Measuring device, control method, program and storage medium

Abstract

The present invention provides a measuring device, a control method, a program, and a storage medium storing a program that can effectively utilize reflected light data without removing it, while suitably eliminating the influence of background light. [Solution] The control unit 7 of the lidar 100 measures the reflected light intensity distribution within the scanning area by irradiating with illumination light, and measures the background light intensity distribution within the scanning area without irradiating with illumination light. The control unit 7 then performs a smoothing process on the reflected light intensity distribution to generate a smoothed background light intensity distribution. The control unit 7 then subtracts the smoothed background light intensity distribution from the reflected light intensity distribution.

Description

Technical Field

[0004] , , ,

[0001] The present invention relates to the measurement of the reflected light of irradiated light.

Background Art

[0002] Conventionally, a distance measuring device is known that irradiates a measurement object with light, detects the reflected light from the measurement object, and calculates the distance to the measurement object based on the time difference between the timing of irradiating the measurement object with light and the timing of detecting the reflected light from the measurement object. Further, Patent Document 1 discloses a distance measuring device that calculates the difference when subtracting the background light information, which is the light reception data of the light receiving means when the illumination means is not irradiating the measurement object, from the measurement light information, which is the light reception data of the light receiving means when the illumination means is irradiating the measurement object, and complements the light reception data for which the difference becomes less than or equal to the threshold value with the light reception data in the vicinity.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In Patent Document 1, the light reception data of the measurement points where background light noise randomly occurs spotwise is removed, and the light reception data of the removed pixels is complemented based on the light reception data in the vicinity. In this case, when the reflected light of the irradiated light is detected at the measurement point where the background light noise has occurred, the data of the reflected light at the measurement point will be removed. At this time, if the reflected light is detected only at the measurement point where the background light noise has occurred and not at the measurement points in the vicinity, the object will not be detected by the above-described complementation process. Thus, in Patent Document 1, there was a possibility that an object existing far away and measured only at one measurement point could not be detected due to the influence of the removal of background light noise.

[0005] The above are just a few examples of problems that the present invention aims to solve. The main objective of the present invention is to provide a measuring device, a control method, a program, and a storage medium storing a program that can effectively utilize reflected light data without removing it, while suitably eliminating the influence of background light. [Means for solving the problem]

[0006] The invention described in the claim is a measuring device comprising: a measuring unit that measures a first intensity distribution, which is the intensity distribution of reflected light in a measurement target area, by irradiating with illumination light, and measures a second intensity distribution, which is the intensity distribution of background light in the measurement target area, without irradiating with illumination light; a smoothing unit that performs a smoothing process on the second intensity distribution to generate a third intensity distribution; and a subtraction unit that subtracts the third intensity distribution from the first intensity distribution.

[0007] Furthermore, the invention described in the claim is a control method performed by a measuring device, comprising: a measurement step of measuring a first intensity distribution, which is the intensity distribution of reflected light in a measurement target area, by irradiating with illumination light, and measuring a second intensity distribution, which is the intensity distribution of background light in the measurement target area, without irradiating with illumination light; a smoothing step of performing a smoothing process on the second intensity distribution to generate a third intensity distribution; and a subtraction step of subtracting the third intensity distribution from the first intensity distribution.

[0008] Furthermore, the invention described in the claims is characterized in that a computer functions as a measurement unit that measures a first intensity distribution, which is the intensity distribution of reflected light in a measurement target area, by irradiating with illumination light, and measures a second intensity distribution, which is the intensity distribution of background light in the measurement target area without irradiating with illumination light; a smoothing unit that performs a smoothing process on the second intensity distribution to generate a third intensity distribution; and a subtraction unit that subtracts the third intensity distribution from the first intensity distribution. [Brief explanation of the drawing]

[0009] [Figure 1]The schematic configuration of the lid according to the embodiment is shown. [Figure 2] This diagram shows the scanning area of ​​the lidar on a virtual plane. [Figure 3] This figure schematically shows the transitions between the background light measurement region and the reflected light measurement region over a period of 5 frames, as well as the derivation process of the corrected reflected light intensity distribution. [Figure 4] (A) A diagram showing the measurement points where background light is measured within the background light measurement area. (B) A diagram showing the background light intensity distribution around the target measurement point. (C) A diagram showing the background light intensity distribution after replacing the background light intensity of the target measurement point with the background light intensity of the surrounding measurement points. [Figure 5] (A) Shows the time waveform of reflected light intensity measured at a certain measurement point. (B) Shows the time waveform of smoothed background light intensity corresponding to the measurement point in question. (C) Shows the time waveform of corrected reflected light intensity at the measurement point in question. [Figure 6] This flowchart shows the procedure for generating a corrected reflected light intensity distribution based on the first generation method. [Figure 7] (A) A diagram showing the measurement points for background light and reflected light in a divided region within the scanning area. (B) A diagram showing the measurement timing of background light, the emission timing of illumination light, and the measurement period of reflected light in chronological order. [Figure 8] This flowchart shows the procedure for generating a corrected reflected light intensity distribution based on the second generation method. [Modes for carrying out the invention]

