Underwater measurement method based on zoom camera and laser diode

Abstract

The invention discloses an underwater measurement method based on a zoom camera and a laser diode, which adopts the zoom camera to measure a laser spot image and greatly expands the application scene of equipment. The lasers A, B and C are manufactured based on laser diodes, the linearity of power adjustment can be well guaranteed, and measurement errors caused by too bright or too dark laser spots in images shot by the camera can be effectively avoided. According to the underwater measurement method provided by the invention, not only can the distance of the target object be measured, but also the feature size of the target object can be measured; in the installation process of the underwater measurement device, an error measurement link of the installation position of the laser is added, and the error is fully considered when the feature size of the target object is measured, so that the measurement precision is improved. During calibration, the average value of the height of the triangle and the corresponding bottom edge ratio in the maximum magnification and minimum magnification states of the zoom camera is taken as an independent variable, so that the influence of magnification change on calibration precision is reduced.

Description

Technical Field

[0001] This invention belongs to the field of underwater measurement technology, specifically relating to an underwater measurement method based on a zoom camera and a laser diode. Background Technology

[0002] Underwater manned submersibles and unmanned underwater vehicles play a crucial role in marine resource development. These robots require ranging technology when operating in scenarios such as obstacle avoidance, seabed take-off and landing, and underwater target location detection. Because electromagnetic waves attenuate significantly in water, commonly used radio ranging methods on land are ill-suited to the underwater environment. Generally, long-range underwater ranging relies primarily on sonar, while short-range ranging relies mainly on optical methods. Common optical methods include underwater lidar, underwater binocular imaging, and underwater laser scanning imaging. Underwater lidar works by emitting pulsed laser light into the water, measuring the echo signal after the pulsed laser reaches the target, and calculating the time difference between the emitted pulse and the echo signal to obtain distance information. Due to backscattering of light during transmission in water, the signal-to-noise ratio of this echo signal is low, requiring high water quality for its application. Underwater binocular imaging and underwater laser scanning imaging can obtain stereo images underwater, thereby obtaining distance information of the target object. However, the stability and effectiveness of these methods are greatly affected by the turbidity of the water and the motion stability of the robot platform, and are more suitable for static measurements in clean water.

[0003] By utilizing the structural characteristics of underwater robots, multiple lasers can be installed around the underwater observation camera used by the robot. The camera captures the laser spot pattern formed on the target surface, allowing the acquisition of target distance information. In related technologies, invention patent ZL202110542914.0 discloses a method for distance measurement using the perimeter of the laser spot formed on the target surface by four parallel laser beams as an independent variable. Before use, calibration is performed in a water tank to obtain the mapping relationship between distance and the perimeter of the laser spot in the camera image. However, because the laser power is fixed, the measurement accuracy is affected when the laser spot brightness is too dim or too bright. Invention patent ZL202410302916.6 discloses a solution that can automatically change the laser spot brightness; however, the optical power adjustment is achieved by changing the driving current of the semiconductor laser, making it difficult to linearly change the laser power during application. Furthermore, both patents mentioned above use fixed-focus cameras. When a zoom camera is used in an underwater robot, if the magnification during camera use differs from the parameters set during calibration, the calibration results will be invalid, making accurate measurement impossible. To address the issues with zoom cameras, Zhang Yunfei from Zhejiang University, in her master's thesis "Image-Based Underwater Three-Point Laser Ranging System," employed a method of illuminating the target surface with three laser beams, capturing the laser spots with a camera, and measuring the distance by comparing the ratio of the height to the depth of the triangle formed by the laser spots. This method, in principle, solves the application challenges of zoom cameras.

[0004] However, the following limitations exist in its application: First, this technology does not consider the impact of spot coordinate detection errors on the measurement results in practical applications. The method is more suitable for clean water bodies. If the water becomes turbid, each spot in the camera will have a strong light trail due to backscattering from the water, and the resulting spot detection error will affect the measurement accuracy. Second, when the camera magnification changes, the shape of the triangle in the spot image will change due to variations in the camera's optical distortion parameters, affecting the measurement accuracy. Finally, the laser power used in the above method is not adjustable; when the spot brightness is too strong or too weak, the measurement accuracy will be affected. Furthermore, the above measurement method only obtains the distance information of the target, not its size information. Summary of the Invention

[0005] To address the aforementioned problems in the prior art, this invention provides an underwater measurement method based on a zoom camera and a laser diode. The technical problem to be solved by this invention is achieved through the following technical solution: This invention provides an underwater measurement method based on a zoom camera and a laser diode, the method comprising: Design phase: Design an underwater measurement device, which includes an underwater measurement module, a camera control module, an image processing and display module, and a laser power control command transmission module; wherein, the underwater measurement module includes three lasers A, B, and C, and one zoom camera, and lasers A, B, and C are all laser diodes. Installation phase: Fix lasers A, B, C and zoom camera together in the underwater measurement module, and measure the installation distance between lasers B and C, as well as the installation angle error between them; Calibration Phase: The underwater measuring device is placed in a simulated working water area. The zoom camera is set to both minimum and maximum magnification using the camera control module. At both minimum and maximum magnification, the output light power of lasers A, B, and C is set using the laser power control command sending module to obtain three simulated laser spots formed on the surface of the simulated target object at different distances. Images of the simulated laser spots are acquired using the zoom camera. The image processing and display module uses the triangle formed by the three simulated laser spots in the simulated laser spot image as a basis. The average ratio of the height of the triangle to its corresponding base at both maximum and minimum magnification is used as the independent variable, and the distance between the underwater measuring device and the surface of the target object is used as the dependent variable. A mapping relationship expression is constructed, and the constant parameters in the mapping relationship expression are obtained by fitting to determine the mapping relationship expression. In the actual measurement phase: the underwater measuring device is placed in the actual working water area. The magnification of the zoom camera is set through the camera control module, and the output light power of lasers A, B, and C is set through the laser power control command sending module to form three measured laser spots on the surface of the target object. The zoom camera is used to acquire images of the measured laser spots. The image processing and display module calculates the distance between the underwater measuring device and the surface of the target object based on the measured laser spot images and the determined mapping relationship expression. Based on the measured laser spot images, the distance between the underwater measuring device and the surface of the target object, the installation spacing between lasers B and C, and the installation angle error, the characteristic dimensions of the target object are calculated.

