OPTICAL SENSING SYSTEM, OPTICAL SENSING DEVICE, AND OPTICAL SENSING METHOD

The optical sensing system includes a three-dimensional scanner and a scanning density determination means. The three-dimensional scanner measures a distance to a measurement target by scanning the measurement target with a laser light and receiving reflected light of the laser light. The scanning density determination means dynamically determines a scanning density based on a distance to a distance measurement point or luminance of the reflected light during scanning of the three-dimensional scanner so as to suppress variation in a point cloud density caused by a length of the distance to the distance measurement point.

INCORPORATION BY REFERENCE

This application is based upon and claims the benefit of priority from Japanese patent application No. 2022-147845, filed on Sep. 16, 2022, the disclosure of which is incorporated herein in its entirety by reference.

TECHNICAL FIELD

The present disclosure relates to an optical sensing system, an optical sensing device, and an optical sensing method.

BACKGROUND ART

International Patent Publication No. WO 2021/020570 discloses a Lidar (Light Detection and Ranging) scanner that scans a measurement target with a laser light, measures a distance to the measurement target based on reflected light of the laser light, and generates point cloud data based on a measurement result. The point cloud data is typically a set of point data including XYZ coordinate values.

SUMMARY

In general, however, the point cloud density at points far from the Lidar scanner will be lower than the point cloud density at points near the Lidar scanner. This characteristic causes the following problems, for example.

If the point cloud density varies in the same point cloud data, inconvenience may occur in various analyses using the point cloud data. The various analyses are, for example, detection of cracks that may occur on the surface of a building as a measurement target.

Therefore, an object of the present disclosure is to provide a technique for suppressing a variation in point cloud density caused by a length of a distance to a distance measurement point.

An example object of the invention is to provide an optical sensing system, an optical sensing device, and an optical sensing method.

In a first example aspect, the optical sensing system includes a three-dimensional scanner configured to measure a distance to a measurement target by scanning the measurement target with a laser light and receiving reflected light of the laser light. The optical sensing system includes a scanning density determination unit for dynamically determining a scanning density based on a distance to a distance measurement point or luminance of the reflected light during scanning of the three-dimensional scanner so as to suppress variation in a point cloud density caused by a length of the distance to the distance measurement point.

In a second example aspect, the optical sensing device includes a three-dimensional scanner configured to measure a distance to a measurement target by scanning the measurement target with a laser light and receiving reflected light of the laser light. The optical sensing device includes a scanning density determination unit for dynamically determining a scanning density based on a distance to a distance measurement point or luminance of the reflected light during scanning of the three-dimensional scanner so as to suppress variation in a point cloud density caused by a length of the distance to the distance measurement point.

In a third example aspect, the optical sensing method includes a distance measurement step of measuring a distance to a measurement target by scanning the measurement target with a laser light and receiving reflected light of the laser light. The optical sensing method includes a scanning density determination step of dynamically determining a scanning density based on a distance to a distance measurement point or luminance of the reflected light during scanning in the distance measurement step so as to suppress variation in a point cloud density caused by a length of the distance to the distance measurement point.

EXAMPLE EMBODIMENT

(Outline of Present Disclosure)

Hereinafter, an outline of the present disclosure will be described with reference toFIG.1.FIG.1illustrates a functional block diagram of an optical sensing system.

As illustrated inFIG.1, an optical sensing system100includes a three-dimensional scanner101and a scanning density determination means102.

The three-dimensional scanner101measures the distance to the measurement target by scanning the measurement target with a laser light and receiving the reflected light of the laser light.

The scanning density determination means102dynamically determines the scanning density based on the distance to the distance measurement point or the luminance of the reflected light during the scanning of the three-dimensional scanner101so as to suppress the variation in the point cloud density caused by the length of the distance to the distance measurement point.

According to the above configuration, it is possible to suppress the variation in the point cloud density caused by the length of the distance to the distance measurement point.

First Example Embodiment

Next, a first example embodiment of the present disclosure will be described with reference toFIGS.2and3.

FIG.2is a functional block diagram of an optical sensing system1. As illustrated inFIG.2, the optical sensing system1includes a three-dimensional Lidar scanner2and a defect detection device3.

The three-dimensional Lidar scanner2generates point cloud data of a building4which is a specific example of a measurement target. The defect detection device3detects a surface defect such as a crack that may occur on the surface of the building4based on the point cloud data generated by the three-dimensional Lidar scanner2. In the present example embodiment, the measurement target is assumed to be a stationary object. The stationary object includes, for example, an object having no movable portion such as a building and an object having a movable portion such as a movable bridge and being in a stationary state.

