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

Abstract

Appropriate scanning conditions in laser scanning are set. A laser scanning device (200) for laser scanning using laser scanning light acquires the distance from the laser scanning device (200) to a reflecting prism (300, 400) as a target, and sets conditions for acquiring laser scanning data defined in the reflecting prism (300, 400). At this time, the laser scanning data defined in the reflecting prisms 300, 400 is laser scanning data of a specific angle range observed from the laser scanning device 200, the specific angle range is set to be relatively small when the distance is relatively long, and the specific angle range is set to be relatively large when the distance is relatively short.

Description

Technical Field

[0001] The present invention relates to a measurement technology. Background Art

[0002] A laser scanning device is known (see, for example, Patent Document 1).

[0003] Prior art literature Patent Literature Patent Document 1: Japanese Patent No. 2926521 Summary of the invention Problem that the invention aims to solve The present invention relates to a technology for setting appropriate scanning conditions in laser scanning.

[0004] Means used to solve problems The present invention is a laser scanning device, comprising: a distance acquisition unit, which acquires the distance from the laser scanning device to a specific object; and a condition setting unit, which sets conditions for obtaining laser scanning data limited to the specific object. The laser scanning data limited to the specific object is laser scanning data within a specific angle range observed from the laser scanning device. When the distance is relatively long, the specific angle range is set to be relatively small, and when the distance is relatively short, the specific angle range is set to be relatively large.

[0005] In the present invention, the following method is cited and the following conditions are set: when the distance is relatively long, the laser scanning density per unit angle range is relatively large, and when the distance is relatively short, the laser scanning density per unit angle range is relatively small.

[0006] In the present invention, the following method is cited, the laser scanning device comprises: a horizontal rotating part that rotates horizontally; and a vertical rotating part, which is arranged on the horizontal rotating part, rotates vertically with the horizontal direction as the rotation axis, and has an optical part that irradiates laser scanning light to the outside, the specific angle range includes the angle range in the horizontal direction, and the angle range in the horizontal direction is adjusted based on the vertical position of the specific object. In the adjustment, the angle range in the horizontal direction is expanded when the vertical position of the specific object is a relatively high vertical angle position compared to when the vertical position of the specific object is a relatively low low vertical angle position.

[0007] In the present invention, the following method is cited: the cross-sectional shape of the laser scanning light emitted from the laser scanning device has a long strip shape, the laser scanning light is reflected by a rotating reflector to perform laser scanning, the cross-sectional shape of the laser scanning light rotates according to the direction of reflection by the reflector, and the conditions for obtaining the laser scanning data are set according to the direction of reflection of the reflector.

[0008] The present invention is a laser scanning method, which uses a laser scanning device to obtain the distance from the laser scanning device to a specific object, and sets conditions for obtaining laser scanning data limited to the specific object. The laser scanning data limited to the specific object is laser scanning data within a specific angle range observed from the laser scanning device. When the distance is relatively long, the specific angle range is set to be relatively small, and when the distance is relatively short, the specific angle range is set to be relatively large.

[0009] The present invention is a program for laser scanning, which enables a computer to control a laser scanning device to perform laser scanning, enables the computer to obtain the distance from the laser scanning device to a specific object, and enables the computer to set conditions for obtaining laser scanning data limited to the specific object. The laser scanning data limited to the specific object is laser scanning data within a specific angle range observed from the laser scanning device. When the distance is relatively long, the specific angle range is set to be relatively small, and when the distance is relatively short, the specific angle range is set to be relatively large.

[0010] Effects of the Invention According to the present invention, it is possible to obtain a technique for setting appropriate scanning conditions in laser scanning. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 This is an overall schematic diagram of an implementation method.

[0012] Figure 2 This is an appearance diagram of a laser scanner.

[0013] Figure 3 (A) and (B) are conceptual diagrams of the optical system.

[0014] Figure 4 is a block diagram of a laser scanning device.

[0015] Figure 5 This is a conceptual diagram for explaining the principle of change in scanning range due to distance.

[0016] Figure 6 This is a schematic diagram for explaining the principle of rotation of a flat beam cross section of laser scanning light.

[0017] Figure 7This is a schematic diagram for explaining the principle of rotation of a flat beam cross section of laser scanning light.

[0018] Figure 8 This is a conceptual diagram showing the rotation state of a flat beam cross section of laser scanning light.

[0019] Fig. 9 This is a conceptual diagram showing a state in which the scanning range is reduced when the vertical angle is increased.

[0020] Fig.10 : is a conceptual diagram showing the scanning range near the vertex.

[0021] Fig.11 is a graph showing the relationship between the angular range and the scanning speed and the distance.

[0022] Fig.12 This is a flowchart showing an example of the processing procedure. DETAILED DESCRIPTION

[0023] 1. First Implementation Method (summary) Figure 1 The laser scanning device 200 and the target reflecting prisms 300 and 400 are shown in the state where the point cloud data is to be obtained. The reflecting prisms 300 and 400 are set at points whose positions are known in the absolute coordinate system. The absolute coordinate system is a coordinate system used in a map or GNSS (Global Navigation Satellite System). In addition, a local coordinate system can also be used as a coordinate system.

[0024] Figure 1 In the figure, scanning objects other than the reflecting prism are omitted, but in fact there are objects to be scanned by the laser other than the reflecting prism (such as terrain or buildings).

[0025] The reflecting prisms 300 and 400 reflect the incident light so that the direction of the incident light is changed by 180 degrees. The reflecting prisms 300 and 400 use commercially available prisms for measurement. In addition to the reflecting prisms, other reflectors such as a retro-reflector may also be used.