[0006] The beneficial effects of this invention are: This invention proposes an underwater measurement method based on a zoom camera and laser diodes. Firstly, it innovatively presents an underwater measurement device comprising an underwater measurement module consisting of one zoom camera and three lasers A, B, and C; a camera control module; an image processing and display module; and a laser power control command transmission module. Lasers A, B, and C are all laser diodes. Based on this underwater measurement device, a corresponding underwater measurement method based on a zoom camera and laser diodes is further proposed, and its feasibility is verified through experiments. More specifically, this method has the following advantages: 1. In the underwater measuring device of the present invention, the use of a zoom camera to measure the laser spot image greatly expands the application scenarios of the device compared with a fixed-focus camera. Since lasers A, B, and C are made based on laser diodes, the output light power of the laser can be controlled by changing the duty cycle of the PWM signal, which can ensure the linearity of power adjustment and effectively avoid measurement errors caused by the laser spot being too bright or too dark in the image captured by the camera.

[0007] 2. The underwater measurement method proposed in this invention can not only measure the distance to the target object, but also measure the characteristic dimensions of the target object. The addition of an error measurement step for the laser installation position during the installation process of the underwater measurement device, and the full consideration of this error when measuring the characteristic dimensions of the target object, helps to improve the measurement accuracy.

[0008] 3. This invention uses the triangle formed by three laser spots in a laser beam image as its basis, taking the ratio of the height of this triangle to its corresponding base as the independent variable, and the distance between the underwater measuring device and the surface of the target object as the dependent variable, to construct a mapping relationship expression. In the calibration stage, using the ratio of the height of the triangle formed by the three laser spots acquired by the zoom camera and its corresponding base as the independent variable eliminates the influence of zoom camera magnification changes on the measurement results. Compared with existing technologies, in the measurement device calibration stage, setting the zoom camera to its minimum magnification verifies and ensures the monotonicity of the change between the measurement distance and the independent variable, helping to eliminate the influence of spot coordinate detection errors on the measurement results. During calibration, using the average value of the triangle's height and its corresponding base ratio at both the maximum and minimum magnification states of the zoom camera as the independent variable helps reduce the impact of magnification changes on calibration accuracy.

[0009] 4. By employing a deep learning-based spot detection method, this invention helps improve the accuracy of spot detection in water bodies with varying turbidity, thus expanding the applicability of the proposed method.

[0010] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0011] Figure 1 This is a schematic flowchart of an underwater measurement method based on a zoom camera and a laser diode provided in an embodiment of the present invention; Figure 2 This is a schematic diagram of the structure of an underwater measuring device based on a zoom camera and a laser diode provided in an embodiment of the present invention; Figure 3 This is a schematic diagram of an underwater measurement module in an underwater measurement device based on a zoom camera and a laser diode, provided in an embodiment of the present invention. Figure 4 This is a schematic diagram of a simulation experimental system for an underwater measurement method based on a zoom camera and a laser diode, provided in an embodiment of the present invention. Figure 5 This is a physical image of the underwater measurement module assembled in a simulation experiment of an underwater measurement method based on a zoom camera and a laser diode, as provided in an embodiment of the present invention. Figure 6 This is an example image of a light spot captured by a zoom camera in a simulated underwater measurement method based on a zoom camera and a laser diode, provided in an embodiment of the present invention. Figure 7 This is a schematic diagram of the fitting effect of simulation test calibration data for an underwater measurement method based on a zoom camera and a laser diode, provided by an embodiment of the present invention. Detailed Implementation

[0012] The present invention will be further described in detail below with reference to specific embodiments, but the implementation of the present invention is not limited thereto.

[0013] Please see Figure 1 This invention provides an underwater measurement method based on a zoom camera and a laser diode, the method comprising: S10. Design Phase: Design underwater measurement devices, such as... Figure 2 and Figure 3 As shown, the underwater measurement device includes an underwater measurement module, a camera control module, an image processing and display module, and a laser power control command transmission module. The underwater measurement module includes three lasers A, B, and C, and one zoom camera. Lasers A, B, and C are all laser diodes. Lasers A, B, and C, as well as the zoom camera, are all underwater-usable equipment.

[0014] The functions of each module in the underwater measuring device designed in this invention are described as follows: Lasers A, B, and C in the underwater measurement module are used to form laser spots on the surface of the target object; The zoom camera in the underwater measurement module is used to acquire images of light spots formed on the surface of the target object. The camera control module is used to control the magnification and focus of the zoom camera in the underwater measurement module. The image processing and display module is used to display the spot image captured by the zoom camera in the underwater measurement module, calculate the distance between the underwater measurement device and the surface of the target object and the feature size of the target object using the spot image, and display the distance and the feature size. The laser power control command sending module is used to control the output light power of lasers A, B, and C in the underwater measurement module. This module can control the output light power of lasers A, B, and C individually or simultaneously.

[0015] The laser diode in this embodiment of the invention includes a PWM (Pulse Width Modulation) voltage signal generation unit, a voltage signal to current signal conversion unit, and a laser diode. The PWM voltage signal generation unit generates a PWM voltage signal with a frequency of not less than 1 kHz under the setting of the laser power control command sending module. The voltage signal to current signal conversion unit converts the PWM voltage signal into a PWM current signal. The laser diode emits laser light under the control of the PWM current signal. The laser power control command sending module sets the duty cycle of the PWM voltage signal to adjust the output light power of the laser emitted by the laser diode by changing the duty cycle of the PWM voltage signal.

[0016] In the underwater measurement module of this invention: during the design phase, the positions and spacing between lasers A, B, and C, and the zoom camera are fixed; the plane formed by the light-emitting apertures of lasers A, B, and C is perpendicular to the optical axis of the zoom camera; the beam emission directions of lasers B and C are parallel and parallel to the optical axis of the zoom camera; the beam emission direction of laser A forms a preset angle with the plane containing the beam emission directions of lasers B and C, and the projection direction in this plane is parallel to the beam emission directions of lasers B and C, wherein the preset angle is determined according to the actual design and ranges from [-45°, 45°].

[0017] S20. Installation phase: Fix lasers A, B, and C and zoom camera together in the underwater measurement module, and measure the installation distance between lasers B and C, as well as the installation angle error between them.

