Calibration Method for Shipborne Hydrographic and Terrestrial Integrated Survey System

Abstract

Calibration method for shipborne integrated water-land measurement system, which relates to the technical field of calibration methods, includes the following steps: Step S1: Calibration of measuring instruments; Step S2: Calibration of the center of a single unit; Step S3: Obtaining the positional relationship between the center point of a single unit and the target; Step S4: Obtaining exterior orientation elements; Step S5: Accuracy calibration; The said Step S4 includes: Observing the target of the inertial navigation system single unit to obtain the position information of the target of the inertial navigation system single unit; Observing the target of the 3D laser scanner to obtain the position information of the target of the 3D laser scanner; According to the positional relationship between the center point of a single unit and the target and the position information of the target of the inertial navigation system single unit and the target of the 3D laser scanner, establishing the coordinate systems of the 3D laser scanner and the inertial navigation system, and obtaining exterior orientation elements. The present invention solves the technical problems of the existence of an included angle between the coordinate axes of the 3D laser scanner and the inertial navigation system and the high installation cost when installing the 3D laser scanner and the inertial navigation system.

Description

Technical Field

[0001] The invention belongs to the technical field of calibration methods, and in particular relates to a calibration method for a shipborne amphibious integrated measurement system. Background Art

[0002] Each sensor in the shipborne integrated water and land measurement system has its own independent coordinate system, so the accuracy of spatial synchronization directly determines the final measurement accuracy of the shipborne integrated water and land measurement system. In order to achieve the effect of spatial synchronization, the shipborne integrated water and land measurement system uses the direct geographic reference information provided by the inertial navigation system to realize the conversion of the target ground point from the laser scanner coordinate system to the Earth-Centered Earth-Fixed (ECEF) coordinate system, so as to uniformly express the data collected synchronously by each sensor in the same coordinate system. This requires obtaining the spatial position relationship between the laser scanner and the inertial navigation system, that is, the external orientation elements of the laser scanner need to be accurately known. However, due to inherent installation limitations, the two are often unable to be accurately installed according to the design parameters of the drawings, and the errors caused are the most significant factors affecting the positioning accuracy of the shipborne integrated water and land measurement system.

[0003] The external orientation elements of a 3D laser scanner include three rotation parameters and three translation parameters. If only the error of the external orientation elements is considered, without considering the influence of the sensor itself and the external environment, it is believed that there is a systematic deviation between the point cloud of a certain target obtained by the ship-borne land-water integrated measurement system and the actual position of the target, and there is also a systematic deviation between the point clouds of the same name repeatedly measured at different orientations by the ship-borne land-water integrated measurement system. The external orientation element calibration of 3D laser scanners is mostly based on this.

[0004] In the past, the most traditional method for calibrating exterior orientation elements was to use professional point cloud visualization software to continuously adjust the exterior orientation elements through manual operation until the point clouds with the same name scanned repeatedly at different orientations by the shipborne integrated land and water measurement system visually overlapped.

[0005] The traditional exterior orientation element calibration method can be implemented when there is professional point cloud visualization software and professional technicians are relatively skilled, but it is difficult to implement in the absence of professional software and skilled technicians, and the construction cost, maintenance cost and operation cost are high; in addition, due to the low calibration efficiency and low accuracy of the traditional exterior orientation element calibration method, the application scenarios are relatively limited, resulting in poor practicality in field production; the traditional exterior orientation element calibration method is mainly based on single feature calibration, the calibration field feature requirements are relatively stringent, and it has great limitations. Summary of the invention

[0006] The object of the present invention is to provide a calibration method for a shipborne water-land integrated measurement system, so as to solve the technical problems of the angle between the coordinate axes of a three-dimensional laser scanner and an inertial navigation system during installation, high cost and great limitations.

[0007] To solve the above technical problems, the specific technical solution of the present invention is as follows:

[0008] A calibration method for a shipborne water-land integrated measurement system includes the following steps:

[0009] Step S1: Calibration of measuring instruments; Step S2: Calibration of the center of each unit; Step S3: Obtaining the position relationship between the center point of each unit and the target; Step S4: Obtaining exterior orientation elements; Step S5: Accuracy calibration.

