A metrological calibration device and method for a dynamic underwater 3D laser scanner

Abstract

This invention discloses a metrological calibration device and method for a dynamic underwater 3D laser scanner. The metrological calibration device includes: a trapezoidal support platform placed at the bottom of a test pool, the trapezoidal support platform having a first plane, a second plane, and a third plane with progressively increasing heights, laser stickers affixed at predetermined positions on each plane, and a reference laser sticker affixed to the center position of the third plane; a travel track laid above the two long side walls of the test pool; and a calibration trolley configured on the travel track, the calibration trolley being equipped with a lifting rod marked with scale graduations, and the dynamic underwater 3D laser scanner mounted on the lifting rod.

Description

Technical Field

[0001] The present invention belongs to the technical field of underwater mapping instrument metrology, and particularly relates to a metering and calibration device and method for a dynamic underwater three-dimensional laser scanner. Background Art

[0002] A dynamic underwater three-dimensional laser scanner is an instrument that uses optical principles to obtain the spatial positions of underwater targets. It has the advantages of fast measurement speed, high accuracy, and convenient use. It is one of the ideal instruments for high-accuracy and short-distance ranging underwater and is widely used in fields such as underwater target detection, underwater terrain information acquisition, and precise measurement of underwater structures.

[0003] However, in actual use of a dynamic underwater three-dimensional laser scanner, due to the absorption and scattering of laser by water, the key performance such as the accuracy of target positioning and the field of view angle will be affected to varying degrees. At present, the metering and calibration methods for dynamic underwater three-dimensional laser scanners are still in a blank stage, resulting in no technical basis for reference in equipment selection, performance evaluation, and guiding engineering applications. Producers and users have a relatively urgent need for metering and calibration of dynamic underwater three-dimensional laser scanners.

[0004] Therefore, there is an urgent need for a metering and calibration device and corresponding calibration method for a dynamic underwater three-dimensional laser scanner. Summary of the Invention

[0005] To solve the above technical problems, the present invention provides a metering and calibration device for a dynamic underwater three-dimensional laser scanner, including: A trapezoidal support platform placed at the bottom of the test pool. The trapezoidal support platform has a first plane, a second plane, and a third plane with gradually increasing heights. Laser stickers are pasted at specified positions on each plane, and a reference laser sticker is pasted at the center position of the third plane; A traveling track laid above the two long side walls of the test pool; A calibration vehicle configured on the traveling track. The calibration vehicle is equipped with a lifting rod marked with scale graduations, and a dynamic underwater three-dimensional laser scanner is installed on the lifting rod.

[0006] Further, the laser stickers pasted at the specified positions on each plane are in a "field" shape.

[0007] Further, a circulating water purification system includes an outlet pipe, a water pump, a filter, and an inlet pipe. The outlet pipe connects the test pool to the inlet of the water pump, the outlet of the water pump connects to the inlet of the filter, and the outlet of the filter connects to the test pool through the inlet pipe; A turbidimeter installed on the short side wall of the test pool; A light-shielding hood, erected around the test pool, includes a support frame, a light-shielding plate, and a light-shielding curtain. The light-shielding plate is installed on the top surface of the support frame, and the light-shielding curtain is laid on the four sides of the support frame.

[0008] Furthermore, the L-shaped wiping bar is composed of a long side bar and a short side bar connected together, and a lint-free cloth is fixed to the inner side of the short side bar.

[0009] This invention also proposes a metrological calibration method based on a metrological calibration device, comprising: Measure the three-dimensional coordinates of each laser patch center, perform coordinate system transformation with the reference laser patch center as the coordinate origin, and use the coordinate values ​​of each laser patch center after transformation as the standard value; Adjust the lifting rod to make the dynamic underwater 3D laser scanner reach the specified water depth, start the calibration trolley to make the dynamic underwater 3D laser scanner completely scan the trapezoidal support platform at a specified speed, and generate point cloud data of the trapezoidal support platform; The point cloud data is vertically translated so that the center of the reference laser patch is located at the origin of the coordinate system. The three-dimensional coordinates of the four intersection points (upper, lower, left, and right) of each laser patch center are obtained. The arithmetic mean of the three-dimensional coordinates is calculated and used as the three-dimensional coordinate measurement value of the corresponding laser patch center point. The root mean square error (RMSE) of the difference between the three-dimensional coordinate measurement value and the corresponding standard value is calculated and used as the calibration result of the positioning error.

[0010] Furthermore, before generating the point cloud data of the trapezoidal support platform, the process includes: starting the calibration trolley to enable the dynamic underwater 3D laser scanner to completely scan the trapezoidal support platform at a specified speed, generating a first 3D point cloud image of the trapezoidal support platform, and performing cropping and filtering preprocessing on the first 3D point cloud image to generate the point cloud data of the trapezoidal support platform.

[0011] Furthermore, before starting the calibration trolley to allow the dynamic underwater 3D laser scanner to completely scan the trapezoidal support platform at a specified speed, the process also includes: using the L-shaped wiping rod to wipe the optical probe of the dynamic underwater 3D laser scanner in one direction until no air bubbles float to the surface.

