Laser scanning control device, laser scanning device, laser scanning control method and program

Abstract

To provide a technology that solves the problem pertaining to strong reflected light from a reflector target in a laser scan.SOLUTION: Provided is a laser scan control device 500 for controlling a laser scan by a laser scan device 200, comprising: a control unit that causes a first laser scan which is carried out under a condition that a detection unit of the laser scan device 200 is saturated and a second laser scan which is carried out under a condition that no saturation occurs to be executed by reflection from reflection prisms 300 and 40; a distance acquisition unit that acquires the distance to the reflection prisms 300 and 400 on the basis of the first laser scan; and an adjustment unit that adjusts the intensity of detection light in the laser scans, on the basis of the distance to the reflection prisms 300 and 400 acquired by the distance acquisition unit in the second laser scan.SELECTED DRAWING: Figure 1

Description

Technical Field

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

Background Art

[0002] For example, laser scanning is used as a surveying means at a construction site. In this technology, laser scanning is performed with a reflection prism installed as a target.

[0003] At this time, the reflected light from the reflection prism is strong, and the light receiving element of the laser scanning device is saturated. Therefore, the positioning of the reflection prism is performed through a dimming filter. This technology is described in, for example, Patent Document 1.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In the above-mentioned positioning of the reflection prism through a dimming filter, an operation of adjusting to an appropriate dimming state is required. This is because if the degree of dimming is large, the intensity of the detected distance measuring light is small and the distance measuring accuracy decreases, while if the degree of dimming is small, the intensity of the detected distance measuring light is large, leading to a decrease in distance measuring accuracy due to saturation of the light receiving part.

[0006] A method of experimentally positioning the reflection prism and finely adjusting or switching the dimming filter so that the distance measuring light reaches an appropriate detection level can be considered. However, this method increases the work procedure and is not practical. Currently, a compromise is made in terms of the positioning accuracy of the reflection prism, and a dimming filter that is generally judged to be appropriate is used.

[0007] Against this backdrop, the present invention aims to provide a technology that solves the problem of strong reflected light from a reflective target in laser scanning. [Means for solving the problem]

[0008] The present invention relates to a laser scanning device equipped with a light-receiving unit, and comprises a control unit that causes the device to perform a first laser scan under conditions in which the light-receiving unit is saturated by reflection from a measuring reflector, and a second laser scan under conditions in which such saturation does not occur, a distance acquisition unit that acquires the distance to the measuring reflector based on the first laser scan, and an adjustment unit that adjusts the intensity of the light received by the light-receiving unit based on the distance to the measuring reflector in the second laser scan.

[0009] In the present invention, the intensity of the detected light is adjusted by an optical attenuator placed in front of the light receiving unit for the detected light. In the present invention, the optical attenuator is adjusted so that the attenuation is relatively small when the distance to the measuring reflector is relatively far, and so that the attenuation is relatively large when the distance to the measuring reflector is relatively close.

[0010] In the present invention, one embodiment is one in which the optical attenuator is adjusted so that the intensity of the detected light remains constant regardless of the distance to the measuring reflector. In the present invention, one embodiment is one in which the intensity of the detected light is adjusted by adjusting the intensity of the measuring light irradiated from the light-emitting part of the laser scanning device onto the scanning target.

[0011] The present invention can also be understood as a laser scanning device that incorporates the laser scanning control device described above.

[0012] In the present invention, the reflector for surveying is a reflective prism, and includes a reflective prism detection unit for detecting reflected light from the reflective prism, wherein in the second laser scan, the reflective prism detection unit detects reflected light from the reflective prism when the output of the light receiving unit is above a certain threshold, and the certain threshold is a value in the range of 5% to 50% of the maximum value of the output of the light receiving unit in the second laser scan.

[0013] In the present invention, the reflector for surveying is a reflective prism, and includes a reflective prism detection unit for detecting reflected light from the reflective prism. The reflective prism detection unit detects, in the first laser scan, reflected light from the reflective prism when the output of the light receiving unit at a position at a distance greater than or equal to a specific distance from the laser scanning device is greater than or equal to a specific threshold. The result of the first scan includes a first group of bright spots whose output of the light receiving unit is less dependent on distance and a second group of bright spots whose output of the light receiving unit is more dependent on distance. The specific distance is defined as the shortest distance at which the maximum value of the output of the light receiving unit for the second group of bright spots is 70% or less of the maximum value of the output of the light receiving unit for the first group of bright spots. The specific threshold is a value exceeding the maximum value of the output of the light receiving unit for the second group of bright spots at the specific distance.

[0014] The present invention can also be understood as a method for controlling a laser scan using a laser scanning device equipped with a light-receiving unit, comprising: a first laser scan performed under conditions in which the light-receiving unit is saturated by reflection from a measuring reflector; and a second laser scan performed under conditions in which such saturation does not occur; the distance to the measuring reflector is obtained based on the first laser scan; and the intensity of the light received by the light-receiving unit is adjusted based on the distance to the measuring reflector in the second laser scan.

[0015] The present invention can also be understood as a program for controlling a laser scanning device provided with a light receiving unit, the program causing a computer to perform a first laser scan under conditions where the light receiving unit saturates due to reflection from a reflector for surveying, a control unit for causing the computer to perform a second laser scan under conditions where saturation does not occur, a distance acquisition unit for acquiring the distance to the reflector for surveying based on the first laser scan, and an adjustment unit for adjusting the intensity of light received by the light receiving unit based on the distance to the reflector for surveying in the second laser scan.

Effects of the Invention

[0016] According to the present invention, problems related to strong reflected light from a reflector target in laser scanning can be solved.

Brief Description of the Drawings

[0017] [Figure 1] A diagram showing an overview of laser scanning. [Figure 2] A diagram showing the appearance of a laser scanning device. [Figure 3] A block diagram of a laser scanning device and a processing device. [Figure 4] A block diagram of an optical system. [Figure 5] A diagram showing the principle of control. [Figure 6] A flowchart showing an example of a processing procedure. [Figure 7] A block diagram of another variation of the optical system. [Figure 8] A block diagram of another variation of the optical system. [Figure 9] A diagram of data showing the relationship between distance in laser scanning and the output of the light receiving unit. [Figure 10] A diagram of data showing the relationship between distance in laser scanning and the output of the light receiving unit.

