JP2023119546A - Laser scan control device, laser scan device, laser scan control method, and program - Google Patents

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

The present invention relates to the technology of laser scanning.

For example, laser scanning is used as a surveying tool at construction sites. In this technique, laser scanning is performed with a reflecting prism set as a target.

At this time, the reflected light from the reflecting prism is strong, and the light receiving element of the laser scanning device is saturated. Therefore, positioning of the reflecting prism is performed through a neutral density filter. This technique is described in Patent Document 1, for example.

Patent No. 2926521

Positioning of the reflecting prism via the above-described neutral density filter requires adjustment to an appropriate light reduction state. This is because if the degree of dimming is large, the intensity of the detected ranging light is low and the accuracy of ranging decreases. This is because the accuracy of distance measurement is lowered due to the saturation of the part.

A conceivable method is to measure the position on a trial basis with respect to the reflecting prism and finely adjust or switch the light-reducing filter so that the detection level of the ranging light is appropriate. However, this method increases the number of work steps and is not practical. At present, a compromise is made in terms of the positioning accuracy of the reflecting prism, and a neutral density filter that is generally judged to be appropriate is used.

In view of this background, the present invention aims to provide a technique for solving the problem of strong reflected light from a reflector target in laser scanning.

The present invention is a device for controlling laser scanning by a laser scanning device having a light receiving portion, wherein a first laser scan is performed under conditions in which the light receiving portion is saturated by reflection from a surveying reflector; A control unit for executing a second laser scan performed under a condition that does not occur, a distance acquisition unit for acquiring the distance to the surveying reflector based on the first laser scan, and the second laser scan 2, the laser scanning control device comprising: an adjustment unit that adjusts the intensity of the light received by the light receiving unit based on the distance to the surveying reflector.

In the present invention, there is a mode in which the adjustment of the intensity of the detection light is performed by an optical attenuator arranged in front of the light receiving section for the detection light. In the present invention, the optical attenuator is adjusted to have a relatively small attenuation when the distance to the surveying reflector is relatively long, and the distance to the surveying reflector is relatively short. case, the attenuation amount is adjusted to be relatively large.

In the present invention, there is a mode in which the optical attenuator is adjusted so that the intensity of the detection light is constant regardless of the distance to the surveying reflector. In the present invention, there is a mode in which the intensity of the detection light is adjusted by adjusting the intensity of the measurement light emitted from the light emitting unit of the laser scanning device to the scanning target.

The present invention can also be understood as a laser scanning device incorporating the above-described laser scanning control device.

In the present invention, the reflector for surveying is a reflecting prism, and includes a reflecting prism detection section for detecting reflected light from the reflecting prism, and the reflecting prism detection section detects, in the second laser scanning, the Reflected light whose output of the light receiving unit is equal to or greater than a specific threshold is detected as reflected light from the reflecting prism, and the specific threshold is 5% to 50% of the maximum value of the output of the light receiving unit in the second laser scan. Examples are embodiments in which the values are in the range of %.

In the present invention, the reflector for surveying is a reflecting prism, and includes a reflecting prism detection section that detects reflected light from the reflecting prism, and the reflecting prism detection section detects the Reflected light at which the output of the light receiving unit is equal to or greater than a specific threshold at a position at a distance from the laser scanning device equal to or greater than a specific distance is detected as reflected light from the reflecting prism, and the result of the first scan is: A first bright spot group in which the output of the light receiving unit has low dependence on distance and a second bright spot group in which the output of the light receiving unit has high dependence on distance are included, and 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 bright spot group is 70% or less of the maximum value of the output of the light receiving unit for the first bright spot group; is a value exceeding the maximum value of the output of the light-receiving unit relating to the second bright spot group at the specific distance.

The present invention is a method for controlling laser scanning by a laser scanning device having a light receiving section, comprising: a first laser scanning performed under conditions in which the light receiving section is saturated by reflection from a surveying reflector; Perform a second laser scan performed under conditions that do not occur, based on the first laser scan, to obtain the distance to the survey reflector, in the second laser scan, the survey reflector It can also be grasped as a laser scanning control method for adjusting the intensity of the light received by the light receiving unit based on the distance to.

The present invention is a program for controlling a laser scanning device having a light receiving portion, wherein a first laser scan is performed by a computer under conditions in which the light receiving portion is saturated by reflection from a surveying reflector; A control unit for executing a second laser scan performed under conditions where saturation does not occur, a distance acquisition unit for acquiring the distance to the surveying reflector based on the first laser scan, and the second laser In scanning, it can also be understood as a program that operates as an adjusting unit that adjusts the intensity of light received by the light receiving unit based on the distance to the surveying reflector.

The present invention solves the problem of strong reflected light from reflector targets in laser scanning.