The three-dimensional Lidar scanner2includes a light emitting unit5, an optical mechanism system6, a measurement unit7, and a point cloud data generation unit8.

The light emitting unit5includes a scanning density determination unit10, a control unit11, an oscillator12, a light source driver13, a light source14, and a scan driver15.

The optical mechanism system6includes an irradiation optical system6aand a light receiving optical system6b. The irradiation optical system6aincludes a lens20, a first optical element21, a lens22, and a mirror23. The light receiving optical system6bincludes a second optical element24and a mirror23. That is, the irradiation optical system6aand the light receiving optical system6bshare the mirror23.

The measurement unit7includes a photodetector30, a sensor31, a lens32, an amplifier33, a signal generation unit34, a data generation unit35, and a data output unit36.

The scanning density determination unit10determines the scanning density, and outputs scanning density data indicating the determined scanning density to the control unit11.

The control unit11controls the oscillator12based on the scanning density data input from the scanning density determination unit10. The light source driver13drives the light source14based on the pulse signal generated by the oscillator12. The light source14is, for example, a laser light source such as a laser diode. The light source14is driven by the light source driver13to intermittently emit a laser light L1. In the present example embodiment, the scanning density data is pulse period data indicating a pulse period of a pulse signal generated by the oscillator12.

The light source14, the lens20, the first optical element21, the second optical element24, and the mirror23are arranged in this order on the optical axis O1of the irradiation optical system6a. The optical axis O1can be defined as a focal axis of the lens20passing through the center position of the lens20.

The lens20collimates the laser light L1intermittently emitted from the light source14and guides the laser light L1to the first optical element21.

The first optical element21is typically a light splitter. The laser light L1passes through the first optical element21, is reflected by the first optical element21, travels along the optical axis O3, and enters the photodetector30.

The second optical element24is typically a half mirror. The laser light L1passes through the second optical element24and enters the mirror23.

The mirror23has a reflecting surface23athat reflects the laser light L1intermittently emitted from the light source14. For example, the reflecting surface23ais rotatable about two rotation axes crossing each other. Thus, the mirror23periodically changes the irradiation direction of the laser light L1. The mirror23is typically a polygon mirror driven by a motor. However, instead of this, micro electro mechanical systems (MEMS) may be adopted.

The control unit11outputs a drive signal to the scan driver15so that the inclination angle of the reflecting surface23aof the mirror23periodically changes. The scan driver15drives the mirror23based on a drive signal input from the control unit11. That is, the control unit11controls the irradiation direction of the laser light L1by driving the scan driver15.

FIG.2illustrates a raster scan method as a scanning method. However, instead of this, a conical scan method may be adopted.

The reflecting surface23aof the mirror23, the second optical element24, the lens32, and the sensor31are arranged on the optical axis O2of the light receiving optical system6bin order of incidence of the reflected light L2. The optical axis O2can be defined as a focal axis of the lens32passing through the center position of the lens32.

The reflecting surface23aallows the reflected light L2traveling along the optical axis O2among the scattered light scattered by the building4to enter the second optical element24. The second optical element24reflects the reflected light L2reflected by the reflecting surface23ato be incident on the lens32of the measurement unit7along the optical axis O2. The lens32condenses the reflected light L2incident along the optical axis O2on the sensor31.

InFIG.2, the optical path of the laser light L1and the optical path of the reflected light L2are separated from each other for clarity. In practice, however, they may overlap. In addition, an optical path at the center of the light flux of the laser light L1is illustrated as the optical axis O1. Similarly, the optical path at the center of the light flux of the reflected light L2is illustrated as the optical axis O2.

The sensor31is typically a photomultiplier. The sensor31converts the luminance of the reflected light L2received via the light receiving optical system6binto an electrical signal.

The measurement unit7measures the distance from the three-dimensional Lidar scanner2to the distance measurement point based on a luminance signal obtained by analog-digital conversion of an electrical signal obtained by converting the reflected light L2into a signal. Specifically, it is as follows.

The signal generation unit34analog-to-digital converts the electrical signal output from the sensor31into a luminance signal. The signal generation unit34outputs the luminance signal to the data generation unit35.

The data generation unit35measures the distance from the three-dimensional Lidar scanner2to the distance measurement point based on the time difference between the timing at which the photodetector30detects the laser light L1and the timing at which the sensor31detects the reflected light L2based on the luminance signal, and generates distance data. In addition, the data generation unit35generates luminance data indicating the luminance of the reflected light L2detected by the sensor31based on the luminance signal. The data generation unit35outputs the distance data to the scanning density determination unit10, and outputs the distance data and the luminance data to the data output unit36.

The data output unit36outputs the distance data and the luminance data to the point cloud data generation unit8.

