Laser scanner, method for processing laser scanned data, and program

Abstract

To reduce the occurrence of measurement errors in a laser scanner.SOLUTION: Provided is a laser scanner 100 comprising: a reflection mirror 105 that emits laser scanning light and is a rotating optical system; a horizontal rotary unit 103 which is a housing for holding the reflection mirror in a rotatable state; and an error calculation unit that calculates an error in an optical direction of the laser scanning light. The horizontal rotary unit 103 has a mark 106 for correction of the optical axis, which is a specific part on which laser scanning by the laser scanning light is performed. The mark 106 for correction of the optical axis is a diagram in which size in a direction parallel to the direction of laser scans is not constant, and calculation of the error is conducted on the basis of laser scanned data of the diagram.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to the technology of laser scanning. [Background technology]

[0002] BACKGROUND ART A laser scanning device that scans a laser distance measuring light in a linear dot pattern is known (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2023-150501 Summary of the Invention [Problem to be solved by the invention]

[0004] After the laser scanning device is turned on, there is a fluctuating measurement error. This error tends to correlate with the temperature inside the laser scanning device. Therefore, it is believed that the above error is caused by heat generation inside the laser scanning device.

[0005] Specifically, it is believed that the above errors occur due to a combination of factors, such as deformation and distortion of the housing and various components caused by the rise in internal temperature after the power is turned on, deformation and distortion of the optical system, changes in the response characteristics of sensor devices such as angle sensors, and changes in the calculation time of the calculation device.

[0006] In this context, an object of the present invention is to provide a technique for reducing the occurrence of measurement errors in a laser scanning device. [Means for solving the problem]

[0007] The present invention is a laser scanning device comprising an optical system that emits laser scanning light and rotates, a housing that holds the optical system in a rotatable state, and an error calculation unit that calculates an error in the optical axis direction of the laser scanning light, wherein a figure that is to be laser scanned with the laser scanning light is arranged in the housing, the figure having a shape whose dimensions are not constant in a direction parallel to the direction of the laser scanning, and the error is calculated based on laser scan data of the figure.

[0008] In the present invention, the error calculation may include calculating an error Δθx of the optical axis in a direction perpendicular to the scanning direction based on a dimension of the figure in the scanning direction obtained by laser scanning the figure.In the present invention, the error calculation may include calculating an error Δθy of the optical axis in the scanning direction based on a center position in the scanning direction of scan data of the figure.

[0009] In the present invention, when calculating the error, an example is where the error of the optical axis in a direction perpendicular to the scanning direction is Δθx and the error of the optical axis in the scanning direction is Δθy, and first scan data, which is scan data of the figure acquired in advance, is compared with second scan data, which is scan data of the figure acquired during operation of the laser scanning device, and Δθx is calculated based on a change in width in the scanning direction between the first scan data and the second scan data, and Δθy is calculated based on a change in center position in the scanning direction between the first scan data and the second scan data.

[0010] The present invention may be embodied in an aspect that includes an optical axis direction correcting unit that corrects information related to the optical axis of the scanning light based on the error.

[0011] In the present invention, an embodiment is provided in which the error calculation unit further calculates an error in the optical axis direction of the laser scan light based on the results of laser scans performed on multiple targets in a horizontal direction with a 180° angle change.

[0012] The present invention is a method for processing laser scan data to obtain an error in the optical axis of a laser scanning device that includes a rotating optical system that emits laser scan light and a housing that holds the optical system in a rotatable state, wherein a figure that is laser scanned with the laser scan light is placed on the housing, the figure having a shape whose dimensions are not constant in a direction parallel to the direction of the laser scan, and the error is calculated based on the laser scan data of the figure.

[0013] The present invention is a program for causing a computer to process laser scan data to obtain an error in the optical axis of a laser scanning device that includes a rotating optical system that emits laser scan light and a housing that holds the optical system in a rotatable state, wherein a figure that is to be laser scanned with the laser scan light is placed on the housing, and the figure has a shape whose dimensions are not constant in a direction parallel to the direction of the laser scan, and the program causes a computer to calculate the error based on the laser scan data of the figure. [Effects of the Invention]

[0014] According to the present invention, it is possible to reduce the occurrence of measurement errors in a laser scanning device. [Brief explanation of the drawings]

[0015] [Figure 1] 1 is an external view of a laser scanning device utilizing the present invention. [Figure 2] FIG. 1 is a functional block diagram of a laser scanning device utilizing the present invention. [Figure 3]FIG. 1 is a functional block diagram of a laser scanning device utilizing the present invention. [Figure 4] 1A, 1B, and 1C are conceptual diagrams of the error in the optical axis of the scanning light. [Figure 5] 1A, 1B, and 1C are conceptual diagrams of the error in the optical axis of the scanning light. [Figure 6] 1A and 1B are conceptual diagrams showing the principle of calculating the error in the optical axis of the scanning light. [Figure 7] 10 is a flowchart illustrating an example of a processing procedure. [Figure 8] 10 is another example of the optical axis correction mark. [Figure 9] FIG. 2 is a conceptual diagram showing each component of an angle error of an optical axis. [Figure 10] FIG. 1 is a conceptual diagram showing the principle of determining the angular error of the optical axis by forward and backward observation. DETAILED DESCRIPTION OF THE INVENTION

[0016] 1. First embodiment (laser scanning device) 1 shows a laser scanning device 100 embodying the invention. The laser scanning device 100 comprises a tripod 101, a base unit 102, a horizontal rotation unit 103, and a vertical rotation unit 104. The base unit 102 is fixed to the top of the tripod 101. The laser scanning device 100 is installed on the ground or floor by means of the tripod 101. The horizontal rotation unit 103 is arranged on the top of the base unit 102 in a state that allows it to rotate horizontally.

