1. A method for correcting a measured distance in a distance measuring device that measures a distance to an object from a propagation time of light, the method comprising:

as a preparatory step for making the correction, there are included:

in a state where a reflection tape made of a retro-reflection member is previously stuck to a floor surface of a measurement space in a direction away from the distance measuring device,

a step of measuring a distance La from an inner area of the reflection belt and a distance Lb from an outer area of the reflection belt adjacent to the inner area by the distance measuring device while scanning the measurement position along the reflection belt; and

a step of generating a correction expression for transforming the distance Lb into the distance La based on a relationship between the distance La and the distance Lb acquired at each measurement position,

the actual measurement step of measuring the distance to the object includes:

a step of obtaining an actual measurement value x by measuring a distance between the distance measuring device and the object; and

and correcting the measured value x by using the correction formula, and calculating a correction value y of the measured distance.

2. The method for correcting a measured distance according to claim 1,

the distance measuring device emits irradiation light and receives reflected light from the object with a plurality of pixels arranged two-dimensionally,

the distance measurement in the preparation step is performed by scanning a measurement window including an inner area of the reflection band and an outer area of the reflection band adjacent to the inner area while receiving reflected light from the measurement window with a plurality of pixels,

comparing the brightness data of the light received by each pixel, determining that the high brightness region is the inner region of the reflection band, and the low brightness region is the outer region of the reflection band,

the distance data of each pixel of the high luminance region and the data of each pixel of the low luminance region are respectively averaged to obtain the distance La and the distance Lb.

3. The method for correcting a measured distance according to claim 2,

in the distance measurement in the preparation step, the intensity of the irradiation light is adjusted so that the luminance data of the reflected light from the measurement window falls within a prescribed range.

4. The method for correcting a measured distance according to claim 1,

as a result of distance measurement in the preparation step, the correction expression is not generated when a difference between the distance La and the distance Lb obtained at each measurement position is smaller than a threshold value,

in the actual measurement step, the actual measurement value x is directly used without being corrected.

5. A distance measuring device for measuring a distance to an object from a propagation time of light, comprising:

a light emitting unit that emits irradiation light to the object;

a light receiving unit that detects reflected light from the object;

a light emission control unit that controls the light emitting unit;

a distance calculation unit for calculating a distance to the object based on the propagation time of the reflected light detected by the light receiving unit;

a distance correction unit for correcting the distance calculated by the distance calculation unit by a correction formula,

a correction formula storage unit for storing the correction formula; and

a correction formula generating unit for generating the correction formula,

the correction formula generating unit is configured to generate a correction formula,

in a measuring space where a reflection tape made of a retro-reflection member is previously stuck to a floor surface in a direction away from the distance measuring means,

measuring, by the distance calculating section, a distance La to an inner region of the reflection belt and a distance Lb to an outer region of the reflection belt adjacent to the inner region while scanning the measurement position along the reflection belt,

based on the relationship between the distance La and the distance Lb acquired at each measurement position, a correction expression for transforming the distance Lb into the distance La is generated.

6. The ranging apparatus as claimed in claim 5,

the light receiving unit receives light reflected from the object with a plurality of pixels arranged two-dimensionally,

the distance measurement by the correction expression generating unit is performed by scanning a measurement window including an inner region of the reflection band and an outer region of the reflection band adjacent to the inner region, and receiving reflected light from the measurement window by a plurality of pixels of the received portion light,

the distance measuring device includes an area determination unit that compares luminance data of light received by each pixel and determines that a high luminance area is an inner area of the reflection band and a low luminance area is an outer area of the reflection band,

the distance data of each pixel of the high luminance region and the data of each pixel of the low luminance region are respectively averaged to obtain the distance La and the distance Lb.

Background

A distance measuring apparatus (hereinafter also referred to as TOF apparatus) using a method of measuring a distance to an object based on a propagation time of light (hereinafter referred to as TOF method: time-of-flight method) is known. By displaying the distance data acquired with the TOF apparatus as a two-dimensional distance image and tracking its change with time, it is possible to obtain, for example, a moving route of a person or the like.

The TOF apparatus is a device that calculates a distance from an object by measuring a time (optical path length) until irradiation light emitted from a light source is reflected by the object and returns to a light receiving unit. In this case, by attaching a member having a characteristic of reflecting light incident on the object in the incident direction (so-called retro-reflection member) to the object, the object can be reliably detected.

