Combined target for point cloud data registration and coordinate unification

Abstract

The combined target for point cloud data registration and coordinate unification comprises a bottom plate, supporting legs, laser scanner target balls, a 360-degree prism and a prism base, the bottom plate is in an equilateral triangle shape, the supporting legs are installed on the bottom faces of the three corners of the bottom plate respectively, the laser scanner target balls are installed on the top faces of the three corners of the bottom plate respectively, and the 360-degree prism is installed on the prism base. The 360-degree prism is installed in the center of the bottom plate through the prism base. The combined target can be used for registering point cloud data and merging the point cloud data into a total station coordinate system at the same time, the time cost for independently arranging a total station calibration target can be saved by using the combined target, and the combined target is not sensitive to illumination and does not need to be flatly placed, the total station can accurately measure, and the combined target can be used together with a laser scanning target.

Description

Technical Field

[0001] The utility model belongs to the technical field of target improvement for laser scanning, and in particular relates to a combined target for point cloud data registration and coordinate unification. Background Art

[0002] 3D laser scanning usually requires multiple measuring stations and multiple angles to obtain all the 3D point cloud data of the target object. Since the coordinate system of each measuring station is relatively independent, the coordinate system of the obtained point cloud data is also different. It is necessary to unify the coordinate system through the point cloud registration method and stitch the point cloud data obtained from each measuring station into a complete data set.

[0003] The registration methods of point cloud data can be divided into two categories: target-controlled registration method and non-target-controlled registration method. The non-target-controlled registration method is generally divided into two stages: coarse registration and fine registration. Among them, the coarse registration stage provides a good initial transformation estimate for the fine registration stage, usually including an initial rotation matrix and an initial translation vector. The fine registration stage further optimizes the registration results of the coarse registration stage on this basis, and iterates the rotation matrix and translation vector with high registration accuracy. In contrast, the target-controlled registration method allows the direct calculation of accurate transformation parameters. In order to obtain the accurate rotation matrix, translation vector and scaling parameters of the point cloud between the two stations, it is usually necessary to set at least 3 targets between the two stations to solve. When scanning with the same device, there is no scaling relationship between the cloud data of the two stations, and the scaling parameter is 1, which is usually not considered in the calculation. Of the two registration methods, the target-controlled registration method allows the use of accurate mathematical models for registration, which can usually achieve higher accuracy and robustness.

[0004] The registration of point cloud data is to stitch all the point clouds of a station into a complete data set. In practical operations, when it is necessary to collect multiple data to calculate deformation or to compare point cloud data with total station data, the accuracy and reliability of the data results of the calculation and comparison are often low due to the inconsistency of the coordinate systems between multiple point cloud data or the coordinate systems of point cloud data and total station. Therefore, it is necessary to unify the coordinates of each point cloud data into the absolute coordinate system or the total station coordinate system. The commonly used method is the total station calibration method, which measures by placing some calibration targets in the scanning area. These calibration targets can be reflective balls and calibration plates. However, it has been found from previous measurements that these calibration targets have many disadvantages: First, reflective balls are sensitive to lighting conditions. The stronger the light, the better the reflection effect of reflective balls. In a weak light or uneven light environment, it may cause problems in the identification and positioning of reflective balls; second, the calibration plate usually needs to be placed on a flat and stable surface. On uneven or unstable ground, the calibration plate may deform or change, affecting the calibration results; third, the measurement accuracy of the total station for reflective balls and calibration plates is lower than that of dedicated prisms, which may accumulate errors in subsequent coordinate conversion calculations; fourth, additional time is required to arrange the calibration targets, which increases the time cost and complexity. Utility Model Content

[0005] In view of the problems existing in the prior art, the utility model provides a combined target for point cloud data alignment and coordinate unification. The purpose is to provide a combined target which is insensitive to light, does not need to be placed flat, can be accurately measured by a total station, and can be used together with a laser scanning target, so as to solve the problems in the prior art that reflective balls may be identified and positioned in a weak light or uneven light environment, and the calibration plate may be deformed or changed on an uneven or unstable ground, affecting the calibration result, and the measurement accuracy of the total station for the reflective ball and the calibration plate is lower than the measurement accuracy of a dedicated prism, which may accumulate errors in the subsequent coordinate conversion calculations, and additional time is required to arrange the calibration targets, increasing the time cost and complexity of the technical problems.

[0006] In order to achieve the above purpose, the specific scheme of the utility model is as follows:

[0007] The combined target used for point cloud data registration and coordinate unification includes a base plate, supporting legs, a laser scanner target ball, a 360° prism and a prism base. The base plate is an equilateral triangle shape, and the supporting legs are respectively installed on the bottom surfaces of the three corners of the base plate, and the laser scanner target ball is respectively installed on the top surface. The 360° prism is installed in the center of the base plate through the prism base.