[0017] The horizontal rotation unit 103 is electrically driven to rotate horizontally relative to the base unit 102. This horizontal rotation is performed around a vertical axis. The base unit 102 is equipped with an adjustment mechanism for ensuring that the horizontal rotation unit 103 is level (aligning the rotation axis with the vertical axis), but as this is an existing technology, illustrations and explanations thereof will be omitted.

[0018] The horizontal rotation unit 103 includes a vertical rotation unit 104, which includes a reflecting mirror 105 on a slanted surface obtained by cutting a cylindrical shape at a 45° angle. The vertical rotation unit 104 is electrically rotated around the cylindrical axis (the central axis of the cylinder) of the cylindrical shape, with the axis held horizontal. This rotation is referred to as vertical rotation. In an actual product, the reflecting mirror 105 is not exposed, but is covered by a cover with a light-transmitting member placed in the optical path.

[0019] The horizontal rotation unit 103 has a concave double-headed structure when viewed from the front, and the vertical rotation unit 104 is arranged so as to be vertically rotatable on one head 103a of the double-headed structure, facing the other head 103b. An optical unit (123 in FIG. 3), not shown in FIG. 1, is arranged on the extension of the rotation axis of the vertical rotation unit 104 on the other head 103b of the double-headed structure. A scanning light (distance measurement laser light) is emitted from this optical unit toward the reflecting mirror 105. This emitted scanning light is reflected by the reflecting mirror 105 and emitted to the outside. The scanning light reflected by the object to be scanned travels the opposite path to the previously emitted light, returns to the reflecting mirror 105, is reflected there, and is received by the optical unit.

[0020] By emitting pulses of scanning light from the optical unit while rotating the vertical rotation unit 104 vertically, laser scanning is performed in a direction perpendicular to the rotation axis of the vertical rotation unit 104 (laser scanning along a vertical plane). At the same time, by rotating the horizontal rotation unit 103 horizontally, the laser scanning along the vertical plane is shifted little by little in the horizontal direction, and laser scanning is performed all around or within a predetermined horizontal angle range.

[0021] The scanning light is a single pulsed laser distance measuring light. The emission frequency (scanning frequency) of the scanning light is, for example, 1 kHz to 50 kHz. The scanning frequency, the vertical rotation speed of the vertical rotation unit 104, and the horizontal rotation speed of the horizontal rotation unit 103 are determined by the required density of scan points. The required density of scan points is, for example, a density that results in point intervals of 1 cm to 5 cm at a distance of 50 m.

[0022] By performing the above-described laser scanning, data on the direction and distance from the laser scanning device 100 to each scan point (a point where the scanning light is reflected) within the scan range is obtained. This data determines the position of each scan point relative to the laser scanning device 100. A collection of data on the position of each scan point relative to the laser scanning device 100 forms point cloud data. If the position and orientation of the laser scanning device 100 in an absolute coordinate system are known, the above-described point cloud data can be described in the absolute coordinate system. An absolute coordinate system is a coordinate system used in maps and GNSS, and describes a position using, for example, latitude, longitude, and altitude.

[0023] An optical axis correction mark 106 is located on the top surface of the horizontal rotation unit 103 directly below the reflecting mirror 105. The optical axis correction mark 106 is an optical surface with a specific shape that differs in reflectivity from its surroundings, designed for the purpose of measuring its shape by laser scanning. In this example, a reflective surface pattern is used for the optical axis correction mark 106, which has a higher reflectivity than its surroundings but not as high as that of a mirror (mirror surface). This is because the reflected light from a mirror would be too strong. The optical axis correction mark 106 reflects a portion of the scanning light as a reference light. The reflectivity characteristics of the optical axis correction mark 106 and its surroundings are determined so that the difference in reflectivity between the optical axis correction mark 106 and its surroundings is clear. The reference light is used to correct errors in the optical axis information of the scanning light. This technology will be described later.

[0024] The optical axis correction mark 106 is also used to adjust the received light intensity of the scanning light. For example, the intensity of reflected light differs significantly between laser scanning targeting terrain or buildings and laser scanning targeting a reflecting prism. Therefore, if the latter laser scanning is performed under the conditions of the former laser scanning, the light receiving element will be saturated, and accurate position data of the reflecting prism will not be obtained. For this reason, in the latter laser scanning, an optical attenuator is inserted in the optical path inside the laser scanning device 100 to reduce the intensity of the scanning light incident on the light receiving element. The scanning light reflected from the optical axis correction mark 106 is used as a reference light to adjust this optical attenuator. Details of the configuration of this technology are outside the scope of the present invention, so a description thereof will be omitted.

[0025] A camera 107 is disposed on the horizontal rotation unit 103. The camera 107 is a camera that captures still or moving images, and captures an image of the target of laser scanning.