[0012] Furthermore, it also includes: Two laser stickers were placed at the bottom center of the test water tank. The positions of the two laser stickers were measured and adjusted with a total station so that the line connecting the centers of the two laser stickers was parallel to the short side wall of the test water tank, and the distance between the centers of the two laser stickers was equal to the preset standard distance. Determine the initial water entry depth of the lifting rod according to the nominal field of view angle of the dynamic underwater three-dimensional laser scanner. Start the calibration vehicle to make the dynamic underwater three-dimensional laser scanner scan two laser stickers completely at a specified speed, generating a second three-dimensional point cloud image. Iteratively adjust the water entry depth of the lifting rod according to the imaging positions of the two laser stickers in the second three-dimensional point cloud image: When the second three-dimensional point cloud image contains two laser stickers and the centers of both laser stickers are located at the edges of the second three-dimensional point cloud image, calculate the actual field of view angle of the dynamic underwater three-dimensional laser scanner according to the distance from the dynamic underwater three-dimensional laser scanner to the bottom of the test pool and the preset standard distance. Take the difference between the actual field of view angle and the nominal field of view angle as the calibration result of the field of view angle indication error.

[0013] Further, it also includes: when the second three-dimensional point cloud image contains two laser stickers and the centers of both laser stickers are not located at the edges of the second three-dimensional point cloud image, increase the water entry depth of the lifting rod and rescan; When the second three-dimensional point cloud image fails to contain all two laser stickers, decrease the water entry depth of the lifting rod and rescan; Repeat adjusting the water entry depth of the lifting rod and scanning until the centers of both laser stickers are located at the edges of the second three-dimensional point cloud image.

[0014] Further, it also includes: read the measurement value of the turbidimeter. When the measurement value of the turbidimeter does not meet the preset turbidity requirement, start the circulating water purification system to purify the water body. After purification, let the water body stand still, and read the measurement value of the turbidimeter again until the measurement value of the turbidimeter meets the preset turbidity requirement.

[0015] Compared with the prior art, the present invention has the following advantages and technical effects: (1) Based on the trapezoidal support platform, establish a laser sticker target with three-dimensional coordinate differentiation, providing calibration states in multiple directions and at multiple heights for positioning error calibration, ensuring the comprehensiveness of the calibration result.

[0016] (2) Construct an ideal calibration environment. Through the circulating water purification system, light shield and bubble wiping process, effectively avoid the influence of external factors such as turbidity, light, and bubbles on the calibration result.

[0017] (3) Take the arithmetic mean of the coordinates of the four intersection points of the "field" - shaped laser sticker as the center point measurement value, and take the root mean square error as the criterion for judging the positioning error, improving the reliability and objectivity of the measurement result, and more accurately reflecting the overall deviation degree of the measured value of the calibrated device relative to the standard value.

[0018] (4) By flexibly adjusting the water depth of the lifting rod, the imaging position of the laser in the point cloud image is changed, and the actual field of view of the calibrated device is obtained efficiently, realizing the iterative calibration of the field of view indication error. Attached Figure Description

[0019] Figure 1 This is a flowchart of the method in Embodiment 1 of the present invention; Figure 2 This is a schematic diagram of the laser-applied adhesive and trapezoidal support platform structure; Figure 3 This is a schematic diagram of positioning error calibration; Figure 4 This is a schematic diagram of the field of view indication error calibration; Figure 5 This is a schematic diagram of the light shield structure; Figure 6 This is a schematic diagram of the L-shaped wiping bar structure; Figure 7 This is a schematic diagram showing the intersection of the laser-applied stickers; Figure 8 This is a schematic diagram of a trapezoidal support platform placed at the bottom of the test pool; Figure 9 It is a dynamic underwater 3D laser scanner in contact with the water surface; Figure 10 This is a schematic diagram of a dynamic underwater 3D laser scanner scanning a trapezoidal support platform. Figure 11 It is a point cloud image after cropping and filtering.

[0020] The accompanying diagram is described as follows: 1—Trapezoidal support platform, 2—Test water tank, 3—First plane, 4—Second plane, 5—Third plane, 6—Laser sticker, 7—Reference laser sticker, 8—Travel track, 9—Long side wall, 10—Calibration trolley, 11—Lifting rod, 12—Scale graduation, 13—Dynamic underwater 3D laser scanner, 14—Outlet pipe, 15—Water pump, 16—Filter, 17—Inlet pipe, 18—Turbidity meter, 19—Short side wall, 20—Support frame, 21—Light shield, 22—Light shield curtain, 23—Long side rod, 24—Short side rod, 25—Dust-free cloth, 26—Total station, 27—Upper intersection point at the center, 28—Lower intersection point at the center, 29—Left intersection point at the center, 30—Right intersection point at the center. Detailed Implementation

[0021] Example 1 This embodiment proposes a metrological calibration device for a dynamic underwater 3D laser scanner, specifically including: like Figure 2As shown in the figure, a trapezoidal support platform 1 is placed at the bottom of the test pool 2. The trapezoidal support platform 1 has a first plane 3, a second plane 4, and a third plane 5 with gradually increasing heights. Laser stickers 6 are pasted at specified positions on each plane, and a reference laser sticker 7 is pasted at the center position of the third plane 5. Specifically, the laser stickers 6 pasted at the specified positions on each plane are in a "field" shape.