[0018] In this embodiment of the invention, lasers A, B, and C, and a zoom camera are fixedly mounted together in an underwater measurement module, with fixed positions and spacing between them. After assembling the underwater measurement module as required in S10, the installation spacing between lasers B and C is measured and marked as... d The angle between the beam exit directions of the two beams is measured as the installation angle error, and is denoted as... θ When the two laser beams gradually move away from each other in the direction of propagation θ It is positive; otherwise, it is negative.

[0019] S30, Calibration Stage: The underwater measuring device is placed in the simulated working water area. The zoom camera is set to the minimum and maximum magnification using the camera control module. At both minimum and maximum magnification, the output light power of lasers A, B, and C is set using the laser power control command sending module to obtain three simulated laser spots formed on the surface of the simulated target object at different distances. Images of the simulated laser spots are acquired using the zoom camera. The image processing and display module uses the triangle formed by the three simulated laser spots in the simulated laser spot image as a basis. The average ratio of the height of the triangle to its corresponding base at the maximum and minimum magnification is used as the independent variable, and the distance between the underwater measuring device and the surface of the target object is used as the dependent variable. A mapping relationship expression is constructed, and the constant parameters in the mapping relationship expression are obtained by fitting to determine the mapping relationship expression.

[0020] The calibration stage of this invention embodiment more specifically includes: The zoom camera's magnification is set to its minimum by the camera control module. The output power of lasers A, B, and C is controlled by the laser power control command sending module, ensuring that simulated laser spots A1, B1, and C1 formed on the simulated target object surface are clearly visible in the zoom camera. Starting from a preset minimum distance, the distance between the underwater measurement module and the simulated target object surface is increased in preset increments until a preset maximum distance is reached. At each distance, the zoom camera captures an image of the first simulated laser spot, and the distance corresponding to each image is recorded. , , This represents the total distance between the underwater measuring device and the surface of the simulated target object during the acquisition of the simulated spot image. The image processing and display modules calculate the center coordinates of simulated laser spots A1, B1, and C1 in the first simulated spot image, and mark them as ( ). x 1,Am , y 1,Am ), ( x 1,Bm , y 1,Bm ), ( x 1,Cm , y 1,Cm ), ( x 1,Am , y 1,Am () indicates distance The center coordinates of the simulated laser spot A1 are ( x 1,Bm , y 1,Bm () indicates distance The center coordinates of the simulated laser spot B1 are ( x 1,Cm , y 1,Cm () indicates distance The center coordinates of the simulated laser spot C1 are determined, and the center coordinates of the simulated laser spots A1, B1, and C1 are calculated using the formula for calculating the positional characteristics of the laser spot. x 1,Am , y 1,Am ), ( x 1,Bm , y 1,Bm ), ( x 1,Cm , y 1,Cm Calculate the positional characteristics of the simulated light spot. Determine the positional features of the simulated light spot. With the target spot position feature quantity If the signs are consistent, then the distance change of the simulated laser spot A1 relative to the line segment BC between simulated laser spots B1 and C1 is calculated using the first distance change calculation formula. If they are inconsistent, the distance change of the simulated laser spot A1 relative to the line segment B1C1 between the simulated laser spots B1 and C1 is calculated using the second distance change calculation formula. ;in, Calculate the simulated spot position characteristics using the formula for spot position characteristics. , is represented as: (1); Calculate the distance change using the first distance change calculation formula. , is represented as: (2); Calculate the distance change using the second distance change calculation formula. , is represented as: (3); The image processing and display module calculates the length of line segment B1C1 between simulated laser spots B1 and C1 based on the center coordinates of the simulated laser spots B1 and C1. Calculate each distance Change in distance over time and length The first ratio, if the distance As the ratio changes from small to large, the first ratio changes monotonically. Record the first ratio and label it as... , Indicates distance The first ratio at; where, length The calculation is expressed by the formula: (4); First ratio The calculation is expressed by the formula: (5); It should be noted here that if the distance During the process of increasing the value, if the first ratio does not change monotonically, then increase the angle between the beam emission direction of laser A and the plane formed by the beam emission directions of lasers B and C, and repeatedly measure the calculation of the installation error between lasers B and C, as well as the processing procedure when the zoom camera is in the minimum magnification state, so that the distance... As the ratio changes from small to large, the first ratio changes monotonically. This first ratio is recorded and labeled as... ; The zoom camera's magnification is set to maximum using the camera control module. The output power of lasers A, B, and C is controlled via the laser power control command sending module, ensuring that simulated laser spots A2, B2, and C2 are clearly visible in the zoom camera. Starting from a preset minimum distance, the distance between the underwater measurement module and the simulated target surface is increased in preset increments until the preset maximum distance is reached. At each distance, the zoom camera captures images of the second simulated laser spot, and the distance corresponding to each second simulated laser spot image is recorded. ; The image processing and display modules calculate the center coordinates of simulated laser spots A2, B2, and C2 in the second simulated spot image, and label them as ( x 2,Am , y 2,Am ), ( x 2,Bm , y 2,Bm ), ( x 2,Cm , y 2,Cm ), ( x 2,Am , y 2,Am () indicates distance The center coordinates of the simulated laser spot A2 are ( x 2,Bm , y 2,Bm () indicates distance The center coordinates of the simulated laser spot B2 are (x 2,Cm , y 2,Cm () indicates distance The center coordinates of the simulated laser spot C2 are determined, and the formula for calculating the center coordinates of the simulated laser spots A2, B2, and C2 is used. x 2,Am , y 2,Am ), ( x 2,Bm , y 2,Bm ), ( x 2,Cm , y 2,Cm Calculate the positional characteristics of the simulated light spot. Determine the positional features of the simulated light spot. With the target spot position feature quantity If the signs of the positive and negative signs are consistent, then the distance change of the simulated laser spot A2 relative to the line segment B2C2 between the simulated laser spots B2 and C2 is calculated using the first distance change calculation formula. If they are inconsistent, the distance change of the simulated laser spot A2 relative to the line segment B2C2 between the simulated laser spots B2 and C2 is calculated using the second distance change calculation formula. ;in, Calculate the simulated spot position characteristics using the formula for spot position characteristics. , is represented as: (6); Calculate the distance change using the first distance change calculation formula. , is represented as: (7); Calculate the distance change using the second distance change calculation formula. , is represented as: (8); The image processing and display module calculates the length of line segment B2C2 between simulated laser spots B2 and C2 based on the center coordinates of the simulated laser spots B2 and C2. Calculate each distance Change in distance over time and length The second ratio, if the distance As the ratio changes from small to large, the second ratio changes monotonically. Record the second ratio and label it as... , Indicates distance The second ratio at the location; where, length The calculation is expressed by the formula: (9); Second ratio The calculation is expressed by the formula: (10); It should be noted here that if the distance If, during the process of increasing the value, a second ratio does not change monotonically, then the angle between the beam emission direction of laser A and the plane formed by the beam emission directions of lasers B and C is increased. The calculation of the installation error between lasers B and C is repeated, along with the processing steps for the zoom camera at its minimum and maximum magnification, to ensure the distance... As the ratio changes from small to large, the second ratio changes monotonically. The second ratio is recorded and labeled as... ; The image processing and display module, based on the first ratio Second ratio Calculate the average ratio , Indicates distance The average ratio at each point, constructing a relationship about distance and average ratio The mapping relationship expression is obtained, and the constant parameters in the mapping relationship expression are obtained by fitting using the least squares method. and According to constant parameters and Determine the mapping relationship expression. Wherein, average ratio The calculation is expressed by the formula: (11); The distance constructed during the calibration phase and average ratio The mapping relationship expression is expressed by the formula: (12); Finally, the constant parameters were obtained through fitting. and The final mapping relationship expression is represented by the formula: (13); in, This indicates the distance between the underwater measuring device and the surface of the target object. The measurement stage is based on the triangle formed by the three measured laser spots in the measured spot image, and the ratio of the height of the triangle to its corresponding base.