[0010] The said Step S4 includes:

[0011] Step S401: Observe the target of the inertial navigation system unit to obtain the position information of the target of the inertial navigation system unit;

[0012] Step S402: Observe the target of the three-dimensional laser scanner to obtain the position information of the target of the three-dimensional laser scanner;

[0013] Step S403: According to the position relationship between the target and the center point of each unit obtained in Step S302 and the position information of the target of the inertial navigation system unit and the target of the three-dimensional laser scanner obtained in Step S401 and Step S402, establish the coordinate systems of the three-dimensional laser scanner and the inertial navigation system, and obtain exterior orientation elements.

[0014] Furthermore, the said Step S1 includes:

[0015] Step S101: Determine two points P1 and P2;

[0016] Step S102: Obtain the distance L between two points P1 and P2;

[0017] Step S103: Use a total station to measure the distance between two points P1 and P2;

[0018] Step S104: Compare and analyze whether the result exceeds the limit.

[0019] Furthermore, the accuracy requirement for whether it exceeds the limit in the said Step S104 is sub-millimeter level.

[0020] Furthermore, the said Step S2 includes the following steps: Step S201: Obtain the bottom surface of each unit; Step S202: Determine the characteristic points of each unit; Step S203: Measure the characteristic points; Step S204: Project each characteristic point; Step S205: Calibrate the center of the unit; Step S206: Compare and analyze whether the result exceeds the limit.

[0021] Further, the accuracy requirement for determining whether there is an overrun in step S206 is sub-millimeter level.

[0022] Further, step S3 includes the following steps: Step S301: Paste the target paper; Step S302: Obtain the positional relationship between the target paper and the center point of the monomer; Step S303: Determine the center point positions of the 3D laser scanner and the inertial navigation system.

[0023] Further, step S403 includes the following steps: Step S4031: Obtain the roll angle; Step S4032: Obtain the pitch angle; Step S4033: Obtain the yaw angle.

[0024] Further, step S4 further includes: Step S404: Correct the error between the 3D laser scanner and the inertial navigation system.

[0025] Further, step S5 includes the following steps: Step S501: Obtain the true radius of the receiver; Step S502: Measure the radius of the receiver; Step S503: Conduct accuracy calibration.

[0026] Further, step S501 includes: Reading the instrument instruction materials to obtain the radius of the receiver.

[0027] The present invention has the following advantages: By step S403 of the present invention, a coordinate system is established to obtain the exterior orientation elements, which solves the problems of offset during the installation of the 3D laser scanner and the inertial navigation system, and the difficulty in observing the center points of each monomer in the waterway integrated measurement system; it avoids the problem of the existence of an included angle between the coordinate axes of the 3D laser scanner and the inertial navigation system during installation, reduces the workload of technicians and the difficulty of instrument operation, can collect river bottom topography and bank data more efficiently, and the measurement equipment is simple and easy to maintain, the operation process is simple, has high practicability, low operation cost, and the method has low requirements for the environment and good applicability.

[0028] Other features and advantages of the present invention will be disclosed in detail in the following specific embodiments and drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 is a schematic flow chart of the technical route of the present invention;

[0030] Figure 2 is a schematic diagram of the position of the feature points in the instrument instruction manual of the 3D laser scanner;

[0031] Figure 3 is a table of the axis system relationship of the feature points in the instrument instruction manual of the 3D laser scanner;

[0032] Figure 4 is a schematic diagram of the roll error;

[0033] Figure 5 Schematic diagram of the influence of rolling on the measurement points

[0034] Figure 6 Schematic diagram of pitching error

[0035] Figure 7 Schematic diagram of the influence of pitching on the measurement points

[0036] Figure 8 Schematic diagram of yaw error

[0037] Figure 9 Schematic diagram of the influence of yaw on the measurement points

[0038] Figure 10 Schematic diagram of coordinate calculation Specific implementation manner

[0039] In order to better understand the purpose, structure and function of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings.