[0010] In a preferred embodiment of the present invention, the measuring device includes a measuring unit that measures a first intensity distribution, which is the intensity distribution of reflected light within a measurement target area, by irradiating with illumination light, and measures a second intensity distribution, which is the intensity distribution of background light within the measurement target area, without irradiating with illumination light; a smoothing unit that performs a smoothing process on the second intensity distribution to generate a third intensity distribution; and a subtraction unit that subtracts the third intensity distribution from the first intensity distribution. According to this embodiment, the measuring device can suitably exclude the influence of background light measured across multiple measurement points from the first intensity distribution, which is the intensity distribution of reflected light within a measurement target area.

[0011] In one embodiment of the above-described measuring device, the measuring device further includes a point cloud information generation unit that generates point cloud information indicating the distance and direction to the object irradiated by the irradiation light in the measurement target area, based on a fourth intensity distribution obtained by subtracting the third intensity distribution from the first intensity distribution. In this embodiment, the measuring device can suitably generate point cloud information indicating the distance and direction to surrounding objects.

[0012] In another embodiment of the above measuring device, the first intensity distribution shows the time waveform of the reflected light intensity at a plurality of measurement points within the measurement target area during the measurement period of the reflected light, the third intensity distribution shows the smoothed intensity of the background light corresponding to the plurality of measurement points, and the subtraction unit subtracts the smoothed intensity of the background light, which is considered to be constant during the measurement period, from the time waveform of the reflected light intensity for each of the plurality of measurement points. In this embodiment, the measuring device can suitably subtract the amount of background light intensity that is continuously measured across the plurality of measurement points from the first intensity distribution.

[0013] In another embodiment of the above measuring device, the measuring unit measures the first intensity distribution in a first region which is a part of the measurement target area and is set to a different region for each frame, and measures the second intensity distribution in a second region which is a region other than the first region within the measurement target area, and the subtraction unit subtracts from the first intensity distribution a third intensity distribution obtained by smoothing the second intensity distribution measured in the same region as the region where the first intensity distribution was measured but in a different frame. In this embodiment, the measuring device can suitably measure the reflected light intensity in each frame while excluding the influence of background light by providing a region for measuring the first intensity distribution and a region for measuring the second intensity distribution for each frame, and by changing these regions.

[0014] In another embodiment of the above measuring device, the measuring unit measures the intensity of the background light each time it irradiates the area with the illumination light and measures the intensity of the reflected light, thereby measuring the first intensity distribution and the second intensity distribution for the entire area of ​​the area to be measured for each frame. This embodiment allows for the measurement of the reflected light intensity in the entire area of ​​the area to be measured for each frame while effectively excluding the influence of the background light.

[0015] In another preferred embodiment of the present invention, a control method performed by a measuring device comprises: a measurement step of measuring a first intensity distribution, which is the intensity distribution of reflected light within a measurement target area, by irradiating with illumination light; and measuring a second intensity distribution, which is the intensity distribution of background light within the measurement target area, without irradiating with illumination light; a smoothing step of performing a smoothing process on the second intensity distribution to generate a third intensity distribution; and a subtraction step of subtracting the third intensity distribution from the first intensity distribution. By performing this control method, the measuring device can suitably exclude the influence of background light measured across multiple measurement points from the first intensity distribution, which is the intensity distribution of reflected light within a measurement target area.

[0016] In another preferred embodiment of the present invention, there is a program executed by a computer, which measures a first intensity distribution that is the intensity distribution of reflected light within a measurement target area by irradiating irradiation light, and measures a second intensity distribution that is the intensity distribution of background light within the measurement target area without irradiating the irradiation light. A smoothing unit that performs a smoothing process on the second intensity distribution to generate a third intensity distribution, and subtracts the third intensity distribution from the first intensity distribution. By executing this program, the computer can preferably exclude the influence of background light measured over a plurality of measurement points from the first intensity distribution that is the intensity distribution of reflected light within the measurement target area. Preferably, the above program is stored in a storage medium.

Example

[0017] Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings.