[0026] (Block diagram) Fig. 2 is a functional block diagram of laser scanning device 100. Fig. 3 is a functional block diagram related to the optical system of laser scanning device 100. As shown in Fig. 2, laser scanning device 100 includes a light emitting unit 111, a light receiving unit 112, a distance calculation unit 113, a vertical rotation drive control unit 114, a horizontal rotation drive control unit 115, a vertical rotation angle detection unit 116, a horizontal rotation angle detection unit 117, an optical axis direction correction data acquisition unit 118, an optical axis direction error calculation unit 119, an optical axis direction correction unit 120, and a point cloud generation unit 121.

[0027] The distance calculation unit 113, vertical rotation drive control unit 114, horizontal rotation drive control unit 115, optical axis direction correction data acquisition unit 118, optical axis direction error calculation unit 119, optical axis direction correction unit 120, and point cloud generation unit 121 are realized by a computer built into the laser scanning device 100. This computer is equipped with a communication interface, a CPU, and a data storage device. This data storage device stores operation programs for realizing each functional unit, as well as operation programs and various data required for the operation of the laser scanning device 100. It is also possible to configure some or all of the above-mentioned functional units using dedicated hardware.

[0028] The light-emitting unit 111 has a light-emitting element that emits pulsed laser light that becomes scanning light, a drive circuit for the light-emitting element, and an optical system. The light-receiving unit 112 has an optical system that receives the scanning light reflected from the scanning target, a light-receiving element, and a peripheral circuit for the light-receiving element.

[0029] 3, the scanning light emitted from the light-emitting unit 111 passes through the optical path combining / separating unit 122 and is output from the optical unit 123 toward the reflecting mirror 105 (see also FIG. 1). The scanning light reflected from the object to be scanned travels the opposite path to the emitted light, is reflected by the reflecting mirror 105, enters the optical unit 123, is separated by the optical path combining / separating unit 122, and enters the light-receiving unit 112. The light-emitting unit 111, the light-receiving unit 112, and the light path combining / separating unit 122 are disposed inside the other head 103a of the horizontal rotation unit 103.

[0030] Distance calculation unit 113 calculates the distance from laser scanning device 100 to the scanning point (the reflection point of the scanning light) based on the principle of optical distance measurement. The starting point (origin) of the distance is, for example, the position of the light emitting element of light emitting unit 111.

[0031] In this example, a reference light path (not shown) with a known optical path length is provided inside the laser scanning device 100. The scanning light emitted from the light emitting unit 111 travels as reference light along the reference light path (not shown) in addition to the path shown in FIG. 3, and enters the light receiving unit 112. The scanning light (distance measuring light) and the reference light are both received by the light receiving unit 112, but because they travel different distances, the output signal from the light receiving unit 112 is two pulse signals with a phase difference. The distance to the scanning point is calculated from the phase difference between these two pulse signals. The distance to the scanning point can also be calculated from the travel time of the scanning light.

[0032] The vertical rotation drive control unit 114 generates a control signal that controls the vertical rotation of the vertical rotation unit 104. This control signal is sent to a drive circuit (not shown) that drives a motor (not shown) that vertically rotates the vertical rotation unit 104. The vertical rotation of the vertical rotation unit 104 is controlled by the vertical rotation drive control unit 114.

[0033] Horizontal rotation drive control unit 115 generates a control signal that controls the horizontal rotation of horizontal rotation unit 103. This control signal is sent to a drive circuit (not shown) that drives a motor (not shown) that vertically rotates horizontal rotation unit 103. The horizontal rotation drive control unit 115 controls the horizontal rotation of horizontal rotation unit 103.

[0034] The vertical rotation angle detection unit 116 detects the vertical rotation angle of the vertical rotation unit 104. The vertical rotation angle is detected by a rotary encoder, and the output of this rotary encoder is processed by the vertical rotation angle detection unit 116 to measure the vertical rotation angle of the vertical rotation unit 104. The horizontal rotation angle detection unit 117 detects the horizontal rotation angle of the horizontal rotation unit 103. The horizontal rotation angle is detected by a rotary encoder, and the output of this rotary encoder is processed by the horizontal rotation angle detection unit 117 to measure the horizontal rotation angle of the horizontal rotation unit 103.

[0035] The optical axis direction correction data acquisition unit 118 acquires laser scan data of the optical axis correction mark 106 as data for correcting errors in the optical axis of the scanning light.

[0036] The optical axis direction error calculation unit 119 calculates the error in the direction of the optical axis of the scanning light based on the laser scan data of the optical axis correction mark 106 obtained by the optical axis direction correction data acquisition unit 118 .

[0037] An example of a process for calculating the error of the optical axis of the scanning light will be described below. In the following description, it is assumed that there are no errors other than Δθx and Δθy, which will be described later. In reality, there may be other errors, but this will be described in the second embodiment.

[0038] The upper surface of the horizontal rotation unit 103 directly below the reflecting mirror 105 is a horizontal plane, on which an optical axis correction mark 106 is disposed. The optical axis correction mark 106 is formed by printing, a sticker, or a thin plate-like member. In this example, the optical axis correction mark 106 is an equilateral or isosceles triangle, and is set so that laser scanning is performed along a direction parallel to its base. Furthermore, the scanning light is set so as to pass near the midpoint of the triangle (so that the scan line passes near the midpoint of the triangle).