[0040] Calibration method for shipborne water-land integrated measurement system, as Figures 1 to 3 shown, includes the following steps: Step S1: Calibration of measurement instruments; Step S2: Calibration of the center of the single body; Step S3: Obtaining the position relationship between the center point of the single body and the target; Step S4: Obtaining exterior orientation elements; Step S5: Accuracy calibration

[0041] The said Step S4 includes: Step S401: Observe the single body target of the inertial navigation system to obtain the position information of the single body target of the inertial navigation system; Step S402: Observe the target of the 3D laser scanner to obtain the position information of the target of the 3D laser scanner; Step S403: According to the position relationship between the target and the center points of each single body obtained in Step S302 and the position information of the single body target of the inertial navigation system and the target of the 3D laser scanner obtained in Step S401 and Step S402, establish the coordinate systems of the 3D laser scanner and the inertial navigation system, and obtain exterior orientation elements.

[0042] The said Step S1 includes the following steps

[0043] Step S101: Determine two points P1 and P2, set up the total station at a position where both points are visible, and perform operations before measurement such as centering and leveling the total station and setting up the measuring station.

[0044] Step S102: Obtain the distance L between two points P1 and P2. Use a steel tape to measure the distance between two points P1 and P2. First measure from P1 to P2, and then measure from P2 to P1, and take the average value of the two distances as L.

[0045] Step S103: Measure the distance between two points P1 and P2 using a total station. Observe points P1 and P2 with the total station to obtain various parameters of points P1 and P2; perform adjustment calculations based on the obtained various parameters to eliminate the contradictions between the observed values and obtain a more reliable result; obtain the coordinates of points P1 and P2 through the adjusted various parameters, and calculate the distance L0 between points P1 and P2 by inversely calculating from the coordinates of points P1 and P2.

[0046] Step S104: Compare and analyze whether the result is out of limits. Subtract the distance L0 between points P1 and P2 inversely calculated from the coordinates of points P1 and P2 in Step S103 from the average value L of the two distances obtained in Step S102. If the obtained difference is at the sub-millimeter level, it meets the accuracy requirements. Optionally, if it does not meet the accuracy requirements, repeat Steps S102 to S106 or replace the total station.

[0047] The said Step S1 is used to verify whether the accuracy of the instrument meets the measurement standard.

[0048] Step S2: Calibrate the center of each unit.

[0049] The said Step S2 includes the following steps:

[0050] Step S201: Measure each unit to obtain the bottom surface of each unit.

[0051] Step S202: Determine the characteristic points of each unit. For example, the bolt mounting holes at the bottom of the 3D laser scanner and the inertial navigation system can both be used as characteristic points.

[0052] Step S203: Measure the characteristic points. Measure the characteristic points of the unit with a total station to obtain the position information of each characteristic point.

[0053] Step S204: Project each characteristic point. Since each characteristic point is not in the same plane, each characteristic point needs to be projected onto the bottom surface obtained in Step S201 so that the measured characteristic points are in the same plane.

[0054] Step S205: Calibrate the center of the unit; according to Steps S203 and S204, obtain the position information of the center of each unit through the obtained position information of each characteristic point and the description of the center of the unit in the instrument manual.

[0055] Step S206: Compare and analyze whether the result is out of limits; fit the measured characteristic points of each unit, compare the radius of the fitted characteristic points with the radius of the characteristic points provided in the instrument manual, and determine whether the error meets the accuracy requirement at the sub-millimeter level.

[0056] Preferably, when measuring a monomer, the instrument should be installed on the frame, and the surface of the monomer can be seen on the frame. Then, as many and evenly as possible target papers should be pasted on the visible surface. The more points there are during observation, the more reliable the result will be.

[0057] The step S2 can obtain the positions of the center points of each instrument in the coordinate system of each monomer, that is, the position information of the center points of each monomer. However, the center points of each monomer cannot be directly measured after the three-dimensional laser scanner and the inertial navigation system are combined. Therefore, an indirect method is used to obtain the position information of the center points of each monomer.

[0058] Step S3: Obtain the position relationship between the center point of the monomer and the target.

[0059] The step S3 specifically includes the following steps:

[0060] Step S301: Paste the target paper; before each monomer is combined, evenly paste the target paper on the observable part of each monomer. Preferably, at least four target papers are provided. The more target papers there are, the more accurate the result of the combined measurement will be.

[0061] Step S302: Obtain the position relationship between the target paper and the center point of the monomer; measure the target paper and the center point of each monomer through the total station to obtain the position information of the target paper and the center point of each monomer; obtain the position relationship between the target and the center point of the monomer by measuring the projections of the target paper and the center point of each monomer on the bottom surface.