[0008] Furthermore, the three corner points of the bottom plate are rounded, and a screw hole for installing the prism base is reserved at the center of the bottom plate. The top surfaces of the three corners of the bottom plate are respectively provided with grooves for adapting to the installation of the laser scanner target ball, and the bottom surfaces of the grooves are provided with iron sheets. The distances from the center points of the three grooves to the center of the bottom plate are equal, and the grooves are circular grooves.

[0009] Furthermore, the supporting leg is installed on the bottom plate through a hinge, the top surface cross-section of the supporting leg is elliptical, the bottom surface cross-section is circular, and a conical iron block is also installed at the bottom end of the supporting leg.

[0010] Furthermore, the laser scanner target ball includes a reflective sphere, a connecting rod and a magnetic base. The reflective sphere is connected to the magnetic base via the connecting rod, and the magnetic base is a cylinder.

[0011] Furthermore, the prism base is L-shaped, and screw hole two and screw hole three are respectively provided at the ends of the short arm and the long arm. The prism base is connected to the base plate by bolts passing through screw hole two and screw hole one. The 360° prism is connected to screw hole three of the long arm of the prism base by bolts, and the center of the 360° prism is located on the normal to the center point of the base plane.

[0012] Furthermore, the vertical distance between the center of the laser scanner target ball and the bottom plate plane is equal to the length of the radius of the laser scanner target ball.

[0013] Furthermore, the vertical distance from the center of the 360° prism to the bottom plate plane is equal to the vertical distance from the third center of the screw hole at the long arm end of the prism base to the bottom surface of the prism base.

[0014] Furthermore, the base plate is made of hard plastic and the supporting legs are made of hard plastic.

[0015] Advantages of the utility model

[0016] 1. The combined target for point cloud data registration and coordinate unification of the utility model can be used for point cloud data registration and incorporating point cloud data into the total station coordinate system at the same time. The use of the combined target can save the time cost of separately arranging the total station calibration target.

[0017] 2. When arranging the combined target, it only needs to be visible to both the laser scanner and the total station. It has low dependence on lighting conditions and does not require strict flat placement, so it is highly practical.

[0018] 3. This combination target uses a high-precision target ball of a laser scanner and a high-precision mini 360° prism of a total station. Compared with other calibration targets, the measurement accuracy is higher. More than three points of the same name are allowed between the point cloud data and the total station coordinate system, and the error of the coordinate system conversion is smaller. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1It is a structural schematic diagram of a combined target used for point cloud data registration and coordinate unification in the utility model.

[0020] Figure 2 for Figure 1 Schematic diagram of the base plate structure.

[0021] Figure 3 for Figure 1 Schematic diagram of the laser scanner target ball structure.

[0022] Figure 4 for Figure 1 Schematic diagram of the prism base structure.

[0023] Figure 5 for Figure 1 Schematic diagram of the connection between the supporting leg structure and the base plate.

[0024] Figure 6 This is a cross-sectional view of the center plane of the combined target in Example 1.

[0025] Figure 7 This is a cross-sectional view of the center plane of the combined target in Example 2.

[0026] In the figure:

[0027] 1: Base plate; 101: Screw hole one; 102: Circular groove; 103: Circular iron sheet; 2: Laser scanner target ball; 201: Magnetic base; 202: Connecting rod; 203: 145mm reflective sphere; 204: 200mm reflective sphere; 3: Prism; 4: Prism base; 401: Screw hole two; 402: Screw hole three; 5: Support leg; 6: The normal of the center point of 360° prism 3 located at the center point of the plane of base plate 1; a1: The vertical distance from the center of the reflective sphere to the plane of base plate; a2: The vertical distance from the center of 360° prism 3 to the plane of base plate; P: The center of the circular plane constructed by the centers of the three target balls 2 in the point cloud coordinate system; Q1: The center of 360° prism 3 in the total station coordinate system; Q2: The point P is obtained by moving the distance along the normal 6 in the direction of the plane of base plate 1. DETAILED DESCRIPTION

[0028] The present invention is further explained and illustrated below in conjunction with the accompanying drawings and specific embodiments. It should be noted that the specific embodiments are not intended to limit the scope of rights of the present invention.