It is a figure which shows the outline|summary of laser scanning. It is a figure which shows the external appearance of a laser scanning apparatus. 1 is a block diagram of a laser scanning device and a processing device; FIG. It is a block diagram of an optical system. It is a figure which shows the principle of control. 4 is a flow chart showing an example of a procedure of processing; FIG. 11 is a block diagram of another variation of the optical system; FIG. 11 is a block diagram of another variation of the optical system; FIG. 4 is a diagram of data showing the relationship between the distance in laser scanning and the output of the light receiving section; FIG. 4 is a diagram of data showing the relationship between the distance in laser scanning and the output of the light receiving section;

1. First embodiment (outline)
FIG. 1 shows a state in which a laser scanning device 200 and reflecting prisms 300 and 400 serving as targets are installed at a site where point cloud data is desired to be acquired.

FIG. 1 also shows a processing device 500 for processing data obtained by laser scanning and for controlling the laser scanning device 200 . The processing device 500 is a computer, and an example using a PC (personal computer) is shown here.

Reflecting prisms 300 and 400 are placed at points whose positions in the absolute coordinate system are known. The absolute coordinate system is the coordinate system used in maps and GNSS. A local coordinate system can also be used as the coordinate system.

In FIG. 1, the objects to be scanned other than the reflecting prism are not shown, but in reality there are objects to be laser scanned (for example, landforms and buildings) other than the reflecting prism.

Reflecting prisms 300 and 400 turn the incident light by 180° and reflect it. Reflecting prisms 300 and 400 are commercially available for surveying. Other reflectors such as retroreflectors can also be used in addition to the reflecting prisms.

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 (for example, an all-around scan) and a second laser scan focused on the reflecting prism.

Here, a wide range of point cloud data is obtained by the first laser scanning, but the position of each point on 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.

Therefore, by the second laser scanning, the positioning of the reflecting prisms 300 and 400 installed at known points in the absolute coordinate system is performed, and the position and orientation of the laser scanning device 200 in the absolute coordinate system are calculated by the retrosection method. .

By knowing the position and orientation of the laser scanning device 200 in the absolute coordinate system, the coordinates in the absolute coordinate system are given to the point cloud data obtained by the first laser scan, and the point cloud data in the absolute coordinate system can be obtained. . Note that the number of reflecting prisms may be three or more.

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

Therefore, a second laser scan is performed for accurate positioning of the reflecting prisms 300 and 400 . At this time, a variable optical attenuator is used to weaken the input level of the distance measuring light to the light receiving element so as to obtain high positioning accuracy. The control of this variable optical attenuator is performed based on the distance information of the reflecting prism obtained by the first laser scanning.

Saturation due to a strong input in the light receiving section 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 peaked, but the accuracy of distance measurement is ensured. When the degree of saturation increases, the distortion of the waveform of the output of the light receiving element becomes conspicuous, an error occurs in distance measurement using the phase difference of the waveform, and the accuracy of distance measurement decreases.

The second scan is performed in a state in which the latter accuracy of distance measurement is not adversely affected (a state in which the accuracy of distance measurement is ensured). Therefore, in the second scan, saturation in the light receiving unit 202 is allowed at a level that does not adversely affect the accuracy of distance measurement.

(Hardware configuration)
FIG. 2 shows the appearance of a laser scanning device (laser scanner) 200. As shown in FIG. The laser scanning device 200 includes a tripod 211 , a base portion 212 fixed to the top of the tripod 211 , a horizontal rotation portion 213 which is a rotating body capable of horizontal rotation on the base portion 212 , and a vertical rotation with respect to the horizontal rotation portion 213 . It has a vertical rotating part 214 which is a possible rotating body. The laser scanning device 200 is operated by an external controller (operating terminal) (not shown) that is wirelessly connected.

The vertical rotation section 214 includes an optical section 215 for emitting and receiving laser scanning light. A pulse of laser scanning light is emitted from the optical unit 215 . This pulse emission is performed along a direction (vertical plane) perpendicular to the rotation axis (horizontally extending axis) while the vertical rotation section 214 rotates. In this case, pulses of laser scanning light are emitted from the optical unit 215 along the vertical direction (angular directions of the elevation angle and the depression angle).

While horizontally rotating the horizontal rotating unit 213 and vertically rotating the vertical rotating unit 214, the optical unit 215 emits a pulse of laser scanning light, and the optical unit 215 receives the reflected light from the object. A laser scan of the surroundings is performed.

By horizontally rotating the horizontal rotation unit 213 at the same time as scanning along the direction of the vertical angle (vertical scanning), the scanning line (vertical scanning line) along the direction of the vertical angle (vertical scanning line) moves in the direction of the horizontal angle (horizontal direction). Move along the edge. Note that when horizontal rotation is also performed at the same time as vertical rotation, scanning along the vertical direction (vertical scanning line) is not completely along the vertical direction, but is slightly slanted. Note that if the horizontal rotation unit 213 does not rotate, the scan along the vertical direction (vertical scan line) will be along the vertical direction.

Rotation of the horizontal rotation section 213 and the vertical rotation section 214 is performed by a motor. The horizontal rotation angle of the horizontal rotation section 213 and the vertical rotation angle of the vertical rotation section 214 are precisely measured by encoders.

Each laser scanning light is a single pulse distance measuring light, and one laser scanning light measures the distance of a scanning point, which is a reflection point hit by the laser scanning light. The position of the scanning point (reflection point of the laser scanning light) with respect to the laser scanning device 200 is calculated from the distance measurement value and the irradiation direction of the laser scanning light.