[0021] Target spot position feature quantity of the present invention The calculation process includes: The simulated target is placed close to the front of the underwater measurement module, with its surface perpendicular to the optical axis of the zoom camera. Along the optical axis of the zoom camera, mark the projection point A formed by the centers of the laser apertures A, B, and C on the surface of the simulated target. J B J C J Use a zoom camera to capture images of the projection points; The image processing and display module calculates the light spot A of the projection point in the projection point image. J B J C J The center coordinates are marked respectively ( x AJ , y AJ ), ( x BJ , y BJ ), ( x CJ , y CJ ), ( x AJ , y AJ ) represents projection point A J The center coordinates, ( x BJ , y BJ ) represents projection point B J The center coordinates, ( x CJ , y CJ ) represents the projection point C J The center coordinates of the light spot are calculated using the formula for calculating the positional characteristics of the light spot based on the projection point A. J B J C J center coordinates ( x AJ , y AJ ), ( x BJ , y BJ ), ( x CJ , y CJCalculate the positional characteristics of the target light spot. .in, Calculate the target spot position feature using the formula for spot position feature calculation. , is represented as: (14).

[0022] S40, Actual Measurement Stage: The underwater measuring device is placed in the actual working water area. The magnification of the zoom camera is set through the camera control module, and the output light power of lasers A, B, and C is set through the laser power control command sending module to form three measured laser spots on the surface of the target object. The zoom camera is used to acquire images of the measured laser spots. The image processing and display module calculates the distance between the underwater measuring device and the surface of the target object based on the measured laser spot images and the determined mapping relationship expression. Based on the measured laser spot images, the distance between the underwater measuring device and the surface of the target object, the installation spacing between lasers B and C, and the installation angle error, the characteristic dimensions of the target object are calculated.

[0023] The actual testing phase of this invention embodiment more specifically includes: Obtain the installation spacing between lasers B and C. d Installation angle error ; The zoom camera's magnification is set by the camera control module, and the output light power of lasers A, B, and C is controlled by the laser power control command sending module, so that the measured laser spots A, B, and C formed on the surface of the measured target object can be clearly seen in the zoom camera, and the measured spot images are acquired by the zoom camera. The image processing and display modules calculate the center coordinates of the measured laser spots A, B, and C in the measured spot image, and mark them as ( ). x A , y A ), ( x B , y B ), ( x C , y C ), ( x A , y A () represents the center coordinates of the measured laser spot A, ( x B , y B () represents the center coordinates of the measured laser spot B, ( x C , yC The coordinates of the center of the measured laser spot C are represented by , and the formula for calculating the center coordinates of the measured laser spots A, B, and C is used. x A , y A ), ( x B , y B ), ( x C , y C Calculate the characteristic quantity of the measured spot position. Determine the positional characteristics of the measured light spot. With the target spot position feature quantity If the signs are consistent, then the distance change between the measured laser spot A and the line segment BC between the measured laser spots B and C is calculated using the first distance change calculation formula. If they are inconsistent, the distance change of the measured laser spot A relative to the line segment BC between the measured laser spots B and C is calculated using the second distance change calculation formula. ;in, Calculate the measured spot position characteristics using the formula for spot position characteristics. , is represented as: (15); Calculate the distance change using the first distance change calculation formula. , is represented as: (16); Calculate the distance change using the second distance change calculation formula. , is represented as: (17); The image processing and display module calculates the length of line segment BC between measured laser spots B and C based on the center coordinates of the measured laser spots B and C. Calculate the change in distance and length The ratio, record the ratio and label it as ; the ratio Substituting the mapping relationship expression determined by formula (13), the distance between the underwater measuring device and the surface of the target object is calculated. ;in, length The calculation is expressed by the formula: (18); ratio The formula is expressed as: (19); The image processing and display module determines the starting and ending coordinates of the measured target object based on the measured spot image, denoted as ( ). x 1, y 1) ( x 2, y 2) Calculate the distance between the starting point coordinates and the ending point coordinates. ;in, distance The calculation is expressed by the formula: (20); According to distance ,length ,distance Installation spacing and installation angle error Calculate the distance between the starting point and the ending point of the measured target object. , the distance The characteristic dimension of the measured target object; wherein, the distance between the start and end points of the measured target object is calculated. The formula is expressed as: (twenty one).