[0022] A travel track 8 is laid above the two long side walls 9 of the test pool 2. A calibration vehicle 10 is configured on the travel track 8. The calibration vehicle 10 is equipped with a lifting rod 11, a scale 12 is marked on the lifting rod 11, and a dynamic underwater three-dimensional laser scanner 13 is installed on the lifting rod 11.

[0023] Specifically, a circulating water purification system includes a water outlet pipe 14, a water pump 15, a filter 16, and a water inlet pipe 17. The water outlet pipe 14 connects the test pool 2 to the inlet of the water pump 15. The outlet of the water pump 15 connects to the inlet of the filter 16. The outlet of the filter 16 is connected to the test pool through the water inlet pipe 17. A turbidimeter 18 is installed on the short side wall 19 of the test pool 2. A light shield (as Figure 5 shown) is built around the test pool 2, including a support frame 20, a light blocking plate 21, and a light blocking curtain 22. The light blocking plate 21 is installed on the top surface of the support frame 20, and the light blocking curtain 22 is suspended on the four side surfaces of the support frame 20.

[0024] Specifically, an L-shaped wiping rod is composed of a long side rod 23 and a short side rod 24 connected. A dust-free cloth 25 is fixed on the inner side of the short side rod 24.

[0025] Embodiment 2 As Figure 1 shown, this embodiment proposes a metering and calibration method based on the metering and calibration device of Embodiment 1, which specifically includes the following steps: Step S1: Measure the three-dimensional coordinates of the centers of each laser sticker 6 through a total station 26, and perform coordinate system conversion with the center of the reference laser sticker 7 as the coordinate origin. The coordinate values of the centers of each laser sticker after conversion are used as standard values. Step S2: Adjust the lifting rod 11 to make the dynamic underwater three-dimensional laser scanner 13 reach a specified water depth. Start the calibration vehicle 10 to make the dynamic underwater three-dimensional laser scanner 13 scan the trapezoidal support platform 1 completely at a specified speed, and generate the point cloud data of the trapezoidal support platform 1. Specifically, before starting the calibration trolley 10 to allow the dynamic underwater 3D laser scanner 13 to completely scan the trapezoidal support platform 1 at a specified speed, the process further includes: using the L-shaped wiping bar (such as...) Figure 6 (As shown) The optical probe of the dynamic underwater 3D laser scanner 13 is wiped unidirectionally until no air bubbles float to the surface in the water.

[0026] Specifically, before generating the point cloud data of the trapezoidal support platform 1, the process further includes: starting the calibration trolley 10 to enable the dynamic underwater 3D laser scanner 13 to completely scan the trapezoidal support platform 1 at a specified speed, generating a first 3D point cloud image of the trapezoidal support platform, and performing cropping and filtering preprocessing on the first 3D point cloud image to generate the point cloud data of the trapezoidal support platform.

[0027] Step S3: Vertically translate the point cloud data so that the center of the reference laser patch is located at the origin of the coordinate system. Obtain the three-dimensional coordinates of the four intersection points (upper side 27, lower side 28, left side 29, and right side 30) of each laser patch center. Calculate the arithmetic mean of the three-dimensional coordinates. Use the arithmetic mean as the three-dimensional coordinate measurement value of the corresponding laser patch center point. Calculate the root mean square error (RMSE) of the difference between the three-dimensional coordinate measurement value and the corresponding standard value. Use the RMS error as the calibration result for the positioning error.

[0028] Specifically, it also includes: placing two laser stickers 6 at the middle position of the bottom of the test water tank, measuring and adjusting the position of the two laser stickers with a total station 26 so that the line connecting the centers of the two laser stickers 6 is parallel to the short side wall 19 of the test water tank, and the distance between the centers of the two laser stickers is equal to the preset standard distance. The initial water entry depth of the lifting rod is determined based on the nominal field of view of the dynamic underwater 3D laser scanner 13. The calibration trolley 10 is then activated to enable the dynamic underwater 3D laser scanner 13 to completely scan the two laser patches 6 at a specified speed, generating a second 3D point cloud image. The water entry depth of the lifting rod 11 is then iteratively adjusted based on the imaging positions of the two laser patches in the second 3D point cloud image. When the second 3D point cloud image contains two laser patches and the centers of both laser patches are located at the edge of the second 3D point cloud image, the actual field of view of the dynamic underwater 3D laser scanner is calculated based on the distance from the dynamic underwater 3D laser scanner to the bottom of the test pool and the preset standard distance. The difference between the actual field of view and the nominal field of view is used as the calibration result of the field of view indication error. Figure 4 As shown.

[0029] Specifically, it also includes: when the second three-dimensional point cloud image contains two laser stickers, and the centers of the two laser stickers are not located at the edge of the second three-dimensional point cloud image, increasing the depth of the lifting rod into the water and rescanning; When the second three-dimensional point cloud image fails to include both laser stickers, reduce the water depth of the lifting rod 11 and rescan; Repeat adjusting the water depth of the lifting rod 11 and scanning until the centers of both laser stickers 6 are located at the edge of the second three-dimensional point cloud image.