As a form of the laser scanning point group output from the laser scanning device 200, there is a form of outputting distance and direction data for each point (each scanning point). A mode is also possible 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 group data. The laser scan point cloud data also includes information on the brightness (intensity of reflected light) of each scan point.

FIG. 3 is a block diagram of laser scanning device 200 and processing device 500 . Laser scanning device 200 includes light emitting unit 201 , light receiving unit 202 , distance measuring unit 203 , direction acquiring unit 204 , light emission control unit 205 , drive control unit 206 , variable optical attenuator 207 , communication device 208 and storage unit 209 .

FIG. 4 is a block diagram of the optical system of the laser scanning device 200. As shown in FIG. 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. Laser scanning light emitted by the light emitting unit 201 is emitted to the outside from the optical unit 215 of FIG. The light combiner/separator 250 is an optical system that uses a half mirror or a dichroic mirror to separate and combine the optical paths of outgoing light and incident light.

The light-receiving unit 202 has a light-receiving element that receives laser scanning light, an optical system related to light reception, and peripheral circuits. The reflected light of the laser scanning light taken in from the optical section 215 is guided from the light combining/separating section 250 to the variable optical attenuator 207 and then to the light receiving section 202 . The variable optical attenuator 207 will be described later.

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 branched into two, one of which is irradiated as laser scanning light onto the target from the optical unit 215, and the other is guided to the reference optical path as reference light.

The laser scanning light reflected from the object and taken in from the optical section 215 and the reference light propagated through the reference optical path are combined and input to the light receiving section 202 . The laser scanning light and the reference light have different propagation distances, and the reference light is first detected by the light receiving element, and then the laser scanning light is detected by the light receiving element.

Here, looking at the output waveform of the light receiving element, the detection waveform of the reference light is first output, and then the detection waveform of the laser scanning light is output after a time lag. The distance to the reflection point of the laser scanning light is calculated from the phase difference (time difference) between these two waveforms. It should be noted that it is also possible to calculate the distance from the flight time of the laser scanning light.

A direction acquisition unit 204 acquires the direction of the optical axis of the laser scanning light. 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 (angle of elevation or angle of depression). The direction acquisition unit 204 has a horizontal angle detection unit 204a and a vertical angle detection unit 204b.

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

By measuring the horizontal rotation angle of the horizontal rotation unit 213 and the vertical rotation angle of the vertical rotation unit 214, the direction of the optical axis of the laser scanning light seen from the laser scanning device 200, that is, the direction of the scanning point can be determined.

The light emission control unit 205 controls the light emission timing of the laser scanning light in the light emitting unit 201 . The drive control unit 206 includes a horizontal rotation drive control unit 206a that performs drive control for horizontally rotating the horizontal rotation unit 213, and a vertical rotation drive control unit 206b that performs drive control for vertically rotating the vertical rotation unit 214. .

The variable optical attenuator 207 attenuates light incident on the light receiving section 202 (see FIG. 4). This attenuation (attenuation rate) can be varied. The attenuation amount is varied based on the distance to the object calculated by the distance measuring unit 203 .

As the variable optical attenuator 207, there are a type that adjusts the transmittance by rotating a semi-transmissive disc whose transmittance is set to change gradually in the circumferential direction, a type that controls the transmittance of the liquid crystal, and the like. . Variable optical attenuator modules are commercially available and can be used by appropriately selecting them.

Since the reflection from the reflecting prism is strong, the light receiving element is saturated, resulting in an error in the distance measurement value. For example, according to experiments by the present inventors, it has been found that in a laser scanner capable of distance measurement with an accuracy of several millimeters, an error on the order of centimeters occurs in the case of reflected light from a reflecting prism. The degree of increase in this error is not constant due to the non-linear operation of the light-receiving element, but it is about several times to ten times the normal measurement error.

By arranging the variable optical attenuator 207 in front of the light receiving section, the intensity of light entering the light receiving section is weakened, thereby suppressing the occurrence of the above problem.

The communication device 208 communicates with the processing device 500, an external controller (not shown), and other devices. Communication is performed using a cable, a wireless LAN, a mobile phone line, or the like. The storage unit 209 is configured by a semiconductor memory or a hard disk device, and stores an operation program and data necessary for the operation of the laser scanning device 200 and data obtained as a result of the operation process.

The processing device 500 performs operation control of the laser scanning device 200 and processes point cloud data (laser scanning point cloud data) obtained by the laser scanning device 200 . A form in which part or all of the processing device 500 is built into the laser scanning device 200 is also possible. A mode is also possible in which a part or all of the functions of the processing device 500 are realized by a data processing server.

The processing device 500 is configured by a PC (personal computer). Part or all of the processing device 500 can also be configured with dedicated hardware.

The processing device 500 includes a laser scanning device control unit 501, a reflecting prism detection unit 502, a distance acquisition unit 503 to the reflecting prism, a variable optical attenuator control unit 504, a point cloud data generation unit 505, a communication device 506, and a storage unit 507. Prepare.