[0018] [Device Configuration] FIG. 1 shows a schematic configuration of a lidar 100 according to this embodiment. The lidar 100 is mounted on a vehicle that performs driving assistance such as autonomous driving, for example. The lidar 100 irradiates a light beam (also referred to as "irradiation light") within a predetermined angular range in the horizontal and vertical directions, and receives the light (also referred to as "reflected light") that is reflected by an object and returns, thereby discretely measuring the distance to the object and generating point cloud information indicating the three-dimensional position of the object. As shown in FIG. 1, the lidar 100 mainly includes a transmission unit 1, a reception unit 2, a beam splitter 3, a scanner 5, a piezo sensor 6, and a control unit 7.

[0019] The transmission unit 1 is a light source that emits pulsed irradiation light toward the beam splitter 3. The transmission unit 1 includes, for example, an infrared laser light emitting element. The transmission unit 1 is driven based on a drive signal "S1" supplied from the control unit 7.

[0020] The reception unit 2 is, for example, an avalanche photodiode, generates a detection signal "S2" corresponding to the amount of received light, and supplies the generated detection signal S2 to the control unit 7.

[0021] The beam splitter 3 transmits the pulsed light emitted from the transmitter 1. The beam splitter 3 also reflects the reflected light, which has been reflected by the scanner 5, towards the receiver 2.

[0022] Scanner 5 is, for example, an electrostatically driven mirror (MEMS mirror), and its tilt (i.e., the angle of optical scanning) changes within a predetermined range based on the drive signal "S3" supplied from the control unit 7. Scanner 5 reflects the illumination light that has passed through the beam splitter 3 toward the outside of the lidar 100, and also reflects the reflected light incident from outside the lidar 100 toward the beam splitter 3. Hereafter, the region on the virtual plane 9 through which the illumination light of the lidar 100 passes and where the illumination light is scanned will be simply called the "scanning region" or "measurement target region". The point on the scanning region that is illuminated by the illumination light will also be called the "measurement point".

[0023] Furthermore, the scanner 5 is equipped with a piezo sensor 6. The piezo sensor 6 detects the strain caused by the stress on the torsion bar that supports the mirror portion of the scanner 5. The piezo sensor 6 supplies the generated detection signal "S4" to the control unit 7. The detection signal S4 is used to detect the orientation of the scanner 5.

[0024] The control unit 7 includes, for example, a processor such as a CPU (Central Processing Unit) or a GPU (Graphics Processing Unit), and memory such as RAM (Random Access Memory) or ROM (Read Only Memory). The control unit 7 executes predetermined processes by running programs stored in memory.

[0025] Functionally, the control unit 7 includes a transmission drive block 70, a scanner drive block 71, a reflected light measurement block 72, a background light measurement block 73, a smoothing processing block 74, a subtraction block 75, a point cloud information generation block 76, and an output block 77.

[0026] The transmission drive block 70 outputs a drive signal S1 to drive the transmission unit 1. The drive signal S1 includes information for controlling the emission time of the laser light-emitting element included in the transmission unit 1 and the emission intensity of the laser light-emitting element. Based on the drive signal S1, the transmission drive block 70 controls the emission intensity of the laser light-emitting element included in the transmission unit 1.

[0027] The scanner drive block 71 outputs a drive signal S3 for driving the scanner 5. This drive signal S3 includes a horizontal drive signal corresponding to the resonant frequency of the scanner 5 and a vertical drive signal for vertical scanning. The scanner drive block 71 also detects the scanning angle of the scanner 5 (i.e., the direction of illumination of the light) by monitoring the detection signal S4 output from the piezo sensor 6.

[0028] The reflected light measurement block 72 measures the reflected light intensity at each measurement point based on the detection signal S2 output by the receiving unit 2. In this case, the reflected light measurement block 72 measures the time waveform of the reflected light intensity output by the receiving unit 2 during a predetermined period after the irradiation light is emitted, as the reflected light intensity at each measurement point. Hereafter, the reflected light intensity for all measurement points within the scanning area where the reflected light measurement block 72 has measured the reflected light intensity will also be called the "reflected light intensity distribution". In the reflected light intensity distribution, the reflected light intensity corresponding to each measurement point is represented by a time waveform. The reflected light intensity distribution is an example of the "first intensity distribution" in the present invention.

[0029] The background light measurement block 73 measures the background light intensity based on the detection signal S2 output by the receiving unit 2 when no illumination light is being emitted. The background light intensity for all measurement points within the scanning area measured by the background light measurement block 73 is also called the "background light intensity distribution." The background light intensity distribution is an example of the "second intensity distribution" in this invention. Furthermore, the reflected light measurement block 72 and the background light measurement block 73 are examples of "measurement units" in this invention.

[0030] The smoothing block 74 applies a smoothing process to the background light intensity distribution generated by the background light measurement block 73 to generate a smoothed background light intensity distribution (also called the "smoothed background light intensity distribution"). The smoothing block 74 generates a background light intensity distribution in which noise components of background light that occur randomly at random locations (also called "background light noise") are suitably excluded by the smoothing process, and this is the smoothed background light intensity distribution. The smoothed background light intensity distribution generated by the smoothing block 74 is an example of the "third intensity distribution" in the present invention. The smoothing block 74 is also an example of the "smoothing unit" in the present invention.