For example, japanese patent application laid-open No. 2019-127375 (hereinafter referred to as patent document 1) describes the following: in order to detect an operator on the traveling path of the overhead traveling crane, a mark made of a retro-reflective member is attached to a helmet of the operator, and the operator is identified.

Disclosure of Invention

When a distance measuring device based on the TOF method is used in an environment where a material having a high reflectance is used on a surrounding wall, floor, or the like, the optical path length appears to be longer due to unnecessary reflection on the wall and floor. This is called a multipath phenomenon, and as a result, the distance to the object is measured to be longer than the actual distance, and a measurement error (distance error) occurs.

It is known to correct a distance error caused by a multipath phenomenon by using a method of using a retro-reflection member described in patent document 1. That is, by measuring the distance to the object by attaching a reflection tape made of a retro-reflection member to the object, it is possible to obtain an accurate distance to the object without being affected by the multipath phenomenon. Then, while changing the position of the object, the distances to the object when the reflection tape is attached and when the reflection tape is removed are measured in advance, and a correction expression is generated from the relationship between the two to correct the distance error.

However, as a preparation for generating the correction formula, the worker must perform the following operations: attaching the reflection tape to a predetermined position (for example, a distance of 2m, 3m … …, etc.) of an object (for example, a floor surface), measuring the distance to the reflection tape and the distance when the reflection tape is removed by a TOF apparatus, and generating a correction equation from the measured values of both, requires a lot of work and work time.

The invention aims to provide a measured value correction method and a distance measuring device, which can reduce the preparation work of an operator for correcting the measured value of the distance measuring device and can automatically generate a correction formula.

A first aspect of the present invention is a method for correcting a measured distance in a distance measuring device that measures a distance to an object based on a propagation time of light,

as a preparatory step for making the correction, there are included:

in a state where a reflection tape made of a retro-reflection member is previously stuck to a floor surface of a measurement space in a direction away from the distance measuring device,

a step of measuring a distance La from an inner area of the reflection belt and a distance Lb from an outer area of the reflection belt adjacent to the inner area by the distance measuring device while scanning the measurement position along the reflection belt; and

a step of generating a correction expression for transforming the distance Lb into the distance La based on a relationship between the distance La and the distance Lb acquired at each measurement position,

the actual measurement step of measuring the distance to the object includes:

a step of obtaining an actual measurement value x by measuring a distance between the distance measuring device and the object; and

and correcting the measured value x by using the correction formula, and calculating a correction value y of the measured distance.

A second aspect of the present invention is a distance measuring device for measuring a distance to an object from a propagation time of light, including:

a light emitting unit that emits irradiation light to the object;

a light receiving unit that detects reflected light from the object;

a light emission control unit that controls the light emitting unit;

a distance calculation unit for calculating a distance to the object based on the propagation time of the reflected light detected by the light receiving unit;

a distance correction unit for correcting the distance calculated by the distance calculation unit by a correction formula,

a correction formula storage unit for storing the correction formula; and

a correction formula generating unit for generating the correction formula,

the correction formula generating unit is configured to generate a correction formula,

in a measuring space where a reflection tape made of a retro-reflection member is previously stuck to a floor surface in a direction away from the distance measuring means,

measuring, by the distance calculating section, a distance La to an inner region of the reflection belt and a distance Lb to an outer region of the reflection belt adjacent to the inner region while scanning the measurement position along the reflection belt,

based on the relationship between the distance La and the distance Lb acquired at each measurement position, a correction expression for transforming the distance Lb into the distance La is generated.

According to the present invention, an operator can automatically generate a correction formula by simply pasting the reflection tape onto the floor surface, which greatly reduces the workload and working time of the operator.

Drawings

These and other features, objects and advantages of the present invention will become more apparent from the following description taken in conjunction with the accompanying drawings in which:

fig. 1 is a diagram showing the structure of the distance measuring device of the present embodiment.

Fig. 2 is a diagram illustrating the principle of distance measurement by the TOF method.

Fig. 3 is a diagram for explaining a multipath phenomenon.

Fig. 4 is a diagram illustrating a method of measuring a distance error in the preparation step.

Fig. 5 is a diagram showing an example of a measurement result of a distance error.

Fig. 6 is a diagram illustrating an example of generating the correction formula.