[0026] The laser scanning device 200 is set at a position suitable for laser scanning, but its position and posture in the absolute coordinate system are unknown. In this example, the laser scanning device 200 performs a first large-scale laser scan (eg, full-circle scan) and a second laser scan narrowed to the reflective prism.

[0027] Here, a wide range of point cloud data is obtained by the first laser scanning, but the position of each point in the absolute coordinate system is unknown at this stage. This is because the position and posture of the laser scanning device 200 in the absolute coordinate system are unknown.

[0028] Therefore, the reflecting prisms 300 and 400 set at known points in the absolute coordinate system are positioned by the second laser scanning, and the position and posture of the laser scanning device 200 in the absolute coordinate system are calculated by the back intersection method.

[0029] By understanding the position and posture of the laser scanning device 200 in the absolute coordinate system, the point cloud data obtained by the first laser scanning is assigned coordinates in the absolute coordinate system to obtain point cloud data in the absolute coordinate system. It should be noted that the number of reflecting prisms can also be more than three.

[0030] In the first laser scan, the reflected light from the reflecting prisms 300 and 400 is too strong, the light receiving unit 202 of the laser scanning device 200 is saturated, and the distance measurement accuracy of the reflecting prisms 300 and 400 is reduced. That is, in the first laser scan, the positioning accuracy of the reflecting prisms 300 and 400 is reduced.

[0031] Therefore, a second laser scan is performed to accurately position the reflective prisms 300 and 400. At this time, a variable optical attenuator is used to reduce the input level of the ranging light to the light receiving element to obtain high positioning accuracy. The control of the variable optical attenuator is performed based on the light intensity and distance information of the reflective prism obtained by the first laser scan.

[0032] In addition, saturation caused by strong input in the light receiving unit 202 mainly occurs in the light receiving element. If the degree of saturation is small, the output of the light receiving element is distorted or the output reaches the limit, but the distance measurement accuracy can be ensured. If the degree of saturation is large, the waveform distortion of the output of the light receiving element becomes significant, and the distance measurement using the phase difference of the waveform generates an error, and the distance measurement accuracy is reduced.

[0033] The second scan is performed in a state that does not adversely affect the distance measurement accuracy of the latter (a state that ensures the distance measurement accuracy). Specifically, as described above, an optical attenuator is inserted into the optical path to make the light receiving element unsaturated. In addition, the optical attenuator is configured on one or both of the light emitting optical system and the light receiving optical system. Usually, an optical attenuator is configured on either optical system. In addition, a method of weakening the light intensity of the light emitting element can also be used.

[0034] The distance from the laser scanning device 200 to the reflecting prisms 300 and 400 obtained based on the result of the first laser scanning is obtained. This distance includes an error, but based on this distance, a condition for obtaining laser scanning data limited to the reflecting prisms 300 and 400 is set. At this time, the laser scanning data limited to the reflecting prisms 300 and 400 is laser scanning data of a specific angle range observed from the laser scanning device 200. When the distance is relatively long, the specific angle range is set to be relatively small, and when the distance is relatively short, the specific angle range is set to be relatively large.

[0035] (Hardware Structure) Figure 2 The figure shows the appearance of a laser scanning device (laser scanner) 200. The laser scanning device 200 includes a tripod 221, a base 222 fixed to the upper part of the tripod 221, a horizontal rotating part 223 which is a rotating body capable of horizontal rotation on the base 222, and a vertical rotating part 224 which is a rotating body capable of vertical rotation relative to the horizontal rotating part 223. The laser scanning device 200 is operated by an external controller (operation terminal) which is wirelessly connected and not shown.

[0036] The vertical rotating unit 224 has an optical unit 225 that emits and receives laser scanning light. The laser scanning light (distance measuring light) is pulsed from the optical unit 225. The vertical rotating unit 224 performs the pulsed emission in a direction (vertical plane) orthogonal to its rotation axis (axis extending in the horizontal direction) while rotating. In this case, the laser scanning light is pulsed from the optical unit 225 in the vertical angle direction (angle direction of elevation and depression). In addition, the vertical angle is measured by taking the horizontal direction as 0° and the vertical direction as 90°.

[0037] There are two structures of optical systems. Figure 3 (A) is a conceptual diagram of the first structure. In this example, the laser scanning light emitted from the light emitting unit 201 is irradiated to the diagonal mirror 252 via the light synthesis separation unit 251. The diagonal mirror 252 is arranged at the front end of the cylindrical vertical rotating member 253 at an angle of 45 degrees. The vertical rotating member 253 uses the axis (axis extended in the horizontal direction) that is consistent with the optical axis of the light emitting unit 201 as the rotation axis, and rotates vertically together with the vertical rotating unit 224.

[0038] Vertical scanning along the vertical plane is performed by emitting laser scanning light in pulses from the light emitting unit 201 while rotating the vertical rotating unit 224. The scanning light reflected from the object is received by the light receiving unit 202 along the reverse path from the diagonal mirror 252 through the light combining and separating unit 251 and the variable optical attenuator 211. In this structure, the light emitting unit 201 and the light receiving unit 202 are fixed inside the horizontal rotating unit 223 and do not rotate vertically.

[0039] Figure 3 (B) in FIG. 1 shows a second structure of the optical system. In this case, the light emitting unit 201, the light receiving unit 202, and the light combining and separating unit 254 are vertically rotated integrally with the vertical rotating unit 224. Figure 3 (A) and Figure 3 Any one of the structures in (B).

[0040] While the horizontal rotating unit 223 is rotated horizontally and the vertical rotating unit 224 is rotated vertically, the optical unit 225 emits pulses of laser scanning light, and the optical unit 225 receives reflected light from the object, thereby performing laser scanning on the surroundings.