[0031] The smoothed background light intensity calculated by the smoothing block 74 for each measurement point is the intensity of the background light (also called "continuous background light") that is continuously detected across multiple measurement points in the measurement results of the lidar 100. Continuous background light is, for example, reflected sunlight from objects with high reflectivity to near-infrared rays, such as clouds, road surfaces, plants, building walls, and glass. Because these objects generally have a large spatial extent, they are measured by the lidar 100 across multiple measurement points.

[0032] The subtraction block 75 subtracts the smoothed background light intensity distribution from the reflected light intensity distribution generated by the reflected light measurement block 72. Specifically, the subtraction block 75 subtracts the time-invariant, smoothed background light intensity for each measurement point from the time waveform of the reflected light intensity for each measurement point shown in the reflected light intensity distribution. As a result, the subtraction block 75 generates a reflected light intensity distribution (also called the "corrected reflected light intensity distribution") that excludes the effect of continuous background light. In the corrected reflected light intensity distribution, the corrected reflected light intensity corresponding to each measurement point is represented by a time waveform. The corrected reflected light intensity distribution is an example of the "fourth intensity distribution" in the present invention. The subtraction block 75 is also an example of the "subtraction unit" in the present invention.

[0033] The point cloud information generation block 76 generates point cloud information for each measurement point within the measurement range of the lidar 100, indicating the distance and direction to the object illuminated by the irradiated light, based on the corrected reflected light intensity distribution. In this case, the point cloud information generation block 76 calculates the time from when the irradiated light is emitted until the receiver 2 detects the reflected light as the time of flight of the light. The point cloud information generation block 76 then generates point cloud information for each measurement point, associating distance information corresponding to the calculated time of flight with information on the direction of irradiation of the irradiated light corresponding to the reflected light received by the receiver 2. The point cloud information generation block 76 is an example of a "point cloud information generation unit" in the present invention.

[0034] The output block 77 outputs the point cloud information generated by the point cloud information generation block 76 to a device that controls driving assistance such as autonomous driving of the vehicle (also called a "driving assistance device"). In this case, the driving assistance device may be, for example, the vehicle's ECU (Electronic Control Unit), or it may be an in-vehicle device such as a car navigation system that is electrically connected to the vehicle.

[0035] [Generating corrected reflected light intensity distribution] Next, we will specifically describe concrete examples of methods for generating corrected reflected light intensity distributions (the first generation method and the second generation method).

[0036] (1) First generation method The first generation method is a method for generating a corrected reflected light intensity distribution that employs a measurement method that separates the measurement range for background light intensity and the measurement range for reflected light intensity in each frame (i.e., for each full rotation by the scanner 5).

[0037] Figure 2 shows the scanning area of ​​the lidar 100 on the virtual plane 9. The solid arrows in Figure 2 indicate the trajectory of the position where the illumination light is projected on the virtual plane 9. In Figure 2, the scanning area is divided into three sub-regions F1 to F3 (see dashed lines).

[0038] In this case, the control unit 7 designates one of the three divided regions F1 to F3 as the background light intensity measurement region (also called the "background light measurement region"), and the remaining divided region as the reflected light intensity measurement region (also called the "reflected light measurement region"). Then, every frame, the control unit 7 shifts the background light measurement region to another divided region, thereby rotating the background light measurement region between the divided regions F1 to F3 with a period of 3 frames. In this case, the transmission drive block 70 does not emit illumination light during the period when scanning the background light measurement region, but emits illumination light during the period when scanning the reflected light measurement region.

[0039] Figure 3 schematically shows the transitions between the background light measurement region and the reflected light measurement region over five frames (frames 1 to 5), and the process of deriving the corrected reflected light intensity distribution based on the background light intensity distribution and the reflected light intensity distribution.

[0040] In Figure 3, in the first frame, the transmission drive block 70 of the control unit 7 controls the illumination light in the transmission unit 1 so that divided region F1 is the background light measurement region, and divided regions F2 and F3 are the reflected light measurement regions. The background light measurement block 73 generates the background light intensity distribution in divided region F1, and the smoothing processing block 74 smooths this background light intensity distribution to generate a smoothed background light intensity distribution "B1". The smoothing processing block 74 stores the generated smoothed background light intensity distribution B1 in memory. This smoothed background light intensity distribution B1 is used to generate the corrected reflected light intensity distribution for the second frame. The reflected light measurement block 72 generates the reflected light intensity distributions in divided regions F2 and F3.