A laser scanning device control unit 501 generates a control signal for controlling the operation of the laser scanning device 200 . This control signal is transmitted from the communication device 506 to the laser scanning device 200 . This control signal includes a control signal for controlling laser scanning and a control signal for controlling the variable attenuator 207 .

Reflecting prism detection unit 502 determines whether or not the measuring light is reflected from the reflecting prism based on the intensity of the measuring light (scanning light reflected from the object) detected by light receiving unit 202. Furthermore, if the light is reflected from the reflecting prism, it is identified and detected as reflected light from the reflecting prism.

A distance acquisition unit 503 to the reflecting prism acquires the distance measurement (distance measurement value) to the reflecting prism detected by the reflecting prism detection unit 502 . Calculation of this distance is performed by the distance measurement unit 203 .

A variable optical attenuator control unit 504 generates a control signal for adjusting the attenuation amount (the degree of light attenuation) of the variable optical attenuator 207 . A variable optical attenuator control unit 504 adjusts the incident light to the light receiving unit 202 to a specific level based on the distance measurement information of the reflecting prism. This principle will be explained below.

The principle is shown in FIG. The horizontal axis of FIG. 5A is the distance (relative value) to the reflection point, and the vertical axis is the light receiving efficiency. The light receiving efficiency is the ratio of emitted light to incident light ((incident light intensity/outgoing light intensity)×100(%)). The light receiving efficiency decreases as the distance increases, and increases as the distance decreases. In addition, in FIG. 5A, the fact that the light-receiving efficiency decreases at extremely short distances is due to the nonlinearity of the optical system.

Therefore, as shown in FIG. 5B, the longer the distance, the smaller the attenuation of the optical attenuator 208 , and the shorter the distance, the larger the attenuation of the variable optical attenuator 207 . The horizontal axis of FIG. 5B is the distance (relative value) to the reflection point, and the vertical axis is the transmittance of the variable optical attenuator 207 . The transmittance is (outgoing light intensity/incident light intensity)×100 (in %) at the variable optical attenuator 207 . The attenuation amount in the variable optical attenuator 207 increases as the transmittance decreases.

By adjusting the transmittance according to the distance as shown in FIG. 5B, as shown in FIG. can set the intensity of the reflected light to a certain level.

That is, when the distance is short, the attenuation of the variable optical attenuator 207 is increased (that is, the transmittance is decreased), and when the distance is long, the reverse control is performed. Thus, ideally, the intensity of the measurement light incident on the light receiving unit 202 can be made constant (see FIG. 5C).

Here, the appropriate light intensity value (appropriate received light intensity) for light reception by the light receiving unit 202 is obtained in advance, and the transmittance of the variable light attenuator 207 required to obtain the appropriate received light intensity according to the distance , and the amount of control required to achieve this transmittance.

Specifically, the distance to the reflecting prism is X, the transmittance of the variable light attenuator 207 is A, and the intensity of the light received by the light receiving unit 202 is an appropriate constant value (or an appropriate range). The relation of A becomes A=f(X). As a tendency, when X increases (the distance to the reflecting prism increases), A increases (more transmission: less attenuation), and when X decreases (the distance to the reflecting prism decreases), A decreases ( attenuate more).

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

The point cloud data creation unit 505 calculates the position and orientation in the absolute coordinate system of the laser scanning device 200 based on the positioning data of the reflecting prisms 300 and 400 obtained in the second laser scan, and based on this, in the first laser scan A process of associating the obtained point cloud data with the absolute coordinate system is performed.

Communication device 506 communicates with laser scanning device 200 and other devices. Communication is performed using a cable, a wireless LAN, a mobile phone line, or the like. The storage unit 507 is configured by a semiconductor memory or a hard disk device, and stores an operation program and data necessary for the operation of the processing device 500 and data obtained as a result of the operation process.

(Example of processing)
FIG. 6 shows an example of the processing procedure. A program for executing the process of FIG. 6 is stored in the storage unit 507 of the processing device 500, read out by the CPU of the computer forming the processing device 500, and executed. A mode is also possible in which the program is stored in an appropriate storage medium and read out from there for use.

Prior to the process of FIG. 6, first, the laser scanning device 200 and the reflecting prisms 300 and 400 are installed at the site where laser scanning is to be performed. Here, the position and attitude of the laser scanning device 200 are unknown, and the reflecting prisms 300 and 400 are installed at points whose positions in the absolute coordinate system are known. Points whose positions in this absolute coordinate system are known have been positioned and positioned by previous survey work. A local coordinate system can also be used as the coordinate system.

At this stage, normal scanning (first laser scanning) is performed (step S101). A normal scan is performed in the area where the acquisition of the point cloud is planned. This planned range includes the entire perimeter and some limited range. The normal scan is for obtaining the point cloud of the survey target, and is performed under the conditions for obtaining the normal laser scan point cloud.

By normal scanning, distance and direction data (point cloud data) from the optical origin of the laser scanning device 200 (the origin of positioning) to each point is obtained. 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 point cloud data and the absolute coordinate system is unknown.

Next, from the point group obtained in step S101, points at which the light amount overflows (the incident light is too strong and the light receiving element is saturated) are extracted as reflection points of the reflecting prism (step S102).

