo vision positioning method uses a binocular camera to perform three-dimensional positioning of underwater target objects, separates the target object from the complex background and determines the position through feature matching. The disadvantages of this method are as follows: 1. Object features are greatly affected by light sources in underwater environments, so the matching accuracy is not high; 2. The binocular camera is limited by its field of view, and the positioning range is relatively small; 3. Underwater distant objects occupy few pixels in the camera and have sparse features, so it is difficult to accurately locate them at long distances underwater. Summary of the invention

[0005] The purpose of the present invention is to provide an underwater laser exit point positioning method based on binocular stereo vision. The method utilizes a binocular camera and an underwater laser to obtain the three-dimensional coordinates of the laser exit point, thereby achieving fast and accurate positioning, increasing the camera detection range, fast processing speed, and high positioning accuracy.

[0006] To achieve the above object, the present invention adopts the following technical solutions:

[0007] A method for locating an underwater laser emission point based on binocular stereo vision comprises the following steps:

[0008] S1: Put the waterproof laser into the water and turn it on to form a thin laser beam underwater. Adjust the laser emission angle while keeping the laser emission point unchanged.

[0009] S2: The binocular camera captures the laser beam, obtains images of the laser beam in the left and right cameras, and obtains two frames of images containing lasers at different underwater positions;

[0010] S3: Perform image processing to calculate the three-dimensional coordinate straight line equation of the laser beam propagation in the two frames of images;

[0011] S4: Use the two laser line equations to calculate the three-dimensional spatial coordinates of the laser emission point relative to the binocular camera.

[0012] Preferably, in S1, the emission angle of the laser is adjusted by using an underwater pan / tilt, so that both the left and right cameras in the binocular camera can capture the underwater laser beam.

[0013] The method of the present invention does not require that the left and right cameras in the binocular camera can completely capture the underwater laser beam when the laser is in the initial state. Instead, the servo motor controls the laser to continuously adjust the laser emission angle. The binocular camera only needs to obtain two or more frames of images that meet the conditions for calculating the laser spatial position during the shooting process. The entire process requires a small amount of data to be collected and processed, with fast computing speed and high processing accuracy. During the working process, the position of the binocular camera is not moved, only the emission angle of the laser is moved, which can effectively calculate the spatial coordinates of the emission point of the long-distance laser, thereby improving the positioning range of underwater positioning. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 is a schematic diagram of the present invention, wherein the origin of the spatial coordinates is the center of the binocular camera; DETAILED DESCRIPTION

[0015] The purpose of the present invention is to locate the laser emission point through binocular stereo vision. It should be clear that in general application scenarios, when the image of the laser underwater is captured by a binocular camera, the position coordinates of the underwater laser emission point can be determined by obtaining multiple frames of images that meet the requirements. However, the types of underwater operations are different. For example, the alignment of the transmitting end and the receiving end of underwater wireless optical communication requires tracking, aiming, and capturing in advance. This process requires the positioning of the underwater laser emission point. The following is a detailed description of the present invention using the application of underwater in-situ detection as an example, but it should be clear that this method is also applicable to other underwater operations that require the positioning of underwater laser emission points, such as the alignment of underwater wireless optical communications.

[0016] Step 1: Place the laser at the location where detection is required, and use the underwater gimbal to control the laser to swing up and down, left and right. The swing speed of this step can be adjusted according to the frame rate of the video shot by the camera. During the swinging process, the laser emission angle can change, but the gimbal needs to control the laser emission point position to remain unchanged;

[0017] Step 2: Use the binocular camera to continuously shoot underwater scenes, and obtain multiple frames of images where both left and right cameras contain laser beams;

[0018] Step 3: Process the captured images that meet the requirements and calculate the laser propagation space equation in each image. The specific steps are as follows:

[0019] First of all, before the binocular camera shooting work begins, the internal and external parameters of the binocular camera need to be calibrated in advance. The calibration method is to place the checkerboard calibration plate underwater, adjust the position of the calibration plate without changing the focal length, and select 10-20 images to solve the underwater camera parameters.

[0020] Then, the images captured by the left and right cameras are stereo-corrected using the camera parameters so that the epipolar lines of the left and right images fall on the same horizontal line. Based on the known laser color, the background in the captured image is removed and the image is grayed out. Based on the principle of laser beam intensity distribution, the laser light in the image is processed and the center line of the laser beam is extracted as the propagation direction of the laser. Each line of laser stripes is processed using the grayscale centroid method, and the position of the optical center is recorded as:

[0021]

[0022] Among them U i represents the optical center position of the i-th row image, g i,j Represents the grayscale value of the image at position (i, j).