[0029] Example 1

[0030] like Figures 1 to 6As shown, this embodiment 1 provides a combined target for point cloud data alignment and coordinate unification, which can be used for high-precision alignment of multi-site clouds in laser scanning measurement, and allows the coordinates of the complete point cloud model after alignment to be converted into the total station coordinate system. The combined target includes a base plate 1, support legs 5, a laser scanner target ball 2, a 360° prism 3 and a prism base 4. The base plate 1 is made of hard plastic and the support legs 5 are made of hard plastic. The base plate 1 is an equilateral triangle shape, and the three corner points of the base plate 1 are respectively rounded. The laser scanner target ball 2 is set to a detachable mode for easy carrying and transportation. In order to ensure the accuracy of installation on the base plate 1, circular grooves 102 of the same size as the magnetic base 201 are preset on the top surfaces of the three corners of the base plate 1, and it is ensured that the distances from the center points of the three circular grooves 102 to the center of the base plate 1 are equal, so that the distances from the centers of the three laser scanner target balls 2 installed in the circular grooves 102 to the center of the base plate 1 are equal. At the same time, a circular iron sheet 103 is embedded in the circular groove 102 to improve the firmness of the laser scanner target ball 2 embedded in the circular groove 102. Each laser scanner target ball includes a reflective sphere 203, a connecting rod 202 and a magnetic base 201. The reflective sphere 203 is connected to the magnetic base 201 through the connecting rod 202. The magnetic base 201 is a cylinder adapted to the circular groove 102, so that each reflective sphere 203 is installed in the circular groove 102 on the bottom plate 1 through the magnetic base 201, and is magnetically connected to the iron sheet 103 on the bottom surface of the circular groove 102. Preferably, the vertical distance a1 from the center of the reflective sphere 203 to the plane of the bottom plate 1 is equal to the length of the radius of the reflective sphere 203. The reflective sphere 203 of this embodiment 1 has a diameter of 145 mm, the magnetic base 201 and the connecting rod 202 have a total height of 8 mm, the circular groove 102 has a depth of 10 mm, the iron disc 103 embedded in the bottom of the circular groove 102 has a thickness of 2 mm, the vertical distance a2 from the center of the 360° prism 3 to the surface of the base plate 1 is 72.5 mm, and the radius of the circle constructed by the center of the reflective sphere 203 is 350 mm.

[0031] A screw hole 101 for installing the prism base 4 is reserved at the center of the bottom plate 1, and the distances from the center points of the three circular grooves 102 to the center of the bottom plate 1 are all equal. The prism base 4 is L-shaped, and the two ends of the short arm and the long arm are respectively provided with a screw hole 2 401 for installing the prism base 4 and a screw hole 3 402 for installing the 360° prism 3. In order to avoid the error that may be caused by multiple disassembly of the 360° prism 3, the 360° prism 3 is installed on the center of the bottom plate 1. Specifically, the short arm of the prism base 4 is connected to the center of the bottom plate 1 through the screw hole 2 401 and the screw hole 1 101 by a bolt assembly, and the 360° prism 3 is installed on the screw hole 3 402 of the long arm of the prism base 4 by a bolt assembly, and the center point of the 360° prism 3 is located on the normal 6 of the center point of the plane of the bottom plate 1. The length from the center of the 360° prism 3 to the center of the surface of the bottom plate 1 is 72.5 mm, and the three corner bottom surfaces located on the bottom plate 1 are respectively installed with support legs 5 through hinges for easy folding and storage. The top cross-section of the support leg 5 is elliptical, the bottom cross-section is circular, and a conical iron block is also installed at the bottom end of the support leg 5. Preferably, the vertical distance a2 from the center of the 360° prism 3 to the plane of the bottom plate 1 is equal to the vertical distance from the center of the screw hole 3 402 of the long arm of the prism base 4 to the bottom surface of the prism base 4. In the combined target of this embodiment 1, a1=a2=72.5 mm, that is, point P and point Q2 are the same point in the point cloud coordinate system, and the center P of the circle constructed by the center Q1 of the 360° prism and the centers of the three target balls is a point of the same name.

[0032] Working principle:

[0033] When in use, the laser scanner target ball 2 is embedded in the circular groove 102 on the top surface of the three corners of the bottom plate 1, and the folded support legs 5 are opened. If the combined target of this embodiment is placed on soft land, it needs to be pressed tightly to prevent the combined target position from changing during measurement. It should be noted that when arranging the combined target, it is necessary to ensure that the 360° prism 3 in the center of the combined target and the total station are in sight, and the three laser scanner target balls 2 can be observed by the front and rear stations of the laser scanner using this round of combined targets to ensure the accuracy of the registration between the cloud data of the two stations; if due to the site conditions, the 360° prism 3 in the field of view of the total station is blocked by the laser scanner target ball 2 anyway, it is allowed to remove the laser scanner target ball 2 that blocks the field of view first, and then install it after the total station measurement is completed. The position of the combined target should be moved as little as possible during this process.