The point cloud data generation unit8generates point cloud data based on the distance data and the luminance data input from the data output unit36. The point cloud data is typically a set of point data having coordinate data and luminance data.

Next, the scanning density determination unit10will be described in detail. The scanning density determination unit10dynamically determines the scanning density based on the distance to the distance measurement point during the scanning of the three-dimensional Lidar scanner2so as to suppress the variation in the point cloud density caused by the length of the distance to the distance measurement point.

Here, the point cloud density can be defined as the number of distance measurement points per unit area in the measurement target.

The scanning density determination unit10dynamically determines the scanning density during the scanning of the three-dimensional Lidar scanner2based on the distance data input from the data generation unit35so as to suppress the above change. That is, the scanning density determination unit10determines the scanning density such that the distance from the three-dimensional Lidar scanner2to the distance measurement point and the scanning density have a positive correlation. In other words, the scanning density determination unit10relatively increases the scanning density when the distance from the three-dimensional Lidar scanner2to the distance measurement point is relatively long, and relatively decreases the scanning density when the distance from the three-dimensional Lidar scanner2to the distance measurement point is relatively short. The scanning density determination unit10outputs scanning density data indicating the determined scanning density to the control unit11.

Here, the scanning density can be defined as the number of distance measurement points per unit solid angle viewed from the three-dimensional Lidar scanner2. The scanning density may also be defined as the reciprocal of the angle between two line segments connecting two distance measurement points successively acquired by the three-dimensional Lidar scanner2to the three-dimensional Lidar scanner2.

The three-dimensional Lidar scanner2of the present example embodiment employs a direct time of flight (dToF) method of irradiating the building4to be measured with a pulsed laser light L1. Therefore, in the case of increasing the scanning density, the three-dimensional Lidar scanner2typically shortens the pulse period of the pulsed laser light L1with which the building4is irradiated. On the contrary, in the case of decreasing the scanning density, the three-dimensional Lidar scanner2typically increases the pulse period of the pulsed laser light L1applied to the building4. Therefore, the scanning density determination unit10dynamically determines the pulse period during the scanning of the three-dimensional Lidar scanner2based on the distance data input from the data generation unit35so as to suppress the above change. That is, the scanning density data in the present example embodiment is pulse period data indicating a pulse period.

Specifically, the scanning density determination unit10dynamically determines the pulse period during the scanning of the three-dimensional Lidar scanner2according to Equation (1) below. As described above, the three-dimensional Lidar scanner2repeats the scanning of the laser light L1and the reception of the reflected light L2to repeatedly measure the distance from the three-dimensional Lidar scanner2to the distance measurement point. In Equation (1), Tnis a pulse period between a pulse of the laser light L1emitted from the light source14for the n-th measurement and a pulse of the laser light L1emitted from the light source14for the (n−1)th measurement. T0and B are constants. rn-1is distance data obtained by the (n−1)th measurement.

According to Equation (1), it is possible to prevent a decrease in the point cloud density due to an increase in the distance from the three-dimensional Lidar scanner2to the distance measurement point during the scanning of the three-dimensional Lidar scanner2. In other words, it is possible to prevent the variation in the point cloud density due to the variation in the distance from the three-dimensional Lidar scanner2to the distance measurement point during the scanning of the three-dimensional Lidar scanner2.

That is, for example, as illustrated inFIG.2, it is assumed that the measurement target surface of the building4is partially recessed, so that the building4has a surface4arelatively close to the three-dimensional Lidar scanner2and a surface4brelatively far from the three-dimensional Lidar scanner2. In this case, when the scanning density is constant, the point cloud density on the surface4bof the building4is lower than the point cloud density on the surface4aof the building4. Therefore, according to Equation (1), it is possible to prevent a decrease in the point cloud density due to an increase in the distance from the three-dimensional Lidar scanner2to the distance measurement point during the scanning of the three-dimensional Lidar scanner2.

Next, an operation of the optical sensing system1will be described with reference toFIG.3.FIG.3illustrates an operation flow of the optical sensing system1.

As illustrated inFIG.3, the control unit11executes (n−1)th distance measurement (S100). Next, the scanning density determination unit10substitutes the distance data obtained by the (n−1)th measurement into Equation (1) to determine the scanning density to be used after the n-th measurement (S110). Next, the control unit11determines whether scanning in a predetermined scanning range has been completed. When determining that the scanning is completed (S120: YES), the control unit11advances the processing to S130. On the other hand, when it is determined that the scanning is not completed (S120: NO), the control unit11returns the processing to S100and executes n-th distance measurement. In S130, the point cloud data generation unit8generates the point cloud data based on the data output from the data output unit36(S130). Then, the defect detection device3detects a defect of the building4based on the point cloud data generated by the point cloud data generation unit8(S140). The defect of the building4is typically a surface defect such as a crack that may occur on the surface of the building4. The point cloud density in the point cloud data generated by the point cloud data generation unit8of the present example embodiment is constant regardless of the length of the distance from the three-dimensional Lidar scanner2. Therefore, the defect detection device3can detect the surface defect of the building4with high accuracy based on the point cloud data generated by the point cloud data generation unit8.