[0062] Step S303: Determine the position of the center point of the three-dimensional laser scanner and the inertial navigation system based on the position relationship between the target paper and the center point of each monomer obtained in step S302. Combine each monomer, and based on the position relationship between the target and the center point of each monomer obtained in step S302, measure the target paper on the observable surface of each monomer after each monomer is combined, and then obtain the position of the center point of the three-dimensional laser scanner and the inertial navigation system according to the position relationship between the target and the center point of each monomer.

[0063] Targets are provided on the target paper.

[0064] The step S4 includes:

[0065] Step S401: Observe the target of the inertial navigation system monomer to obtain the position information of the target of the inertial navigation system monomer;

[0066] Step S402: Observe the target of the three-dimensional laser scanner to obtain the position information of the target of the three-dimensional laser scanner;

[0067] Step S403: Based on the positional relationship between the target and the center points of each monomer obtained in step S302 and the positional information of the inertial navigation system monomer target and the 3D laser scanner target obtained in steps S401 and S402, establish the coordinate systems of the 3D laser scanner and the inertial navigation system, and obtain the exterior orientation elements.

[0068] Steps S401 and S402 are observed by a total station.

[0069] The obtaining of the exterior orientation elements includes the following steps: obtaining the roll angle; obtaining the pitch angle; obtaining the yaw angle.

[0070] As Figures 4 to 9 shown, the roll angle refers to the rotational oscillatory motion of the instrument around the horizontal axis along the longest extension direction or the wave incidence direction when the ship is moving in the water. In this method, it refers to the lateral inclination error between the 3D laser scanner and the inertial navigation system, and its error value is equal to the angular error value of the projection of the 3D laser scanner coordinate system and the inertial navigation system coordinate system on the YOZ plane.

[0071] The attitude information of the shipborne integrated water-land measurement system is obtained through the inertial navigation system. Therefore, the installation angle error between the 3D laser scanner and the inertial navigation system is naturally transmitted to the 3D laser scanner and the system, resulting in an error angle between the laser beam obtained by the system and the actual laser beam of the 3D laser scanner. The generation of the roll angle causes a deviation in the Y-axis and Z-axis directions between the collected point cloud data and the actual ground object data.

[0072] Pitch refers to the rotational oscillatory motion of the instrument around the transverse axis when the ship is moving in the water. In this method, it refers to the longitudinal inclination error between the 3D laser scanner and the inertial navigation system, and its error value is equal to the angular error value of the projection of the 3D laser scanner coordinate system and the inertial navigation system coordinate system on the XOZ plane.

[0073] Due to the existence of the pitch error, there is an included angle between the measurement line of the 3D laser scanner laser beam considered by the system and the measurement line of the actual laser beam, which results in a forward and backward deviation in the X-axis direction of the ground object data measured by the system.

[0074] Yaw refers to the rotational oscillatory motion of the instrument around the vertical axis of the ship when the ship is moving in the water. In this method, it refers to the angular error value of the projection of the coordinate systems of the 3D laser scanner and the inertial navigation system on the XOY plane.

[0075] Due to the existence of yaw error, there is a rotation angle between the 3D laser scanner and the inertial navigation system in the XOY plane. This angle is transmitted to the system through the inertial navigation system, resulting in an angular error between the 3D laser scanning laser beam obtained by the system and the actual scanning laser beam in the XOY plane, thus affecting the final result data. The yaw error has no effect on the Z coordinate. The influence it has on the coordinates is mainly concentrated on the X coordinate error and has a relatively small influence on the Y coordinate.

[0076] The step S4 further includes: step S404: Correct the error between the 3D laser scanner and the inertial navigation system.

[0077] Affected by factors such as instrument installation and vibration during the movement of the carrier in the shipborne integrated water-land measurement system, there will be errors in the three axes of the coordinate systems of the 3D laser scanner and the inertial navigation system. Through the angular errors of these three lines, the rotation matrix of the error between the 3D laser scanner and the inertial navigation system can be obtained, and the error between the 3D laser scanner and the inertial navigation system can be corrected through the rotation matrix.