[0039] Fig. 4(A) is an enlarged conceptual diagram of the reflecting mirror 105 and the optical axis correction mark 106. Fig. 4(A) shows a state in which scanning light is emitted in the negative direction of the X axis from the head 103b on the right side of the horizontal rotation unit 103 in Fig. 1, and this scanning light is reflected by the reflecting mirror 105 in the direction of the optical axis correction mark 106 (downward). This is also the case in Fig. 5(A).

[0040] 4(A) shows the scan line A-A' when there is no error in the direction of the optical axis of the scanning light. The scan line A-A' is parallel to the base of the optical axis correction mark 106 (parallel to the Y axis) and passes through the vicinity of the midpoint of the optical axis correction mark 106. When the pulsed scanning light repeatedly strikes the reflecting mirror 105, the vertical rotation unit 104 rotates, forming scan points dotted on the scan line A-A'.

[0041] FIG. 4B shows the relationship between the detected intensity I (vertical axis) of the reflected light of the scanning light and the vertical rotation angle V (rotation angle around the X-axis) (horizontal axis) of the vertical rotation unit 104 in this case. FIG. 4B shows a waveform formed by an envelope connecting the peak positions of the pulsed detection light (reflected light of the scanning light). This waveform is the waveform of the light intensity distribution measurement of the laser scanning light with respect to the optical axis correction mark 106. This is also the case in FIGS. 5 and 6.

[0042] Here, a case is shown in which reflected light from the optical axis correction mark 106 is detected at a relatively high intensity compared to other locations. The vertical rotation angle V is a measurement value indicating the direction of the scanning light relative to the reflecting mirror 105, and is measured by the vertical rotation angle detection unit 116. In this case, the vertical rotation angle V is the elevation or depression angle of the scanning light. The vertical rotation angle V can also be understood as a time parameter. The width V1 of the rectangular waveform in Figure 4(B) corresponds to the length L1 of the width of the optical axis correction mark 106 on the scan line A-A'.

[0043] 4(B) shows the waveform when there is no error Δθx in the X-axis direction in the optical axis of the scanning light reflected by reflecting mirror 105. When Δθx=0, the optical axis of the reflecting surface of reflecting mirror 105 (the axis perpendicular to the mirror surface) is within the XZ plane, and the optical axis of the scanning light reflected by reflecting mirror 105 coincides with the vertical axis (Z-axis).

[0044] Here, when the optical axis of the reflecting surface of reflecting mirror 105 is within the XZ plane, the optical axis of the scanning light reflected by reflecting mirror 105 is shifted by an angle Δθx in the X-axis direction rather than vertically (Z-axis). Δθx is the error of the optical axis in the direction perpendicular to the scanning direction. This shift occurs for various reasons, including heat.

[0045] When the above-mentioned Δθx deviation (Δθx>0) occurs, the scan line passing through the optical axis correction mark 106 becomes the line B-B'. Figure 4(C) shows the relationship between the intensity I of the reflected light of the scan light detected in this case and the vertical rotation angle V of the vertical rotation unit 104. The width V2 of the rectangular waveform in Figure 4(C) corresponds to the length L2 of the width of the optical axis correction mark 106 in the portion of the scan line B-B'.

[0046] As can be seen by comparing Figures 4(B) and 4(C), when a deviation Δθx occurs in the optical axis of the scanning light within the XZ plane, the measurement value of the width of the optical axis correction mark 106 obtained by laser scanning changes from V1 to V2 (V1>V2). Note that when an error occurs in the negative direction of the X axis, V2>V1. Here, the difference between V1 and V2 is defined as ΔV.

[0047] In this way, when Δθx occurs, a change ΔV occurs in the width of the waveform of the light intensity distribution measurement of the laser scan light for the optical axis correction mark 106. In the case of Figure 4, as ΔV increases, Δθx also increases. Note that if the orientation of the optical axis correction mark 106 in the X-axis direction is reversed by 180°, this relationship is reversed. In either case, there is a correlation between ΔV and Δθx. Therefore, by acquiring this correlation in advance, it is possible to obtain Δθx from the measured value of ΔV.

[0048] That is, when the laser scanning device 100 is in operation (after startup), ΔV is measured based on the laser scan data of the optical axis correction mark 106, and Δθx can be obtained by comparing it with the correlation between Δθx and ΔV obtained in advance. Once Δθx is obtained, the data on the direction of the scanning light as seen from the laser scanning device 100 that corresponds to Δθx is corrected taking this into consideration. This corrects errors in the point cloud data caused by Δθx.

[0049] According to actual measurement data, Δθx occurs at a maximum of several tens of seconds. The above method can reduce this error. Note that Δθx gradually increases and fluctuates after the laser scanning device 100 is started. The behavior of the change in Δθx is affected by the operating state.

[0050] Next, we will explain what happens when an angular error Δθy occurs in the optical axis of the scanning light in a direction perpendicular to Δθx. Δθy is the error in the Y-axis direction (scanning direction) of the optical axis of the scanning light reflected by the reflecting mirror 105. FIG. 5(A) shows the scan line A-A'. The scan line A-A' is parallel to the base of the optical axis correction mark 106 and passes through the vicinity of its midpoint.

