Measurement program, measurement method, and measurement device

Abstract

This measurement program causes a computer to execute: processing for acquiring a measurement result from an optical system for measuring a distance to each sample point within a predetermined range by scanning emission light from a light-emitting element in a frame unit with respect to the predetermined range and receiving reflected light from the predetermined range; processing for selecting a combination of measurement wavelengths of the optical system by changing the measurement wavelength for each frame and comparing the results of measurement for the number of frames corresponding to the number of designated measurement wavelengths; processing for selecting representative measurement data to be used for measurement at each sample point by sequentially acquiring, for each frame, a measurement result from the optical system with respect to each measurement wavelength of the combination and comparing the measurement results at the respective sample points; and processing for generating measurement data by using the selected representative measurement data.　

Description

Measurement program, measurement method, and measurement device

[0001] The present invention relates to a measurement program, a measurement method, and a measurement device.

[0002] There is a demand for a technique for measuring the accurate shape of an object using a measuring device that measures distance (see, for example, Patent Document 1).

[0003] Japanese Patent Application Laid-Open No. 2017-181209

[0004] For example, LiDAR (Light Detection and Ranging) with multiple wavelengths has been developed to address the wavelength dependency of absorbance in marine areas (such as shallow waters and deep waters). For example, it has been considered to measure using a single wavelength corresponding to the marine area. However, since the reflectance of an object also depends on wavelength, measurement using a single wavelength may result in unmeasurable areas (missing measurements). Therefore, in order to eliminate missing measurements, it has been considered to change the wavelength for each frame and perform measurements at all wavelengths. However, in this case, it takes a long time to obtain measurement results.

[0005] In one aspect, the present invention aims to provide a measurement program, a measurement method, and a measurement device that can measure an object.

[0006] In one aspect, the measurement program causes a computer to perform the following processes: acquiring measurement results from an optical system that scans a predetermined range with light emitted from a light-emitting element on a frame-by-frame basis and measures the distance to each sample point within the predetermined range by receiving reflected light from the predetermined range; selecting a combination of measurement wavelengths by changing the measurement wavelength of the optical system for each frame and comparing the measurement results for a number of frames equal to the number of measurement wavelengths specified; acquiring measurement results from the optical system in sequence for each measurement wavelength of the combination for each frame and comparing the measurement results for each sample point to select representative measurement data to be used for measurement at each sample point; and generating measurement data using the selected representative measurement data.

[0007] The object can be measured.

[0008] 1 is a diagram illustrating the configuration of a measurement device according to a first embodiment; FIG. 1A is a functional block diagram of a control device, and FIG. 1B is a block diagram illustrating the hardware configuration of each part of the control device; FIG. 1C is an explanatory diagram of a TOF method; FIG. 1A is a diagram illustrating an object and sample points for distance measurement, and FIG. 1B is a diagram illustrating a scanning trajectory; FIG. 1A is a diagram illustrating an object and an object in a liquid, and FIG. 1B is a diagram illustrating distance measurement; FIG. 1A and FIG. 1B are diagrams illustrating wavelength dependency; FIG. 1C is a diagram illustrating a flowchart showing the operation of the measurement device; FIG. 1D is a diagram illustrating an overview of the operation of the measurement device;

[0009] Before describing the examples, an overview of measurement technology using LiDAR will be described.

[0010] There is a growing need for underwater 3D data acquisition for applications such as offshore wind power plant inspections and blue carbon algae volume calculations. One solution is underwater LiDAR measurement. Underwater LiDAR is mounted on underwater robots such as autonomous underwater vehicles (AUVs) and remotely controls them to acquire data.

[0011] Until now, measurements have been made using monochromatic LiDAR, but the areas where it is most suitable to use it are limited by differences in the absorbance of light in seawater in different ocean areas (shallow water, deep water, etc.).Recently, to resolve these issues, underwater LiDAR with multiple wavelengths (for example, three wavelengths) has been introduced.

[0012] For example, measurements can be taken at one wavelength corresponding to the sea area. Also, distance detection for one wavelength is possible for one sample point. Wavelength switching is performed for each frame.

[0013] However, the reflectance of the measurement object also depends on the wavelength, and measurement using one wavelength may result in an unmeasurable area (missing measurement). In the following example, an example in which the object can be measured will be described.