Since normal scanning requires detection of reflected light from sources other than the reflecting prism, the intensity of emitted light and the detection sensitivity of incident light are set to achieve the purpose. On the other hand, under normal scanning conditions, the reflected light from the reflecting prism is too strong, causing the overflow described above.

In laser scanning, the detection intensity of the detection light (the output level of the light receiving element) is also obtained as point (reflection point) information. In step S102, points with detection intensities exceeding a predetermined level are extracted.

Next, the distance of the point extracted in step S102 (distance from the laser scanning device 200) is obtained (step S103). The distance acquired here is the distance calculated by the distance measurement unit 203 . Since the light-receiving element is saturated, the distance measured here contains a larger error than usual, and the accuracy is not satisfactory for use in surveying. No problem to. The process of step S102 is performed by the distance acquisition unit 503 to the reflecting prism.

Next, based on the distance to the reflecting prism obtained in step S103, the attenuation (transmittance) of the variable optical attenuator 207 is set (step S104). This processing is performed in the control section 504 of the variable optical attenuator 207 .

Next, light control scanning (second laser scanning) is performed (step S105). Light control scanning is laser scanning based on the conditions set in step S104. In light control scanning, laser scanning is performed by adjusting the light receiving section 202 so that it is not saturated by reflected light from the reflecting prisms 300 and 400 . That is, laser scanning is performed by attenuating the detection light entering the light receiving section 202 with the variable optical attenuator 207 .

Dimming scans allow accurate positioning of reflecting prisms 300 and 400 . A dimming scan is performed in a focused range on reflecting prisms 300 and 400 . This is to suppress useless scanning. Of course, the dimming scan may be performed on the entire circumference.

By performing light control scanning, the reflecting prisms 300 and 400 are accurately positioned, and the positional relationship between the laser scanning device 200 and the reflecting prisms 300 and 400 can be identified.

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

The principle of the processing performed in step S106 will be briefly described below. First, the positional relationship among the laser scanning device 200, the reflecting prisms 300, and the reflecting prisms 400 is known from the result of the light control scanning in step S105. Accordingly, the shape of a triangle with the positions of the laser scanning device 200, the reflecting prisms 300, and the reflecting prisms 400 as vertices is determined.

On the other hand, the positions in the absolute coordinate system of reflecting prisms 300 and 400 are known. That is, the positions of the two vertices of the triangle are determined in the absolute coordinate system. Therefore, the positions in the absolute coordinate system of the laser scanning device 200, which are the remaining vertices of the triangle, are obtained.

Also, since the orientation of each side of the triangle in the absolute coordinate system is known, the attitude of the laser scanning device 200 in the absolute coordinate system can be obtained. Thus, the position and orientation of the laser scanning device 200 in the absolute coordinate system are obtained. This processing is performed by the point cloud data creation unit 505 . Separately, an exterior orientation element calculation unit may be prepared and the processing of step S106 may be performed there.

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

For example, in association with each point, the data of the distance and direction of each point with the laser scanning device 200 as the origin, the coordinates of the origin in the absolute coordinate system, and the posture of the laser scanning device in the absolute coordinate system are created. This becomes point cloud data that can be handled on the absolute coordinate system.

Also, point cloud data obtained by normal scanning may be converted into point cloud data described on 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 normal scanning can be coordinate-converted into the coordinates in the absolute coordinate system. Specifically, regarding the translation and rotation information required for coordinate transformation, the position of the laser scanning device 200 in the absolute coordinate system provides the translation information, and the attitude of the laser scanning device 200 in the absolute coordinate system. gives the rotation information. Then, based on these pieces of information, the point cloud data obtained by the normal scanning are translated and further rotated to obtain the point cloud data described on the absolute coordinate system. This process may be performed in step S107.

(Superiority)
Excessive input to the light receiving unit 202 is suppressed, and the problem of strong reflected light from a reflector target in laser scanning can be resolved. Further, since the attenuation amount of the optical attenuator is set according to the distance to the reflecting prism so as to provide a light receiving condition that enables highly accurate distance measurement, the distance measuring of the reflecting prism can be performed with high accuracy. Therefore, the accuracy of the finally obtained point cloud data can be increased.

2. Second Embodiment FIG. 7 shows an example in which a variable optical attenuator 207 is arranged in front of the light emitting section 201. FIG. In this case, the measurement light emitted from the light emitting unit 201 is attenuated by the attenuator, and is adjusted so as to obtain a reflection intensity suitable for positioning of the reflecting prism.

3. Third Embodiment FIG. 8 shows a case where a variable output light emitting section 260 capable of varying the light emission intensity is used. In this case, the control unit 261 adjusts the light emission intensity of the output variable light emission unit 260 so that the reflection intensity suitable for the positioning of the reflecting prism can be obtained.

4. Fourth Embodiment A form using a device capable of adjusting the sensitivity of the light receiving element is also possible. For example, an avalanche photodiode used as a light receiving element can control the multiplication factor by applying a reverse voltage. By using this, the multiplication factor is lowered when strong reflected light is detected (when the distance is short), and the multiplication factor is increased when weak reflected light is detected (when the distance is long). If the dynamic range cannot be ensured only by adjusting the multiplication factor, the variable optical attenuator described in the other embodiments is used in combination, or the emission intensity is adjusted in combination.