[0041] Next, in the second frame, the transmission drive block 70 controls the illumination light in the transmission unit 1 so that divided region F2 is the background light measurement region, and divided regions F1 and F3 are the reflected light measurement regions. As a result, the reflected light measurement block 72 generates the reflected light intensity distribution in divided regions F1 and F3. The background light measurement block 73 generates the background light intensity distribution in divided region F2, and the smoothing processing block 74 smooths this background light intensity distribution to generate the smoothed background light intensity distribution "B2". The smoothing processing block 74 stores the generated smoothed background light intensity distribution B2 in memory.

[0042] Furthermore, since the smoothed background light intensity distribution B1 of the divided region F1 is obtained in the first frame, the subtraction block 75 subtracts the smoothed background light intensity distribution B1 in the divided region F1 obtained in the second frame from the reflected light intensity distribution "R1" in the same region (R1-B1). As a result, the subtraction block 75 generates a corrected reflected light intensity distribution in the divided region F1 and supplies the generated corrected reflected light intensity distribution to the point cloud information generation block 76. In this case, the point cloud information generation block 76 generates point cloud information in the divided region F1 based on the supplied corrected reflected light intensity distribution.

[0043] Next, in the third frame, the transmission drive block 70 controls the illumination light in the transmission unit 1 so that divided region F3 is the background light measurement region, and divided regions F1 and F2 are the reflected light measurement regions. The background light measurement block 73 generates the background light intensity distribution in divided region F3, and the smoothing processing block 74 smooths this background light intensity distribution to generate the smoothed background light intensity distribution "B3". The smoothing processing block 74 stores the generated smoothed background light intensity distribution B3 in memory. The reflected light measurement block 72 generates the reflected light intensity distribution "R2" in divided region F1 and the reflected light intensity distribution "R3" in divided region F2.

[0044] Furthermore, the subtraction block 75 subtracts the reflected light intensity distribution R2 in the divided region F1 and the reflected light intensity distribution R3 in the divided region F2 obtained in the third frame from the smoothed background light intensity distribution B1 and the smoothed background light intensity distribution B2 in the same region, respectively (i.e., it performs "R2-B1" and "R3-B2"). As a result, the subtraction block 75 generates corrected reflected light intensity distributions in the divided region F1 and the divided region F2, respectively, and supplies the generated corrected reflected light intensity distributions to the point cloud information generation block 76.

[0045] Next, in the fourth frame, the transmission drive block 70 controls the illumination light in the transmission unit 1 so that divided region F1 is the background light measurement region, and divided regions F2 and F3 are the reflected light measurement regions. The background light measurement block 73 generates the background light intensity distribution in divided region F1, and the smoothing processing block 74 generates the smoothed background light intensity distribution "B4" by smoothing the background light intensity distribution. The smoothing processing block 74 stores the generated smoothed background light intensity distribution B4 in memory. In this case, the smoothing processing block 74 should delete the previously generated smoothed background light intensity distribution B1 for the same divided region F1 from memory. The reflected light measurement block 72 generates the reflected light intensity distribution "R4" in divided region F2 and the reflected light intensity distribution "R5" in divided region F3.

[0046] Furthermore, the subtraction block 75 subtracts the reflected light intensity distribution R4 in the divided region F2 and the reflected light intensity distribution R5 in the divided region F3 obtained in the fourth frame from the smoothed background light intensity distribution B2 and the smoothed background light intensity distribution B3 in the same region, respectively (i.e., it performs "R4-B2" and "R5-B3"). As a result, the subtraction block 75 generates corrected reflected light intensity distributions in the divided region F2 and the divided region F3, and supplies the generated corrected reflected light intensity distributions to the point cloud information generation block 76.

[0047] Similarly, in the fifth frame, the transmission drive block 70 controls the illumination light in the transmission unit 1 so that divided region F2 is the background light measurement region, and divided regions F1 and F3 are the reflected light measurement regions. The background light measurement block 73 generates the background light intensity distribution in divided region F2, and the smoothing processing block 74 generates a smoothed background light intensity distribution by smoothing the background light intensity distribution. The smoothing processing block 74 stores the generated smoothed background light intensity distribution in memory. In this case, the smoothing processing block 74 should delete the previously generated smoothed background light intensity distribution B2 for the same divided region F2 from memory. The reflected light measurement block 72 generates the reflected light intensity distribution "R6" in divided region F1 and the reflected light intensity distribution "R7" in divided region F3.