[0014] Fig. 1 is a diagram illustrating the configuration of a measurement apparatus 100 according to a first embodiment. As illustrated in Fig. 1, the measurement apparatus 100 includes a control device 10 and an optical system 20. The optical system 20 includes a light-emitting element 21, a collimating lens 22, a scanning mirror 23, an angle expanding lens 24, a condensing lens 25, and a light-receiving element 26. The light-emitting element 21, the collimating lens 22, the scanning mirror 23, and the angle expanding lens 24 constitute an output optical system 27. The condensing lens 25 and the light-receiving element 26 constitute an input optical system 28.

[0015] Fig. 2A is a functional block diagram of the control device 10. As illustrated in Fig. 2A, the control device 10 functions as a control unit 11, a 3D data generation unit 12, and the like.

[0016] Fig. 2(b) is a block diagram illustrating an example of the hardware configuration of each unit of the control device 10. As illustrated in Fig. 2(b), the control device 10 includes a CPU 101, a RAM 102, a storage device 103, a display device 104, and the like.

[0017] The CPU (Central Processing Unit) 101 is a central processing unit. The CPU 101 includes one or more cores. The RAM (Random Access Memory) 102 is a volatile memory that temporarily stores programs executed by the CPU 101, data processed by the CPU 101, and the like. The storage device 103 is a non-volatile storage device. Examples of the storage device 103 include a read-only memory (ROM), a solid-state drive (SSD) such as a flash memory, and a hard disk driven by a hard disk drive. The storage device 103 stores a measurement program. The display device 104 is a device that displays 3D data generated by the 3D data generation unit 12, and is, for example, an LCD screen device. The CPU 101 executes the measurement program to realize each component of the control device 10. Each component of the control device 10 may be implemented using hardware such as a dedicated circuit.

[0018] An overview of the operation of the measurement device 100 will be described below with reference to FIGS. 1 and 2A. The light-emitting element 21 emits laser pulses as emitted light. The collimating lens 22 suppresses the divergence of the light emitted by the light-emitting element 21 to convert it into approximately parallel light. The scanning mirror 23 deflects the angle of the parallel light emitted from the collimating lens 22 in the horizontal and vertical directions. The angle expanding lens 24 further expands the angle deflected by the scanning mirror 23. The angle of the light emitted from the angle expanding lens 24 corresponds to the projection angle. The light emitted from the angle expanding lens 24 is irradiated onto an object, scattered (reflected), and returns to the condenser lens 25. This returned light is condensed by the condenser lens 25 and received by the light-receiving element 26. The light emitted by the light-emitting element 21 and the angle of the scanning mirror 23 are controlled by the control unit 11.

[0019] The 3D data generation unit 12 measures the distance to the target by employing a time-of-flight (TOF) method. FIG. 3 is an explanatory diagram of the TOF method. As illustrated in FIG. 3, the 3D data generation unit 12 measures the round-trip time (ΔT) between when the light-emitting element 21 emits light and when the reflected light returns from the target, and calculates the distance to the target by multiplying this by the speed of light. The reflected light returning from the target can be detected when the light-receiving element 26 receives light at a threshold value or higher.

[0020] 4A is a diagram illustrating an example of an object 30 for distance measurement and sample points P. The control unit 11 scans the emitted light over a predetermined range including the object by changing the angle of the scanning mirror 23. The control unit 11 can measure the distance to each sample point P by receiving the light reception results of the light receiving element 26 at predetermined time intervals. When each sample point P is viewed from the measurement device 100, the sample points P appear to be spread out two-dimensionally.

[0021] 4B is a diagram illustrating an example of a scanning trajectory. For example, the control unit 11 causes the emitted light to travel back and forth in a substantially horizontal direction (X-axis direction) within a predetermined range on the XY plane. When the emitted light travels back and forth multiple times in the X direction, it also travels back and forth once in a substantially vertical direction (Y-axis direction). This allows the emitted light to be irradiated onto each sample point P on the XY plane. The period of one round trip in the Y-axis direction is called one frame.

[0022] Here, a measurement mode when three-dimensional data (3D data) is created using the measurement results of the optical system 20 will be described. Because absorbance in liquids such as seawater, rivers, and lakes is wavelength-dependent, some wavelengths are suitable for measurement, while others are not, depending on the liquid. Therefore, when measuring an object in a liquid, it is desirable to use a wavelength suitable for the liquid. Therefore, a mode when using one wavelength as the measurement wavelength will be described.