Modes for Carrying Out the Invention

[0018] 1. First Embodiment (Overview) Fig. 1 shows a state where a laser scanning device 200, and reflecting prisms 300 and 400 as targets are installed at a site where point cloud data is to be acquired.

[0019] Fig. 1 also shows a processing device 500 that processes data obtained by laser scanning and controls the laser scanning device 200. The processing device 500 is a computer, and here, an example of using a PC (personal computer) is shown.

[0020] The reflecting prisms 300 and 400 are installed at points whose positions in the absolute coordinate system are known. The absolute coordinate system is a coordinate system used in maps and GNSS. Note that a local coordinate system can also be used as the coordinate system.

[0021] In Fig. 1, scan targets other than the reflecting prisms are not shown, but in reality, there are laser scan targets (e.g., terrain and buildings) other than the reflecting prisms.

[0022] The reflecting prisms 300 and 400 reflect incident light by changing its direction by 180°. The reflecting prisms 300 and 400 use commercially available ones for surveying. Other reflectors such as retroreflectors can also be used in addition to the reflecting prisms.

[0023] The laser scanning device 200 is installed at a position suitable for laser scanning, but its position and orientation in the absolute coordinate system are unknown. In this example, the laser scanning device 200 performs a first wide - range laser scan (e.g., a full - circle scan) and a second laser scan focused on the reflecting prisms.

[0024] Here, a wide - range point cloud data is obtained by the first laser scan, but the position of each point in the absolute coordinate system at that stage is unknown. This is because the position and orientation of the laser scanning device 200 in the absolute coordinate system are unknown.

[0025] Therefore, a second laser scan is performed to determine the position of the reflective prisms 300 and 400, which are placed at known points in the absolute coordinate system, and the position and orientation of the laser scanning device 200 in the absolute coordinate system are calculated using the resection method.

[0026] Knowing the position and orientation of the laser scanning device 200 in the absolute coordinate system allows the point cloud data obtained from the first laser scan to be assigned coordinates in the absolute coordinate system, thus obtaining point cloud data in the absolute coordinate system. The number of reflective prisms may be three or more.

[0027] In the first laser scan described above, the reflected light from the reflective prisms 300 and 400 is too strong, causing the light-receiving unit 202 of the laser scanning device 200 to saturate, and reducing the distance measurement accuracy of the reflective prisms 300 and 400. In other words, the positioning accuracy of the reflective prisms 300 and 400 is reduced in the first laser scan.

[0028] Therefore, a second laser scan is performed to accurately position the reflective prisms 300 and 400. At this time, in order to obtain high positioning accuracy, the input level of the distance measuring light to the photodetector is weakened using a variable optical attenuator. The control of this variable optical attenuator is performed based on the distance information of the reflective prisms obtained in the first laser scan.

[0029] Furthermore, saturation due to strong input in the light-receiving unit 202 mainly occurs in the photodetector element. If the degree of saturation is small, distortion of the output of the photodetector element and a plateauing of the output will occur, but the accuracy of distance measurement will be ensured. If the degree of saturation is large, the distortion of the waveform of the output of the photodetector element becomes significant, errors occur in distance measurement using the phase difference of the waveform, and the accuracy of distance measurement decreases.

[0030] The second scan is performed under conditions that do not adversely affect the accuracy of the latter distance measurement (i.e., conditions that ensure the accuracy of the distance measurement). Therefore, in the second scan, saturation at the light-receiving unit 202 at a level that does not adversely affect the accuracy of the distance measurement is acceptable.

[0031] (Hardware configuration) Figure 2 shows the external appearance of the laser scanning device (laser scanner) 200. The laser scanning device 200 comprises a tripod 211, a base 212 fixed to the top of the tripod 211, a horizontal rotating part 213 which is a rotating body that can rotate horizontally on the base 212, and a vertical rotating part 214 which is a rotating body that can rotate vertically relative to the horizontal rotating part 213. The laser scanning device 200 is operated by an external controller (operating terminal) (not shown) that is wirelessly connected.

[0032] The vertical rotating unit 214 is equipped with an optical unit 215 that emits and receives laser scan light. The optical unit 215 emits pulsed laser scan light. This pulsed emission occurs along a direction perpendicular to the axis of rotation (the axis extending horizontally) of the vertical rotating unit 214 (a vertical plane) as the unit rotates. In this case, the optical unit 215 emits pulsed laser scan light along the vertically angular direction (the angular direction of elevation and depression).

[0033] By rotating the horizontal rotation unit 213 horizontally and the vertical rotation unit 214 vertically, the optical unit 215 emits pulsed laser scanning light, and the optical unit 215 receives the reflected light from the object, thereby performing a laser scan of the surroundings.

[0034] As the horizontal rotation unit 213 rotates horizontally simultaneously with the scan along the vertical angle (vertical scan), the scan line along the vertical angle (vertical scan line) moves in a way that causes it to shift along the horizontal angle (horizontal direction). Note that if horizontal rotation is performed simultaneously with vertical rotation, the scan along the vertical angle (vertical scan line) will not be perfectly aligned with the vertical direction, but will be slightly slanted. Note that if the horizontal rotation unit 213 does not rotate, the scan along the vertical angle (vertical scan line) will be aligned with the vertical direction.

[0035] The rotation of the horizontal rotating section 213 and the vertical rotating section 214 is performed by motors. The horizontal rotation angle of the horizontal rotating section 213 and the vertical rotation angle of the vertical rotating section 214 are precisely measured by encoders.

[0036] Each laser scan beam is a single pulsed ranging beam, and one laser scan beam measures the distance to the scan point, which is the reflection point where the laser scan beam strikes. From this distance value and the direction of irradiation of the laser scan beam, the position of the scan point (reflection point of the laser scan beam) relative to the laser scanning device 200 is calculated.

[0037] The laser scan point cloud output from the laser scanning device 200 can be configured to output distance and direction data for each point (each scan point). It is also possible for the laser scanning device 200 to calculate the position of each point in a specific coordinate system and output the 3D coordinate position of each point as point cloud data. Furthermore, the laser scan point cloud data also includes information on the brightness (intensity of reflected light) of each scan point.