[0078] The exterior orientation elements refer to the translation and rotation parameters generated during the process of reducing the center point of the 3D laser scanner to the center point of the inertial navigation system. Therefore, these elements can be obtained by calculating the included angles between the coordinate axes of the inertial navigation system and the 3D laser scanner. When installing the 3D laser scanner, the actual position and the ideal position will not be exactly the same, and there are a series of factors that affect the actual position of the 3D laser scanner during the ship's movement, such as shaking. Therefore, the coordinate axes of the self-coordinate system of the 3D laser scanner and the coordinate axes of the self-coordinate system of the inertial navigation system do not coincide or are parallel, and there is a certain angular error. However, the attitude data of the 3D laser scanner in the system is provided by the inertial navigation system. Therefore, the non-coincidence or non-parallelism of the coordinate axes will cause a certain angular error between the attitude data of the 3D laser scanner and the actual attitude. Therefore, it is necessary to obtain these angles for error correction.

[0079] The step S5 includes the following steps:

[0080] Step S501: Obtain the true radius of the receiver. Read the instrument instruction materials to obtain the radius of the receiver, denoted as R.

[0081] Step S502: Measure the radius of the receiver. Measure the receiver with a total station, and obtain the radius of the receiver as R0 through plane fitting based on the measured points. Optionally, mark the total station measurement points on the 3D laser scanner and the inertial navigation system measurement equipment. For example, mark 8 measurement points on the receiver, and obtain the circular surface where the measurement points are located through fitting of these measurement points, and then obtain the radius R0 of this circular surface.

[0082] Step S503: Precision calibration. Compare the receiver radii obtained in steps S501 and S502. If the result error obtained by subtracting R0 from R is sub-millimeter level, it meets the precision requirements.

[0083] Optionally, the calculation of coordinate points includes the following steps:

[0084] Set up two total stations at points A and B. The length of the reference ruler with endpoints P1 and P2 is L. Assume that A is the origin, its Z-axis is the zenith direction, and the line AB' connecting the projection point B' of point B and point A is the X-axis to establish a right-handed independent coordinate system A-XYZ. First, observe the horizontal angles αi, βi (i = 1, 2) and zenith distances Zi(A), Zi(B) (i = 1, 2) of the two ends P1, P2 of the reference ruler at the survey stations A and B respectively, as well as the zenith distance between A and B (when the height difference h between A and B is unknown), calculate the length b of the baseline AB, and then perform intersection positioning on each spatial target from points A and B.

[0085] Step 11: Calculation of the three-dimensional coordinates of the endpoints of the baseline ruler

[0086] If the approximate length of the baseline between points A and B is b0, then according to Figure 10 the geometric relationship, the formula for calculating the three-dimensional coordinates of point Pi from point A can be deduced as:

[0087]

[0088]

[0089]

[0090] The formula for calculating the three-dimensional coordinates of point Pi from point A is:

[0091]

[0092] The average value of the z coordinates of point Pi measured from points A and B is:

[0093]

[0094] Step 12: Calculation of the height difference between the two total stations

[0095] The height difference h between the horizontal axes of the two total stations can be measured by aiming at the same target approximately in the horizontal direction and using trigonometric leveling methods to measure the height difference respectively, and calculate h according to the difference between the height differences measured by the two instruments.

[0096] Step 13: Calculation of the baseline length between the center points of the survey stations

[0097] The calculated length of the reference ruler can be obtained from the coordinates of the two endpoints P1 and P2 of the reference ruler as:

[0098]

[0099] If the reference scale is horizontally installed, it can be calculated by the following formula:

[0100]

[0101] Since the exact length L of the reference scale is known, the exact length of the baseline can be calculated by the following formula

[0102]

[0103] Step 14: Calculation of the three-dimensional coordinates of the target point

[0104] Having obtained the exact length b of the baseline, the three-dimensional coordinates of any target point can be calculated by intersection. For the convenience of programming the calculator, the calculation formula can be rewritten as follows:

[0105]

[0106]

[0107] x i = D i cosα i

[0108] y i = D i sinα i

[0109] z A = D A cot Z i (A)

[0110] z B = D B cot Z i (B) + h

[0111] Optionally, the steps for measuring the position information by the total station include the following:

[0112] Step 21: Determine the point to be measured, set up the total station at a position where it can see the point to be measured, and perform operations before measurement such as centering and leveling the total station and setting up the measuring station.