[0030] Specifically, it further includes: reading the measurement value of the turbidimeter 18. When the measurement value of the turbidimeter 18 does not meet the preset turbidity requirement, activate the circulating water purification system to purify the water body. After purification, let the water body stand still, and read the measurement value of the turbidimeter 18 again until the measurement value of the turbidimeter 18 meets the preset turbidity requirement.

[0031] Embodiment 3 As Figure 3 shown, the positioning error calibration of this embodiment sequentially includes the following 5 steps: target production and layout, water body turbidity removal, point cloud image acquisition, calculation of the center point coordinates of the laser sticker, and calculation of the positioning error, which are specifically as follows: [[ID=I4]]1. Target production and layout Manufacture a trapezoidal support platform with the first plane size of 1.000 m × 0.500 m (length × width), the second plane size of 1.000 m × 0.500 m (length × width), and the third plane size of 1.000 m × 1.000 m (length × width). The second plane is 0.300 m higher than the first plane, and the third plane is 0.300 m higher than the second plane. Select 8 square "field"-shaped laser stickers with a side length of 50 mm. Paste the No. 1 laser sticker at the center position of the left short side of the first plane, paste the No. 2 laser sticker at the center position of the right short side of the first plane, paste the No. 3 laser sticker at the center position of the left short side of the second plane, paste the No. 4 laser sticker at the center position of the right short side of the second plane, paste the No. 5 laser sticker at the left front corner of the third plane, paste the No. 6 laser sticker at the right front corner of the third plane, paste the No. 7 laser sticker at the left rear corner of the third plane, and paste the No. 8 laser sticker at the right rear corner of the third plane. Select another 1 square "field"-shaped laser sticker with a side length of 50 mm as the reference laser sticker (i.e., the No. 9 laser sticker) and paste it at the geometric center position of the third plane.

[0032] Taking a high-precision total station as the standard instrument, measure the three-dimensional coordinates of the center of each laser sticker, perform coordinate system conversion. After conversion, the coordinate system takes the center of the No. 9 laser sticker as the coordinate origin, the direction along the long side of the trapezoidal support platform as the positive direction of the X-axis, the direction along the short side of the trapezoidal support platform as the positive direction of the Y-axis, and the vertically downward direction as the positive direction of the Z-axis. The coordinate values of the centers of each laser sticker are used as the standard values. Build a rectangular test pool with a length of not less than 10 m, a width of not less than 3 m, and a depth of not less than 3.5 m, as Figure 8As shown, the trapezoidal support platform is placed at the bottom center of the test water tank, and the trapezoidal support platform is rotated horizontally so that its long side is aligned with the long side of the test water tank.

[0033] 2. Water turbidity removal Four turbidity meters were installed on the short sidewall of the test water tank. Before calibration, the readings of the four turbidity meters were taken. When the maximum turbidity value exceeded 20 NTU or the turbidity uniformity exceeded 5 NTU, the circulating water purification system was activated. Turbidity uniformity was calculated according to formula (1): (1) In the formula: —The uniformity of turbidity in the test pool; —The maximum value among the measurements of all turbidimeters at the same time; —The minimum value among the turbidimeter readings at the same time.

[0034] The water pump draws water from the test tank through the outlet pipe to the filter. After purification, the water is returned to the test tank through the inlet pipe. After purification, the water is left to stand for at least 2 hours, and the turbidity meter readings are taken again for evaluation until the turbidity measurement results meet the above requirements.

[0035] 3. Point cloud image acquisition A light-shielding enclosure was erected around the test pool, with light-shielding panels installed on the top surface of the support frame and the two short side walls, and light-shielding curtains laid on the two long side walls. A dynamic underwater 3D laser scanner was mounted on the lifting boom of the calibration trolley, and the boom was adjusted to allow the scanner to reach a depth of 1.000 m. An L-shaped wiping rod was used to wipe the optical probe unidirectionally until no more air bubbles rose to the surface. After closing the light-shielding curtains, the calibration trolley was set to a speed of 0.2 m / s and started, allowing the dynamic underwater 3D laser scanner to completely scan the trapezoidal support platform and acquire 3D point cloud images.

[0036] The method for determining the water immersion depth is as follows: Record the scale reading at the same height as the zero position of the calibration trolley when the dynamic underwater 3D laser scanner contacts the water surface. When the reading on the lifting rod scale is At that time, the dynamic underwater 3D laser scanner entered the water at a depth of 1,000 m.

[0037] 4. Calculate the coordinates of the center point of the laser patch. The 3D point cloud image acquired by the dynamic underwater 3D laser scanner was opened using CloudCompare software. The point cloud data was cropped and filtered preprocessed to remove irrelevant point clouds such as the bottom of the test pool, the side walls of the test pool, and other noise points, retaining only the point cloud data of the trapezoidal support platform. The point cloud was then translated in the Z-axis, and after the translation, the center of the 9th laser patch was moved to the origin of the coordinate system.