[0038] Figure 3 is a block diagram of the laser scanning device 200 and the processing device 500. The laser scanning device 200 includes a light-emitting unit 201, a light-receiving unit 202, a distance-measuring unit 203, a direction acquisition unit 204, a light-emitting control unit 205, a drive control unit 206, a variable optical attenuator 207, a communication device 208, and a storage unit 209.

[0039] Figure 4 is a block diagram of the optical system of the laser scanning device 200. The light-emitting unit 201 has a light-emitting element that emits laser scanning light, an optical system related to light emission, and peripheral circuits. The laser scanning light emitted by the light-emitting unit 201 is emitted to the outside from the optical section 215 in Figure 2 via the photosynthesis / separation unit 250. The photosynthesis / separation unit 250 is an optical system that separates and combines the optical paths of the emitted light and the incident light using half mirrors and dichroic mirrors.

[0040] The light-receiving unit 202 has a light-receiving element for receiving laser scan light, an optical system related to light reception, and peripheral circuits. The reflected light of the laser scan light taken in from the optical unit 215 is guided from the photosynthesis / separation unit 250 to the variable optical attenuator 207, and further guided to the light-receiving unit 202. The variable optical attenuator 207 will be described later.

[0041] The distance measuring unit 203 calculates the distance from the laser scanning device 200 to the reflection point (scan point) of the laser scan light based on the output of the light receiving unit 202. In this example, a reference optical path is provided inside the laser scanning device 200. The laser scan light output from the light-emitting element is split into two; one is irradiated onto the target from the optical unit 215 as laser scan light, and the other is guided to the reference optical path as reference light.

[0042] The laser scan light reflected from the target and captured by the optical unit 215, along with the reference light propagated along the above-mentioned reference optical path, are combined and input to the light receiving unit 202. The laser scan light and the reference light have different propagation distances, so the reference light is detected by the light receiving element first, followed by the laser scan light.

[0043] Here, observing the output waveform of the photodetector, the detection waveform of the reference light is output first, followed by the detection waveform of the laser scan light after a time delay. The distance to the reflection point of the laser scan light is calculated from the phase difference (time difference) between these two waveforms. It is also possible to calculate the distance from the flight time of the laser scan light.

[0044] The direction acquisition unit 204 acquires the direction of the optical axis of the laser scan beam. The direction of the optical axis is obtained by measuring the angle of the optical axis in the horizontal direction (horizontal angle) and the angle of the optical axis in the vertical direction (elevation angle or depression angle). The direction acquisition unit 204 has a horizontal angle detection unit 204a and a vertical angle detection unit 204b.

[0045] The horizontal angle detection unit 204a detects the horizontal rotation angle of the horizontal rotation unit 213. Horizontal rotation is rotation with the vertical direction as the axis of rotation. The angle is detected by an encoder. The vertical angle detection unit 204b detects the vertical rotation angle (elevation angle or depression angle) of the vertical rotation unit 214. Vertical rotation is rotation with the horizontal direction as the axis of rotation. The angle is detected by an encoder.

[0046] By measuring the horizontal rotation angle of the horizontal rotating section 213 and the vertical rotation angle of the vertical rotating section 214, the direction of the optical axis of the laser scan beam as seen from the laser scanning device 200, i.e., the direction of the scan point, can be determined.

[0047] The light emission control unit 205 controls the timing of light emission of the laser scan light in the light emission unit 201. The drive control unit 206 includes a horizontal rotation drive control unit 206a that controls the drive to rotate the horizontal rotation unit 213 horizontally, and a vertical rotation drive control unit 206b that controls the drive to rotate the vertical rotation unit 214 vertically.

[0048] The variable optical attenuator 207 attenuates the light incident on the light receiving unit 202 (see Figure 4). This attenuation amount (attenuation rate) is variable. The attenuation amount is varied based on the distance to the target calculated by the distance measuring unit 203.

[0049] Variable optical attenuators 207 can be of various types, including those that adjust transmittance by rotating a semi-transparent disc set to gradually change transmittance in the circumferential direction, and those that control the transmittance of liquid crystal. Variable optical attenuator modules are commercially available and can be selected and used as appropriate.

[0050] Because the reflection from the reflective prism is strong, the photodetector saturates, causing errors in the distance measurement. For example, experiments by the inventors have shown that in a laser scanner capable of measuring distance with an accuracy of a few millimeters, reflected light from a reflective prism results in errors at the centimeter level. The degree of this error increase is not constant, partly due to the nonlinear operation of the photodetector, but it is several times to about 10 times the normal measurement error.

[0051] By placing the variable optical attenuator 207 in front of the light receiving unit, the intensity of the light entering the light receiving unit is reduced, thereby suppressing the occurrence of the above-mentioned problems.

[0052] The communication device 208 communicates with the processing unit 500, an external controller (not shown), and other devices. Communication is performed using wired, wireless LAN, mobile phone lines, etc. The storage unit 209 is composed of semiconductor memory or a hard disk drive and stores the operation program, data, and data obtained from the operation process and results of the laser scanning device 200 that are necessary for its operation.

[0053] The processing unit 500 controls the operation of the laser scanning device 200 and processes the point cloud data (laser scan point cloud data) obtained by the laser scanning device 200. It is also possible to integrate part or all of the processing unit 500 into the laser scanning device 200. It is also possible to implement part or all of the functions of the processing unit 500 in a data processing server.

[0054] The processing unit 500 is comprised of a PC (personal computer). It is also possible to configure part or all of the processing unit 500 with dedicated hardware.

[0055] The processing unit 500 includes a laser scanning device control unit 501, a reflection prism detection unit 502, a distance acquisition unit to the reflection prism 503, a control unit for a variable optical attenuator 504, a point cloud data creation unit 505, a communication device 506, and a storage unit 507.

[0056] The laser scanning device control unit 501 generates control signals to control the operation of the laser scanning device 200. These control signals are transmitted from the communication device 506 to the laser scanning device 200. These control signals include control signals for controlling the laser scan and control signals for controlling the variable attenuator 207.