[0113] Step 22: Use the total station to observe the point to be measured and obtain various parameters of the point to be measured; perform adjustment calculations based on the obtained various parameters to eliminate the contradictions between the observed values and obtain more reliable results; obtain the coordinates of the point to be measured through the adjusted various parameters.

[0114] It is understood that the present invention is described by way of some embodiments. Those skilled in the art will know that various changes or equivalent substitutions can be made to these features and embodiments without departing from the spirit and scope of the present invention. Additionally, under the teaching of the present invention, these features and embodiments can be modified to adapt to specific circumstances and materials without departing from the spirit and scope of the present invention. Therefore, the present invention is not limited by the specific embodiments disclosed herein, and all embodiments falling within the scope of the claims of the present application belong to the scope protected by the present invention.

Claims

1. A calibration method for an on-ship integrated water-land measurement system, characterized in that The shipborne integrated water-land measurement system includes a 3D laser scanner, an inertial navigation system, and a receiver. The method includes the following steps: Step S1: Calibration of measurement instruments; Step S2: Calibration of the center of each unit; Step S3: Obtaining the positional relationship between the center point of each unit and the target; Step S4: Obtaining exterior orientation elements; Step S5: Calibration of the receiver accuracy; The said Step S2 includes the following steps: Step S201: Obtaining the bottom surface of each unit; Step S202: Determining the characteristic points of each unit; Step S203: Measuring the characteristic points; Step S204: Projecting each characteristic point; Step S205: Calibration of the center of the unit; Step S206: Comparing and analyzing whether the result exceeds the limit. The said Step S4 includes: Step S401: Observing the target of the inertial navigation system unit to obtain the position information of the target of the inertial navigation system unit; Step S402: Observing the target of the 3D laser scanner to obtain the position information of the target of the 3D laser scanner; Step S403: According to the obtained positional relationship between the target and the center point of each unit and the position information of the target of the inertial navigation system unit and the target of the 3D laser scanner obtained in Step S401 and Step S402, establishing the coordinate systems of the 3D laser scanner and the inertial navigation system, and obtaining the exterior orientation elements of the 3D laser scanner and the inertial navigation system; Wherein, the measurement instrument includes a total station, and Step S401 and Step S402 are observed through the total station; The said unit includes a 3D laser scanner and an inertial navigation system, and the calibration of the center of the unit includes obtaining the position information of the center point of each unit.

2. The calibration method of the shipborne integrated water-land measurement system according to claim 1, characterized in that The said Step S1 includes: Step S101: Determining two points P1 and P2; Step S102: Obtaining the distance L between P1 and P2; Step S103: Measuring the distance between P1 and P2 using a total station; Step S104: Comparing and analyzing whether the result exceeds the limit.

3. The calibration method for the shipborne water-land integrated measurement system according to claim 2, wherein The accuracy requirement for whether it exceeds the limit in Step S104 is sub-millimeter level.

4. The calibration method of the shipborne water-land integrated measurement system according to claim 1, wherein The accuracy requirement for whether it exceeds the limit in Step S206 is sub-millimeter level.

5. The calibration method of the shipborne water-land integrated measurement system according to claim 1, characterized in that The said Step S3 includes the following steps: Step S301: Pasting the target paper; Step S302: Obtaining the positional relationship between the target paper and the center point of the unit; Step S303: Determining the center point positions of the 3D laser scanner and the inertial navigation system.

6. The calibration method of the shipborne integrated water-land measurement system according to claim 5, characterized in that, The said Step S403 includes the following steps: Step S4031: Obtaining the roll angle; Step S4032: Obtaining the pitch angle; Step S4033: Obtaining the yaw angle.

7. The calibration method of the shipborne water-land integrated measurement system according to claim 6, characterized in that The said Step S4 also includes: Step S404: Correcting the error between the 3D laser scanner and the inertial navigation system.

8. The calibration method of the shipborne integrated water-land measurement system according to claim 7, characterized in that The said Step S5 includes the following steps: Step S501: Obtaining the true radius of the receiver; Step S502: Measuring the radius of the receiver; Step S503: Calibrating the accuracy.

9. The calibration method of the shipborne water-land integrated measurement system according to claim 8, characterized in that, The said Step S501 includes: Reading the instrument instruction materials to obtain the radius of the receiver.

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