[0024] As can be seen from the above, the embodiments of the present invention use the same formula for calculating the spot position feature in both the calibration and measurement stages, which is expressed as: (twenty two); Among them, the calibration stage: simulates the positional characteristics of the light spot. During calculation, , , The distances used are respectively The center coordinates of the simulated laser spots A1, B1, and C1 are ( x 1,Am , y 1,Am ), ( x 1,Bm , y 1,Bm ), ( x 1,Cm , y 1,Cm Simulated light spot position characteristics During calculation, , , The distances used are respectively The center coordinates of the simulated laser spots A2, B2, and C2 are ( x 2,Am , y 2,Am ), ( x 2,Bm , y 2,Bm ), ( x 2,Cm , y 2,Cm ); Target spot position feature quantity During calculation, , , The target laser spot A was used respectively. J B J C J center coordinates ( x AJ , y AJ ), ( x BJ , y BJ ), ( x CJ , y CJ ); Measurement phase: Measured spot position characteristics During calculation, , , The coordinates of the centers of the measured laser spots A, B, and C were used respectively. x A , y A ), ( x B , y B ), ( x C , y C ), ( x A , y A ).

[0025] The same formula for calculating the first distance change was used in both the calibration and measurement phases. The formula is as follows: (twenty three); The same formula for calculating the second distance change was used in both the calibration and measurement phases. The formula is as follows: (twenty four); Among them, the calibration stage includes the distance change. During calculation, , , The distances used are respectively The center coordinates of the simulated laser spots A1, B1, and C1 are ( x 1,Am , y 1,Am ), ( x 1,Bm , y 1,Bm ), ( x 1,Cm , y 1,Cm ); Distance change During calculation, , , The distances used are respectively The center coordinates of the simulated laser spots A2, B2, and C2 are ( x 2,Am , y 2,Am ), ( x 2,Bm , y 2,Bm ), ( x 2,Cm , y 2,Cm ); Measurement phase: Distance change During calculation, , , The coordinates of the centers of the measured laser spots A, B, and C were used respectively. x A , y A ), ( x B , y B ), ( x C , y C ), ( x A , y A ).

[0026] This invention uses a triangle formed by three collected laser spots as a basis. The average of the ratio of the triangle's height to its corresponding base under the zoom camera's maximum and minimum magnification states is used as the independent variable, and the distance between the underwater measuring device and the target object's surface is used as the dependent variable to construct a mapping expression. Here, the height of the triangle represents the change in distance between the laser spot corresponding to laser A and the line segment between the laser spots corresponding to lasers B and C, and the base represents the length of the line segment between the simulated laser spots corresponding to lasers B and C. The ratio Z between these two is then calculated, and this ratio Z is used as the independent variable. For example, during the calibration phase: when the zoom camera is at its minimum magnification state, the height of the triangle is... The bottom edge is The ratio between the two is When the zoom camera is at maximum magnification, the height of the triangle is... The bottom edge is The ratio between the two is Finally, , average As the independent variable in the calibration stage; in the actual measurement stage, the height of the triangle is... The bottom edge is The ratio between the two is ,Will As an independent variable in the experimental phase.

[0027] It should also be noted that a deep learning method is used in the image processing and display module of this embodiment to calculate the center coordinates of the laser spot in the spot image. Specifically, the processing is carried out according to the following steps: the spot image is scaled proportionally and filled to a specified size; the spot image filled to the specified size is input into the YOLOv5_obb network model for detection; the detected rotated bounding boxes are subjected to non-maximum suppression to filter out high-confidence, low-overlap target boxes from the model's detection boxes, thereby outputting the final detection result for each spot image, and obtaining the center of the smallest bounding circle of the final detection box as the center coordinates of the laser spot. The network model used in the detection process is not limited to the YOLOv5_obb network model; here, the deep learning method can improve the spot detection accuracy in water bodies with different turbidity levels.

[0028] To verify the effectiveness of the underwater measurement method based on a zoom camera and laser diode proposed in this invention, an experimental simulation device was built, such as... Figure 4 As shown in the diagram, the underwater measurement module, consisting of "Laser A", "Laser B", "Laser C" and a zoom camera, as well as the "target board" used to simulate the measurement of planar targets, are placed in the water tank; "Computer 1", "Computer 2", and "Computer 3" are placed outside the water tank and connected to the underwater measurement device via watertight cables.

[0029] During the design phase, "Laser A", "Laser B", and "Laser C" are made using laser diodes with a center wavelength of 520nm and are fixed to the zoom camera using a pre-designed mechanical structure. The plane formed by the centers of the light-emitting apertures of "Laser A", "Laser B", and "Laser C" is perpendicular to the optical axis of the zoom camera. The beam emission directions of "Laser B" and "Laser C" are parallel, and the beam emission direction of "Laser A" points to the plane containing the beam emission directions of "Laser B" and "Laser C", and its projection onto this plane is parallel to the beam emission directions of "Laser B" and "Laser C".

[0030] During the installation phase: Please refer to Figure 5 , Figure 5 This is a physical diagram of an underwater measurement module assembled in a simulation experiment according to an embodiment of the present invention. After actual mechanical installation, the light-emitting holes of "Laser A", "Laser B", and "Laser C" form an isosceles triangle, where the centers of the light-emitting holes of "Laser B" and "Laser C" serve as the base of the triangle, with a distance of 10cm between them, and the transmission pointing angle of their emitted beams is 0.2° (installation angle error); the line connecting the center of the light-emitting hole of "Laser A" to the centers of the light-emitting holes of "Laser B" and "Laser C" serves as the height of the triangle, with a distance of 5cm.

[0031] During the calibration phase: "Computer 1#" is connected to the zoom camera to simulate the camera control module. The computer's host software controls the zoom camera's magnification and focus. "Computer 2#" simulates the image processing and display module, displaying images and videos captured by the zoom camera and processing them. "Computer 3#" simulates the laser power control command sending module. The host software sends setting commands to "Laser A," "Laser B," and "Laser C," controlling the PWM voltage signal to vary its duty cycle from 4% to 100%. Changing the duty cycle controls the emission power of the three lasers. The "target plate," a 45cm long and 18m wide aluminum plate with a black, frosted surface to prevent glare from laser beams, can move within the tank. During measurement, the lasers emitted by the two lasers are perpendicularly incident on the target plate. The distance between the center of the aperture of "Laser A" and the target plate surface is used as the distance between the underwater measuring device and the target plate surface.