[0051] FIG. 5B shows the relationship between the intensity I (vertical axis) of the reflected light of the scanning light detected in this case and the vertical rotation angle V (rotation angle around the X axis) (horizontal axis) of the vertical rotation unit 104. FIG. 5B shows the case where Δθy=0. The width of the rectangular waveform in FIG. 5B corresponds to the length L1 of the width of the optical axis correction mark 106 in the portion of the scan line A-A'.

[0052] Here, it is assumed that the optical axis of the scanning light reflected by the reflecting mirror 105 is misaligned in the Y-axis direction by an angle Δθy. This misalignment occurs due to various factors, including heat. Note that Δθy is related to the measurement error of the V angle (vertical angle (elevation angle, depression angle)) in the zenith-nadir direction, and is related to the measurement error of the horizontal angle near the horizontal plane. Δθx is the opposite.

[0053] 5, the scan line passing through the optical axis correction mark 106 is on the line A-A', but a deviation corresponding to Δθy occurs in the angular position of the scan light that captures the optical axis correction mark 106. As a result, the waveform (waveform of the light intensity distribution measurement of the laser scan light with respect to the optical axis correction mark 106) showing the relationship between the intensity I of the reflected light (vertical axis) and the vertical rotation angle V (rotation angle around the X axis) (horizontal axis) of the vertical rotation unit 104 becomes as shown in FIG. 5(C).

[0054] That is, compared to the waveform in Fig. 5(B) when there is no deviation of Δθy, the waveform in Fig. 5(C) has the same width on the time axis as in Fig. 5(B), but has a deviation of a time difference ΔV2 corresponding to Δθy. Note that if Δθy occurs in the opposite direction to that shown in the figure, the positional relationship on the horizontal axis of the waveforms in Fig. 5(B) and Fig. 5(A) will be reversed.

[0055] That is, the deviation of ΔV2 causes a deviation in the center position (center position on the horizontal axis (angular direction)) of the waveform of the light intensity distribution measurement of the laser scanning light for the optical axis correction mark 106. This deviation correlates with Δθy.

[0056] In the above case, as ΔV2 increases, Δθy also increases. Therefore, by acquiring this correlation in advance, measuring ΔV2 while the laser scanning device 100 is in operation, and comparing the measured value with the above correlation, Δθy can be calculated.

[0057] In reality, Δθx and Δθy may occur simultaneously. In this case, it is necessary to acquire Δθx and Δθy separately. This method will be explained below.

[0058] In this case, in an environment where Δθx = Δθy = 0 can be assumed in advance, the waveform of the light intensity distribution measurement of the laser scanning light for the optical axis correction mark 106 is acquired as a reference waveform (FIG. 6(A)), and the width value and center position of this reference waveform are acquired. This value may be calculated from the design value.

[0059] Then, while the laser scanning device 100 is operating, the waveform (FIG. 6(B)) of the light intensity distribution measurement of the laser scanning light for the optical axis correction mark 106 is measured, and this waveform is compared with the above-mentioned reference waveform. Then, the amount of change in the width of the measured waveform relative to the reference waveform and the amount of change in the center position of the waveform from the center position of the reference waveform are obtained. Then, using the above-mentioned method, Δθx is calculated from the amount of change in the width of the waveform, and Δθy is calculated from the amount of change in the center position of the waveform.

[0060] The process for obtaining the above-mentioned Δθx and Δθy is carried out in the optical axis direction error calculation unit 119.

[0061] The optical axis direction corrector 120 corrects the optical axis direction of each scan light in the laser scan data of the survey object based on the above-mentioned Δθx and Δθy calculated by the optical axis direction correction data analyzer 119.

[0062] The point cloud generation unit 121 calculates the coordinates of each scan point based on the information on the direction of the optical axis of the scan light that has been corrected as described above and the distance to the scan point, and generates point cloud data, which is a collection of position information for each scan point. That is, the direction of the optical axis of the scan light for each scan point is corrected using Δθx and Δθy obtained by the optical axis direction correction data analysis unit 119, and the position of each scan point relative to the laser scanning device 100 is calculated based on this corrected direction of the optical axis and the distance to the scan point. The point cloud can be in the form of a list of the direction and distance from the laser scanning device for each point, or a list obtained by calculating the three-dimensional coordinates of each point on an appropriate coordinate system.

[0063] The laser scanning device 100 is equipped with a communication interface and an operation panel (not shown), but these are standard equipment and will not be described here.

[0064] (Example of processing) Fig. 7 is a flowchart showing an example of the procedure of processing performed in the laser scanning device 100. The processing shown in Fig. 7 is executed by a computer installed in the laser scanning device 100. A program for executing the processing in Fig. 7 is stored in the storage device of the computer. This program can also be stored in an appropriate storage medium and downloaded from there.

[0065] Prior to the processing, the laser scanning device 100 is installed in the environment where the laser scanning will be performed. The position and orientation of the laser scanning device 100 may be calculated in advance, or may be calculated by resection after the laser scanning using a reference target set in the scanning range.