5. Fifth Embodiment In a surveying site, there may be a reflector (hereinafter referred to as a reflector) that reflects visible light with a high reflectance in addition to the reflecting prism. Examples of reflectors include reflective tapes for ensuring safety, various signs, tail lamps of vehicles and heavy machinery, and the like. Since the wavelength of the measurement light from the laser scanner is about 500 nm to 1500 nm, the reflected light from the laser scanner is also reflected with high efficiency from the reflector.

Against this background, in steps S102 and S105 of FIG. 6, it is necessary to prevent the reflected light from a reflector other than the reflecting prism from being erroneously detected as the reflected light from the reflecting prism.

In this embodiment, when there is a reflector such as a sign or a reflector plate in addition to the reflecting prism, detection of the reflecting prism is performed in two stages while suppressing the above-described erroneous detection. Here, the first-stage detection is performed on the results of normal scanning. A second stage of detection is performed on the result of the dimming scan.

As will be described later, in the first-stage detection, the reflecting prism and the reflector cannot be distinguished at a short distance, and there is a possibility that the reflector is erroneously detected. A reflecting prism can be reliably detected by distinguishing it from a body. Here, the non-reflecting prism means a reflector that is not a reflecting prism (a highly reflective light-reflecting object such as a reflective tape). The processes related to the first-stage detection and second-stage detection are performed in the reflecting prism detection section 502 .

A detailed description will be given below. First, detection at the first stage will be described. FIG. 9 shows measured values of the relationship between the detected intensity (vertical axis) of reflected light from various reflectors and the distance (m) from the laser scanner to the reflection target in normal scanning. Here, the detected intensity on the vertical axis is the relative value of the output of the light receiving section 202 .

In Figure 9, the safety vest is a vest with a sheet of reflective material. Signs, tail lights, and guardrail reflectors have reflectors constructed of light-reflective materials to enhance visibility. Reflecting prisms 1 and 2 are reflecting prisms of different model numbers that are commercially available for surveying.

From FIG. 9, when the distance from the laser scanner is somewhat long (60 m or more in the case of FIG. 9), the output of the light receiving unit 202 that received the reflected light from the reflecting prism and the light receiving unit that received the reflected light from the reflector It can be seen that there is a difference from the output of 202 .

Using this phenomenon, in step S102, the reflected light is excluded (not selected) from the non-reflecting prism. In this example, the position of the output value of 8000 on the vertical axis of FIG. 9 is set as the threshold, and when the output value is greater than that, it is selected as reflected light from the reflecting prism.

The above threshold value is set to a value exceeding the maximum value of the output of the light receiving unit 202 that receives reflected light from a reflector other than a reflecting prism at a specific distance from the laser scanner. Here, the specific distance from the laser scanner is determined as follows.

As shown in FIG. 9, the result of normal scanning includes a first bright spot group in which the output of the light receiving unit 202 does not change much with distance, and a second bright spot group in which the output of the light receiving unit 202 greatly decreases with increasing distance. point cloud. That is, in the scan point group obtained by normal scanning, there are a first bright point group in which the output of the light receiving unit 202 is less dependent on the distance, and a second bright point group in which the output of the light receiving unit 202 is highly dependent on the distance. A bright spot group is included.

As the distance increases further, the output of the light receiving section 202 of the first bright spot group gradually decreases. This is because the intensity of the reflected light to be detected gradually decreases as the distance increases due to scattering of the scanning light in the air and spread of the beam of the scanning light. Even so, the bright spots in the first group in which the intensity of the reflected light from the reflecting prism is less dependent on the distance and the second group in which the intensity of the reflected light from the non-reflecting prism is highly dependent on the distance clearly divided into luminescent spots.

Here, the specific distance is the shortest distance at which the maximum value of the output of the light receiving unit 202 related to the second bright spot group is 70% or less of the maximum value of the output of the light receiving unit 202 related to the first bright spot group. Defined as distance.

An example of a specific procedure for obtaining the specific distance will be described below. First, the results of the normal scan were analyzed, and a group of bright spots (first group of bright spots) in which the output of the light receiving unit 202 did not decrease so much even when the distance increased, and a group of bright spots in which the output of the light receiving unit 202 decreased as the distance increased. find a group of bright spots (second bright spot group). Then, an approximate distance Lth at which separation occurs between the two groups is obtained.

In the case of FIG. 9, it is estimated that Lth=40 m to 60 m, but here the minimum value is taken and Lth=40 m. The first bright spot group is the bright spot group of the reflecting prism, and the second bright spot group is the bright spot group from the reflector other than the reflecting prism.

Next, in a range of 40 m or longer, the maximum value Pmax1 of the first group of relatively high-brightness spots and the maximum value Pmax2 of the second group of relatively low-brightness spots are obtained. Then, Pmax2/Pmax1 is obtained in a range of 40 m or more, and the minimum value of the distance satisfying Pmax2/Pmax1<0.7 is obtained. In the case of FIG. 9, this distance is approximately 60 m.