[0032] Place the target plate close to the front of the underwater measurement module, ensuring that the surface of the target plate is perpendicular to the optical axis of the zoom camera in the underwater measurement module. Mark the projection point of the center of the light output aperture of "Laser A", "Laser B", and "Laser C" onto the simulated target surface along the optical axis of the zoom camera, denoted as A. J BJ C J Determine its center coordinates ( x AJ , y AJ ), ( x BJ , y BJ ), ( x CJ , y CJ The result calculated using formula (14) JG If the result is negative, record the result.

[0033] Then, the assembled underwater measurement module is used to illuminate the "target board," with the optical axis of the zoom camera in the module perpendicular to the surface of the simulated target. See also... Figure 6 , Figure 6 This is an example image of a light spot captured by a zoom camera in a simulation experiment provided in this embodiment of the invention. Light spots A, B, and C are generated by "laser A", "laser B", and "laser C", respectively. The zoom camera is controlled by "computer 1#" to minimize its magnification, and the distance between the "target board" and the underwater measuring device is changed. The output light power of the underwater laser is adjusted by "computer 3#". While ensuring that the zoom camera can clearly capture the light spot image, a set of light spot images is captured every 10cm in the range of 60cm to 140cm by "computer 2#" through the zoom camera. The distance corresponding to each image is recorded. In the image processing and display module, the center coordinates of the three laser light spots A, B, and C in the captured light spot image are calculated by existing image processing algorithms. Based on these coordinates, the length of the line segment BC between points B and C and the magnitude of the change in distance of point A relative to line segment BC are calculated using formulas (2) to (4). The ratio between the change in distance of point A relative to line segment BC and the length of line segment BC at each distance is calculated according to formula (5), as shown in the second column of Table 1. As can be seen, this ratio decreases monotonically with increasing distance.

[0034] The zoom camera's magnification is set to maximum magnification using the camera control module. The distance between the target plate and the underwater measuring device is changed. The output power of the underwater laser is adjusted using "Computer 3#". While ensuring that the zoom camera can clearly capture the light spot image, "Computer 2#" is used to collect a set of light spot images every 10cm within a range of 60cm to 140cm using the zoom camera. The distance corresponding to each image is recorded. The center coordinates of the three laser light spots A, B, and C in the collected light spot images are calculated using image processing algorithms. Based on these coordinates, the length of the line segment BC between points B and C, and the magnitude of the change in distance of point A relative to line segment BC are calculated using formulas (7) to (9). The ratio between the change in distance of point A relative to line segment BC and the length of line segment BC at each distance is calculated using formula (10), as shown in the third column of Table 1. It can be seen that this ratio decreases monotonically as the distance increases. Thus, by formula (11), the average value of the ratio between the change in distance of point A relative to line segment BC and the length of line segment BC at each distance when the zoom camera is at the maximum and minimum magnification is obtained, as shown in the fourth column of Table 1.

[0035] The first column in Table 1 shows the distances at the calibration time. Based on the first and fourth columns in Table 1, the least squares method is used to fit the data according to formula (12), as follows: Figure 7 As shown, Figure 7 This is a schematic diagram illustrating the fitting effect of calibration data in a simulation experiment provided in this embodiment of the invention. Figure 7 The horizontal axis represents the average ratio. (Average of scale coefficients), with the vertical axis representing distance. L At a distance L When the unit is centimeters, the constant parameter is obtained from this. a The size is 168.6530. b The value is -311.6443.

[0036] Table 1. Data processing results collected during the calibration of the underwater measuring device

[0037] In the actual test phase: A 10cm long black tape was pasted on the target board to simulate the actual length of the object. The output power of the underwater laser was adjusted by "Computer 3#" to ensure that the zoom camera could clearly capture the light spot image. The zoom camera was controlled by "Computer 1#" to make its magnification between the maximum and minimum magnification. A set of light spot images was collected every 10cm in the range of 60cm~140cm by "Computer 2#" through the zoom camera. Four sets of light spot images were collected under four different magnification conditions of the zoom camera. The center coordinates of light spots A, B, and C in these target images were obtained by the image processing and display module through the image processing algorithm. The length of the line segment BC between point B and point C was calculated by the image processing and display module according to the center coordinates of the laser light spot in each light spot image by formula (18). The distance change of point A relative to line segment BC was calculated according to formulas (16)~(17). g The size of the distance is calculated using the image processing and display module according to formula (19), which calculates the ratio between the change in distance of point A relative to line segment BC and the length of line segment BC. Substituting Z into formula (13) yields the distance between the underwater measuring device and the surface of the target object. The distance results obtained under four different magnifications of the zoom camera are shown in Table 2. It can be seen that the distance measurement error is within 5cm.

[0038] Table 2. Distance measurement verification data processing results

[0039] Meanwhile, the image processing and display module is used to determine the coordinates of the start and end points of the black tape in the spot image, and the distance between them in the spot image is calculated using formula (20). Based on the installation spacing of 10cm between "laser B" and "laser C", the installation angle error between their beam emission directions of 0.2°, and the distance between B and C as described in formula (18), and the distance between the start and end points of the black tape in the spot image is calculated using formula (20). The actual distance between the start and end points of the black tape is obtained using formula (21). Thus, the measured results of the actual length of the black tape in all spot images are between 9.5cm and 10.7cm.

[0040] The above test results verify the effectiveness of the underwater measurement device and method based on a zoom camera and a laser diode provided by the present invention.

[0041] In summary, the underwater measurement method based on a zoom camera and laser diodes proposed in this invention first innovatively proposes an underwater measurement device comprising an underwater measurement module consisting of one zoom camera and three lasers A, B, and C, a camera control module, an image processing and display module, and a laser power control command transmission module. Lasers A, B, and C are all laser diodes. Based on the proposed underwater measurement device, a corresponding underwater measurement method based on a zoom camera and laser diodes is further proposed, and the feasibility of the method is verified through experiments. More specifically, this method has the following advantages: 1. The underwater measuring device of this invention uses a zoom camera to measure laser spot images, which greatly expands the application scenarios of the device compared to a fixed-focus camera. Since lasers A, B, and C are made based on laser diodes, the output light power of the laser can be controlled by changing the duty cycle of the PWM signal, which can ensure the linearity of power adjustment and effectively avoid measurement errors caused by the laser spot being too bright or too dark in the image captured by the camera.

[0042] 2. The underwater measurement method proposed in this invention can not only measure the distance to the target object, but also measure the characteristic dimensions of the target object. The addition of an error measurement step for the laser installation position during the installation process of the underwater measurement device, and the full consideration of this error when measuring the characteristic dimensions of the target object, helps to improve the measurement accuracy.