The first example embodiment has been described above, and the first example embodiment has the following features.

The optical sensing system1includes the three-dimensional Lidar scanner2(three-dimensional scanner) and the scanning density determination unit10(scanning density determination means). The three-dimensional Lidar scanner2measures the distance to the building4by scanning the building4(measurement target) with the laser light L1and receiving the reflected light L2of the laser light. The scanning density determination unit10dynamically determines the scanning density based on the distance to the distance measurement point during the scanning of the three-dimensional Lidar scanner2so as to suppress the variation in the point cloud density caused by the length of the distance to the distance measurement point. The distance measurement point is a portion irradiated with the laser light L1in the building4. The distance measurement point is typically a portion irradiated with the laser light L1on the wall surface of the building4. For example, when there is a local recess on the wall surface of the building4, the scanning density determination unit10dynamically determines the scanning density so that the scanning density when the laser light L1is emitted to the inside of the recess becomes higher than the scanning density when the laser light L1is emitted to the outside of the recess. Dynamically determining the scanning density means determining the scanning density in real time during the scanning of the three-dimensional Lidar scanner2. According to the above configuration, it is possible to suppress the variation in the point cloud density caused by the length of the distance to the distance measurement point.

Furthermore, the scanning density determination unit10determines the scanning density so that the distance to the distance measurement point and the scanning density have a positive correlation. According to the above configuration, it is possible to effectively suppress the variation in the point cloud density caused by the length of the distance to the distance measurement point.

In addition, the three-dimensional Lidar scanner2increases or decreases the pulse period of the laser light L1with which the building4is irradiated based on the scanning density determined by the scanning density determination unit10. According to the above configuration, the scanning density determined by the scanning density determination unit10can be realized by simple control.

In addition, the optical sensing system1includes the point cloud data generation unit8. The point cloud data generation unit8generates point cloud data based on the distance measured by the three-dimensional Lidar scanner2. According to the above configuration, the point cloud data in which the variation in the point cloud density is suppressed is realized.

In the first example embodiment, the three-dimensional Lidar scanner2includes the scanning density determination unit10and the point cloud data generation unit8. That is, the three-dimensional Lidar scanner2, the scanning density determination unit10, and the point cloud data generation unit8are realized by a single device. However, the three-dimensional Lidar scanner2, the scanning density determination unit10, and the point cloud data generation unit8may be realized by distributed processing by a plurality of devices. For example, a computer capable of performing bidirectional communication with the three-dimensional Lidar scanner2may function as the scanning density determination unit10and the point cloud data generation unit8, and this computer may be a cloud computer.

First Modified Example

Next, a first modified example of the first example embodiment will be described. The first example embodiment is as follows. That is, the scanning density determination unit10dynamically determines the scanning density based on the distance to the distance measurement point during the scanning of the three-dimensional Lidar scanner2so as to suppress the variation in the point cloud density caused by the length of the distance to the distance measurement point.

However, instead of this, the following may be applied. That is, the scanning density determination unit10dynamically determines the scanning density based on the luminance of the reflected light L2during the scanning of the three-dimensional Lidar scanner2so as to suppress the variation in the point cloud density caused by the length of the distance to the distance measurement point. Specifically, the scanning density determination unit10determines the scanning density such that the luminance of the reflected light L2and the scanning density have a negative correlation. That is, the scanning density determination unit10sets the scanning density to be relatively low when the luminance of the reflected light L2is relatively high, and sets the scanning density to be relatively high when the luminance of the reflected light L2is relatively low. This is because when the intensity of the laser light L1emitted from the three-dimensional Lidar scanner2is constant, the luminance of the reflected light L2increases or decreases according to the distance from the three-dimensional Lidar scanner2to the distance measurement point.

Second Modified Example

Next, a second modified example of the first example embodiment will be described. The first example embodiment is as follows. That is, the scanning density determination unit10dynamically determines the scanning density based on the reciprocal of the distance from the three-dimensional Lidar scanner2to the distance measurement point.