[0038] As shown Figure 7 in the figure, the "field" - shaped laser sticker is divided into four quadrants by horizontal and vertical dividing lines for a 50 mm×50 mm sticker, and the width of the dividing lines is 2 mm. The three - dimensional coordinates of the four intersection points on the upper side, lower side, left side, and right side at the center of each laser sticker are picked up respectively (the upper intersection point is the intersection of the horizontal dividing line and the upper - half vertical dividing line, the lower intersection point is the intersection of the horizontal dividing line and the lower - half vertical dividing line, the left intersection point is the intersection of the vertical dividing line and the left - half horizontal dividing line, and the right intersection point is the intersection of the vertical dividing line and the right - half horizontal dividing line). The arithmetic mean is calculated according to formulas (2) to (4) as the measured value of the three - dimensional coordinates of the center point of the laser sticker: (2) (3) (4) Where: ——The measured value of the X - coordinate of the center point of the th laser sticker; ——The measured value of the X - coordinate of the upper intersection point at the center of the th laser sticker; ——The measured value of the X - coordinate of the lower intersection point at the center of the th laser sticker; ——The measured value of the X - coordinate of the left intersection point at the center of the th laser sticker; ——The measured value of the X - coordinate of the right intersection point at the center of the th laser sticker; 、 And the meanings of each of them and their components are similar to ; The subscript is the laser - sticker number, taking an integer from 1 to 8.

[0039] [[ID=,46]]5. Calculate the positioning error Calculate the root - mean - square error of the difference between the measured values of the X - coordinate, Y - coordinate, and Z - coordinate of the center point of each laser sticker and the standard value respectively. The root - mean - square error is taken as the calibration result of the positioning error of the dynamic underwater three - dimensional laser scanner in the X - direction, Y - direction, and Z - direction respectively. The calculation formulas are as shown in formulas (5) to (7): (5) [[ID=5,3]] (6) (7) Where: ——The positioning error in the X - direction; ——The positioning error in the Y - direction; ——The positioning error in the Z - direction; ——No. X-coordinate measurement of the center point of the laser patch; ——No. Standard X-coordinate value of the center point of the laser patch; ——No. The Y-coordinate measurement value of the center point of the laser sticker; ——No. Standard value of the Y coordinate of the center point of the laser sticker; ——No. Z-coordinate measurement value of the center point of the laser sticker; ——No. Standard Z-coordinate value of the center point of the laser sticker; —The total number of laser stickers involved in the calculation is 8; —The laser-printed stickers are numbered from 1 to 1. Integers.

[0040] In this embodiment, the field of view indication error calibration includes the following three steps: laser patch installation, water turbidity removal, and point cloud image acquisition and interpretation, specifically including the following steps: 1. Laser application equipment Two square laser stickers (laser sticker number 10 and laser sticker number 11) with a side length of 40 mm were placed at the center of the bottom of the test water tank. The plane coordinates of the centerline of the short side at the starting end of the test water tank were measured using a total station. Planar coordinates of the short side midline at the termination end Calculate the azimuth angle of the test pool according to formula (8). : (8) In the formula: —Azimuth angle of the test pool; —The plane coordinates of the centerline of the short side at the starting end of the test pool; —The plane coordinates of the centerline of the short side at the end of the test pool.

[0041] Adjust the positions of the two laser stickers according to the azimuth angle of the test pool until the line connecting the two laser stickers is parallel to the short side wall of the test pool, and the distance between the centers of the two laser stickers is 2 m.

[0042] 2. Water turbidity removal The water turbidity removal procedure is the same as the water turbidity removal procedure in the positioning error calibration. The maximum turbidity value in the test water tank must not exceed 20 NTU, and the turbidity uniformity must not exceed 5 NTU. Subsequent calibration operations can only proceed after these requirements are met.

[0043] 3. Point cloud image acquisition and interpretation A dynamic underwater 3D laser scanner is installed on the lifting boom of the calibration vehicle, based on the nominal field of view of the dynamic underwater 3D laser scanner. The initial water depth of the lifting rod is determined according to formula (9): (9) In the formula: —The initial distance from the dynamic underwater 3D laser scanner to the bottom of the test pool; —The preset standard distance between the centers of the two laser stickers ; —Nominal field of view of a dynamic underwater 3D laser scanner.

[0044] The optical probe was wiped unidirectionally using an L-shaped wiping rod until no more air bubbles floated to the surface. The light-shielding curtain was closed, and the calibration trolley was set to a speed of 0.2 m / s. The calibration trolley was then started, allowing the dynamic underwater 3D laser scanner to completely scan both laser patches. The acquired point cloud image was opened using CloudCompare software and interpreted according to the following rules: (1) When the point cloud image contains two laser stickers and the centers of both laser stickers are located at the edge of the point cloud image, record the distance from the dynamic underwater 3D laser scanner to the bottom of the test pool at this time. Calculate the actual field of view angle according to formula (10); (2) When the point cloud image contains two laser stickers but the centers of the two laser stickers are not both located at the edge of the point cloud image, increase the depth of the lifting rod into the water and rescan; (3) When the point cloud image fails to contain both laser patches, reduce the depth of the lifting rod in the water and rescan.

[0045] Repeat the above adjustments until both laser patch centers are located at the edge of the point cloud image, and calculate the actual field of view according to equation (10): (10) In the formula: —The actual field of view of the dynamic underwater 3D laser scanner; —The preset standard distance between the centers of the two laser stickers ; — The distance from the bottom of the test pool to the dynamic underwater 3D laser scanner when both laser patch centers are located at the edge of the point cloud image.