[0023] 5A is a diagram illustrating an example of an object 201 and an object 202 in a liquid. In this case, if both the object 201 and the object 202 are objects that easily reflect the measurement wavelength, the distances to both the object 201 and the object 202 can be measured.

[0024] In this case, as illustrated in Fig. 5(b), the 3D data generation unit 12 can measure the distance to each sample point P on both the object 201 and the object 202. Furthermore, the 3D data generation unit 12 can obtain the received light intensity for each sample point P, and can generate a single-color grayscale image using the received light intensity. 3D data (a three-dimensional image) can be generated from these distances and the grayscale image.

[0025] However, there are cases where the object 201 is reflective at the measurement wavelength A but not at the measurement wavelength B, and the object 202 is not reflective at the measurement wavelength A but is reflective at the measurement wavelength B. In this case, as illustrated in Fig. 6(a), the object 201 can be measured at the measurement wavelength A, but it is difficult to measure the object 202. Furthermore, as illustrated in Fig. 6(b), the object 202 can be measured at the measurement wavelength B, but it is difficult to measure the object 201. Such inability to measure an object is sometimes referred to as a measurement omission.

[0026] In order to suppress measurement omissions, it is conceivable to perform measurements using multiple measurement wavelengths. For example, it is conceivable to switch wavelengths for each frame. In this case, object 201 can be measured in a frame using measurement wavelength A, and object 202 can be measured in a frame using measurement wavelength B. Furthermore, since grayscale images can be obtained at these multiple wavelengths, it becomes possible to generate 3D data with the fewest omissions by combining the grayscale images.

[0027] However, if wavelength change is repeated for each frame, a number of frames equal to the number of wavelengths is required for each repetition, which results in a long time required to measure the object. Therefore, the measurement device 100 according to this embodiment has a configuration that enables measurement of each object in a short time.

[0028] Fig. 7 is a diagram illustrating a flowchart showing the details of the operation of the measuring device 100 according to this embodiment. Figs. 8 and 9 are diagrams illustrating an outline of the operation of the measuring device 100. The operation of the measuring device 100 will be described below with reference to Figs. 7 to 9.

[0029] First, the control unit 11 specifies the number of wavelengths to be used in measurement in order to ensure a desired frame rate (step S1). In the example of Fig. 8, multiple types of wavelengths are prepared, such as measurement wavelength A, measurement wavelength B, measurement wavelength C, ..., measurement wavelength X, and the number of wavelengths to be used is determined by this process. As a result, by reducing the number of measurement wavelengths to be used below the maximum number of wavelengths usable by the optical system 20, it becomes possible to ensure the desired frame rate.

[0030] Next, the control unit 11 controls each part of the optical system 20 so that measurement results are obtained for each frame in order for all prepared measurement wavelengths. Also, the 3D data generation unit 12 acquires the measurement results for each measurement wavelength from the optical system 20 (step S2).

[0031] Next, the 3D data generation unit 12 determines whether each sample point P is a measurement point or an unmeasurable point for each wavelength. An unmeasurable point is a point within a predetermined distance where the distance cannot be measured using the measurement wavelength. If an object is present, the light receiving intensity of the light receiving element 26 is equal to or greater than a threshold. Therefore, if the light receiving intensity of the light receiving element 26 is less than the threshold, the sample point can be determined to be an unmeasurable point. The light receiving intensity of the light receiving element 26 can be calculated from the current value obtained by photoelectric conversion in the light receiving element 26. Therefore, the 3D data generation unit 12 checks the "or" of measurable points for each sample point P for all wavelengths and counts the number of unmeasurable points (step S3). Therefore, the number of unmeasurable points can be counted when all frames acquired in step S2 are combined.

[0032] Next, the 3D data generation unit 12 checks the "or" of measurable points for each sample point P for all combinations of the specified wavelengths (step S4). Here, a sample point that is a measurable point for at least one of the specified wavelengths is determined to be a measurable point. For example, if the number of specified wavelengths is two, all combinations of two wavelengths are checked, such as the combination of wavelength A and wavelength B, and the combination of wavelength A and wavelength C. If the number of specified wavelengths is three, all combinations of three wavelengths are checked, such as the combination of wavelength A, wavelength B, and wavelength C.

[0033] Next, the 3D data generator 12 selects the wavelength combination with the fewest number of unmeasurable points from the results of the search in step S3 (step S5). In the example of Fig. 8, the combination of wavelengths B and C has the fewest number of unmeasurable points, so the combination of wavelengths B and C is selected.