Fig. 7 is a flowchart showing a generation sequence of the correction formula.

Detailed Description

Embodiments of the present invention will be described below. However, the present invention should not be construed as being limited to the description of the embodiments shown below. It is to be understood by those skilled in the art that the specific structure can be changed without departing from the spirit or scope of the present invention.

In the structure of the present invention described below, the same reference numerals are used in common for the same portions or portions having the same functions in different drawings, and redundant description may be omitted.

The distance measuring apparatus (TOF apparatus) of the present embodiment has a function of correcting a distance measurement value by a correction formula, and also has a function of generating a correction formula for correction by itself. Hereinafter, the step of generating the correction formula in advance is referred to as a "preparation step", and the step of correcting the measured value using the correction formula is referred to as an "actual measurement step". In the preparation step, data for generating the correction formula is acquired using the reflection band as the object to be measured.

Fig. 1 is a diagram showing the structure of a distance measuring device according to the present embodiment. The distance measuring device (TOF device) 1 includes, as an actual measurement step: a light emitting unit 11 that irradiates pulsed light from a light source such as a Laser Diode (LD) or a Light Emitting Diode (LED) to a target object; a light receiving unit 12 for receiving the pulsed light reflected from the object by a CCD sensor, a CMOS sensor, or the like; a light emission control section 13 for performing lighting/turning-off and light emission amount control of the light emitting section 11; a distance calculation unit 14 for calculating a distance to the object based on the detection signal (light reception data) of the light reception unit 12; and a distance correcting unit 15 for correcting the distance data output from the distance calculating unit 14, wherein a correction formula for correction is stored in the correction formula storage unit 16 in advance.

Further, in the present embodiment, as a preparatory step for generating the correction formula to be stored in the correction formula storage section 16, distance data with the reflection band as the object is acquired by the distance calculation section 14. At this time, the method includes: an area determination unit 17 for determining a measurement area (inside or outside the reflection band) of the object based on the luminance data in the received light data; and a correction formula generating unit 18 for generating a correction formula using the distance data from the distance calculating unit 14 and the area information from the area determining unit 17. The generated correction formula is stored in the correction formula storage unit 16 and used in the actual measurement step.

As details of the preparation step, a reflection tape made of a retro-reflection member is pasted on the floor surface of the measurement space in a direction away from the TOF apparatus 1, which will be described later. Then, while scanning the measurement position along the reflection band, the distance to the inner region of the reflection band and the distance to the outer region of the reflection band adjacent thereto are measured at prescribed positions. The correction expression generating unit 18 generates a correction expression for correcting the difference (distance error) between the two using the measurement values at the respective positions. These series of actions are automatically performed by a dedicated program for generating a correction formula stored in the TOF apparatus 1.

In the actual measurement step, the distance data corrected by the distance correction unit 15 of the TOF apparatus 1 is transmitted to the external processing apparatus 2. The external processing device 2 is configured by, for example, a personal computer, executes a coloring process for changing the hue of each part of the object based on the distance correction data, generates a distance image, and outputs the distance image to a display for display. Further, by tracking the change in the position of the object based on the distance data, the movement route of the person or the like can be acquired.

Fig. 2 is a diagram for explaining the principle of distance measurement by the TOF method. The TOF apparatus 1 includes a light emitting portion 11 and a light receiving portion 12, and emits irradiation light 31 for distance measurement from the light emitting portion 11 toward an object 3 (e.g., a person). The two-dimensional sensor 12a for the light receiving unit 12 receives the reflected light 32 reflected by the object 3. The two-dimensional sensor 12a is a sensor configured by two-dimensionally arranging a plurality of pixels such as a CCD sensor, and is capable of obtaining two-dimensional distance data from light reception data of each pixel.

The object 3 is located at a distance L from the light emitting unit 11 and the light receiving unit 12. Here, assuming that the speed of light is c and the time difference between the emission of the irradiation light 31 from the light emitting unit 11 and the reception of the reflected light 32 by the light receiving unit 12 is t, the distance L to the object 3 can be determined by L ═ c × t/2. In the actual distance measurement performed by the distance calculating unit 14, an irradiation pulse having a predetermined width is emitted instead of the time difference t, the irradiation pulse is received while being shifted from the timing of the exposure shutter of the two-dimensional sensor 12a, and the distance L is calculated from the value of the light receiving amount (accumulated amount) at different timings.