However, instead of this, the following may be applied. That is, the scanning density determination unit10may dynamically determine the scanning density based on a comparison result obtained by comparing the distance from the three-dimensional Lidar scanner2to the distance measurement point with a predetermined value (first distance). Specifically, the scanning density determination unit10sets the scanning density to the first scanning density when the distance from the three-dimensional Lidar scanner2to the distance measurement point is longer than a predetermined value, and sets the scanning density to the second scanning density lower than the first scanning density when the distance is shorter than the predetermined value. According to the above configuration, it is possible to suppress the variation in the point cloud density caused by the length of the distance to the distance measurement point by extremely simple calculation.

The same applies to a case where the scanning density determination unit10dynamically determines the scanning density based on the luminance of the reflected light L2. That is, the scanning density determination unit10may dynamically determine the scanning density based on a comparison result obtained by comparing the luminance of the reflected light L2with a predetermined value (first distance). Specifically, the scanning density is set to the first scanning density when the luminance of the reflected light L2is lower than a predetermined value (first luminance), and the scanning density is set to the second scanning density lower than the first scanning density when the luminance is higher than the predetermined value. According to the above configuration, it is possible to suppress the variation in the point cloud density caused by the length of the distance to the distance measurement point by extremely simple calculation.

Third Modified Example

Next, a third modified example will be described with reference toFIG.4.FIG.4is a functional block diagram of the optical sensing system1.

As illustrated inFIG.4, in the present modified example, the scanning density determination unit10includes a scanning density determination table10a. The scanning density determination table10ais a table indicating the correspondence relationship between the distance from the three-dimensional Lidar scanner2to the distance measurement point and the scanning density. In the scanning density determination table10a, the distance from the three-dimensional Lidar scanner2to the distance measurement point and the scanning density have a positive correlation. Then, the scanning density determination unit10refers to the scanning density determination table10ato dynamically determine the scanning density. According to the above configuration, it is possible to suppress the variation in the point cloud density caused by the length of the distance to the distance measurement point without requiring special calculation.

The same applies to a case where the scanning density determination unit10dynamically determines the scanning density based on the luminance of the reflected light L2. In this case, the scanning density determination table10aindicates the correspondence relationship between the luminance of the reflected light L2and the scanning density. In the scanning density determination table10a, the luminance of the reflected light L2and the scanning density have a negative correlation. Then, the scanning density determination unit10refers to the scanning density determination table10ato dynamically determine the scanning density. According to the above configuration, it is possible to suppress the variation in the point cloud density caused by the length of the distance to the distance measurement point without requiring special calculation.

Fourth Modified Example

Next, a fourth modified example of the first example embodiment will be described.

In the first example embodiment, when dynamically determining the scanning density, the scanning density determination unit10specifically determines the pulse period of the laser light L1closely corresponding to the scanning density.

However, instead of this, the present modified example is as follows. That is, when determining the scanning density, the scanning density determination unit10specifically determines a scanning speed closely corresponding to the scanning density. That is, the scanning density determination unit10determines the scanning speed of the laser light L1with which the building4is irradiated. The scanning speed of the laser light L1is typically a rotation speed of a motor that drives a polygon mirror as the mirror23.

The rotational speed and the scanning density have a negative correlation. That is, the scanning density is decreased when the rotation speed is increased, and the scanning density is increased when the rotation speed is decreased. Therefore, for example, in a case where the distance from the three-dimensional Lidar scanner2to the distance measurement point increases during the scanning of the three-dimensional Lidar scanner2, the scanning density determination unit10decreases the rotation speed in order to increase the scanning density. Conversely, in a case where the distance from the three-dimensional Lidar scanner2to the distance measurement point decreases during the scanning of the three-dimensional Lidar scanner2, the scanning density determination unit10increases the rotation speed in order to decrease the scanning density.

Specifically, the scanning density determination unit10dynamically determines the rotation speed according to Equation (2) below. As described above, the three-dimensional Lidar scanner2repeats the scanning of the laser light L1and the reception of the reflected light L2to repeatedly measure the distance from the three-dimensional Lidar scanner2to the distance measurement point. In Equation (2), Vnis a rotation speed at the time of the n-th measurement. V0and C are constants. rn-1is distance data obtained by the (n−1)th measurement.

Then, the control unit11of the three-dimensional Lidar scanner2increases or decreases the scanning speed of the laser light L1with which the building4is irradiated based on the scanning density determined by the scanning density determination unit10. Specifically, the control unit11of the three-dimensional Lidar scanner2outputs a drive signal indicating the rotation speed determined by the scanning density determination unit10to the scan driver15. According to the above configuration, the scanning density determined by the scanning density determination unit10can be reflected by simple control.