[0057] The reflective prism detection unit 502 determines, based on the intensity of the measurement light (scan light reflected from the target) detected by the light receiving unit 202, whether or not the measurement light was reflected from a reflective prism. Furthermore, if it was reflected from a reflective prism, it identifies and detects it as reflected light from a reflective prism.

[0058] The distance acquisition unit 503 acquires the distance (measured distance value) to the reflective prism detected by the reflective prism detection unit 502. This distance is calculated by the distance measurement unit 203.

[0059] The control unit 504 of the variable optical attenuator generates a control signal to adjust the attenuation amount (the degree to which light is attenuated) of the variable optical attenuator 207. Based on the distance measurement information of the reflecting prism, the variable optical attenuator control unit 504 adjusts the incident light to the light receiving unit 202 to a specific level. The principle of this is explained below.

[0060] Figure 5 illustrates the principle. In Figure 5(A), the horizontal axis represents the distance to the reflection point (relative value), and the vertical axis represents the light receiving efficiency. The light receiving efficiency is the ratio of the emitted light to the incident light ((incident light intensity / emitted light intensity) × 100 (%)). The light receiving efficiency decreases with increasing distance and increases with decreasing distance. Note that the decrease in light receiving efficiency at very short distances in Figure 5(A) is due to the nonlinearity of the optical system.

[0061] Therefore, as shown in Figure 5(B), the greater the distance, the smaller the attenuation of the optical attenuator 208, and the closer the distance, the larger the attenuation of the variable optical attenuator 207. In Figure 5(B), the horizontal axis is the distance to the reflection point (relative value), and the vertical axis is the transmittance of the variable optical attenuator 207. The transmittance in the variable optical attenuator 207 is (outgoing light intensity / incident light intensity) × 100 (%). The lower the transmittance, the larger the attenuation in the variable optical attenuator 207.

[0062] As shown in Figure 5(B), by adjusting the transmittance according to the distance, the intensity of the reflected light from the reflective prism detected by the light-receiving element of the light-receiving unit 202 can be kept at a constant level, regardless of the distance to the reflective prism, as shown in Figure 5(C).

[0063] In other words, when the distance is short, the attenuation by the variable optical attenuator 207 is increased (i.e., the transmittance is reduced), and when the distance is long, the opposite control is performed. Ideally, this makes it possible to keep the intensity of the measurement light incident on the light receiving unit 202 constant (see Figure 5(C)).

[0064] Here, we first obtain the appropriate light intensity value (appropriate light reception intensity) for receiving light with the light receiving unit 202, and then determine the transmittance of the variable light attenuator 207 necessary to achieve the above appropriate light reception intensity according to the distance, as well as the control amount required to achieve this transmittance.

[0065] Specifically, under the conditions that the distance to the reflective prism is X, the transmittance in the variable optical attenuator 207 is A, and the light intensity received by the light receiving unit 202 is set to an appropriate constant value (or an appropriate range), the relationship between X and A is A = f(X). As a general trend, when X increases (the distance to the reflective prism increases), A increases (more transmission: less attenuation), and when X decreases (the distance to the reflective prism decreases), A tends to decrease (more attenuation).

[0066] This relationship is acquired in advance, and based on this relationship, the variable optical attenuator control unit 209 adjusts the attenuation amount of the variable optical attenuator 207 (adjusts the transmittance) according to the distance measurement value of the reflecting prism. This adjustment is performed by sending a control signal (for example, a control voltage) from the variable optical attenuator control unit 209 to the variable optical attenuator 207.

[0067] The point cloud data creation unit 505 calculates the position and orientation of the laser scanning device 200 in the absolute coordinate system based on the positioning data of the reflective prisms 300 and 400 obtained in the second laser scan, and performs processing to associate the point cloud data obtained in the first laser scan with the absolute coordinate system based on this calculation.

[0068] The communication device 506 communicates with the laser scanning device 200 and other devices. Communication is performed using wired, wireless LAN, mobile phone lines, etc. The storage unit 507 is composed of semiconductor memory or a hard disk drive and stores the operation program, data, and data obtained from the operation process and results of the operation that are necessary for the operation of the processing unit 500.

[0069] (An example of processing) Figure 6 shows an example of the processing procedure. The program that executes the processing shown in Figure 6 is stored in the storage unit 507 of the processing unit 500 and read and executed by the CPU of the computer that constitutes the processing unit 500. It is also possible to store the program in a suitable storage medium and read and use it from there.

[0070] Prior to the process shown in Figure 6, the laser scanning device 200 and reflective prisms 300 and 400 are first installed at the site where the laser scan will be performed. Here, the position and orientation of the laser scanning device 200 are unknown, while the reflective prisms 300 and 400 are installed at points whose positions in the absolute coordinate system are known. These points whose positions in the absolute coordinate system are determined by prior surveying work. Note that a local coordinate system can also be used as the coordinate system.

[0071] At this stage, a normal scan (first laser scan) is performed (step S101). The normal scan is performed over the area where point cloud acquisition is planned. This planned area may be the entire circumference or a limited area. The normal scan is for obtaining the point cloud of the surveyed object and is performed under the conditions for obtaining a normal laser scan point cloud.

[0072] A normal scan yields distance and direction data (point cloud data) from the optical origin (the point that serves as the origin for positioning) of the laser scanning device 200 to each point. At this stage, the position and orientation of the laser scanning device 200 in the absolute coordinate system are unknown, so the relationship between the above point cloud data and the absolute coordinate system is unknown.

[0073] Next, from the point cloud obtained in step S101, points where the light intensity overflowed at the photodetector (the incident light was too strong and the photodetector became saturated) are extracted as reflection points of the reflective prism (step S102).

[0074] Normal scanning requires detecting reflected light from sources other than the reflective prism, so the intensity of the emitted light and the detection sensitivity of the incident light are set to achieve this purpose. On the other hand, under normal scanning conditions, the reflected light from the reflective prism is too strong, causing the overflow described above.

[0075] In laser scanning, the detection intensity of the detected light (output level of the photodetector) is also acquired as point (reflection point) information. In step S102, points with detection intensity exceeding a predetermined level are extracted.