[0041] At the same time as the scanning in the vertical direction (vertical scanning) described above, the horizontal rotation unit 223 rotates horizontally, whereby the scanning line in the vertical direction (vertical scanning line) moves in a shifted manner in the horizontal direction (horizontal direction). In addition, when the horizontal rotation is performed simultaneously with the vertical rotation, the scanning in the vertical direction (vertical scanning line) is not completely in the vertical direction, but becomes a slightly inclined line. However, if the horizontal rotation unit 223 does not rotate, the scanning in the vertical direction (vertical scanning line) becomes a line in the vertical direction.

[0042] The horizontal rotation unit 223 and the vertical rotation unit 224 are rotated by a motor. The horizontal rotation angle of the horizontal rotation unit 223 and the vertical rotation angle of the vertical rotation unit 224 are precisely measured by an encoder.

[0043] Each laser scanning light is a pulsed distance measurement light, and the distance to the reflection point reached by the laser scanning light, i.e., the scanning point, is measured by a laser scanning light. Based on the distance measurement value and the irradiation direction of the laser scanning light, the position of the scanning point (the reflection point of the laser scanning light) relative to the laser scanning device 200 is calculated.

[0044] As a method of outputting point cloud data (laser scanning point cloud) from the laser scanning device 200, there can be cited a method of outputting data on the distance and direction of each point (each scanning point). It can also be a method in which the position of each point in a specific coordinate system is calculated inside the laser scanning device 200, and the three-dimensional coordinate position of each point is output as point cloud data. In addition, the point cloud data also includes information on the brightness (intensity of reflected light) of each scanning point.

[0045] Figure 4 is a block diagram of the laser scanning device 200. Figure 4 Part of the functional unit shown is a separate structure, and is externally connected to the laser scanning device 200. For example, the following method can be used: a PC (personal computer) and a server are used to form a Figure 3A part of the functional units shown transmits data from the laser scanning device 200 to the PC and the server, and the PC and the server perform data processing.

[0046] The laser scanning device 200 has a light emitting unit 201, a light receiving unit 202, a distance measuring unit 203, a direction acquiring unit 204, a light emitting control unit 205, a drive control unit 206, a reflecting prism detecting unit 207, a distance acquiring unit 208 for acquiring the distance to the reflecting prism, a direction acquiring unit 209 of the reflecting prism, a variable light attenuator control unit 210, a variable light attenuator 211, a scanning condition setting unit 212, a point cloud data creating unit 213, a center calculating unit 214 of the reflecting prism, a communication device 215, a storage unit 216 and an action control unit 217.

[0047] The light emitting unit 201 includes a light emitting element for emitting laser scanning light, an optical system related to light emission, and a peripheral circuit. The laser scanning light emitted by the light emitting unit 201 is transmitted to the optical synthesis and separation unit. Figure 2 The optical unit 225 emits the light to the outside. The light combining and separating unit is an optical system that uses a half mirror or a dichroic mirror to separate and combine the optical paths of the outgoing light and the incident light.

[0048] The light receiving unit 202 includes a light receiving element for receiving the laser scanning light, an optical system related to light reception, and a peripheral circuit. The reflected light of the laser scanning light obtained from the optical unit 225 is guided from the light combining and separating unit to the variable optical attenuator 211, and then guided to the light receiving unit 202 (refer to Figure 3 ). The variable optical attenuator 211 will be described later.

[0049] The distance measuring unit 203 calculates the distance from the laser scanning device 200 to the reflection point (scanning point) of the laser scanning 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 scanning light output from the light emitting element is divided into two paths, one of which is irradiated toward the object from the optical unit 225 as the laser scanning light, and the other is guided to the above-mentioned reference optical path as the reference light.

[0050] The laser scanning light reflected from the object and obtained from the optical part 225 and the reference light propagated in the above-mentioned reference optical path are synthesized and input into the light receiving part 202. The propagation distances of the laser scanning light and the reference light are different. First, the reference light is detected by the light receiving element, and then the laser scanning light is detected by the light receiving element. Here, if the output waveform of the light receiving element is observed, the detection waveform of the reference light is output first, and then the detection waveform of the laser scanning light is output with a time difference. The distance from the laser scanning device 200 to the reflection point of the laser scanning light is calculated based on the phase difference (time difference) between the two waveforms. It should be noted that the distance can also be calculated based on the flight time of the laser scanning light.

[0051] The direction acquisition unit 204 acquires the optical axis direction of the laser scanning light. The optical axis direction is obtained by measuring the optical axis angle in the horizontal direction (horizontal angle) and the optical axis angle in the vertical direction (vertical angle: equivalent to the elevation angle or depression angle). The direction acquisition unit 204 includes a horizontal angle detection unit 204a and a vertical angle detection unit 204b.

[0052] The horizontal angle detection unit 204a detects the horizontal rotation angle of the horizontal rotation unit 223. Horizontal rotation is rotation with the vertical direction as the rotation axis. 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 224. Vertical rotation is rotation with the horizontal direction as the rotation axis. The angle is detected by an encoder.

[0053] By measuring the horizontal rotation angle of the horizontal rotation unit 223 and the vertical rotation angle of the vertical rotation unit 224 , the optical axis direction of the laser scanning light observed from the laser scanning device 200 , that is, the direction of the scanning point, is understood.

[0054] The light emission control unit 205 controls the emission timing of the laser scanning light in the light emission unit 201. The drive control unit 206 includes a horizontal rotation drive control unit 206a for performing drive control for rotating the horizontal rotation unit 223 horizontally and a vertical rotation drive control unit 206b for performing drive control for rotating the vertical rotation unit 224 vertically.