[0034] Next, the control unit 11 controls each part of the optical system 20 so that measurement results are obtained for each frame for each wavelength of the combination selected in step S5 (step S6). When wavelengths B and C are used, measurement results are obtained for a frame measured at wavelength B and a frame measured at wavelength C, as shown in FIG.

[0035] Next, the 3D data generation unit 12 compares the light receiving intensities of the light receiving element 26 for each sample point P (step S7). In the example of Fig. 9, the light receiving intensities of wavelengths B and C are compared for sample point 1, the light receiving intensities of wavelengths B and C are compared for sample point 2, and similarly, the light receiving intensities of wavelengths B and C are compared up to the final sample point X.

[0036] Next, the 3D data generation unit 12 uses the comparison result of step S7, the result of the wavelength with the greater received light intensity as representative measurement data, and generates one frame of 3D data (step S8). The result of step S6 is output from the 3D data generation unit 12. Thereafter, by repeating steps from step S6, it is possible to generate multiple frames of 3D data. This makes it possible to generate 3D video data, etc. The 3D data generated in step S8 is displayed on the display device 104.

[0037] According to this embodiment, the measurement wavelength of the optical system 20 is changed for each frame, and measurement results are compared for the number of frames equal to the specified number of measurement wavelengths, thereby selecting a combination of measurement wavelengths. Furthermore, measurement results are acquired sequentially from the optical system 20 for each measurement wavelength in the combination for each frame, and the measurement results are compared for each sample point P, thereby selecting representative measurement data to be used for measurement at each sample point P. Furthermore, 3D data is generated using the selected representative measurement data. In this way, when changing the wavelength for each frame, frames for all wavelengths are not required. Meanwhile, a measurement wavelength suitable for the measurement is selected. Therefore, it is possible to measure each object in a short time.

[0038] Furthermore, when selecting a combination of measurement wavelengths, if the received light intensity of the reflected light in the optical system 20 for each sample point P is less than a threshold value, it is determined to be an unmeasurable point, and by selecting the combination of measurement wavelengths that results in the fewest number of unmeasurable points, it is possible to minimize missed measurements.

[0039] Furthermore, when selecting representative measurement data, by selecting the measurement result with the higher received intensity of reflected light in the optical system 20 for each sample point P as the representative measurement data, it becomes possible to select the measurement result that is suitable for the measurement.

[0040] In the above embodiment, the optical system 20 is an example of an optical system that scans a predetermined range with light emitted from a light-emitting element in frame units and receives reflected light from the predetermined range to measure the distance to each sample point within the predetermined range.

[0041] In addition, the 3D data generation unit 12 changes the measurement wavelength of the optical system for each frame and compares the measurement results for the number of frames equal to the specified number of measurement wavelengths to select a combination of measurement wavelengths, acquires measurement results from the optical system for each measurement wavelength of the combination in sequence for each frame, compares the measurement results for each sample point, selects representative measurement data to be used for measurement at each sample point, and generates measurement data using the selected representative measurement data. This allows the measurement device 100 to acquire three-dimensional shape data of objects in the ocean in real time. Furthermore, the measurement device 100 can improve the measurement accuracy of three-dimensional shape data of objects in the ocean.

[0042] Furthermore, the measuring device 100 can construct a digital twin using the 3D data generated by the 3D data generation unit 12. In other words, the measurement data is data for constructing a digital twin that virtually reproduces the state of the ocean in real space. For example, the 3D data generation unit 12 places the 3D data generated by the 3D data generation unit 12 on a digital twin that virtually reproduces the state of the ocean in real space. For example, the control device 10 places 3D data of pipes and coral reefs installed underwater on the digital twin. In this way, the control device 10 can create a digital twin that reproduces the 3D shape data of objects existing in the ocean.

[0043] Although the embodiments of the present invention have been described in detail above, the present invention is not limited to such specific embodiments, and various modifications and changes are possible within the scope of the gist of the present invention as described in the claims.