[0046] Calculate the field of view indication error according to formula (11): (11) In the formula: —Field of view indication error of dynamic underwater 3D laser scanner; —— Nominal field of view angle of the dynamic underwater three-dimensional laser scanner; —— Actual field of view angle of the dynamic underwater three-dimensional laser scanner.

[0047] Example 4 This example is used to illustrate the calibration of the positioning error, specifically including: Step 1: Production and layout of the target object (1) Fabricate a trapezoidal support platform with the following production requirements: the first plane size is 1.000 m × 0.500 m (length × width), the second plane size is 1.000 m × 0.500 m (length × width), the third plane size is 1.000 m × 1.000 m (length × width), the second plane is 0.300 m higher than the first plane, and the third plane is 0.300 m higher than the second plane.

[0048] (2) Select 8 square "field" - shaped laser stickers with a side length of 50 mm. Paste the No. 1 laser sticker at the center position of the left short side of the first plane of the trapezoidal support platform, paste the No. 2 laser sticker at the center position of the right short side of the first plane, paste the No. 3 laser sticker at the center position of the left short side of the second plane, paste the No. 4 laser sticker at the center position of the right short side of the second plane, paste the No. 5 laser sticker at the left front corner of the third plane, paste the No. 6 laser sticker at the right front corner of the third plane, paste the No. 7 laser sticker at the left rear corner of the third plane, and paste the No. 8 laser sticker at the right rear corner of the third plane. Additionally, select 1 "field" - shaped laser sticker with a side length of 50 mm (i.e., the No. 9 laser sticker) and paste it at the geometric center position of the third plane.

[0049] (3) Use a total station to measure the three - dimensional coordinates of the center of each laser sticker, and perform coordinate transformation. After transformation, the coordinate system takes the center of the No. 9 laser sticker as the coordinate origin, the positive direction of the X - axis is along the long side direction of the trapezoidal support platform, the positive direction of the Y - axis is along the short side direction of the trapezoidal support platform, and the positive direction of the Z - axis is vertically downward. The coordinate values of the center of each laser sticker are used as standard values, and the measurement results are shown in Table 1.

[0050] Table 1 Standard values of the coordinates of the center points of laser stickers (4) Build a rectangular test pool with a length of 10 m, a width of 3 m, and a depth of 3.5 m. Place the trapezoidal support platform at the middle position of the bottom of the test pool, and horizontally rotate the trapezoidal support platform so that its long side direction is consistent with the long side direction of the test pool.

[0051] Step 2: Turbidity removal of the water body (1) The test water tank is equipped with a circulating water purification system, which consists of four parts: water outlet pipe, water pump, filter and water inlet pipe; two turbidity meters are installed on each of the two short side walls of the test water tank, for a total of four.

[0052] (2) Before calibration, the measurement values ​​of the four turbidity meters were read, and the measurement results are shown in Table 2. As can be seen from the table, the maximum turbidity of the test water pool is 16.3 NTU, which does not exceed 20 NTU; the turbidity uniformity of the test water pool is 5.3 NTU, which exceeds 5 NTU. Therefore, it is necessary to turn on the circulating water purification device to reduce the turbidity of the test water pool.

[0053] Table 2. Turbidity Measurement Results of the Test Pool Before Calibration (3) Turn on the circulating water purification device. The water pump draws the water in the test water tank from the outlet pipe to the filter. After purification by the filter, the water re-enters the test water tank through the inlet pipe. After purification by the circulating water purification device, the water in the test water tank is left to stand for 2 hours, and the turbidity meter measurement results are read again, as shown in Table 3. As can be seen from the table, the maximum turbidity of the test water tank is 10.9 NTU, which does not exceed 20 NTU; the turbidity uniformity of the test water tank is 1.4 NTU, which does not exceed 5 NTU. Therefore, the turbidity of the test water tank meets the requirements for subsequent calibration.

[0054] Table 3. Turbidity Measurement Results of the Test Water Pool After Purification Step 3: Point Cloud Image Acquisition (1) A light shield is built around the test pool, and the light shield is installed on the top surface of the support frame and the two short side walls.

[0055] (2) A travel track is laid above the two long side walls of the test pool, and a calibration trolley is installed on the travel track; the calibration trolley is equipped with a lifting rod, the maximum water depth of the lifting rod is not less than 2 m, and the lifting rod is marked with a scale.

[0056] (3) such as Figure 9 As shown, a dynamic underwater 3D laser scanner is installed on the lifting boom of the calibration trolley. The lifting boom is started, and it stops rising and falling when the dynamic underwater 3D laser scanner touches the water surface. The scale reading at the same height as the zero position of the calibration trolley on the lifting boom is recorded as follows. In this embodiment .

[0057] (4) Start the lifting boom. When the lifting boom reaches the specified scale... The descent and ascent stop when the calibrated trolley reaches the same height as the zero position. At this point, the dynamic underwater 3D laser scanner is submerged to a depth of 1,000 m.

[0058] (5) Make an L-shaped wiping rod, fix the lint-free cloth to the inside of the short side of the wiping rod, and insert the wiping rod into the water to wipe the dynamic underwater three-dimensional laser scanner probe in one direction until no air bubbles float to the surface.