[0034] In order to avoid the situation in which multiple 360° prisms 3 in a small range affect the total station measurement during the measurement of the combined target of this embodiment 1, only one 360° prism 3 is set on the combined target. In actual use, at least three rounds are required to ensure that there are more than three points of the same name between the point cloud data and the total station data, so as to ensure that the point cloud data is incorporated into the total station coordinate system. For the point cloud data coordinate system 1, the more points of the same name between the two sets of data, the smaller the error in the conversion calculation. Therefore, in the actual measurement process, the more rounds the combined target uses, the better. Three rounds are only the minimum requirement. In special cases such as when the total station's field of view is blocked by buildings, the combined target can be used only for point cloud registration.

[0035] Example 2

[0036] like Figure 1-Figure 5 and Figure 7 As shown, this embodiment 2 provides a combined target for point cloud data alignment and coordinate unification, which can be used for high-precision alignment of multi-site clouds in laser scanning measurement, and allows the coordinates of the complete point cloud model after alignment to be converted into the total station coordinate system. The structure and working principle of the combined target are the same as those of embodiment 1. The diameter of the laser scanner target ball 2 of this embodiment 2 is set to 200 mm, the total height of the magnetic base 201 and the connecting rod 202 is 8 mm, the circular groove 102 is 10 mm deep, the circular iron sheet 103 embedded in the bottom surface of the circular groove 102 is 2 mm thick, the vertical distance a1 from the center of the reflective sphere 204 to the surface of the bottom plate 1 is 100 mm, and the radius of the circle constructed by the center of the laser scanner target ball 2 is 350 mm. The mini 360° prism 3 is installed at the center of the base plate 1 through the prism base 4. The center of the 360° prism 3 is located on the normal 6 of the center point of the plane of the base 1, and the vertical distance a2 between the center of the 360° prism 3 and the center of the surface of the base plate 1 is 72.5 mm. The supporting legs 5 are connected to the triangular position below the base plate 1 through hinges and can be folded and retracted.

[0037] In the combined target of this embodiment 2, a1=100mm, a2=72.5mm, a1-a2=27.5mm, that is, the center point P of the circle constructed by the centers of the three laser scanner target balls 2 with the same name point Q1 of the 360° prism 3 is moved 27.5mm along the normal line of the circular plane to the point Q2 in the direction of the bottom plate plane.

Claims

1. A combined target for point cloud data registration and coordinate unification, characterized in that: It includes a base plate, supporting legs, a laser scanner target ball, a 360° prism and a prism base. The base plate is an equilateral triangle. The supporting legs are installed on the bottom surfaces of the three corners of the base plate, and the laser scanner target ball is installed on the top surface. The 360° prism is installed in the center of the base plate through the prism base.

2. The combined target according to claim 1, characterized in that: The three corner points of the bottom plate are rounded, and a screw hole for installing the prism base is reserved at the center of the bottom plate. The top surfaces of the three corners of the bottom plate are respectively provided with grooves for adapting to the installation of the laser scanner target ball, and the bottom surfaces of the grooves are provided with iron sheets. The distances from the center points of the three grooves to the center of the bottom plate are equal, and the grooves are circular grooves.

3. The combined target according to claim 1, characterized in that: The supporting legs are installed on the bottom plate through hinges. The top surface section of the supporting legs is elliptical, the bottom surface section is circular, and a conical iron block is also installed at the bottom end of the supporting legs.

4. The combined target according to claim 1, characterized in that: The laser scanner target ball comprises a reflective sphere, a connecting rod and a magnetic base. The reflective sphere is connected to the magnetic base via the connecting rod, and the magnetic base is a cylinder.

5. The combined target according to claim 1, characterized in that: The prism base is L-shaped, and screw holes 2 and 3 are respectively provided at the two ends of the short arm and the long arm. The prism base is connected to the base plate by bolts passing through screw holes 2 and 1. The 360° prism is connected to screw hole 3 of the long arm of the prism base by bolts, and the center of the 360° prism is located on the normal line of the center point of the base plate plane.

6. The combined target according to claim 1, characterized in that: The vertical distance between the center of the target ball of the laser scanner and the bottom plate plane is equal to the length of the radius of the target ball of the laser scanner.

7. The combined target according to claim 1, characterized in that: The vertical distance between the center of the 360° prism and the bottom plate plane is equal to the vertical distance between the three centers of the screw holes on the long arm of the prism base and the bottom surface of the prism base.

8. The combined target according to claim 1, characterized in that: The bottom plate and the supporting legs are both made of hard plastic material.

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