[0076] Next, the distance to the point extracted in step S102 (distance from the laser scanning device 200) is obtained (step S103). The distance obtained here is the distance calculated by the distance measuring unit 203. Because the light-receiving element is saturated, the distance measured here contains a larger error than usual and is of unsatisfactory accuracy for use in surveying, but it is not a problem for setting the attenuation amount of the variable optical attenuator 207, which will be described later. The processing in step S102 is performed by the distance acquisition unit 503 to the reflecting prism.

[0077] Next, based on the distance to the reflecting prism obtained in step S103, the attenuation amount (transmittance) of the variable optical attenuator 207 is set (step S104). This process is performed in the control unit 504 of the variable optical attenuator 207.

[0078] Next, a dimming scan (second laser scan) is performed (step S105). The dimming scan is a laser scan based on the conditions set in step S104. In the dimming scan, the laser scan is performed while adjusting so that the light receiving unit 202 does not become saturated by the reflected light from the reflective prisms 300 and 400. That is, the laser scan is performed by attenuating the detected light entering the light receiving unit 202 with the variable optical attenuator 207.

[0079] Dimming scans enable accurate positioning of reflective prisms 300 and 400. The dimming scan is performed within a limited range of reflective prisms 300 and 400 to minimize unnecessary scans. Of course, dimming scans can also be performed around the entire circumference.

[0080] By performing a dimming scan, the reflective prisms 300 and 400 are accurately positioned, and the relative positions of the laser scanning device 200 and the reflective prisms 300 and 400 can be determined.

[0081] After performing the dimming scan, the position and orientation of the laser scanning device 200 in the absolute coordinate system are determined using the resection method (step S106).

[0082] The principle of the process performed in step S106 is briefly explained below. First, the positional relationship between the laser scanning device 200, the reflective prism 300, and the reflective prism 400 can be determined from the results of the dimming scan in step S105. Therefore, the shape of a triangle with the positions of the laser scanning device 200, the reflective prism 300, and the reflective prism 400 as its vertices is determined.

[0083] On the other hand, the positions of the reflecting prisms 300 and 400 in absolute coordinate systems are known. That is, the positions of the two vertices of the above triangle in absolute coordinate systems are determined. Therefore, the position of the laser scanning device 200, which is the remaining vertex of the above triangle, in absolute coordinate systems can be determined.

[0084] Furthermore, since the orientation of each side of the triangle in the absolute coordinate system is known, the orientation of the laser scanning device 200 in the absolute coordinate system can be determined. In this way, the position and orientation of the laser scanning device 200 in the absolute coordinate system can be determined. This process is performed by the point cloud data creation unit 505. Alternatively, an external orientation element calculation unit may be provided, and the process in step S106 may be performed there.

[0085] After step S106, data is obtained by associating the point cloud data obtained by the normal scan with an absolute coordinate system. In this way, point cloud data that can be handled on an absolute coordinate system by the laser scanning device 200 is obtained (step S107).

[0086] For example, by associating each point with the laser scanning device 200 as the origin, data is created showing the distance and direction of each point, the coordinates of the origin in the absolute coordinate system, and the orientation of the laser scanning device in the absolute coordinate system. This becomes point cloud data that can be handled in the absolute coordinate system.

[0087] Alternatively, point cloud data obtained by a normal scan may be converted into point cloud data described in an absolute coordinate system. That is, by knowing the position and orientation of the laser scanning device 200 in the absolute coordinate system, the point cloud data obtained by a normal scan can be coordinated to coordinates in the absolute coordinate system. Specifically, regarding the translation and rotation information required for the coordinate transformation, the position of the laser scanning device 200 in the absolute coordinate system provides translation information, and the orientation of the laser scanning device 200 in the absolute coordinate system provides rotation information. Based on this information, the point cloud data obtained by the normal scan is translated and then rotated to obtain point cloud data described in an absolute coordinate system. This process may be performed in step S107.

[0088] (Superiority) Excessive input to the light receiving unit 202 is suppressed, solving the problem of strong reflected light from the reflective target in laser scanning. Furthermore, the attenuation amount of the optical attenuator is set according to the distance to the reflective prism to ensure high-precision light receiving conditions, enabling highly accurate distance measurement of the reflective prism. Therefore, the accuracy of the final point cloud data can be improved.

[0089] 2. Second Embodiment Figure 7 shows an example in which a variable optical attenuator 207 is placed in front of the light-emitting unit 201. In this case, the measurement light emitted from the light-emitting unit 201 is attenuated by the attenuator and adjusted to obtain a reflection intensity appropriate for positioning the reflective prism.

[0090] 3. Third Embodiment Figure 8 shows a case where a variable output light-emitting unit 260, which can vary the light emission intensity, is used. In this case, the light emission intensity of the variable output light-emitting unit 260 is adjusted by the control unit 261 so that an appropriate reflection intensity is obtained for positioning the reflective prism.

[0091] 4. Fourth Embodiment It is also possible to use a device that allows adjustment of the sensitivity of the photodetector. For example, an avalanche photodiode used as a photodetector can have its amplification factor controlled by the applied reverse voltage. Using this, the amplification factor can be lowered when detecting strong reflected light (when the distance is short) and increased when detecting weak reflected light (when the distance is far). If the dynamic range cannot be ensured by adjusting only the amplification factor, this can be addressed by using a variable optical attenuator as described in other embodiments, or by adjusting the light emission intensity.

[0092] 5. Fifth Embodiment In surveying work, there are sometimes reflectors other than reflective prisms that reflect visible light with high reflectivity (hereinafter referred to as "reflectors"). Examples of reflectors include reflective tape for safety, various signs, and taillights of vehicles and heavy machinery. Since the wavelength of the measurement light from a laser scanner is approximately 500nm to 1500nm, the light reflected by the laser scanner is also reflected with high efficiency from the above-mentioned reflectors.

[0093] Given this background, in steps S102 and S105 of Figure 6, it is necessary to prevent the misdetection of reflected light from reflectors other than the reflective prism as reflected light from the reflective prism.

[0094] In this embodiment, when there are reflectors other than the reflective prism, such as signs or reflectors, the detection of the reflective prism is performed in two stages, suppressing the above-mentioned false detection. Here, the first stage of detection is performed on the results of a normal scan, and the second stage of detection is performed on the results of a dimmed scan.