[0055] In the first laser scan, the reflection prism detection unit 207 identifies and detects the reflected light from the reflection prism based on the output of the light receiving element of the light receiving unit 202. The distance measuring light reflected by the reflection prism has an intensity that is an order of magnitude higher than that of other reflected light. Using this intensity difference, the reflected light from the reflection prism is detected from the received reflected light.

[0056] In addition, because the intensity of the reflected light from the reflecting prism is strong, the output waveform of the light receiving element that receives the reflected light from the reflecting prism becomes a saturated waveform. Specifically, the upper end is deformed and becomes a flat waveform, and the waveform is output in a state of tailing longer than the light receiving time. By identifying this special output waveform, it is also possible to detect the reflected light from the reflecting prism among the multiple reflected lights.

[0057] The distance acquisition unit 208 for acquiring the distance to the reflection prism acquires the distance from the laser scanner 200 to the reflection prism detected by the reflection prism detection unit 207. The reflected light from the reflection prism detected by the reflection prism detection unit 207 is determined, and the distance is measured by the distance measurement unit 203. In the first laser scan, the reflected light from the reflection prism is particularly strong, and the light receiving element of the light receiving unit 202 is saturated, and the accuracy of distance measurement is reduced. Therefore, the distance information to the reflection prism acquired by the distance acquisition unit 208 in the first laser scan contains errors.

[0058] In the second laser scan, the intensity of the laser scan light input to the light receiving element is adjusted by using the variable optical attenuator 211, thereby enabling accurate distance measurement. In the second laser scan, the difference in the intensity of the received light is also used to determine whether it is reflected light from the reflection prism.

[0059] The reflection prism direction acquisition unit 209 acquires the direction from the laser scanner 200 to the reflection prism detected by the reflection prism detection unit 207 . The direction acquisition unit 204 acquires the direction.

[0060] The control unit 210 of the variable optical attenuator controls the attenuation amount in the variable optical attenuator 211 described later. The variable optical attenuator 211 attenuates the light incident on the light receiving unit 202. The attenuation amount (attenuation rate) can be changed. Based on the intensity of the light received at the light receiving unit 202 and the distance to the object calculated by the distance measuring unit 203, the control unit 210 of the variable optical attenuator performs control to change the attenuation amount. This technology is described in, for example, Japanese Patent Application No. 2022-112957 and Japanese Patent Application No. 2022-112959.

[0061] The variable optical attenuator 211 includes a method of adjusting transmittance by rotating a semi-transparent disk whose transmittance gradually changes in the circumferential direction, a method of controlling the transmittance of liquid crystal, etc. Variable optical attenuator modules are commercially available and can be appropriately selected and used.

[0062] Since the reflection from the reflection prism is strong, the light receiving element is saturated in the first laser scan, and the distance measurement value of the reflection prism generates an error. For example, according to the experiment of the inventors, in a laser scanner capable of measuring distance with an error of several millimeters (mm), an error of the centimeter (cm) level is generated in the case of reflected light from the reflection prism. The increase in this error is also related to the nonlinear action of the light receiving element, and is not fixed, but is several to 10 times the conventional measurement error.

[0063] By placing the variable optical attenuator 207 before the light receiving unit 202, the intensity of light entering the light receiving unit 202 is reduced, thereby suppressing the problem caused by the saturation of the light receiving element.

[0064] The scanning condition setting unit 212 sets the scanning conditions for the second laser scan that is narrowed down to the reflecting prism. In order to avoid useless laser scanning and acquisition of useless laser scanning data, the second laser scan for precise positioning of the reflecting prism is performed with the limited range narrowed down to the direction of the reflecting prism as the object. The setting of the scanning conditions at this time is performed in the scanning condition setting unit 212. The scanning conditions include the angle range and scanning density for acquiring scanning data. In the case of this example, the angle range for acquiring scanning data is determined by the range of horizontal angles and the range of vertical angles.

[0065] Scan density is the density of scanning in the scanned object. Specifically, it is the density of reflection points. If the reflection points are small and dense, and the interval between adjacent reflection points is small, it is a high scan density. On the contrary, if the distribution of reflection points is sparse (sparse), and the interval between adjacent reflection points is large, it is a low scan density.

[0066] The scanning density is adjusted by changing the scanning speed and / or the oscillation frequency of the pulsed light. The change of the oscillation frequency is not common, so the scanning density is generally adjusted by adjusting the scanning speed.

[0067] Specifically, the rotation speed of the horizontal rotating unit 223 during scanning is slowed down to increase the scanning density in the horizontal direction. When the oscillation frequency of the laser scanning light is the same, by slowing down the rotation speed of the horizontal rotating unit 223, the number of laser scanning lights in a unit angle range in the horizontal direction increases, and the density of scanning points (reflection points of the laser scanning light) in the horizontal direction increases.

[0068] Based on the same principle, the scanning density in the vertical direction is increased by slowing down the rotation speed of the vertical rotating unit 224 during scanning. When the scanning density is reduced, the opposite tendency is shown.

[0069] The setting of the above-mentioned scanning conditions is determined based on two factors: (factor 1) the distance to the positioning target and (factor 2) the vertical angle to the positioning target.

[0070] (Element 1) In the setting of the scanning conditions of element 1, the vertical angle range and the horizontal angle range for acquiring the scanning data are adjusted according to the distance L. This will be described in detail below.

[0071] Furthermore, a limited angle range including the determined range is scanned in the horizontal direction, and scan data of the set horizontal angle range is acquired (acquired as data to be used) as point cloud data.