Fig. 3 is a diagram for explaining a multipath phenomenon. The irradiation light emitted from the light emitting portion 11 is reflected by the object 3 and returns to the light receiving portion 12, and normally has an optical path indicated by a solid line 30, which is the shortest path. The light on this optical path is referred to as "direct light". However, in an environment in which a wall or floor surface 4 made of a material having a high reflectance exists around, a part of the irradiated light is reflected by the wall or floor surface 4 or the like, and returns to the light receiving section 12 along the optical path indicated by the broken line 40. This phenomenon is called "multipath phenomenon", and light on the optical path is called "indirect light". Since the indirect light is not a straight line having the shortest optical path between the light emitting portion 11 and the object 3 or between the object 3 and the light receiving portion 12, but a broken line, the optical path 40 of the indirect light has a longer optical path length than the optical path 30 of the direct light. Since the direct light and the indirect light are incident on the light receiving unit 12 in a mixed manner, an error occurs in the distance measured by the TOF apparatus 1.

When the multipath phenomenon occurs, not only one optical path of indirect light but also a plurality of indirect optical paths are generally present, and the intensity ratio of indirect light to direct light is also varied. The direct light and the indirect light having a time delay longer than that are incident on the light receiving unit 12. In the case of the exposure shutter method, the amount of light received detected during a predetermined shutter period deviates from the original amount of light received during direct light only, and this causes an error in the calculation of the distance.

If a measurement error is caused due to a multipath phenomenon, a distance to an object is calculated to be greater than an actual distance, thereby causing various problems. For example, assume a case where a plurality of TOF apparatuses are provided to acquire a moving path of an object (person) in a room. In an environment such as an elevator hall where marble having a high reflectance is used for surrounding walls and floors, an error easily occurs in a distance measurement value from each TOF device to a person due to a multipath phenomenon. As a result, when the coordinates of the person are determined from the distance measurement values and the moving path is tracked by inheriting the coordinates, the path of one person is divided into two paths or the coordinates cannot be connected at the joint between the TOF apparatuses, so that a problem of path interruption occurs.

In order to cope with such a multipath phenomenon, in the present embodiment, the TOF apparatus is set in a measurement environment, and an object (a reflection tape) is attached to a predetermined position in advance to measure a distance error occurring in the actual environment. Then, a correction formula for correcting the generated distance error is generated based on the generated distance error. The preparation step is automated to reduce the burden on the operator. Hereinafter, the preparation step will be described in detail.

Fig. 4 is a diagram for explaining a method of measuring a distance error in the preparation step. First, the operator sets the TOF apparatus 1 in an actual use environment, and attaches a reflection tape as a measurement object to a floor surface of a measurement space. Here, it is assumed that the inside is a measurement space, but in the case of the outside, a reflection tape may be pasted on a road surface or the like.

In fig. 4, (a) is a side view of the measurement environment, (b) is a plan view of the measurement environment, and (c) is a plan view showing the measurement region including the reflection band. Here, as coordinate axes for explanation, it is assumed that a forward direction viewed from the TOF apparatus 1 is a Y axis, a left-right direction is an X axis, an up-down direction is a Z axis, and a position of the TOF apparatus 1 is a coordinate origin (X ═ Y ═ Z ═ 0).

As shown in (a) and (b) in fig. 4, the TOF apparatus 1 is mounted on a ceiling, and takes an obliquely downward direction as a measurement space. At this time, it is assumed that indirect light is generated by light reflection of the floor surface 4 and the side wall 6 of the measurement space, and thus is affected by multipath. Therefore, the measured value Lb (broken line) when affected by multipath has a larger value in terms of the distance from the TOF apparatus 1 to the position P on the floor surface 4 than the measured value La (solid line) when there is no multipath. In other words, the position P of the floor surface 4 seems to sink to the position P 'of the floor surface 4' due to the multipath phenomenon. The difference (Lb-La) between the two measurement values La, Lb is a distance error, but since the degree of generation of indirect light varies depending on the position in the measurement space, the distance error varies depending on the measurement position.

In order to effectively measure a distance error while changing a measurement position, in the present embodiment, the reflection band 5 is used as a measurement object. The reflection band 5 is made of a retro-reflection member having a characteristic of reflecting incident light in an incident direction, and therefore indirect light is less likely to be generated and is less susceptible to multipath influence.