[0044] REFERENCE SIGNS LIST 10 control device 11 control unit 12 3D data generation unit 20 optical system 21 light emitting element 22 collimating lens 23 scanning mirror 24 angle magnification lens 25 condensing lens 26 light receiving element 27 emission optical system 28 incidence optical system 100 measuring device

Claims

1. A measurement program that causes a computer to execute the following processes: acquiring measurement results from an optical system that scans a specified range with light emitted from a light-emitting element on a frame-by-frame basis and measures the distance to each sample point within the specified range by receiving reflected light from the specified range; selecting a combination of measurement wavelengths by changing the measurement wavelength of the optical system for each frame and comparing the measurement results for the number of frames equal to the number of measurement wavelengths specified; acquiring measurement results from the optical system for each measurement wavelength of the combination in order for each frame and comparing the measurement results for each sample point to select representative measurement data to be used for measurement at each sample point; and generating measurement data using the selected representative measurement data.

2. The measurement program described in claim 1, characterized in that when selecting the combination of measurement wavelengths, if the received light intensity of the reflected light in the optical system is less than a threshold value for each sample point, it is determined to be an unmeasurable point, and the combination of measurement wavelengths with the fewest number of unmeasurable points is selected.

3. The measurement program according to claim 1, characterized in that when selecting the representative measurement data, the measurement result with the higher received intensity of the reflected light in the optical system is selected as the representative measurement data for each sample point.

4. The measurement program according to claim 1, wherein the specified number of measurement wavelengths is less than the maximum number of measurement wavelengths that can be used by the optical system.

5. The measurement program according to claim 1, wherein the optical system emits the emitted light toward an object in a liquid.

6. The measurement program according to claim 5, wherein the liquid is seawater.

7. The measurement program according to claim 6, characterized in that the measurement data is data for constructing a digital twin that virtually reproduces the state of the ocean in real space.

8. A measurement method characterized by a computer executing the following processes: a process of acquiring measurement results from an optical system that scans a predetermined range with light emitted from a light-emitting element on a frame-by-frame basis and measures the distance to each sample point within the predetermined range by receiving reflected light from the predetermined range; a process of selecting a combination of measurement wavelengths by changing the measurement wavelength of the optical system for each frame and comparing the measurement results for the number of frames equal to the number of measurement wavelengths specified; a process of acquiring measurement results from the optical system for each measurement wavelength of the combination in order for each frame and comparing the measurement results for each sample point to select representative measurement data to be used for measurement at each sample point; and a process of generating measurement data using the selected representative measurement data.

9. The measurement method described in claim 8, characterized in that when selecting the combination of measurement wavelengths, if the received light intensity of the reflected light in the optical system is less than a threshold value for each sample point, it is determined to be an unmeasurable point, and the combination of measurement wavelengths with the fewest number of unmeasurable points is selected.

10. A measurement method as described in claim 8, characterized in that when selecting the representative measurement data, the measurement result with the higher received intensity of the reflected light in the optical system is selected as the representative measurement data for each sample point.

11. The measurement method according to claim 8, wherein the specified number of measurement wavelengths is less than the maximum number of measurement wavelengths that can be used by the optical system.

12. The measurement method according to claim 8, wherein the optical system emits the emitted light toward an object in a liquid.

13. The measurement method according to claim 12, wherein the liquid is seawater.

14. A measurement device comprising: an optical system that scans a predetermined range with light emitted from a light-emitting element in frame units and measures the distance to each sample point within the predetermined range by receiving reflected light from the predetermined range; and a generation unit that changes the measurement wavelength of the optical system for each frame and compares measurement results for a number of frames equal to the number of measurement wavelengths specified, thereby selecting a combination of measurement wavelengths, acquires measurement results from the optical system for each measurement wavelength of the combination for each frame in order, compares measurement results for each sample point, selects representative measurement data to be used for measurement at each sample point, and generates measurement data using the selected representative measurement data.

15. The measurement device described in claim 14, characterized in that when selecting the combination of measurement wavelengths, the generation unit determines that each sample point is an unmeasurable point if the received light intensity of the reflected light in the optical system is less than a threshold value, and selects the combination of measurement wavelengths that results in the fewest number of unmeasurable points.

16. The measurement device described in claim 14, characterized in that when selecting the representative measurement data, the generation unit selects, for each sample point, the measurement result with the higher received intensity of the reflected light in the optical system as the representative measurement data.

17. The measuring device according to claim 14, wherein the specified number of measurement wavelengths is less than the maximum number of measurement wavelengths that can be used by the optical system.

18. The measuring device according to claim 14, wherein the optical system emits the emitted light toward an object in a liquid.

19. The measuring device according to claim 18, wherein the liquid is seawater.

Images