[0095] As described later, in the first stage of detection, it may not be possible to distinguish between a reflective prism and a reflector at close range, potentially leading to the false detection of a reflector. However, in the second stage of detection, a reflective prism can be reliably detected by distinguishing it from a reflector that is a non-reflective prism. Here, a non-reflective prism refers to a reflector that is not a reflective prism (such as a highly reflective object like reflective tape). The processing related to the first and second stages of detection described above is performed in the reflective prism detection unit 502.

[0096] The following provides a detailed explanation. First, let's describe the first stage of detection. Figure 9 shows the measured relationship between the detection intensity of reflected light from various reflectors (vertical axis) and the distance (m) from the laser scanner to the reflective object during a normal scan. Here, the detection intensity on the vertical axis is the relative value of the output of the light receiving unit 202.

[0097] In Figure 9, the safety vest is a vest equipped with a sheet-like reflective material. The signs, taillights, and guardrail reflectors are equipped with reflectors made of light-reflective material to enhance visibility. Reflective prisms 1 and 2 are commercially available reflective prisms with different model numbers for surveying purposes.

[0098] Figure 9 shows that when the distance from the laser scanner is somewhat far (more than 60m in the case of Figure 9), there is a difference between the output of the light receiving unit 202 that receives reflected light from the reflecting prism and the output of the light receiving unit 202 that receives reflected light from the reflector.

[0099] This phenomenon is used in step S102 to exclude (not select) reflected light from the non-reflective prism. In this example, the threshold is set at an output value of 8000 on the vertical axis in Figure 9, and if the output value is greater than or equal to this, it is selected as reflected light from the reflective prism.

[0100] The threshold value described above is set to a value that exceeds the maximum output of the light-receiving unit 202, which receives reflected light from a reflector that is not a reflective prism at a specific distance from the laser scanner. Here, the specific distance from the laser scanner is determined as follows.

[0101] As shown in Figure 9, the results of a normal scan include a first group of bright spots where the output of the light-receiving unit 202 does not change much with distance, and a second group of bright spots where the output of the light-receiving unit 202 decreases significantly with increasing distance. In other words, the scan point group obtained by a normal scan includes a first group of bright spots where the output of the light-receiving unit 202 is not highly dependent on distance, and a second group of bright spots where the output of the light-receiving unit 202 is highly dependent on distance.

[0102] Furthermore, as the distance increases, the output of the light-receiving unit 202 of the first group of bright spots gradually decreases. This is because, due to scattering of the scan light in the air and beam spreading of the scan light, the intensity of the reflected light detected gradually decreases as the distance increases. Even so, the bright spots of the first group, which have little dependence on the intensity of the reflected light from the reflecting prisms with respect to distance, and the bright spots of the second group, which have a high dependence on the intensity of the reflected light from the non-reflecting prisms with respect to distance, are clearly separated.

[0103] Here, the specific distance is defined as the shortest distance at which the maximum output of the light-receiving unit 202 for the second group of bright spots is 70% or less of the maximum output of the light-receiving unit 202 for the first group of bright spots.

[0104] The following describes an example of a specific procedure for determining the aforementioned distance. First, the results of a normal scan are analyzed to find a group of bright spots where the output of the light-receiving unit 202 does not decrease significantly even as the distance increases (the first group of bright spots), and a group of bright spots where the output of the light-receiving unit 202 decreases as the distance increases (the second group of bright spots). Then, the approximate distance Lth at which separation occurs between these two groups is determined.

[0105] In the case of Figure 9, Lth is estimated to be around 40m to 60m, but here we take the minimum value and set Lth to 40m. Note that the first group of bright spots is the group of bright spots from the reflecting prism, and the second group of bright spots is the group of bright spots from reflectors that are not reflecting prisms.

[0106] Next, within a range of 40m or more, the maximum value Pmax1 of the first group of bright spots (relatively high brightness) and the maximum value Pmax2 of the second group of bright spots (relatively low brightness) are obtained. Then, within a range of 40m or more, Pmax2 / Pmax1 is calculated, and the minimum distance at which Pmax2 / Pmax1 < 0.7 is found is determined. In the case of Figure 9, this distance is approximately 60m.

[0107] In the case of Figure 9, the maximum output of the light receiving unit 202 for reflected light from a reflector that is not a reflective prism at a distance of 60m from the laser scanner device is estimated to be approximately 6500 to 6750. Therefore, to allow for a margin, the threshold is set to 8000.

[0108] In the case of Figure 9, at distances of 60m or more, the reflected light from the reflective prism can be reliably detected by the set threshold described above, while reflected light from reflectors other than reflective prisms can be ignored. This reduces the frequency of unnecessarily detecting many reflection points that could be candidates for dimming scans, thereby improving processing efficiency.

[0109] On the other hand, in the case of Figure 9, at short distances of 40m or less, it is impossible to distinguish between reflected light from signs, reflective sheets, taillights, and guardrail reflectors and reflected light from a reflective prism. Therefore, in point cloud data obtained by normal scanning, it is possible that reflected light from reflectors other than reflective prisms may be mistakenly detected as reflected light from a reflective prism.

[0110] Therefore, in this embodiment, the following second stage of reflective prism detection is performed. Here, filtering using a threshold is also performed in the dimming scan in step S105.

[0111] Figure 10 shows the results obtained under dimming scan conditions, similar to the data in Figure 9. In this dimming scan, the intensity of the scan light entering the photodetector is significantly reduced compared to the normal scan in Figure 9. Note that the rate of reduction is not uniform because the attenuation amount of the attenuator is changed according to the distance.

[0112] As can be seen from Figure 10, in dimming scan, there is a large (order of magnitude) difference in the output of the light receiving unit 202 between the reflected light from the reflective prism and the reflected light from a reflector that is not a reflective prism. The reason for this is thought to be as follows.

[0113] In Figure 10, the detection level of the reflected light from the reflector is 50 or less when viewed as a relative value on the vertical axis. On the other hand, the detection level of the reflected light from the reflective prism is 1000 or more. Therefore, in terms of the output level of the light receiving unit 202, the reflected light from the reflector is 1 / 20 or less compared to the reflected light from the reflective prism.