[0059] (6) Pull the light-blocking curtain to shield the test pool from direct sunlight.

[0060] (7) For example Figure 10 As shown, the calibration trolley speed is set to 0.2 m / s. The calibration trolley is started, allowing the dynamic underwater 3D laser scanner to completely scan the trapezoidal support platform and acquire 3D point cloud images.

[0061] Step 4: Calculate the coordinates of the center point of the laser patch (1) such as Figure 11 As shown, the three-dimensional point cloud image acquired by the dynamic underwater three-dimensional laser scanner was opened using CloudCompare software. The point cloud data was cropped and filtered preprocessed to remove irrelevant point clouds such as the bottom of the test pool, the side walls of the test pool, and other noise points, retaining only the point cloud data of the trapezoidal support platform.

[0062] (2) The point cloud is translated in the Z direction. After the translation, the center of the 9th laser sticker is moved to the origin of the coordinate system.

[0063] (3) Pick the three-dimensional coordinates of the four intersection points of the center of each laser patch from No. 1 to No. 8, and calculate the arithmetic mean according to formula (2) to (4) as the measured value of the center point coordinate of the laser patch. The measurement results are shown in Table 4 and Table 5.

[0064] Table 4. Measured coordinates of the laser-attached intersection points (unit: m) Table 5. Measured coordinates of the center point of the laser patch (unit: m) Step 5: Calculate the positioning error The root mean square errors in the X, Y, and Z directions are calculated using equations (5) to (7), and the results are used as calibration results for the positioning error of the dynamic underwater 3D laser scanner. The positioning error in the X direction is calculated from the data in Tables 1 and 5. Y-direction positioning error Z-direction positioning error .

[0065] Example 5 This embodiment illustrates the calibration of field of view indication error, specifically including: Step A: Laser application setup (1) Select two square laser stickers with a side length of 40 mm (laser sticker No. 10 and laser sticker No. 11) and place them in the middle of the bottom of the test pool.

[0066] (2) Use a total station to measure the plane coordinates of the centerline of the short side at the starting end of the test pool. ;Measure the plane coordinates of the centerline of the short side at the end of the test pool The azimuth angle of the test pool was calculated according to formula (8). .

[0067] (3) Based on the azimuth angle of the test pool Adjust the positions of the two laser stickers until the line connecting the two laser stickers is parallel to the short sidewall of the test pool, and the distance between the centers of the two laser stickers is 2 m.

[0068] Step B: Water Turbidity Removal Before calibration, the measured values ​​of four turbidity meters were read, as shown in Table 6. As can be seen from the table, the maximum turbidity of the test water tank was 11.3 NTU, which did not exceed 20 NTU; the turbidity uniformity was 1.5 NTU, which did not exceed 5 NTU. Therefore, the turbidity of the test water tank met the calibration requirements, and there was no need to turn on the circulating water purification device.

[0069] Table 6. Turbidity Measurement Results of the Test Pool Before Field Angle Calibration Step C: Point cloud image acquisition and interpretation (1) Install the dynamic underwater 3D laser scanner on the lifting boom of the calibration trolley. The nominal field of view of the dynamic underwater 3D laser scanner being calibrated is... Calculate the initial depth of entry into the water according to formula (9): Adjust the lifting rod to make the distance between the dynamic underwater 3D laser scanner and the bottom of the test pool 1.732 m.

[0070] (2) Insert the L-shaped wiping rod into the water and wipe the dynamic underwater three-dimensional laser scanner probe in one direction until no air bubbles float to the surface.

[0071] (3) Open the light-blocking curtain to shield the test water pool from direct sunlight.

[0072] (4) Set the calibration vehicle speed to 0.2 m / s, start the calibration vehicle, and make the dynamic underwater 3D laser scanner completely scan the two laser stickers.

[0073] (5) Open the point cloud image using CloudCompare software. The result is: the point cloud image contains two laser stickers, but the center of the two laser stickers is not located at the edge of the point cloud image. That is, the actual field of view of the calibrated dynamic underwater 3D laser scanner is greater than the nominal value of 60°. The depth of the lifting rod in the water needs to be increased further.

[0074] (6) Repeatedly lower the lifting boom and make the dynamic underwater 3D laser scanner completely scan the two laser stickers until the distance between the dynamic underwater 3D laser scanner and the bottom of the test pool is reached. At this time, the centers of both laser patches are located at the edges of the point cloud image. The actual field of view is calculated according to equation (10): (7) Calculate the field of view indication error according to formula (11): The field-of-view indication error of the calibrated dynamic underwater 3D laser scanner is... .

[0075] The above are merely preferred embodiments of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A calibration device for a dynamic underwater three-dimensional laser scanner, characterized in that, Comprising: A trapezoidal support platform placed at the bottom of the test pool. The trapezoidal support platform has a first plane, a second plane, and a third plane with gradually increasing heights. Laser stickers are pasted at specified positions on each plane, and a reference laser sticker is pasted at the central position of the third plane. A traveling track laid above the two long side walls of the test pool. A calibration vehicle configured on the traveling track. The calibration vehicle is equipped with a lifting rod marked with scale graduations, and a dynamic underwater three-dimensional laser scanner is installed on the lifting rod.