Second Example Embodiment

Next, a second example embodiment will be described with reference toFIG.5. Hereinafter, differences between the first example embodiment and the present example embodiment will be mainly described, and redundant description will be omitted. In the present example embodiment, the three-dimensional Lidar scanner2adopts a frequency modulated continuous wave (FMCW) method. That is, the three-dimensional Lidar scanner2continuously irradiates the building4with a frequency-modulated laser light L1.

The light emitting unit5of the present example embodiment includes a direct digital synthesizer (DDS)16instead of the oscillator12. The DDS16outputs a sweep signal whose frequency increases or decreases with time to the light source driver13. As a result, the laser light L1emitted from the light source14becomes a frequency-modulated continuous wave.

The emission signal output from the photodetector30and the light reception signal output from the sensor31are input to the signal generation unit34of the present example embodiment. Then, the signal generation unit34performs multiplication calculation on the emission signal and the light reception signal, and outputs an intermediate frequency signal (IF signal) that is a calculation result to the data generation unit35.

The data generation unit35includes a scanning density determination unit37. The scanning density determination unit37determines a sampling period of the intermediate frequency signal. The data generation unit35samples the intermediate frequency signal received from the signal generation unit34based on the sampling period determined by the scanning density determination unit37. The data generation unit35measures the distance from the three-dimensional Lidar scanner2to the distance measurement point based on the sampled intermediate frequency signal and generates distance data. Then, the scanning density determination unit37determines the scanning density based on the distance from the three-dimensional Lidar scanner2to the distance measurement point. Specifically, the scanning density determination unit37determines the sampling period of the intermediate frequency signal closely corresponding to the scanning density. The scanning density and the sampling period have a negative correlation. That is, the sampling period may be shortened to increase the scanning density, and the sampling period may be lengthened to decrease the scanning density.

Specifically, the scanning density determination unit37dynamically determines the sampling period according to Equation (3) below. As described above, the three-dimensional Lidar scanner2repeatedly measures the distance from the three-dimensional Lidar scanner2to the distance measurement point by sampling the intermediate frequency signal. In Equation (3), Tnis a sampling period at the time of the n-th measurement. T0and D are constants. rn-1is distance data obtained by the (n−1)th measurement.

According to Equation (3), it is possible to prevent a decrease in the point cloud density due to an increase in the distance from the three-dimensional Lidar scanner2to the distance measurement point during the scanning of the three-dimensional Lidar scanner2. In other words, it is possible to prevent the variation in the point cloud density due to the variation in the distance from the three-dimensional Lidar scanner2to the distance measurement point during the scanning of the three-dimensional Lidar scanner2. According to the above configuration, the scanning density determined by the scanning density determination unit37can be reflected by simple control.

The first example embodiment and the second example embodiment of the present disclosure have been described above. The first to fourth modified examples of the first example embodiment can be applied to the second example embodiment.

The present disclosure is not limited to the above example embodiment, and can be appropriately changed without departing from the gist.

For example, in each of the above example embodiments, the distance measurement method of the three-dimensional Lidar scanner2is a direct time of flight (dToF) method or a frequency modulated continuous wave (FMCW) method. However, instead of this, an Amplitude-modulated continuous wave (AMCW) may be adopted.

In each of the above example embodiments, one building, that is, the building4has been exemplified as an object to be measured by the three-dimensional Lidar scanner2. However, the object to be measured by the three-dimensional Lidar scanner2may include a plurality of buildings. Examples of the plurality of buildings include a plurality of steel towers having different distances from the three-dimensional Lidar scanner2and a plurality of bridge piers (piers: so-called bridge lower structures) having different distances from the three-dimensional Lidar scanner2. As described above, even in a case where the object to be measured by the three-dimensional Lidar scanner2includes a plurality of buildings, it is possible to suppress the variation in the point cloud density caused by the length of the distance to the distance measurement point.

Furthermore, for example, the scanning density determination unit10and the scanning density determination unit37may use a learned model learned so as to suppress variations in point cloud density due to the length of the distance from the three-dimensional Lidar scanner2to the distance measurement point during the scanning of the three-dimensional Lidar scanner2. The scanning density determination unit10and the scanning density determination unit37dynamically determine the scanning density using the learned model. The learned model is typically a neural network that outputs a scanning density when a distance is input.

Furthermore, when determining the scanning density, the scanning density determination unit10and the scanning density determination unit37may express the determined scanning density at levels of 10 stages, for example.

The scanning density determination unit10, the scanning density determination unit37and the point cloud data generation unit8may be realized in a hardware circuit, such as FPGA (Field Programmable Gate Array), ASIC (Application-Specific Integrated Circuit), Microcontroller, Microprocessor, Digital Signal Processor (DSP), GPU (Graphics Processing Unit).