[0114] This can be explained as follows: First, in the detection of reflected light from a reflective prism during normal scanning, saturation of the photodetector occurs, and the linearity between the input (incident light) and output (corresponding to the vertical axis in Figures 9 and 10) of the photodetector is greatly lost.

[0115] As a result, the accuracy of the distance measurement decreases, and the output of the photodetector does not accurately reflect the intensity of the detected light. Specifically, even if the input increases, the output does not increase, and the output is smaller than the value that should be output.

[0116] Therefore, the detected value of the reflected light from the reflective prism in Figure 9 is lower than the actual value. In other words, the output of the photodetector saturates around a relative value of 10000 on the vertical axis, and even if the input increases, it will not output a value greater than that.

[0117] Furthermore, in the range of distances of 40m or less shown in Figure 9, the detected light values ​​from the reflective prism and the reflector are close. However, considering that stronger reflected light is received at closer distances, the degree of saturation of the light-receiving element at close range is (reflected light from the reflective prism) >> (reflected light from the reflector).

[0118] Therefore, even when performing a dimming scan as shown in Figure 10, the detection level of the reflected light from the reflective prism (the output level of the photodetector) does not decrease linearly. In other words, even if the input decreases when the degree of saturation of the photodetector is high, the output does not decrease significantly in proportion to the input. That is, with respect to the reflected light from the reflective prism, the output of the photodetector does not decrease significantly even when switching from a normal scan to a dimming scan. This can be understood as a phenomenon where, in a normal scan to a dimming scan, the detection level of the reflected light from the highly saturated reflective prism is stuck at its maximum value, and even if the input decreases, the decrease in output is not significant.

[0119] In contrast, the photodetector receiving reflected light from a reflector has a low degree of saturation (or is not saturated at all), so if the input (intensity of incident light) decreases, the output level also decreases accordingly. Therefore, for reflected light from a non-reflective prism, when switching from normal scanning to dimming scanning, the output of the photodetector decreases in accordance with the input.

[0120] In the above situation, when transitioning from a normal scan (Figure 9) to a dimmed scan (Figure 10), the decrease in the detection level of reflected light from the reflector becomes more pronounced than the decrease in the detection level of the reflective prism. Thus, in a dimmed scan, the detection level of reflected light from the reflector becomes less than 1 / 20 of the detection level of the reflective prism.

[0121] Furthermore, the above mechanism can also explain why the bright spots in Figure 9 split into two groups at distances of 60m or more. In Figure 9, the fact that the output of the light-receiving unit 202 related to the bright spots of the reflecting prism does not decrease even at distances of 60m or more suggests that the light-receiving element is still in a saturation state where no decrease in output occurs, and this state continues within the distance range shown in Figure 9. Therefore, as the distance increases further, the effect of saturation of the light-receiving element decreases, and a decrease in the output of the light-receiving unit 202 is expected to occur.

[0122] Here, the reflected light from the reflective prism and the reflected light from the non-reflective prism in the scan data obtained during the dimming scan are distinguished (differentiated) using the following method. First, the maximum value of the output of the light receiving unit 202 for each point obtained by the dimming scan is acquired. In the case of Figure 10, the value at approximately 1750 on the vertical axis is the maximum value. If the maximum value is known or can be predicted in advance, that value may be used. Alternatively, instead of the maximum value, the average value of the top N points (N=50~1000) of the output of the light receiving unit 202 may be used.

[0123] Next, a threshold value of 20% of the above maximum value, in this case 1750 × 0.2 = 350, is set as the threshold for determination. Then, reflection points where the output from the light receiving unit 202 is less than the above threshold value of 350 are identified as reflections from a non-reflective prism, and reflection points where the output from the light receiving unit 202 is 350 or more are identified as reflections from a reflective prism.

[0124] As shown in Figure 10, in dimming scan, the difference between the reflected light from the reflective prism and the reflected light from the non-reflective prism is more than 20 times, as measured by the output level of the light receiving unit 202. Therefore, by setting the threshold as described above, the reflected light from the reflective prism can be reliably detected.

[0125] In the example above, the threshold was set at 20% of the maximum output of the light-receiving unit 202, but the threshold can be set within the range of 5% to 50%. If this threshold is less than 5% of the maximum output of the light-receiving element, there is a higher possibility of misdetecting a non-reflective prism as a reflective prism, and if it exceeds 50%, there is a higher possibility of missing reflected light from a reflective prism.

[0126] Furthermore, it is possible to set thresholds according to the distance range. For example, this method is effective when the maximum value varies greatly with distance. One example is to set a first threshold for distances less than 50m, a second threshold for distances between 50m and 100m, and a third threshold for distances greater than 100m. The thresholds for each distance range are set using the method described above.

[0127] According to this embodiment, firstly, unnecessary detections can be suppressed in the detection of dimming scan candidates based on the results of a normal scan. Secondly, the possibility of falsely detecting an object that is not a reflective prism (such as reflective tape) as a reflective prism during dimming scanning can be eliminated.

[0128] 6. Others Multiple embodiments described herein can also be combined. [Explanation of Symbols]

[0129] 200... Laser scanning device, 211... Tripod, 212... Base unit, 213... Horizontal rotation unit, 214... Vertical rotation unit, 215... Optical unit.

Claims

1. A device for controlling laser scanning using a laser scanning device equipped with a light receiving unit, A control unit that causes a first laser scan to be performed under conditions in which the light receiving unit is saturated by reflection from a reflective prism, which is a reflector used for surveying, and a second laser scan to be performed under conditions in which the saturation does not occur. A distance acquisition unit that acquires the distance to the reflective prism based on the first laser scan, In the second laser scan, an adjustment unit adjusts the intensity of the light received by the light receiving unit based on the distance to the reflective prism, A reflection prism detection unit for detecting reflected light from the reflection prism, Equipped with, In the second laser scan, the reflection prism detection unit detects reflected light from the reflection prism when the output of the light receiving unit is above a certain threshold, A laser scan control device in which the specific threshold is a value in the range of 5% to 50% of the maximum output of the light receiving unit in the second laser scan.