2. The metrological calibration device for a dynamic underwater three-dimensional laser scanner as described in claim 1, characterized in that, The laser stickers pasted at the specified positions on each plane are in a "field" shape.

3. The metrological calibration device for a dynamic underwater three-dimensional laser scanner as described in claim 1, characterized in that, A circulating water purification system, including an outlet pipe, a water pump, a filter, and an inlet pipe. The outlet pipe connects the test pool to the inlet of the water pump, the outlet of the water pump connects to the inlet of the filter, and the outlet of the filter connects to the test pool through the inlet pipe. A turbidimeter installed on the short side wall of the test pool. A light shield built around the test pool, including a support frame, light-shielding plates, and light-shielding curtains. The light-shielding plates are installed on the top surface of the support frame, and the light-shielding curtains are laid on the four side surfaces of the support frame.

4. The metrological calibration device for a dynamic underwater three-dimensional laser scanner as described in claim 1, characterized in that, An L-shaped wiping rod composed of a long side rod and a short side rod connected. A dust-free cloth is fixed on the inner side of the short side rod.

5. A metrological calibration method based on the metrological calibration device according to any one of claims 1-4, characterized in that, Comprising: Measure the three-dimensional coordinates of the centers of each laser sticker, perform coordinate system conversion with the center of the reference laser sticker as the coordinate origin, and use the coordinate values of the centers of each laser sticker after conversion as standard values. Adjust the lifting rod to make the dynamic underwater three-dimensional laser scanner reach a specified water depth, start the calibration vehicle to make the dynamic underwater three-dimensional laser scanner scan the trapezoidal support platform completely at a specified speed, and generate the point cloud data of the trapezoidal support platform. Vertically translate the point cloud data to make the center of the reference laser sticker located at the coordinate origin. Respectively obtain the three-dimensional coordinates of the four intersection points on the upper side, lower side, left side, and right side of the center of each laser sticker, calculate the arithmetic mean of the three-dimensional coordinates, use the arithmetic mean as the measured value of the three-dimensional coordinates of the corresponding laser sticker center, calculate the root mean square error of the difference between the measured value of the three-dimensional coordinates and the corresponding standard value, and use the root mean square error as the calibration result of the positioning error.

6. A metrological calibration method as described in claim 5, characterized in that, Before generating the point cloud data of the trapezoidal support platform, it further includes: starting the calibration vehicle to make the dynamic underwater three-dimensional laser scanner scan the trapezoidal support platform completely at a specified speed, generating the first three-dimensional point cloud image of the trapezoidal support platform, and performing cropping and filtering preprocessing on the first three-dimensional point cloud image to generate the point cloud data of the trapezoidal support platform.

7. A metrological calibration method as described in claim 5, characterized in that, Before starting the calibration vehicle to make the dynamic underwater three-dimensional laser scanner scan the trapezoidal support platform completely at a specified speed, it further includes: using the L-shaped wiping rod to wipe the optical probe of the dynamic underwater three-dimensional laser scanner unidirectionally until no water bubbles float up.

8. A metrological calibration method as claimed in claim 5, characterized in that, It also includes: Two laser stickers were placed at the bottom center of the test water tank. The positions of the two laser stickers were measured and adjusted with a total station so that the line connecting the centers of the two laser stickers was parallel to the short side wall of the test water tank, and the distance between the centers of the two laser stickers was equal to the preset standard distance. The initial water entry depth of the lifting mast is determined based on the nominal field of view of the dynamic underwater 3D laser scanner. The calibration trolley is then activated to allow the dynamic underwater 3D laser scanner to completely scan the two laser patches at a specified speed, generating a second 3D point cloud image. The water entry depth of the lifting mast is then iteratively adjusted based on the imaging positions of the two laser patches in the second 3D point cloud image. When the second three-dimensional point cloud image contains two laser stickers and the centers of the two laser stickers are both located at the edge of the second three-dimensional point cloud image, the actual field of view of the dynamic underwater three-dimensional laser scanner is calculated based on the distance from the dynamic underwater three-dimensional laser scanner to the bottom of the test pool and the preset standard distance. The difference between the actual field of view and the nominal field of view is used as the calibration result of the field of view indication error.

9. A metrological calibration method as claimed in claim 8, characterized in that, Also includes: When the second three-dimensional point cloud image contains two laser stickers, and the centers of the two laser stickers are not located at the edge of the second three-dimensional point cloud image, increase the depth of the lifting rod into the water and rescan. If the second 3D point cloud image fails to contain both laser stickers, reduce the depth of the lifting rod in the water and rescan. Repeatedly adjust the water depth of the lifting rod and scan until the centers of the two laser stickers are located at the edge of the second three-dimensional point cloud image.

10. A metrological calibration method as claimed in claim 5 or 8, characterized in that, Also includes: The turbidity meter reading is read. When the turbidity meter reading does not meet the preset turbidity requirement, the circulating water purification system is turned on to purify the water. After purification, the water is left to stand, and the turbidity meter reading is read again until the turbidity meter reading meets the preset turbidity requirement.

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