[0072] Regarding the limited scanning range in the vertical direction, it is mechanically difficult to stop scanning only within a specific vertical angle range. Therefore, a full-circle (360° vertical rotation) scanning is actually performed, and data is acquired as point cloud data only within a specific angle range.

[0073] By doing so, the burden on the hardware can be reduced and the data area to be used can be reduced. Of course, a method of scanning only within a specific angle range is not excluded.

[0074] Figure 5 The figure shows a situation where a laser scanning device is arranged at point O and scanning data is obtained within a horizontal angle range and a vertical angle range limited to a certain range. Figure 5 The figure shows scanning range 1 when the distance from the laser scanning device is L1 and scanning range 2 when the distance is L2 under the same horizontal angle range and vertical angle range. Comparing scanning range 1 and scanning range 2, it can be seen that even under the same horizontal angle range and vertical angle range, the scanning range (area to be scanned) is different if the distance is different. Specifically, even under the same horizontal angle range and vertical angle range, the longer the distance, the larger the scanning range.

[0075] In the small-range scan (second scan) with the reflecting prism as the object, a limited scanning range of about 10 cm to 1 m square is set centered on the position of the reflecting prism obtained by the first laser scan (this includes the error caused by the saturation of the light receiving element).

[0076] For example, at the position where the reflection prism is estimated to be, the scanning range is a distance H in the horizontal direction and a distance V in the vertical direction. In this case, if the distance from the reflection prism is L and the scanning range of the horizontal angle is θ H , set the vertical scanning range to θ V , when the angle range is small enough, Lθ H =H, if the vertical scanning angle is set to θ V , then to satisfy Lθ V =V to set θ H and θ V According to this formula, when V and H are fixed, if L is large, θ can be reduced. H and θ V When L is small (when the distance is short), the opposite tendency is shown.

[0077] The setting of the scan based on the element (1) is based on the distance data L from the reflecting prism obtained by the first laser scan, and is performed according to the above principle. Specifically, given the above H and V, based on L, θ is set. H and θV .

[0078] In addition, when L is large, θ H and θ V Specifically, the rotation speed of at least one of the horizontal rotation unit 223 and the vertical rotation unit 224 during scanning is reduced. This suppresses a decrease in scanning density at a position where L is large.

[0079] That is, for an object with a large L (far distance), the density of scanning points at a position with a distance L is suppressed from decreasing by making the number of laser scanning lights in a unit angle range relatively large compared to a case where L is small.

[0080] (Element 2) In setting the scanning range of element 2, the horizontal angle range of the scan needs to be increased in proportion to the vertical angle. Also, the horizontal angle range needs to be set to the entire circumference near the vertex.

[0081] In the combination of horizontal rotation and vertical rotation Figure 2 In the illustrated laser scanning device 200 , even if the angle range that determines the scanning range in the horizontal direction is the same, the area to be scanned at a certain distance varies depending on the vertical angle.

[0082] Fig. 9 The principle diagram is shown. For example, at a specific distance of 0° vertical angle (0° elevation angle: horizontal direction), a specific distance range in the horizontal direction (arc 1) is set. The angle range of the horizontal angle corresponding to arc 1 is Δθ. In addition, regarding the vertical angle, the horizontal direction is set to 0°, and the vertical top (vertex) is set to 90°.

[0083] like Fig. 9 As shown in (A) in FIG. 1 , in a scan combining horizontal rotation and vertical rotation, if the vertical angle increases, the horizontal scanning range corresponding to the horizontal angle range Δθ decreases from the range of arc 1 to the range of arc 2. Fig. 9 As can be seen from (A) in the figure, the distance of arc 1 is greater than the distance of arc 2. The closer to the vertex (90° vertical angle), the smaller the distance of the arc becomes. At the vertex (90° vertical angle), the distance of the arc corresponding to the range of horizontal angles becomes 0.

[0084] That is, when the horizontal angle scanning range Δθ of the arc 1 is set in the horizontal direction, the higher the vertical angle (higher the elevation angle), the smaller the scanning range captured by the horizontal distance becomes. Fig. 9 In (B), when the horizontal angle range is set to the same, the scanning range changes (decreases) in the manner of S1 ⇒ S2 according to the vertical angle.

[0085] exist Fig. 9 In the case of (B), when the horizontal angle range is set to the same, if the scanning range captured by the area in the horizontal direction (the range of vertical angle close to 0°) is S1, then at a high vertical angle, the scanning range captured by the area is reduced to S2. Compared with S1, the reduction in the area of ​​S2 is proportional to the reduced horizontal distance range ( Figure 1 The area of ​​the scanning range is reduced. Therefore, it is necessary to intentionally expand the range of the horizontal angle at a position with a large vertical angle to correct the area difference between S1 and S2.

[0086] At the vertex part (extended angle = 90°) which is the extreme value, the horizontal angle range needs to be expanded to the full circle (360°). For example, near the vertex there is Fig. 9 In the case of such a circular scanning range, by rotating the horizontal angle 360° within the range from vertical angle 2 (e.g., 85°, etc.) to the vertex angle (90°), data near the vertex can be obtained. In this case, by eliminating the scanning data in the range from vertical angle = 0° to vertical angle 2, appropriate scanning data can be obtained.

[0087] (An example of optimizing scanning conditions) An example of optimization of the scanning conditions taking the above-mentioned factors 1 and 2 into consideration will be described below.