An optical sensing system including:a three-dimensional scanner configured to measure a distance to a measurement target by scanning the measurement target with a laser light and receiving reflected light of the laser light; anda scanning density determination means for dynamically determining a scanning density based on a distance to a distance measurement point or luminance of the reflected light during scanning of the three-dimensional scanner so as to suppress variation in a point cloud density caused by a length of the distance to the distance measurement point.

The optical sensing system according to Supplementary note 1, wherein the scanning density determination means determines the scanning density such that the distance to the distance measurement point and the scanning density have a positive correlation, or determines the scanning density such that the luminance and the scanning density have a negative correlation.

The optical sensing system according to Supplementary note 2, wherein the scanning density determination means is configured to:determine the scanning density as a first scanning density when the distance to the distance measurement point is longer than a first distance or when the luminance is lower than a first luminance; anddetermine the scanning density as a second scanning density lower than the first scanning density when the distance to the distance measurement point is shorter than the first distance or when the luminance is higher than the first luminance.

The optical sensing system according to Supplementary note 2, wherein the scanning density determination means determines the scanning density by referring to a scanning density determination table indicating a correspondence relationship between the distance to the distance measurement point and the scanning density or a correspondence relationship between the luminance and the scanning density.

The optical sensing system according to any one of Supplementary notes 1 to 4, wherein when the three-dimensional scanner adopts a direct time of flight (dToF) method of irradiating the measurement target with a pulsed laser light,the three-dimensional scanner increases or decreases a pulse period of the laser light with which the measurement target is irradiated based on the scanning density determined by the scanning density determination means.

The optical sensing system according to any one of Supplementary notes 1 to 4, wherein when the three-dimensional scanner adopts a frequency modulated continuous wave (FMCW) method of continuously irradiating the measurement target with a frequency-modulated laser light, the three-dimensional scanner increases or decreases a sampling period of an intermediate frequency signal based on the scanning density determined by the scanning density determination means.

The optical sensing system according to any one of Supplementary notes 1 to 4, wherein the three-dimensional scanner increases or decreases a scanning speed of the laser light with which the measurement target is irradiated based on the scanning density determined by the scanning density determination means.

The optical sensing system according to any one of Supplementary notes 1 to 4, further including a point cloud data generation means for generating point cloud data based on the distance measured by the three-dimensional scanner.

An optical sensing device including:a three-dimensional scanner configured to measure a distance to a measurement target by scanning the measurement target with a laser light and receiving reflected light of the laser light; anda scanning density determination means for dynamically determining a scanning density based on a distance to a distance measurement point or luminance of the reflected light during scanning of the three-dimensional scanner so as to suppress variation in a point cloud density caused by a length of the distance to the distance measurement point.

The optical sensing device according to Supplementary note 9, wherein the scanning density determination means determines the scanning density such that the distance to the distance measurement point and the scanning density have a positive correlation, or determines the scanning density such that the luminance and the scanning density have a negative correlation.

The optical sensing device according to Supplementary note 10, wherein the scanning density determination means is configured to:determine the scanning density as a first scanning density when the distance to the distance measurement point is longer than a first distance or when the luminance is lower than a first luminance; anddetermine the scanning density as a second scanning density lower than the first scanning density when the distance to the distance measurement point is shorter than the first distance or when the luminance is higher than the first luminance.

The optical sensing device according to Supplementary note 10, wherein the scanning density determination means determines the scanning density by referring to a scanning density determination table indicating a correspondence relationship between the distance to the distance measurement point and the scanning density or a correspondence relationship between the luminance and the scanning density.

The optical sensing device according to any one of Supplementary notes 9 to 12, wherein when the three-dimensional scanner adopts a direct time of flight (dToF) method of irradiating the measurement target with a pulsed laser light,the three-dimensional scanner increases or decreases a pulse period of the laser light with which the measurement target is irradiated based on the scanning density determined by the scanning density determination means.

The optical sensing device according to any one of Supplementary notes 9 to 12, wherein when the three-dimensional scanner adopts a frequency modulated continuous wave (FMCW) method of continuously irradiating the measurement target with a frequency-modulated laser light,the three-dimensional scanner increases or decreases a sampling period of an intermediate frequency signal based on the scanning density determined by the scanning density determination means.

The optical sensing device according to any one of Supplementary notes 9 to 12, wherein the three-dimensional scanner increases or decreases a scanning speed of the laser light with which the measurement target is irradiated based on the scanning density determined by the scanning density determination means.

The optical sensing device according to any one of Supplementary notes 9 to 12, further including a point cloud data generation means for generating point cloud data based on the distance measured by the three-dimensional scanner.