[0048] Furthermore, the subtraction block 75 subtracts the reflected light intensity distribution R6 in the divided region F1 and the reflected light intensity distribution R7 in the divided region F3 obtained in the fifth frame from the smoothed background light intensity distribution B4 and the smoothed background light intensity distribution B3 in the same region, respectively (i.e., it performs "R6-B4" and "R7-B3"). As a result, the subtraction block 75 generates corrected reflected light intensity distributions in the divided region F1 and the divided region F3, and supplies the generated corrected reflected light intensity distributions to the point cloud information generation block 76.

[0049] Here, we will provide a supplementary explanation of the processing shown in Figure 3. Based on the idea that continuous background light does not change significantly between frames, the control unit 7 smooths the background light intensity of the divided region (referred to as the "Nth divided region") which was used as the background light measurement area in the target frame (referred to as the "Mth frame") to generate a smoothed background light intensity distribution, which is then applied to the M+1th and M+2nd frames. The control unit 7 then subtracts the smoothed background light intensity distribution in the Nth divided region from the reflected light intensity distribution of the Nth divided region measured in the M+1st and M+2nd frames. The corrected reflected light intensity distribution of the Nth divided region obtained in this way is sequentially output to the point cloud information generation block 76. When the scanning area is divided into three sections as in the examples in Figures 2 and 3, a corrected reflected light intensity distribution and point cloud information reflecting the latest reflected light intensity measurement results are obtained in two of the three divided regions F1 to F3 within one frame. Therefore, for example, when a driver assistance system performs obstacle detection based on point cloud information, compared to a case where the scanning area is not divided and the background light measurement area and the reflected light measurement area are switched for each frame, the driver assistance system can detect pedestrians suddenly appearing based on the point cloud information supplied from the lidar 100 more quickly.

[0050] Although Figures 2 and 3 show a representative example of dividing the scanning area into three parts, the number of divisions of the scanning area is not limited to this and can be any number of divisions (for example, 1 to 4).

[0051] Next, we will explain the smoothing process performed by the smoothing block 74. Here, as an example, we will explain the smoothing process using a median filter, which replaces the value (intensity) of the target measurement point with the median value of the surrounding measurement points.

[0052] Figure 4(A) is a diagram that clearly shows the measurement points where background light is measured within the background light measurement area. In Figure 4(A), the order of measurement points is indicated by arrows. When the background light intensity of each measurement point within the divided area that constitutes the background light measurement area is obtained based on the detection signal S2, the smoothing processing block 74 sequentially designates each of the measurement points within the divided area that constitutes the background light measurement area as a measurement point to be processed. Then, the smoothing processing block 74 performs a process to replace the value of the measurement point to be processed with the median value of the values ​​of the surrounding measurement points. For example, when the smoothing processing block 74 targets measurement point Ptag, it performs the above replacement process by referring to the intensity of each measurement point within the dashed frame 10 surrounding measurement point Ptag.

[0053] Figure 4(B) shows the background light intensity distribution at measurement points around measurement point Ptag shown in Figure 4(A). Figure 4(C) shows the background light intensity distribution at each measurement point after replacing the background light intensity at measurement point Ptag with the background light intensity of the surrounding measurement points.

[0054] As shown in Figure 4(B), the intensity of measurement point Ptag is higher than that of surrounding measurement points due to background light noise. In contrast, as shown in Figure 4(C), the smoothing block 74 replaces the value of measurement point Ptag with "20," which is the median value of the background light intensity of the nine measurement points including measurement point Ptag. This allows the smoothing block 74 to effectively remove the background light noise generated at measurement point Ptag.

[0055] The smoothing block 74 then repeats the substitution process shown in Figures 4(B) and 4(C), sequentially changing the measurement points to be processed. Generally, background light noise caused by shot noise, thermal noise, and illumination from other lidars has a high probability of occurring in random, spot-like locations. Therefore, the smoothing block 74 can suitably remove background light noise within the background light measurement area by the above-described process.

[0056] In addition, the smoothing block 74 may use various filters used to remove image noise, such as a Gaunsian filter or a moving average filter, instead of a median filter, for the smoothing process.

[0057] Next, we will explain a specific example of the process that subtraction block 75 performs.

[0058] Figure 5(A) shows the time waveform of reflected light intensity measured at a certain measurement point. Figure 5(B) shows the time waveform of smoothed background light intensity corresponding to the measurement point in question. Figure 5(C) shows the time waveform of corrected reflected light intensity at the measurement point in question.