[0088] A specific example is shown below. In addition, the object is a reflecting prism. First, point cloud data based on the reflected light from the reflecting prism is extracted from the result of the first laser scan, and the distance L and the vertical angle from the laser scanning device 200 to the reflecting prism are obtained. The distance L includes an error caused by the strong reflected light, but can be used for setting the range of the second laser scan without any problem. The vertical angle is the angle of the vertical direction of the reflecting prism observed from the laser scanning device 200. When the reflecting prism can be observed in the horizontal direction from the laser scanning device 200, the vertical angle = 0°.

[0089] The adjustment of element 1 is performed in the following manner. Here, the horizontal direction of the scanning range of the search reflection prism is set to Hm, and the vertical direction is set to Vm. This range is pre-set based on the size of the reflection prism. For example, when the apparent size of the reflection surface of the reflection prism observed from the front is a circle with a diameter of 5 cm, a margin is left and the range of H=10 cm and V=10 cm is set as the scanning range. At this time, the scanning range is determined in such a way that the point as the reflection center of the reflection prism obtained by the first laser scan is located at the center of the scanning range.

[0090] Here, the horizontal angle scanning range is set to θ H (rad), set the vertical scanning range to θ V(rad). Here, to satisfy Lθ H =H、Lθ V = V to find θ H and θ V .

[0091] In short, there is a method as follows, that is, preparing in advance Fig.11 The calibration curve shown is used as H (deg, degrees) and θ V (deg, degrees), select the angle range of the left vertical axis according to the distance L. Fig.11 This is a calibration curve when a range of approximately 10 cm square in length and width is selected as the scanning range.

[0092] Fig.11 The vertical axis on the right side is the scanning speed. Fig.11 In the setting of the scanning speed shown, the scanning speed is slowed down as the distance L becomes larger so as not to reduce the scanning density. The scanning speed is adjusted by adjusting the rotation speeds of the horizontal rotating unit 223 and the vertical rotating unit 124 .

[0093] Specifically, if the rotation speed of the horizontal rotation unit 223 during scanning is slowed down, the scanning density (density of scanning points) in the horizontal direction becomes higher. In addition, if the rotation speed of the vertical rotation unit 214 during scanning is slowed down, the scanning density (density of scanning points) in the vertical direction becomes higher.

[0094] Ideally, it is desirable to adjust the scanning speed in order to suppress a decrease in scanning density in both the horizontal rotating unit 223 and the vertical rotating unit 224 .

[0095] Next, the result of considering the above-mentioned factor 1 is corrected by considering the factor 2. Regarding the factor 2, the vertical angle corresponding to the vertical angle is obtained in advance. Fig. 9 The correction coefficient k (1≤k) of arc 1 (vertical angle = 0°) is used to correct the above θ H The correction coefficient k increases in proportion to the vertical angle.

[0096] If the vertical angle increases, the correction value of the horizontal scanning range becomes kθ H For example, k can be obtained by k=1 / cosθ (θ: vertical angle, but θ=90° is excluded). In addition, when the vertical angle is 90°, the horizontal scanning range becomes a full circumference (360° around the horizontal direction) (refer to Fig.10 ).

[0097] The point cloud data creation unit 213 creates point cloud data based on the result of the laser scanning. The point cloud data is data on the distance and direction of each point (each scanning point) and data on the brightness (intensity of reflected light) of each scanning point.

[0098] In this example, the limited scanning in the horizontal direction is performed by horizontally rotating the horizontal rotation unit 223 within a limited angle range. In practice, the horizontal rotation is performed within a slightly larger range with a certain degree of margin, and the scan data of the predetermined horizontal angle range is extracted from the scan data obtained at this time as point cloud data. The predetermined horizontal angle range is set by the scan condition setting unit 212.

[0099] At the same time, the vertical rotation unit 224 is rotated vertically in a full circle while performing vertical scanning. Then, the scanning data of a predetermined vertical angle range is extracted from the obtained full circle scanning data as point cloud data. The predetermined vertical angle range is set by the scanning condition setting unit 212.

[0100] In this way, the scan data in the predetermined horizontal angle range and vertical angle range are extracted as point cloud data. This processing is performed in the point cloud data creation unit 213. By not performing data processing on unnecessary scan points, the calculation burden is reduced and the consumption of data capacity is suppressed.

[0101] The center calculation unit 214 of the reflecting prism calculates the position of the reflection center of the reflecting prism based on the point cloud data of the reflecting prism obtained in the laser scanning. Specifically, the position of the center of gravity is calculated based on a plurality of point cloud data obtained from the reflected light from the reflecting prism, and the position is used as the reflection center of the reflecting prism for calculation. In addition, due to the accuracy of the point cloud data as the basis, the accuracy of the positioning position of the reflecting prism based on the result of the first laser scanning is relatively low, and the accuracy of the positioning position of the reflecting prism based on the result of the second laser scanning is relatively high.

[0102] The communication device 215 communicates with an external controller or other device (not shown). The communication is performed using a wired or wireless LAN, a mobile phone line, etc. The storage unit 216 is composed of a semiconductor memory or a hard disk device, and stores the action program and data required for the action of the laser scanning device 200, and the data obtained according to the action process or the action result. The action control unit 217 is a computer that controls the action of the laser scanning device 200.

[0103] (Explanation of the cross-sectional shape of the scanning light beam) The following describes the Figure 3The rotation of the cross-sectional shape of the laser scanning light (distance measuring light) generated in the case of the vertical scanning (longitudinal scanning) method (A). The scanning conditions and the content of the scanning data processing can also be determined by taking into account the rotation of the cross-sectional shape of the laser scanning light.