[0043] 3. This invention uses the triangle formed by three laser spots in a laser beam image as its basis, taking the ratio of the height of this triangle to its corresponding base as the independent variable, and the distance between the underwater measuring device and the surface of the target object as the dependent variable, to construct a mapping relationship expression. In the calibration stage, using the ratio of the height of the triangle formed by the three laser spots acquired by the zoom camera and its corresponding base as the independent variable eliminates the influence of zoom camera magnification changes on the measurement results. Compared with existing technologies, in the measurement device calibration stage, setting the zoom camera to its minimum magnification verifies and ensures the monotonicity of the change between the measurement distance and the independent variable, helping to eliminate the influence of spot coordinate detection errors on the measurement results. During calibration, using the average value of the triangle's height and its corresponding base ratio at both the maximum and minimum magnification states of the zoom camera as the independent variable helps reduce the impact of magnification changes on calibration accuracy.

[0044] 4. By employing a deep learning-based spot detection method, this invention helps improve the accuracy of spot detection in water bodies with varying turbidity, thus expanding the applicability of the proposed method.

[0045] In the description of this invention, it should be understood that the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified.

[0046] Although the invention has been described herein in conjunction with various embodiments, those skilled in the art, by reviewing the specification and accompanying drawings, will understand and implement other variations of the disclosed embodiments in carrying out the claimed invention. In the specification, the word "comprising" does not exclude other components or steps, and "a" or "an" does not exclude a plurality. While certain measures are described in different embodiments, this does not mean that these measures cannot be combined to produce good results.

[0047] The above description, in conjunction with specific preferred embodiments, provides a further detailed explanation of the present invention. It should not be construed that the specific implementation of the present invention is limited to these descriptions. For those skilled in the art, various simple deductions or substitutions can be made without departing from the concept of the present invention, and all such modifications and substitutions should be considered within the scope of protection of the present invention.

Claims

1. An underwater measurement method based on a zoom camera and a laser diode, characterized in that, The method includes: Design phase: Design an underwater measurement device, which includes an underwater measurement module, a camera control module, an image processing and display module, and a laser power control command transmission module; wherein, the underwater measurement module includes three lasers A, B, and C, and one zoom camera, and lasers A, B, and C are all laser diodes. Installation phase: Fix lasers A, B, C and zoom camera together in the underwater measurement module, and measure the installation distance between lasers B and C, as well as the installation angle error between them; Calibration Phase: The underwater measuring device is placed in a simulated working water area. The zoom camera is set to both minimum and maximum magnification using the camera control module. At both minimum and maximum magnification, the output light power of lasers A, B, and C is set using the laser power control command sending module to obtain three simulated laser spots formed on the surface of the simulated target object at different distances. Images of the simulated laser spots are acquired using the zoom camera. The image processing and display module uses the triangle formed by the three simulated laser spots in the simulated laser spot image as a basis. The average ratio of the height of the triangle to its corresponding base at both maximum and minimum magnification is used as the independent variable, and the distance between the underwater measuring device and the surface of the target object is used as the dependent variable. A mapping relationship expression is constructed, and the constant parameters in the mapping relationship expression are obtained by fitting to determine the mapping relationship expression. In the actual measurement phase: the underwater measuring device is placed in the actual working water area. The magnification of the zoom camera is set through the camera control module, and the output light power of lasers A, B, and C is set through the laser power control command sending module to form three measured laser spots on the surface of the target object. The zoom camera is used to acquire images of the measured laser spots. The image processing and display module calculates the distance between the underwater measuring device and the surface of the target object based on the measured laser spot images and the determined mapping relationship expression. Based on the measured laser spot images, the distance between the underwater measuring device and the surface of the target object, the installation spacing between lasers B and C, and the installation angle error, the characteristic dimensions of the target object are calculated.

2. The underwater measurement method based on a zoom camera and a laser diode according to claim 1, characterized in that, The laser diode includes a PWM voltage signal generation unit, a voltage signal to current signal conversion unit, and a laser diode; among which, The PWM voltage signal generation unit is used to generate a PWM voltage signal with a frequency of not less than 1KHz under the settings of the laser power control command sending module. The voltage signal to current signal unit is used to convert PWM voltage signals into PWM current signals; A laser diode is used to emit laser light under the control of a PWM current signal. The laser power control command sending module sets the duty cycle of the PWM voltage signal to adjust the output light power of the laser emitted by the laser diode by changing the duty cycle of the PWM voltage signal.

3. The underwater measurement method based on a zoom camera and a laser diode according to claim 1, characterized in that, During the design phase, in the underwater measurement module: The positions and spacing between lasers A, B, C, and the zoom camera are fixed; The plane formed by the light-emitting apertures of lasers A, B, and C is perpendicular to the optical axis of the zoom camera; The beams emitted from lasers B and C are parallel and parallel to the optical axis of the zoom camera; The beam emission direction of laser A forms a preset angle with the plane containing the beam emission directions of lasers B and C, and the projection direction in this plane is parallel to the beam emission directions of lasers B and C.