[0066] Also, a calibration process is performed in advance to obtain the data shown in Figures 4(B), 5(B), and 6(A), and this data is stored in a storage unit or an appropriate storage area within the laser scanning device 100. Note that when the laser scanning device 100 starts operating, a calibration laser scan may be performed to obtain the data shown in Figures 4(B), 5(B), and 6(A), which may then be used to perform processing related to the optical axis error.

[0067] Once the laser scanning device 100 is installed, laser scanning begins (step S101). By performing laser scanning, laser scan data of the surveying object is obtained (step S102), and laser scan data related to the optical axis correction mark 106 is also obtained (step S103). The laser scan data includes the direction of the scanning light, the distance to the scanning point, the received light intensity of the scanning light, and the time of reception of the scanning light.

[0068] Once the laser scan data is obtained, the laser scan is terminated and the processes from step S104 onwards are carried out. In step S104, the deviation of the optical axis of the scanning light (Δθx in FIG. 4, Δθy in FIG. 5) is calculated based on the laser scan data related to the optical axis correction mark 106. This process is carried out by an optical axis direction error calculation unit 119.

[0069] The calculation of the optical axis deviation is performed once every 5 to 20 seconds. This process can be performed more frequently, but the processing load increases. Furthermore, if the frequency of this process is reduced, the interval at which correction data for the optical axis of the scanning light is obtained becomes shorter, and the accuracy of the correction decreases.

[0070] After obtaining the information on the deviation of the optical axis of the scanning light, the calculation interval for the deviation is set to T (5 to 20 seconds in this example), and the direction of the optical axis of the scanning light in the laser scan data of the surveying object is corrected within a range of T / 2 before and after the central acquisition time of the scan data used to calculate the deviation (step S105). This process is performed by the optical axis direction corrector 120.

[0071] After step S105, a point cloud is created based on the laser scan data in which the data on the optical axis direction for each scan point has been corrected (step S106). This process is performed in the point cloud generation unit 121.

[0072] (Conclusion) The laser scanning device 100 has a reflecting mirror 105, which is an optical system that emits laser scanning light and rotates, a horizontal rotation unit 103, which is a housing that holds the reflecting mirror 105 in a rotatable state, and an optical axis direction error calculation unit 119, which is an error calculation unit that calculates the error in the optical axis direction of the laser scanning light.The horizontal rotation unit 103 has an optical axis correction mark 106, which is a figure on which laser scanning is performed using the laser scanning light, arranged.The optical axis correction mark 106 is a figure (a triangle in this example) whose dimension in a direction parallel to the direction of the laser scanning is not constant in the X-axis direction (a direction perpendicular to the laser scanning direction), and the error is calculated based on the laser scan data of the optical axis correction mark 106.

[0073] In particular, in this embodiment, a change in error in a direction perpendicular to the scan direction is detected from a change in the width in the scan direction of the scan data of the optical axis correction mark 106 (the width of the range scanned by the mark), and a change in error in the scan direction is detected from a change in the position of the range scanned by the mark (a change in its center position). With this configuration, the error in the optical axis of the scanning light can be found based on the laser scan data of the optical axis correction mark 106, and by finding the positions of the scan points taking this error into consideration, the error in the point cloud caused by the above error can be reduced.

[0074] (others) The optical axis correction mark 106 is an optical surface having a specific shape with a reflectance different from that of its surroundings, which is provided for the purpose of reading its shape by laser scanning. In the above embodiment, by making the optical axis correction mark 106 have a relatively high reflectance and the surroundings have a relatively low reflectance, it is possible to identify the scanning light reflected from the optical axis correction mark 106 during laser scanning.

[0075] In order to enable identification of the scanning light from the optical axis correction mark 106 in laser scanning, it is also possible to make the optical axis correction mark 106 have a relatively low reflectance and the surrounding area have a relatively high reflectance.

[0076] The shape of the optical axis correction mark 106 may be a right triangle or a trapezoid. The sides that the scan line crosses may also be curved. The important thing is that the shape should be one that increases or decreases the scanned range depending on the value of Δθx.

[0077] Fig. 8 shows another example of the optical axis correction mark. Fig. 8(A) shows an example of a circular optical axis correction mark 131, and Fig. 8(B) shows an example of an elliptical optical axis correction mark 132.

[0078] In this case, the scan line is set to pass through the center of the circle or ellipse without any error. In this example, there is a difference in reflectance between portions 131a and 131b. There is also a difference in reflectance between portions 132a and 132b. This difference in reflectance determines whether Δθx in the case of Figure 4 is positive or negative. Here, examples of circles and ellipses are shown, but other shapes are also possible, such as a rhombus or a triangle with a base extending in the X-axis direction.

[0079] The optical axis correction mark may have a specific shape, such as the triangle shown as an example, that is raised (or depressed) from the surrounding area, and the shape of the optical axis correction mark can be determined from the difference in laser scan data in the height direction compared to the surrounding area.

[0080] It is also possible to use an optical system in which a light emitting unit and a light receiving unit are provided in the vertical rotation unit 104. In this case, when the vertical rotation unit 104 rotates vertically, the optical system including the light emitting unit and the light receiving unit also rotates vertically.