[0104] Figure 6 This is a schematic diagram showing the principle that the cross-sectional shape of the beam of distance measuring light rotates as the reflector rotates. Figure 6 (A) in FIG. 1 shows a case where the laser scanning light is incident on the reflector 601 from the positive X-axis direction, and the laser scanning light has a beam cross section with a flat shape having a length direction in the Y-axis direction. In this case, the components of the normal vector of the reflection surface of the reflector 601 are (X, Y, Z) = (1, -1, 0). In this case, the laser scanning light is reflected by the reflector 601 in the negative Y-axis direction. The length direction of the cross section of the reflected light becomes the X-axis direction.

[0105] Figure 6 (B) shows the reflector 601 from Figure 6 The state (A) is a state rotated 90° about the X-axis (90° counterclockwise when viewed from the negative X-axis direction).

[0106] exist Figure 6 In the case of (B), the components of the normal vector of the reflection surface of the reflector 601 are (X, Y, Z) = (1, 1, 0). In this case, the laser scanning light is reflected by the reflector 601 in the positive Z-axis direction. The longitudinal direction of the cross section of the reflected light is the same as that of the incident light, that is, the Y-axis direction.

[0107] Wherein, the reflector 601 is made to Figure 6 The state (A) in the figure gradually rotates to Figure 6 In the state (B), consider the change in the length direction of the beam cross section of the reflected light during this period. Figure 7 As shown. Figure 7 As shown, when the reflector is rotated for vertical scanning, the beam cross section having a length direction in the X-axis direction rotates in the horizontal direction as the vertical angle increases (the elevation angle with respect to the horizontal increases), becoming a state in which the beam cross section has a length direction in the Y-axis direction and is extended by an angle of 90° (vertical direction).

[0108] Figure 8 An example of the relationship between the vertical angle and the rotation of the beam cross section is shown. Figure 8 The figure shows how laser scanning light having an elliptical beam cross section rotates due to a difference in the vertical angle. Figure 8 The diagram shows how an elliptical beam having a long axis in the horizontal direction at a low vertical angle rotates as the vertical angle increases, and how the beam size in the H direction and the beam size in the V direction change.

[0109] In addition, when the cross section of the light beam incident on the reflector is circular, the above-mentioned rotation effect does not occur. In addition, when the cross section of the light beam incident on the reflector is square, the above-mentioned rotation effect occurs strictly speaking, but there is no particular problem.

[0110] The following describes Figure 6~Figure 8 An example of control related to the rotation of the beam cross section is shown. Here, the case of setting the scanning range in the second laser scanning is considered.

[0111] like Figure 8 As shown in the example, in the case of laser scanning light with a long cross-section, the beam diameter (the size of the beam cross-section) in the V direction and the H direction changes according to the vertical angle. Among them, for example, when the overlap degree of the scanning light is optimal at a vertical angle of 0° (horizontally long beam), a gap in the horizontal direction may occur at a high vertical angle.

[0112] In this case, the scanning density in the H direction is increased at a high vertical angle according to the vertical position of the beam center. In addition, in this case, the beam becomes longitudinally long at a high vertical angle and the overlap in the V direction becomes excessive, so the scanning density in the V direction is reduced. In fact, the change adjustment of the scanning speed in the V direction is not appropriate, so the acquisition density of the point cloud data is adjusted according to the vertical angle (conversely, the rejection density is adjusted). The scanning density in the V direction is adjusted in this way.

[0113] In addition, in Figure 8 On the contrary, when the beam cross section is long in the vertical direction at a vertical angle of 0°, the beam cross section becomes long in the horizontal direction as the vertical angle increases, and a gap may be generated in the scanning in the V direction depending on the scanning conditions. In this case, the scanning density in the V direction is increased at a high vertical angle.

[0114] (An example of processing order) Fig.12 is a flowchart illustrating an example of the processing sequence. Fig.12 The program for the processing is stored in the storage unit 216 or an appropriate storage medium, and is executed by the CPU of the computer constituting the action control unit 217.

[0115] First, in Figure 1 The first laser scan is performed in the state (step S101). Among them, the positions of the reflection prisms 300 and 400 in the absolute coordinate system are known, and the position and posture of the laser scanning device 200 in the absolute coordinate system are unknown. As a coordinate system, a local coordinate system can also be used. The first laser scan is performed on the terrain and buildings, etc., and the first laser scan is performed over the entire circumference under general conditions without considering the strong reflection from the reflection prism and reducing the light.

[0116] From the scan data obtained by the first laser scan, scan data related to reflection from the reflection prisms 300 and 400 is extracted (step S102 ). This process is performed based on the detected light intensity of the laser scan light and its detected waveform.

[0117] Next, the centroid position of the scan data obtained in step S102 is calculated (step S103). Thus, the position of the reflection center of the reflection prisms 300 and 400 is obtained. Next, the distance to the centroid position obtained in step S102 (the separation distance from the laser scanning device 200) is obtained (step S104). Thus, the distance L1 from the laser scanning device 200 to the reflection prism 300 and the distance L2 from the laser scanning device 200 to the reflection prism 400 are obtained. In addition, the direction of the reflection center of the reflection prism 300 observed from the laser scanning device 200 and the direction of the reflection center of the reflection prism 400 observed from the laser scanning device 200 are obtained.

[0118] Then, according to Figure 5 The method described in the related description sets the scanning range corresponding to the distance taking into account the element 1 (step S105). The scanning range for the precise scanning of the reflecting prism 300 corresponding to the distance L1 and the scanning range for the precise scanning of the reflecting prism 300 corresponding to the distance L2 are set.