2. A device for controlling a laser scan by a laser scanning device equipped with a light receiving unit, A control unit that causes a first laser scan to be performed under conditions in which the light receiving unit is saturated by reflection from a reflective prism, which is a reflector used for surveying, and a second laser scan to be performed under conditions in which the saturation does not occur. A distance acquisition unit that acquires the distance to the reflective prism based on the first laser scan, In the second laser scan, an adjustment unit adjusts the intensity of the light received by the light receiving unit based on the distance to the reflective prism, A reflection prism detection unit for detecting reflected light from the reflection prism, Equipped with, The reflection prism detection unit, in the first laser scan, detects reflected light from the reflection prism when the output of the light receiving unit at a position where the distance from the laser scanning device is greater than or equal to a specific distance is greater than or equal to a specific threshold, The results of the first laser scan include a first group of bright spots that have low dependence on the distance of the output of the light-receiving unit and a second group of bright spots that have high dependence on the distance of the output of the light-receiving unit. The aforementioned specific distance is defined as the shortest distance at which the maximum output of the light-receiving unit for the second bright spot group is 70% or less of the maximum output of the light-receiving unit for the first bright spot group. A laser scan control device wherein the specific threshold is a value that exceeds the maximum value of the output of the light receiving unit relating to the second group of bright spots at the specific distance.

3. The laser scanning control device according to claim 1 or 2, wherein the intensity of the light received by the light receiving unit is adjusted by an optical attenuator positioned in front of the light receiving unit.

4. The control device for laser scanning according to claim 3, wherein the optical attenuator is adjusted to have a relatively small attenuation when the distance to the reflective prism is relatively far, and to have a relatively large attenuation when the distance to the reflective prism is relatively close.

5. The laser scanning control device according to claim 3, wherein the optical attenuator is adjusted so that the intensity of the light received by the light receiving unit remains constant regardless of the distance to the reflective prism.

6. The laser scan control device according to claim 1 or 2, wherein the intensity of the light received by the light receiving unit is adjusted by adjusting the intensity of the measurement light irradiated onto the scan target from the light emitting unit of the laser scan device.

7. A laser scanning device incorporating the laser scanning control device described in claim 1 or 2.

8. A method for controlling a laser scan using a laser scanning device equipped with a light-receiving unit, A first laser scan is performed under conditions in which the light receiving unit is saturated by reflection from a reflective prism, which is a reflector used for surveying, and a second laser scan is performed under conditions in which saturation does not occur. Based on the first laser scan, the distance to the reflective prism is obtained, In the second laser scan described above, the intensity of the light received by the light receiving unit is adjusted based on the distance to the reflective prism. In the second laser scan described above, the output of the light receiving unit is detected as reflected light from the reflecting prism when the reflected light is above a certain threshold. A laser scan control method in which the specific threshold is a value in the range of 5% to 50% of the maximum output of the light receiving unit in the second laser scan.

9. A method for controlling a laser scan using a laser scanning device equipped with a light receiving unit, A first laser scan is performed under conditions in which the light receiving unit is saturated by reflection from a reflective prism, which is a reflector used for surveying, and a second laser scan is performed under conditions in which saturation does not occur. Based on the first laser scan, the distance to the reflective prism is obtained, In the second laser scan described above, the intensity of the light received by the light receiving unit is adjusted based on the distance to the reflective prism. In the first laser scan, the output of the light receiving unit at a position where the distance from the laser scanning device is greater than or equal to a specific distance is detected as reflected light from the reflecting prism if the output of the light receiving unit is greater than or equal to a specific threshold. The results of the first laser scan include a first group of bright spots that have low dependence on the distance of the output of the light-receiving unit and a second group of bright spots that have high dependence on the distance of the output of the light-receiving unit. The aforementioned specific distance is defined as the shortest distance at which the maximum output of the light-receiving unit for the second bright spot group is 70% or less of the maximum output of the light-receiving unit for the first bright spot group. A laser scan control method wherein the specific threshold is a value that exceeds the maximum value of the output of the light receiving unit relating to the second group of bright spots at the specific distance.

10. A program for controlling a laser scanning device equipped with a light-receiving unit, Computer A control unit that causes a first laser scan to be performed under conditions in which the light receiving unit is saturated by reflection from a reflective prism, which is a reflector used for surveying, and a second laser scan to be performed under conditions in which the saturation does not occur. A distance acquisition unit that acquires the distance to the reflective prism based on the first laser scan, In the second laser scan, an adjustment unit adjusts the intensity of the light received by the light receiving unit based on the distance to the reflective prism, A reflection prism detection unit for detecting reflected light from the reflection prism, To operate as, In the second laser scan, the reflection prism detection unit detects reflected light from the reflection prism when the output of the light receiving unit is above a certain threshold, The program wherein the specific threshold is a value in the range of 5% to 50% of the maximum output of the light receiving unit in the second laser scan.

11. A program for controlling a laser scanning device equipped with a light receiving unit, Computer A control unit that causes a first laser scan to be performed under conditions in which the light receiving unit is saturated by reflection from a reflective prism, which is a reflector used for surveying, and a second laser scan to be performed under conditions in which the saturation does not occur. A distance acquisition unit that acquires the distance to the reflective prism based on the first laser scan, In the second laser scan, an adjustment unit adjusts the intensity of the light received by the light receiving unit based on the distance to the reflective prism, A reflection prism detection unit for detecting reflected light from the reflection prism, To operate as, The reflection prism detection unit, in the first laser scan, detects reflected light from the reflection prism when the output of the light receiving unit at a position where the distance from the laser scanning device is greater than or equal to a specific distance is greater than or equal to a specific threshold, The results of the first laser scan include a first group of bright spots that have low dependence on the distance of the output of the light-receiving unit and a second group of bright spots that have high dependence on the distance of the output of the light-receiving unit. The aforementioned specific distance is defined as the shortest distance at which the maximum output of the light-receiving unit for the second bright spot group is 70% or less of the maximum output of the light-receiving unit for the first bright spot group. A program in which the specific threshold is a value that exceeds the maximum value of the output of the light receiving unit relating to the second group of bright spots at the specific distance.

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