In the case of FIG. 9, the maximum value of the output of the light receiving unit 202 of the reflected light from the reflector other than the reflecting prism at the separation distance of 60 m from the laser scanner device is estimated to be about 6500-6750. Therefore, the threshold is set to 8000 with some margin.

In the case of FIG. 9, if the distance is 60 m or more, the reflected light from the reflecting prism can be reliably detected by the set threshold, and at the same time, the reflected light from the reflector other than the reflecting prism can be undetected. As a result, the frequency of detecting a large number of reflection points that are candidates for dimming scanning can be suppressed, and the efficiency of processing can be improved.

On the other hand, in the case of FIG. 9, at a short distance of 40 m or less, the reflected light from the sign, reflective sheet, tail lamp, and guardrail reflector cannot be distinguished from the reflected light from the reflecting prism. Therefore, reflected light from a reflector other than a reflecting prism may be erroneously detected as reflected light from a reflecting prism in point cloud data obtained by normal scanning.

Therefore, in this embodiment, the following second step of detecting the reflecting prism is performed. Here, filtering using a threshold value is also performed in the dimming scan in step S105.

FIG. 10 shows the result of obtaining the same data as in FIG. 9 under the condition of light control scanning. In the dimming scan in this case, the intensity of the scan light entering the light receiving element is greatly reduced compared to the normal scan in FIG. Note that the rate of decrease is not uniform because the attenuation of the attenuator is changed according to the distance.

As can be seen from FIG. 10, in the dimming scan, a large (order of magnitude) difference occurs in the output of the light receiving unit 202 between the reflected light from the reflecting prism and the reflected light from the reflector that is not the reflecting prism. The reason for this is considered as follows.

In the case of FIG. 10, the detection level of 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 of the reflecting prism is 1000 or more. Therefore, in terms of the output level of the light receiving section 202, the reflected light from the reflector is 1/20 or less of the reflected light from the reflecting prism.

This can be considered as follows. First, in the detection of the reflected light from the reflecting prism in normal scanning, saturation of the light receiving element occurs, and the linearity of the input (incident light) and the output (corresponding to the vertical axis in FIGS. 9 and 10) of the light receiving element is greatly lost.

Therefore, the accuracy of distance measurement is lowered, and the output of the light receiving element 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 original value that should be output.

Therefore, the detected value of the reflected light from the reflecting prism in FIG. 9 is lower than the actual value. In other words, the output of the light-receiving element is saturated around the relative value of 10000 on the vertical axis, and even if the input increases, no larger value is output.

In the range of 40 m or less in FIG. 9, the light reception detection values of the reflecting prism and the reflector are close values. The degree of saturation of the light receiving element is (reflected light from reflecting prism) >> (reflected light from reflector).

Therefore, the detection level of the reflected light from the reflecting prism (the output level of the light receiving element) does not linearly decrease even after the light adjustment scan of FIG. In other words, even if the input decreases in a state where the degree of saturation of the light receiving element is large, the output does not decrease so much in proportion to the input. In other words, regarding the reflected light from the reflecting prism, the output of the light-receiving element does not decrease so much even if the normal scan changes to the dimming scan. This is because the detection level of the reflected light of the reflecting prism, which is highly saturated, is stuck at the maximum value in the normal scan ⇒ dimming scan, and even if the input decreases, the output does not decrease that much. It is understandable that there is no phenomenon.

On the other hand, the light-receiving element that receives the reflected light from the reflector has a small degree of saturation (or is not saturated), so if the input (incident light intensity) decreases, the output level also goes down. Therefore, with respect to the reflected light from the non-reflecting prism, the output of the light receiving element decreases according to the input when the normal scan changes to the dimming scan.

Under the above circumstances, when normal scanning (FIG. 9) shifts to dimming scanning (FIG. 10), the drop in the detection level of the reflected light from the reflector is more pronounced than the drop in the detection level of the reflecting prism. Become. Thus, in the dimming scan, the detection level of reflected light from the reflector is 1/20 or less of the detection level from the reflecting prism.

In addition, the above mechanism can also explain the reason why there are two bright spot groups at 60 m or more in FIG. 9 . In FIG. 9, the reason why the output of the light receiving unit 202 related to the bright spot of the reflecting prism does not decrease even at 60 m or more is that the light receiving element is in a saturated state in which the output does not decrease even at 60 m or more. We can assume that it continues. Therefore, as the distance increases, the effect of saturation of the light-receiving element decreases, and the output of the light-receiving unit 202 decreases.

Here, the following method is used to identify (distinguish) the reflected light from the reflecting prism and the reflected light from the non-reflecting prism in the scan data obtained in the dimming scan. 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 FIG. 10, the value at about 1750 on the vertical axis is the maximum value. If the maximum value is known in advance or can be predicted, that value may be used. There is also a method of adopting the average value of the top N points (N=50 to 1000) of the output of the light receiving section 202 instead of the maximum value.

Next, a value of 20% of the maximum value, in this case 1750×0.2=350, is set as a threshold for determination. Reflection points where the output from the light receiving unit 202 is less than the above threshold of 350 are reflected from the non-reflecting prism, and reflection points where the output from the light receiving unit 202 is above the threshold of 350 are reflected from the reflecting prism. Identify as reflex.