[0059] As shown in Figure 5(A), the reflected light intensity at each measurement point is represented by a time waveform over a time duration corresponding to the maximum measurement distance. The subtraction block 75 then assumes that the background light intensity is constant (time-invariant) during the period in which the reflected light intensity is measured, as shown in Figure 5(B). The subtraction block 75 then calculates the corrected reflected light intensity time waveform shown in Figure 5(C) by subtracting the reflected light intensity time waveform shown in Figure 5(B) from the reflected light intensity time waveform shown in Figure 5(A). In this case, the subtraction block 75 can obtain a corrected reflected light intensity time waveform from which the continuous background light component has been suitably removed. In this case, as shown in Figure 5(C), the corrected reflected light intensity time waveform is near zero during time periods other than the peak position (see dashed circle 90) measured when the reflected light is received. Therefore, in this case, the point cloud information generation block 76 can accurately grasp the timing of the reception of the reflected light by determining a threshold for the corrected reflected light intensity and accurately calculate the distance to the object illuminated by the light.

[0060] The subtraction block 75 generates a corrected reflected light intensity distribution in the target divided region by performing the processes shown in Figures 5(A) to 5(C) for each measurement point within the divided region where reflected light intensity is measured. Then, the point cloud information generation block 76 generates point cloud information corresponding to the target divided region from the generated corrected reflected light intensity distribution.

[0061] Figure 6 is a flowchart showing the procedure for generating a corrected reflected light intensity distribution based on the first generation method.

[0062] First, the background light measurement block 73 of the control unit 7 generates a background light intensity distribution by measuring the background light intensity in a divided region within the scanning region which is to be used as the background light measurement area (step S11). At this time, the transmission drive block 70 stops the emission of irradiation light by the transmission unit 1 during the measurement period of the target divided region. Then, the smoothing processing block 74 generates a smoothed background light intensity distribution by applying a smoothing process to the background light intensity distribution and stores the generated smoothed background light intensity distribution in memory (step S12).

[0063] Furthermore, the reflected light measurement block 72 measures the intensity of the reflected light corresponding to the irradiation light emitted from the transmitting unit 1 in the scanning area other than the divided area where the background light intensity was measured (i.e., the reflected light measurement area) (step S13). In this way, the reflected light measurement block 72 obtains the reflected light intensity distribution in the reflected light measurement area. Note that the processing in step S13 may be performed before the processing in steps S11 and S12.

[0064] Then, the subtraction block 75 generates a corrected reflected light intensity distribution by subtracting the smoothed background light intensity distribution obtained in the same region of a different frame from the reflected light intensity distribution in the reflected light measurement region (step S14). In this case, the subtraction block 75 generates a corrected reflected light intensity distribution by subtracting the time waveform of the smoothed background light intensity from the time waveform of the reflected light intensity for each measurement point in the reflected light measurement region.

[0065] The point cloud information generation block 76 calculates the flight time for each measurement point from the corrected reflected light intensity distribution in the reflected light measurement area, and generates point cloud information representing the distance and direction to the object according to the calculated flight time. Then, the output block 77 outputs the point cloud information generated for the reflected light measurement area to the driver assistance device (step S15).

[0066] The control unit 7 then determines whether or not to stop scanning (step S16). For example, the control unit 7 determines to stop scanning if it receives a signal from the driver assistance device indicating that scanning should be stopped. If the control unit 7 determines that scanning should be stopped (step S16; Yes), it terminates the processing in the flowchart. On the other hand, if the control unit 7 determines that scanning should not be stopped (step S16; No), it shifts the divided region that will be used as the background light measurement area (step S17). Then, the control unit 7 returns to step S11.

[0067] (2) Second generation method The second generation method is a method for generating a corrected reflected light intensity distribution that employs a measurement method that performs both background light intensity measurement and reflected light intensity measurement for the same region within the same frame.

[0068] Figure 7(A) shows the measurement points for background light and reflected light in a divided region within the scanning area. In Figure 7(A), the measurement points for background light are indicated by "○" and the measurement points for reflected light are indicated by "●". Figure 7(B) shows the measurement timing of background light, the emission timing of illumination light, and the measurement period of reflected light in time series.

[0069] As shown in Figures 7(A) and (B), the control unit 7 sets the background light measurement timing to immediately before the reflected light measurement timing at each measurement point. Specifically, as shown in Figure 7(B), the control unit 7 emits illumination light after measuring the background light, provides a measurement (receiving) period for the reflected light corresponding to the illumination light, and repeats this while changing the direction of illumination light emission.

[0070] Then, the smoothing block 74 of the control unit 7 smooths the background light intensity distribution in each divided region after scanning is completed. The subtraction block 75 then subtracts the smoothed background light intensity distribution calculated by the smoothing block 74 from the reflected light intensity distribution in the target divided region to generate a corrected reflected light intensity distribution. Subsequently, the point cloud information generation block 76 generates point cloud information corresponding to the target divided region from the corrected reflected light intensity distribution, and the output block 77 outputs point cloud information corresponding to the measurement points within the target divided region. The number of divisions in which the scanning region is divided may be any number of one or more.