[0081] 2, part or all of the optical axis direction correction data acquisition unit 118, optical axis direction error calculation unit 119, optical axis direction correction unit 120, and point cloud generation unit 121 can also be realized in an external data processing device (for example, a personal computer or a data processing server) prepared separately from the laser scanning device 100. In this case, the scan data is sent to the external data processing device, and part or all of the processes related to the optical axis direction error calculation, optical axis direction correction, and point cloud creation are performed there.

[0082] 2. Second embodiment (overview) In the first embodiment, a case has been described in which there is no error in the orientation of the reflecting mirror 105 at the start of operation, and drift components Δθx and / or Δθy occur during operation.

[0083] In actual products, the orientation of the reflecting mirror 105 may not be ideal and may be tilted from the ideal state due to component precision, assembly precision, and changes over time. This tilt of the reflecting mirror 105 can be considered as three components: M, MH (M: mirror, H: horizontal axis), and V0, as shown in FIG. 9. M is the deviation from the 45° angle between the mirror rotation axis and the mirror surface. MH is the deviation of the mirror rotation axis from the horizontal axis reference plus the vertical component of the deviation of the optical axis from the mirror rotation axis reference. V0 is the deviation of the mirror 0 position from the vertical axis reference. These three components result in errors in the optical axis direction of the scanning light, which are factors that cause errors in the laser scan data.

[0084] In other words, the errors in the direction of the optical axis of the scanning light of the laser scanning device 100 include M, MH, V0, Δθx, and Δθy, and if higher accuracy is required, it is necessary to take these error components into account and correct the optical axis direction of each scanning light.

[0085] Regarding correction of the optical axis direction of the scanning light, if the correction amount in the Δθx direction is ΔX and the correction amount in the Δθy direction is ΔY, then there is a relationship of ΔX=MH+M+Δθx and ΔY=V0+Δθy.

[0086] Here, M, MH, and V0 can be obtained by a diagonal observation, which is a calibration process carried out in advance before the survey. Diagonal observation will be explained below.

[0087] In this embodiment, at least two reflective targets with different heights are used for the forward and backward observation. For example, the first reflective target is installed in a direction substantially horizontal to the laser scanning device 100, and the second reflective target is placed at a different height from the first reflective target. The two reflective targets are spaced apart by a distance that allows them to be separated by laser scanning. The distance from the laser scanning device 100 to the two reflective targets is several tens of meters.

[0088] Then, the two reflective targets are subjected to a first laser scan (forward observation) by the laser scanning device 100, and then a second laser scan (reverse observation) is performed after the horizontal rotation unit 103 is rotated horizontally by 180° (inverted) from that state. This results in two sets of forward and reverse laser scan data for the first reflective target and two sets of forward and reverse laser scan data for the second reflective target.

[0089] Here, we calculate the positive / negative error. The positive / negative error is the difference between two laser scan data points, one for the positive and one for the negative target. Here, the difference between the direction of the reflecting prism obtained by the positive observation and the direction of the reflecting prism obtained by the negative observation is obtained as the positive / negative error.

[0090] Two sets of positive and negative errors are obtained, one for the first reflecting prism and one for the second reflecting prism. From this data on positive and negative errors, M, MH, and V0 can be obtained using the following method.

[0091] First, V0 is calculated by V0 = (vertical angle error in positive and negative directions ÷ 2). In this case, multiple reflective targets are used, so V0 is calculated from the average value of the multiple obtained positive and negative directions errors.

[0092] Here, the measured value of the vertical angle of each reflective target corrected by V0 calculated above is set to Z. Also, using the positive and negative errors in the horizontal angle of each reflective target, calculate E = (positive and negative error in horizontal angle ÷ 2).

[0093] Then, with cos(Z) on the horizontal axis and Esin(Z) on the vertical axis, the graph shown in Fig. 10 is created. On this graph, the cos(Z) value (horizontal axis) and Esin(Z) value (vertical axis) for the first reflective target are plotted, and the cos(Z) value (horizontal axis) and Esin(Z) value (vertical axis) for the second reflective target are plotted.

[0094] Here, by creating a difference in height between the first and second reflective targets, the positions of the two plot points on the graph can be separated. Then, a straight line passing through these two plot points is created. If there are three or more plot points, a straight line fitting to the distribution of the points is created. The slope of this line is MH, and the intercept value is M. In this way, the values ​​of M, MH, and V0 in Figure 9 can be determined by forward and backward observation.

[0095] (Example of processing procedure) It is assumed that, when the laser scanning device 100 is shipped as a product, during the final assembly process, during maintenance, etc., the waveform of the light intensity distribution measurement of the laser scanning light for the optical axis correction mark 106 described in the first embodiment is detected, initial values ​​for the width and center position of the waveform are determined, and further the above-mentioned forward and reverse observation is performed to determine initial values ​​for M, MH, and V0. It is also assumed that during laser scanning, the optical axis direction of the scanning light is corrected taking into account the above-mentioned initial values ​​of M, MH, and V0.

[0096] Here, an example will be described in which correction is performed for the influence of the drift components Δθx and θy that occur during operation of the laser scanning device 100, and the variations ΔM, ΔMH, and ΔV0 from the initial values ​​of M, MH, and V0.