4. The underwater measurement method based on a zoom camera and a laser diode according to claim 1, characterized in that, The calibration phase includes more specifically: The zoom camera's magnification is set to its minimum by the camera control module. The output power of lasers A, B, and C is controlled by the laser power control command sending module, ensuring that simulated laser spots A1, B1, and C1 formed on the simulated target object surface are clearly visible in the zoom camera. Starting from a preset minimum distance, the distance between the underwater measurement module and the simulated target object surface is increased in preset increments until a preset maximum distance is reached. At each distance, the zoom camera captures an image of the first simulated laser spot, and the distance corresponding to each image is recorded. , , This represents the total distance between the underwater measuring device and the surface of the simulated target object during the acquisition of the simulated light spot image. The image processing and display module calculates the center coordinates of simulated laser spots A1, B1, and C1 in the first simulated laser spot image, and calculates the simulated laser spot position feature quantity based on the center coordinates of simulated laser spots A1, B1, and C1 using the laser spot position feature quantity calculation formula. Determine the positional features of the simulated light spot. With the target spot position feature quantity If the signs are consistent, then the distance change of the simulated laser spot A1 relative to the line segment BC between simulated laser spots B1 and C1 is calculated using the first distance change calculation formula. If they are inconsistent, the distance change of the simulated laser spot A1 relative to the line segment B1C1 between the simulated laser spots B1 and C1 is calculated using the second distance change calculation formula. ; The image processing and display module calculates the length of line segment B1C1 between simulated laser spots B1 and C1 based on the center coordinates of the simulated laser spots B1 and C1. Calculate each distance Change in distance over time and length The first ratio, if the distance As the ratio changes from small to large, the first ratio changes monotonically. Record the first ratio and label it as... ; The zoom camera's magnification is set to maximum using the camera control module. The output power of lasers A, B, and C is controlled via the laser power control command sending module, ensuring that simulated laser spots A2, B2, and C2 are clearly visible in the zoom camera. Starting from a preset minimum distance, the distance between the underwater measurement module and the simulated target surface is increased in preset increments until the preset maximum distance is reached. At each distance, the zoom camera captures images of the second simulated laser spot, and the distance corresponding to each second simulated laser spot image is recorded. ; The image processing and display module calculates the center coordinates of simulated laser spots A2, B2, and C2 in the second simulated spot image, and calculates the simulated spot position feature quantity based on the center coordinates of simulated laser spots A2, B2, and C2 using the spot position feature quantity calculation formula. Determine the positional features of the simulated light spot. With the target spot position feature quantity If the signs of the positive and negative signs are consistent, then the distance change of the simulated laser spot A2 relative to the line segment B2C2 between the simulated laser spots B2 and C2 is calculated using the first distance change calculation formula. If they are inconsistent, the distance change of the simulated laser spot A2 relative to the line segment B2C2 between the simulated laser spots B2 and C2 is calculated using the second distance change calculation formula. ; The image processing and display module calculates the length of line segment B2C2 between simulated laser spots B2 and C2 based on the center coordinates of the simulated laser spots B2 and C2. Calculate each distance Change in distance over time and length The second ratio, if the distance As the ratio changes from small to large, the second ratio changes monotonically. Record the second ratio and label it as... ; The image processing and display module, based on the first ratio Second ratio Calculate the average ratio , construct about distance and average ratio The mapping relationship expression is obtained, and the constant parameters in the mapping relationship expression are obtained by fitting using the least squares method. and According to constant parameters and Determine the mapping expression.

5. The underwater measurement method based on a zoom camera and a laser diode according to claim 4, characterized in that, Target spot position feature quantity The calculation process includes: The simulated target is placed close to the front of the underwater measurement module, with its surface perpendicular to the optical axis of the zoom camera. Along the optical axis of the zoom camera, mark the projection point A formed by the centers of the laser apertures A, B, and C on the surface of the simulated target. J B J C J Use a zoom camera to capture images of the projection points; The image processing and display module calculates projection point A in the projection point image. J B J C J The center coordinates of the light spot are calculated using the formula for calculating the positional characteristics of the light spot based on the projection point A. J B J C J Calculate the target spot position feature quantity using the center coordinates .

6. The underwater measurement method based on a zoom camera and a laser diode according to claim 4, characterized in that, The distance constructed during the calibration phase and average ratio The mapping expression is: ； in, and Represents a constant parameter.

7. The underwater measurement method based on a zoom camera and a laser diode according to claim 1, characterized in that, The actual testing phase includes more specific aspects such as: The image processing and display module obtains the installation spacing between lasers B and C. d Installation angle error ; The zoom camera's magnification is set by the camera control module, and the output light power of lasers A, B, and C is controlled by the laser power control command sending module, so that the measured laser spots A, B, and C formed on the surface of the measured target object can be clearly seen in the zoom camera, and the measured spot images are acquired by the zoom camera. The image processing and display module calculates the center coordinates of the measured laser spots A, B, and C in the measured spot image, and uses the spot position feature calculation formula to calculate the measured spot position feature based on the center coordinates of the measured laser spots A, B, and C. Determine the positional characteristics of the measured light spot. With the target spot position feature quantity If the signs are consistent, then the distance change between the measured laser spot A and the line segment BC between the measured laser spots B and C is calculated using the first distance change calculation formula. If they are inconsistent, the distance change of the measured laser spot A relative to the line segment BC between the measured laser spots B and C is calculated using the second distance change calculation formula. ; The image processing and display module calculates the length of line segment BC between measured laser spots B and C based on the center coordinates of the measured laser spots B and C. Calculate the change in distance and length The ratio, record the ratio and label it as ; the ratio Substituting the given mapping expression, the distance between the underwater measuring device and the surface of the target object is calculated. ; The image processing and display module determines the starting and ending coordinates of the measured target object based on the measured spot image, and calculates the distance between the starting and ending coordinates. According to distance ,length ,distance Installation spacing and installation angle error Calculate the distance between the starting point and the ending point of the measured target object. , the distance As the feature size of the target object being measured.

8. The underwater measurement method based on a zoom camera and a laser diode according to claim 4, 5, or 7, characterized in that, The formula for calculating the positional characteristic of the light spot is: ； Among them, the calibration stage: simulates the positional characteristics of the light spot. During calculation, , , The distances used are respectively The center coordinates of the simulated laser spot A1, B1, and C1; the positional characteristics of the simulated laser spot. During calculation, , , The distances used are respectively The center coordinates of the simulated laser spot A2, B2, and C2; the positional characteristics of the target laser spot. During calculation, , , The projection point A is used respectively. J B J C J The center coordinates; Measurement stage: Measured spot position characteristics During calculation, , , The center coordinates of the measured laser spots A, B, and C were used respectively.

9. The underwater measurement method based on a zoom camera and a laser diode according to claim 4 or 7, characterized in that, The formula for calculating the first distance change is: ； The formula for calculating the second distance change is: ； Among them, the calibration stage includes the distance change. During calculation, , , The distances used are respectively The center coordinates of the simulated laser spot A1, B1, and C1; the distance change. During calculation, , , The distances used are respectively Simulated center coordinates of laser spot A2, B2, C2; Measurement phase: distance change During calculation, , , The center coordinates of the measured laser spots A, B, and C were used respectively.

10. The underwater measurement method based on a zoom camera and a laser diode according to claim 7, characterized in that, Calculate the distance between the starting point and the ending point of the measured target object. The formula is expressed as: 。

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