[0071] Thus, according to the second generation method, the lidar 100 outputs point cloud information corresponding to the target divided region each time scanning of a divided region within the scanning area is completed. In this case, unlike the first generation method, the lidar 100 can suitably generate point cloud information for all scanning areas in each frame. That is, in the first generation method, since reflected light intensity cannot be measured in a divided region where background light intensity has been measured, the point cloud information for that divided region is generated in the next frame. In contrast, in the second generation method, point cloud information corresponding to all divided regions is suitably generated in every frame. Furthermore, according to the second generation method, since background light intensity is measured immediately before reflected light intensity is measured, a corrected reflected light intensity distribution can be generated based on the background light intensity measured at a timing closer to the reflected light intensity measurement timing.

[0072] In the examples shown in Figures 6 and 7, the control unit 7 measured the reflected light intensity after measuring the background light intensity, but alternatively, it may measure the background light intensity after measuring the reflected light intensity.

[0073] Figure 8 is a flowchart showing the procedure for generating a corrected reflected light intensity distribution based on the second generation method.

[0074] First, the reflected light measurement block 72 and the background light measurement block 73 of the control unit 7 successively measure the background light intensity and the reflected light intensity at each measurement point (step S21). Then, the control unit 7 determines whether or not the measurement in step S21 within the divided region being scanned has been completed (step S22). If the measurement in step S21 within the target divided region has not been completed (step S22; No), the control unit 7 continues to execute the process in step S21.

[0075] On the other hand, if the measurement in step S21 within the target divided region is completed (step S22; Yes), the smoothing block 74 generates a smoothed background light intensity distribution by smoothing the background light intensity distribution within the target divided region (step S23). Then, the subtraction block 75 subtracts the smoothed background light intensity distribution from the reflected light intensity distribution within the target divided region (step S24). In this case, the subtraction block 75 considers the measurement point where the background light intensity was measured in step S21 to be the same point as the measurement point where the reflected light intensity was measured continuously with the background light intensity, and subtracts the time-invariant smoothed background light intensity from the time waveform of the reflected light intensity for each measurement point. As a result, the subtraction block 75 generates a corrected reflected light intensity distribution.

[0076] The point cloud information generation block 76 calculates the flight time for each measurement point from the corrected reflected light intensity distribution in the reflected light measurement area, and generates point cloud information representing the distance and direction to the object according to the calculated flight time. Then, the output block 77 outputs the point cloud information generated for the reflected light measurement area to the driver assistance device (step S25).

[0077] The control unit 7 then determines whether or not to stop scanning (step S26). For example, if the control unit 7 receives a signal from the driver assistance device indicating that scanning should be stopped, it determines that scanning should be stopped. If the control unit 7 determines that scanning should be stopped (step S26; Yes), it terminates the processing in the flowchart. On the other hand, if the control unit 7 determines that scanning should not be stopped (step S26; No), it shifts the target divided region within the scanning region (step S27). Then, the control unit 7 returns to step S21.

[0078] As described above, the control unit 7 of the lidar 100 in this embodiment measures the reflected light intensity distribution within the scanning area by irradiating it with illumination light, and measures the background light intensity distribution within the scanning area without irradiating it with illumination light. The control unit 7 then performs a smoothing process on the background light intensity distribution to generate a smoothed background light intensity distribution. The control unit 7 then subtracts the smoothed background light intensity distribution from the reflected light intensity distribution. As a result, the control unit 7 can calculate the reflected light intensity which suitably excludes the influence of continuous background light present across multiple frames.

[0079] For example, since vehicle rear reflectors exist in pairs, the rear reflectors of a vehicle traveling at a distance may only be detected as objects at two measurement points separated by a certain distance. In this case, if the distance between the two measurement points is equivalent to the width of the vehicle, it can be determined that there is a high probability that the two measurement points represent the vehicle's rear reflectors. Thus, even reflected light measured at only one measurement point may contain important information. In this regard, the present invention makes it possible to improve the accuracy of reflected light measurement data by subtracting noise-removed background light measurement data without removing the reflected light measurement data. In other words, according to the present invention, it is possible to provide a measuring device that can effectively utilize reflected light data without removing it. [Explanation of Symbols]

[0080] 1. Transmitter 2. Receiving Unit 3-beam splitter 5 Scanners 6. Piezo sensor 7 Control Unit 100 Riders

Claims

[Claim 1] A measurement unit that measures a first intensity distribution, which is the intensity distribution of reflected light within the measurement target area, by irradiating with illumination light, and measures a second intensity distribution, which is the intensity distribution of background light within the measurement target area, without irradiating with illumination light. A smoothing unit that performs a smoothing process on the second intensity distribution to generate a third intensity distribution, A subtraction unit that subtracts the third intensity distribution from the first intensity distribution, A measuring device having the following features.

Images