An optical sensing method including:a distance measurement step of measuring a distance to a measurement target by scanning the measurement target with a laser light and receiving reflected light of the laser light; anda scanning density determination step of dynamically determining a scanning density based on a distance to a distance measurement point or luminance of the reflected light during scanning in the distance measurement step so as to suppress variation in a point cloud density caused by a length of the distance to the distance measurement point.

The optical sensing method according to Supplementary note 17, wherein the scanning density determination step involves determining the scanning density such that the distance to the distance measurement point and the scanning density have a positive correlation, or determines the scanning density such that the luminance and the scanning density have a negative correlation.

The optical sensing method according to Supplementary note 18, wherein the scanning density determination step involves:determining the scanning density as a first scanning density when the distance to the distance measurement point is longer than a first distance or when the luminance is lower than a first luminance; anddetermining the scanning density as a second scanning density lower than the first scanning density when the distance to the distance measurement point is shorter than the first distance or when the luminance is higher than the first luminance.

The optical sensing method according to Supplementary note 18, wherein the scanning density determination step involves determining the scanning density by referring to a scanning density determination table indicating a correspondence relationship between the distance to the distance measurement point and the scanning density or a correspondence relationship between the luminance and the scanning density.

The optical sensing method according to any one of Supplementary notes 17 to 20, wherein when the distance measurement step adopts a direct time of flight (dToF) method of irradiating the measurement target with a pulsed laser light,the distance measurement step involves increasing or decreasing a pulse period of the laser light with which the measurement target is irradiated based on the scanning density determined in the scanning density determination step.

The optical sensing method according to any one of Supplementary notes 17 to 20, wherein when the distance measurement step adopts a frequency modulated continuous wave (FMCW) method of continuously irradiating the measurement target with a frequency-modulated laser light,the distance measurement step involves increasing or decreasing a sampling period of an intermediate frequency signal based on the scanning density determined in the scanning density determination step.

The optical sensing method according to any one of Supplementary notes 17 to 20, wherein the distance measurement step involves increasing or decreasing a scanning speed of the laser light with which the measurement target is irradiated based on the scanning density determined in the scanning density determination step.

The optical sensing method according to any one of Supplementary notes 17 to 20, further including a point cloud data generation step of generating point cloud data based on the distance measured in the distance measurement step.

A program for causing a computer to function as:a three-dimensional scanner configured to measure a distance to a measurement target by scanning the measurement target with a laser light and receiving reflected light of the laser light; anda scanning density determination means for dynamically determining a scanning density based on a distance to a distance measurement point or luminance of the reflected light during scanning of the three-dimensional scanner so as to suppress variation in a point cloud density caused by a length of the distance to the distance measurement point.

The program according to Supplementary note 25, wherein the scanning density determination means determines the scanning density such that the distance to the distance measurement point and the scanning density have a positive correlation, or determines the scanning density such that the luminance and the scanning density have a negative correlation.

The program according to Supplementary note 26, wherein the scanning density determination means is configured to:determine the scanning density as a first scanning density when the distance to the distance measurement point is longer than a first distance or when the luminance is lower than a first luminance; anddetermine the scanning density as a second scanning density lower than the first scanning density when the distance to the distance measurement point is shorter than the first distance or when the luminance is higher than the first luminance.

The program according to Supplementary note 26, wherein the scanning density determination means determines the scanning density by referring to a scanning density determination table indicating a correspondence relationship between the distance to the distance measurement point and the scanning density or a correspondence relationship between the luminance and the scanning density.

The program according to any one of Supplementary notes 25 to 28, wherein when the three-dimensional scanner adopts a direct time of flight (dToF) method of irradiating the measurement target with a pulsed laser light,the three-dimensional scanner increases or decreases a pulse period of the laser light with which the measurement target is irradiated based on the scanning density determined by the scanning density determination means.

The program according to any one of Supplementary notes 25 to 28, wherein when the three-dimensional scanner adopts a frequency modulated continuous wave (FMCW) method of continuously irradiating the measurement target with a frequency-modulated laser light,the three-dimensional scanner increases or decreases a sampling period of an intermediate frequency signal based on the scanning density determined by the scanning density determination means.

The program according to any one of Supplementary notes 25 to 28, wherein the three-dimensional scanner increases or decreases a scanning speed of the laser light with which the measurement target is irradiated based on the scanning density determined by the scanning density determination means.

The program according to any one of Supplementary notes 25 to 28, causing the computer to further function as:a point cloud data generation means for generating point cloud data based on the distance measured by the three-dimensional scanner.

An example advantage according to the above-described embodiments is that it is possible to suppress variation in the point cloud density due to the length of the distance to the distance measurement point.

The first and second embodiments can be combined as desirable by one of ordinary skill in the art.