[0097] First, the laser scanning device 100 is installed at the surveying site. At this time, the horizontal position of the laser scanning device 100 is ensured. Next, the waveform of the light intensity distribution measurement of the laser scanning light for the optical axis correction mark 106 described in the first embodiment is detected, and the amount of change in the width of the waveform from the initial value (width change amount) and the amount of change in the center position of the waveform (center position change amount) are calculated.

[0098] Next, the above-mentioned multiple reflective targets are used to perform forward and reverse observations to determine M, MH, and V0, and then ΔM, ΔMH, and ΔV0, which are the differences from the initial values.

[0099] The amount of change from the initial value of the width of the waveform of the light intensity distribution measurement of the laser scanning light for the optical axis correction mark 106 (width change amount) includes the influence of ΔMH. That is, there is a relationship of width change = ΔMH + Δθx. Furthermore, the amount of change in the center position of the waveform of the light intensity distribution measurement (center position change amount) includes the influence of ΔV0. That is, there is a relationship of (center position change amount) = ΔV0 + Δθy.

[0100] From the above relational expressions, Δθx and θy can be found. In this way, ΔM, ΔMH, ΔV0, Δθx, and Δθy can be obtained. These processes are performed in the optical axis direction error calculation unit in Figure 2.

[0101] Next, a laser scan is performed for surveying to obtain point cloud data (laser scan point cloud). Then, the optical axis of the scanning light for each point in the obtained laser scan point cloud is corrected as ΔX=ΔMH+ΔM+Δθx and ΔY=ΔV0+Δθy. This process is performed by the optical axis direction correction unit shown in Figure 2.

[0102] As the laser scanning device 100 continues to operate, a drift in Δθx and Δθy occurs due to the rise in temperature inside the housing during operation. This fluctuation is acquired by the above-mentioned processing performed at appropriate times, and the result is used to correct the laser scan data (correct errors).

[0103] As described above, since the error factors ΔM, ΔMH, and ΔV0 are acquired in advance, the influence of these factors can be eliminated and the drift components Δθx and Δθy can be detected with high accuracy.

[0104] (others) It is also possible to configure the laser scanning device 100 so that a temperature sensor is placed inside the device and Δθx and Δθy are detected based on the temperature change detected by the temperature sensor. It is also possible to configure the device so that Δθx and Δθy are constantly detected while laser scanning is being performed, and the direction of the optical axis of the scanning light is corrected when the deviation of Δθx and / or Δθy from the initial value exceeds a predetermined threshold. [Explanation of symbols]

[0105] 100...laser scanning device, 101...tripod, 102...base part, 103...horizontal rotation part, 103a...one head of the double-headed structure, 103b...other head of the double-headed structure, 104...vertical rotation part, 105...reflecting mirror, 106...optical axis correction mark, 107...camera.

Claims

1. an optical system that emits a laser scanning beam and rotates; a housing that holds the optical system in a rotatable state; an error calculation unit that calculates an error in the optical axis direction of the laser scanning light; and a figure to be laser scanned by the laser scanning light is arranged on the housing; the figure has a shape that does not have a constant size in a direction parallel to the direction of the laser scan; A laser scanning device that calculates the error based on laser scan data of the graphic.

2. In calculating the error, 2. The laser scanning device according to claim 1, wherein an error Δθx of the optical axis in a direction perpendicular to the scanning direction is calculated based on a dimension of the figure in the scanning direction obtained by laser scanning the figure.

3. In calculating the error, 2. The laser scanning device according to claim 1, wherein the error Δθy of the optical axis in the scanning direction is calculated based on a center position in the scanning direction of the scan data of the graphic.

4. In calculating the error, When the error of the optical axis in the direction perpendicular to the scanning direction is Δθx and the error of the optical axis in the scanning direction is Δθy, First scan data, which is scan data of the figure acquired in advance, is compared with second scan data, which is scan data of the figure acquired during operation of the laser scanning device; The Δθx is calculated based on a change in width in the scanning direction between the first scan data and the second scan data; 2. The laser scanning device according to claim 1, wherein the Δθy is calculated based on a change in the center position in the scanning direction between the first scan data and the second scan data.

5. The laser scanning device according to claim 1 , further comprising an optical axis direction correcting unit that corrects information relating to the optical axis of the scanning light based on the error.

6. The error calculation unit 2. The laser scanning device according to claim 1, further comprising: a calculation of an error in the direction of the optical axis of the laser scanning light based on the results of laser scanning a plurality of targets in directions that are changed by 180 degrees in the horizontal direction.

7. an optical system that emits a laser scanning beam and rotates; a housing that holds the optical system in a rotatable state; A method for processing laser scan data to obtain an error of an optical axis in a laser scanning device comprising: a figure to be laser scanned by the laser scanning light is arranged on the housing; the figure has a shape that does not have a constant size in a direction parallel to the direction of the laser scan; A laser scan data processing method in which the error is calculated based on laser scan data of the figure.

8. an optical system that emits a laser scanning beam and rotates; a housing that holds the optical system in a rotatable state; A program for causing a computer to process laser scan data to obtain an error in an optical axis in a laser scanning device comprising: a figure to be laser scanned by the laser scanning light is arranged on the housing; the figure has a shape that does not have a constant size in a direction parallel to the direction of the laser scan; A program that causes a computer to calculate the error based on laser scan data of the figure.

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