As shown in FIG. 10, in the dimming scan, the reflected light from the reflecting prism and the reflected light from the non-reflecting prism have a difference of 20 times or more in comparison with the output level of the light receiving section 202 . Therefore, by setting the threshold value as described above, the reflected light from the reflecting prism can be reliably detected.

In the above example, the threshold is 20% of the maximum value of the output of the light receiving unit 202, but the threshold can be set in the range of 5% to 50%. If this threshold is less than 5% of the maximum value of the output of the light-receiving element, the possibility of misdetecting a non-reflecting prism as a reflecting prism increases, and if it exceeds 50%, the reflected light from the reflecting prism may be overlooked. increase.

Also, it is possible to set a threshold according to the distance range. For example, this method is effective when the maximum value fluctuates greatly depending on the distance. For example, a first threshold is set for less than 50 m, a second threshold is set for 50 m to 100 m, and a third threshold is set for a range exceeding 100. The method described above is used to set the threshold in each distance range.

According to this embodiment, useless detection can be suppressed in detection of dimming scan candidates based on the result of normal scanning. Next, it is possible to eliminate the possibility of erroneously detecting an object (such as a reflective tape) that is not a reflective prism as a reflective prism during light control scanning.

6. Others It is also possible to combine multiple of the embodiments described herein.

200... Laser scanning device, 211... Tripod, 212... Base part, 213... Horizontal rotating part, 214... Vertical rotating part, 215... Optical part.

Claims (10)

A device for controlling laser scanning by a laser scanning device having a light receiving unit,
A control unit that executes a first laser scan performed under a condition that the light receiving unit is saturated by reflection from a surveying reflector, and a second laser scan performed under a condition that the saturation does not occur;
a distance acquisition unit that acquires the distance to the surveying reflector based on the first laser scan;
A controller for laser scanning, comprising: an adjusting unit that adjusts the intensity of light received by the light receiving unit based on the distance to the surveying reflector in the second laser scanning. 2. A laser scanning control device according to claim 1, wherein the adjustment of the intensity of the detection light is performed by an optical attenuator arranged in front of the light receiving section for the detection light. The optical attenuator is adjusted to have a relatively small attenuation amount when the distance to the surveying reflector is relatively long, and when the distance to the surveying reflector is relatively short, the relative 3. A laser scanning control device according to claim 2, wherein the attenuation is adjusted to be substantially large. 3. The laser scanning control device according to claim 2, wherein the optical attenuator is adjusted so that the intensity of the detection light is constant regardless of the distance to the surveying reflector. 2. The laser scanning control device according to claim 1, wherein the adjustment of the intensity of the detection light is performed by adjusting the intensity of the measurement light emitted from the light emitting unit of the laser scanning device to the scanning target. A laser scanning device incorporating the laser scanning control device according to claim 1 . The surveying reflector is a reflecting prism,
A reflecting prism detection unit that detects reflected light from the reflecting prism,
The reflecting prism detection unit is
In the second laser scanning, the output of the light-receiving unit is detected as the reflected light from the reflecting prism, the reflected light having a specific threshold value or more;
2. The controller for a laser scanning device according to claim 1, wherein said specific threshold value is a value within a range of 5% to 50% of the maximum value of the output of said light receiving section in said second laser scanning. The surveying reflector is a reflecting prism,
A reflecting prism detection unit that detects reflected light from the reflecting prism,
The reflecting prism detection unit is
In the first laser scanning, the output of the light receiving unit at a position where the distance from the laser scanning device is equal to or greater than a specific distance is detected as reflected light from the reflecting prism, the output of which is equal to or greater than a specific threshold;
The results of the first scan include a first group of bright spots in which the output of the light receiving section is less dependent on the distance, and a second group of bright spots in which the output of the light receiving section is more dependent on the distance. includes
The specific distance is the shortest distance at which the maximum value of the output of the light receiving unit for the second bright spot group is 70% or less of the maximum value of the output of the light receiving unit for the first bright spot group. is defined as
2. The control device for a laser scanning device according to claim 1, wherein said specific threshold value is a value exceeding the maximum value of the output of said light receiving unit relating to said second bright spot group at said specific distance. A method for controlling laser scanning by a laser scanning device having a light receiving unit,
A first laser scan performed under conditions where the light receiving unit is saturated due to reflection from a surveying reflector, and a second laser scan performed under conditions where the saturation does not occur,
Based on the first laser scan, obtain the distance to the survey reflector,
A control method of laser scanning, wherein, in the second laser scanning, intensity of light received by the light receiving unit is adjusted based on the distance to the surveying reflector. A program for controlling a laser scanning device having a light receiving unit,
A control unit that causes a computer to perform a first laser scan under conditions in which the light receiving unit is saturated by reflection from a surveying reflector, and a second laser scan under conditions in which the saturation does not occur;
a distance acquisition unit that acquires the distance to the surveying reflector based on the first laser scan;
and an adjusting unit that adjusts the intensity of light received by the light receiving unit based on the distance to the surveying reflector in the second laser scan.

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