[0023] Calculate the pixel difference of the laser center point on the same epipolar line of the left and right cameras, and use it as the parallax to calculate the spatial coordinates of each point on the laser. The calculation formula is as follows:

[0024] [X,Y,Z,W] T =Q×[x,y,disparity(x,y),1] T (2)

[0025] Where X, Y, and Z represent the spatial coordinates of the point on the laser line relative to the left camera, Q is the perspective projection matrix of the binocular camera, x and y are the pixel coordinates of the point on the laser line on the left camera, and disparity(x, y) is the pixel difference between the point on the laser line in the left and right cameras.

[0026] After calculating the spatial coordinates of the upper point of the laser relative to the left camera, it is converted into coordinates relative to the center of the binocular camera according to the measurement results. The spatial straight line coordinates of the laser underwater relative to the center of the binocular camera in an image are calculated through the RANSAC straight line fitting algorithm.

[0027] Step 4: Use the two laser line equations to calculate the three-dimensional spatial coordinates of the laser emission point relative to the binocular camera, which specifically includes the following steps:

[0028] According to the calculation formula of solid geometry, the points on two straight lines in space that are closest to another straight line are calculated respectively, and the center point of the two points is taken as the spatial coordinates of the laser emission point.

[0029] The present invention discloses an underwater laser exit point positioning method based on binocular stereo vision. The laser exit point that can be positioned by the method is not limited to the field of view of a binocular camera, and the target object that can be positioned is not limited to the laser exit point. In the process of swinging the laser, only one point on the laser needs to be kept unchanged, and the point can also be used as a target point for positioning.

[0030] In practical applications, the positioning accuracy is related to the length of the binocular camera baseline and the spatial distance between the underwater laser emission point and the binocular camera. It is necessary to determine the length of the binocular camera baseline according to the specific problem and use this method for fast and accurate positioning.

[0031] The above embodiments are only illustrative of the concept and implementation of the invention, not limiting thereof. It should be understood that the present invention is not limited to the form disclosed herein, and should not be regarded as excluding other embodiments, but can be used in various other combinations, modifications and environments, and can be modified within the scope of the invention concept described herein through the above teachings or the technology or knowledge in the relevant field. The changes and modifications made by those skilled in the art shall not deviate from the spirit and scope of the present invention, and shall be within the scope of protection of the claims attached to the present invention.

Claims

1. A method for locating a laser emission point with stereo vision, characterized in that Follow these steps: S1: Place the waterproof laser on a pan-tilt with adjustable pitch angle and place it in water. Use the laser emitting device to emit monochromatic laser into the water to form a laser beam underwater. Use the underwater pan-tilt to control the laser at the same position to ensure that the laser emission point remains unchanged. S2: Control the gimbal to change the pitch angle, thereby changing the propagation path of the laser beam in the water, but still within the shooting screen of the two lenses of the binocular camera, hereinafter referred to as the left and right cameras, and save the camera images to obtain two frames of binocular images with different laser beam propagation paths; S3: Perform image processing to calculate the three-dimensional coordinate straight line equation of the laser beam propagation in the two frames of images; According to the principle of laser beam intensity distribution, the laser light in the image is processed and the center line of the laser beam is extracted as the propagation direction of the laser. The grayscale centroid method is used to process each line of laser stripes and the position of the optical center is recorded as: Among them U i represents the optical center position of the i-th row image, g i,j Represents the gray value of the image at position (i, j); Calculate the pixel difference of the laser center point on the same epipolar line of the left and right cameras, and use it as the parallax to calculate the spatial coordinates of each point on the laser. The calculation formula is as follows: [X,Y,Z,W] T =Q×[x,y,disparity(x,y),1] T (2) Where X, Y, and Z represent the spatial coordinates of the point on the laser line relative to the left camera, Q is the perspective projection matrix of the binocular camera, x and y are the pixel coordinates of the point on the laser line on the left camera, and disparity(x, y) is the pixel difference between the point on the laser line in the left and right cameras; After calculating the spatial coordinates of the laser point relative to the left camera, convert them into coordinates relative to the center of the binocular camera according to the measurement results. The spatial linear coordinates of the laser in an image relative to the center of the binocular camera underwater are calculated using the RANSAC straight line fitting algorithm. S4: Calculate the three-dimensional spatial coordinates of the laser emission point relative to the binocular camera using the two laser line equations; The equations of the two laser space lines are calculated based on the images of the two frames of laser at different spatial positions underwater. The point closest to the two space lines is calculated through the spatial geometric equation, which is the three-dimensional spatial coordinate of the laser emission point.

2. The method for locating a stereoscopic laser emission point according to claim 1, wherein: In S1, the binocular cameras capture the light beam formed by the laser beam underwater, and the laser beam pattern exists in both the left and right cameras.

3. The stereoscopic vision positioning method according to claim 1, wherein: In S2, two frames of images containing lasers at different underwater positions are acquired.

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