[0119] In step S105, the direction of the reflection prism 300 is taken as the center, and the scanning range corresponding to the distance to the reflection prism 300 is further set. In addition, in step S105, the direction of the reflection prism 400 is taken as the center, and the scanning range corresponding to the distance to the reflection prism 400 is further set. In addition, in step S105, the scanning range is set at a vertical angle of 0°.

[0120] Next, the scanning range obtained in step S105 is set (corrected) in consideration of factor 2 (step S106). Fig. 9 As described above, the higher the vertical angle, the smaller the scanning range becomes, so the scanning range is intentionally expanded at a high vertical angle. In addition, in the case of a vertical angle of 90° as a unique value, the range of a horizontal angle of 360° is used as the scanning range (however, the acquisition range of the longitudinal scanning data is limited).

[0121] After step S106 , a second laser scan is performed (step S107 ). The second laser scan is performed on the scan range obtained after step S106 by narrowing down the specific range.

[0122] In the second laser scan, a variable optical attenuator 211 is inserted before the light receiving unit 202 to reduce the intensity of the laser scanning light input to the light receiving unit 202. This prevents the saturation of the light receiving element and suppresses the reduction of the distance measurement accuracy. The degree of light reduction is adjusted based on the intensity of the detection light obtained in the first laser scan and the distance to the reflective prism as the target.

[0123] For example, assuming that the scanning range obtained in step S106 is 90° to 91° for horizontal angles and 5° to 6° for right angles. In addition, regarding horizontal angles, the north direction is regarded as 0° when viewed from vertically above and measured clockwise. Regarding vertical angles, the horizontal direction is regarded as 0° and the vertically above is regarded as 90° for measurement.

[0124] In this case, the horizontal angle scanning range is set to 3° to 8° with a margin, and the scanning data obtained from the range of 5° to 6° is used. The vertical scanning is performed over the entire circumference (360°), and the scanning data obtained from the range of 0° to 1° is used. This makes the processing efficient.

[0125] Next, the centroid position of the scanning data of the reflecting prisms 300 and 400 obtained by the second laser scanning is calculated (step S108), and the reflection center position of the reflecting prisms 300 and 400 is obtained based on the centroid position (step S109). The position data obtained here does not have the problem of saturation of the light receiving element, so it has high accuracy.

[0126] If the positions of the reflecting prisms 300 and 400 are obtained, the position and posture of the laser scanning device 200 in the absolute coordinate system are calculated by the back intersection method (step S110). If the position and posture of the laser scanning device 200 in the absolute coordinate system are calculated, the position of each point of the point cloud data obtained by the first laser scanning in the absolute coordinate system is calculated using the position and posture (step S111).

[0127] The processing of steps S110 and S111 is performed using a computer for data processing instead of the laser scanning device 200. That is, the data of step S109 is sent to the computer for data processing, and the computer performs the processing of steps S110 and S111.

[0128] (Superiority) According to this embodiment, it is possible to set appropriate scanning conditions in laser scanning, thereby making the process efficient.

[0129] Description of Reference Numerals 200 laser scanning device, 221 tripod, 223 horizontal rotating unit, 224 vertical rotating unit, 225 optical unit.

Claims

1. A laser scanning device, characterized in that: have: a distance acquisition unit that acquires the distance from the laser scanning device to a specific object; and a condition setting unit for setting a condition for acquiring laser scanning data limited to the specific object, The laser scanning data limited to the specific object is laser scanning data within a specific angle range observed from the laser scanning device. In the case where the distance is relatively long, the specific angle range is set to be relatively small. In the case where the distance is relatively short, the specific angle range is set relatively large.

2. The laser scanning device according to claim 1, characterized in that: Set the following conditions: When the distance is relatively long, the laser scanning density per unit angle range is relatively large. When the distance is relatively short, the laser scanning density per unit angle range is relatively small.

3. The laser scanning device according to claim 1 or 2, characterized in that: The laser scanning device comprises: A horizontal rotating portion that rotates horizontally; and The vertical rotating part is arranged on the horizontal rotating part, and is vertically rotated with the horizontal direction as the rotation axis, and has an optical part for irradiating the laser scanning light to the outside. The specific angle range includes the angle range in the horizontal direction, Based on the vertical position of the specific object, the horizontal angle range is adjusted. In this adjustment, the angle range in the horizontal direction is expanded when the vertical angle position of the specific object is a relatively high vertical angle position, compared to when the vertical angle position of the specific object is a relatively low low vertical angle position.

4. The laser scanning device according to any one of claims 1 to 3, characterized in that: The cross-sectional shape of the laser scanning light emitted from the laser scanning device is a long strip shape. The laser scanning light is reflected by the rotating reflector to perform laser scanning. The cross-sectional shape of the laser scanning light rotates according to the direction in which it is reflected by the reflector, According to the direction of reflection of the reflecting mirror, the conditions for acquiring the laser scanning data are set.

5. A laser scanning method, using a laser scanning device, characterized in that: Obtaining the distance from the laser scanning device to a specific object, setting conditions for obtaining laser scanning data limited to the specific object, The laser scanning data limited to the specific object is laser scanning data within a specific angle range observed from the laser scanning device. In the case where the distance is relatively long, the specific angle range is set to be relatively small. In the case where the distance is relatively short, the specific angle range is set relatively large.

6. A laser scanning program, which enables a computer to control a laser scanning device to perform laser scanning, characterized in that: The computer is used to obtain the distance from the laser scanning device to the specific object. causing the computer to set conditions for obtaining laser scanning data limited to the specific object, The laser scanning data limited to the specific object is laser scanning data within a specific angle range observed from the laser scanning device. In the case where the distance is relatively long, the specific angle range is set to be relatively small. In the case where the distance is relatively short, the specific angle range is set relatively large.

Images