As shown in fig. 4 (b), the reflection tape 5 is pasted to the floor surface 4(XY plane) in the measurement direction of the TOF apparatus 1 along the Y-axis direction. The shape of the reflection band 5 is, for example, about 5cm in width and 10m in length. The measurement range 50 of the TOF device 1 is a rectangular area including a reflection band 5 in the center, arranged: the distance on the Y axis from the TOF device 1 is in the range of Y1 to Yn (e.g., 2m to 8m), and the width Xw (e.g., 1m) that can cover the area of the floor surface 4 adjacent to the reflection band 5.

Fig. 4 (c) shows an enlarged measurement region. While scanning the measurement window 51 in the Y-axis direction with respect to the measurement range 50, the distance to the region within the measurement window 51 at each position Yi (i ═ 1, 2, … … n) on the Y-axis is measured. The measurement window 51 has a size equal to the width Xw of the measurement range 50 in the X direction, and a width Yw in the Y direction, for example, 2 cm. The measurement window 51 is constituted by an area 51a on the inner side of the reflection band 5 and an area 51b adjacent to the area 51a on the outer side of the reflection band 5, and distance data can be obtained from these two areas. The scanning operation of the measurement window 51 can be performed by selectively scanning the respective pixel regions within the two-dimensional sensor 12a of the light receiving section 12.

The distance data from the inside of the measurement window 51 is divided into distance data to an area 51a on the inner side of the reflection band 5 and distance data to an area 51b on the outer side of the reflection band 5. In order to separate the distance data, the region determination unit 17 determines whether the measurement position is within the region 51a or the region 51b using the luminance data from the light receiving unit 12. That is, the light receiving amount (luminance) of each pixel is compared within the measurement window 51, and a pixel group having high luminance and a pixel group having low luminance are separated. Then, the high-luminance pixel group is made to correspond to the region 51a on the inner side of the reflection band 5, and the distance data of each pixel is averaged to obtain the measured value La. On the other hand, the low-luminance pixel group is made to correspond to the region 51b on the outer side of the reflection band 5 (i.e., the floor surface 4), and the distance data of each pixel is averaged to obtain the measured value Lb.

In this way, at the same measurement position Yi, the measurement value La in the inner area 51a of the reflection belt 5 not affected by the multipath and the measurement value Lb in the outer area 51b of the reflection belt 5 affected by the multipath can be simultaneously acquired, and therefore the measurement efficiency can be greatly improved.

Within the measurement range 50, the intensity of the reflected light varies depending on the distance from the TOF apparatus 1 (the position Yi of the measurement window 51). When the measurement position is close, the sensor 12a of the light receiving unit 12 is saturated, and when the measurement position is far, light reception is insufficient. Therefore, the light emission control unit 13 adjusts the intensity of the irradiation light from the light emitting unit 11 based on the luminance data from the light receiving unit 12, and controls the luminance level within a predetermined range.

Fig. 5 is a diagram showing an example of a measurement result of a distance error. The horizontal axis plots a measurement position (Y coordinate), and the vertical axis plots a measurement value La (good quality mark) on the inner side of the reflection belt and a measurement value Lb (x mark) on the outer side of the reflection belt. The measurement value La on the inner side of the reflection band is not affected by the multipath, but the measurement value Lb on the outer side of the reflection band is affected by the multipath and is therefore larger than the measurement value La.

It can also be seen that the distance error (Lb-La) due to multipath is not constant but varies with the measurement position (Y). This means that the influence of the measuring environment (the degree of indirect light reflected on the floor or wall) varies with the measuring location.

When the measured values La and Lb of the multipath are acquired in this way, the correction expression generating unit 18 generates a correction expression based on the relationship between the two. The correction expression is an approximate expression for converting the measurement value Lb into the measurement value La, and can be automatically obtained by a known method such as a least square method.

Fig. 6 is a diagram showing an example of generating a correction expression. The horizontal axis is the measured value Lb outside the reflection band (with multipath),the vertical axis is the measured value La inside the reflection band (without multipath). The measurements for both of fig. 5 are plotted with the ● label. The dotted line indicates the use of a quadratic equation (y ═ ax)²+ bx + c) as a case of performing nonlinear approximation by an approximate expression of these measurement points. In the correction formula, the variable x corresponds to the measured value Lb, and the variable y corresponds to the measured value La. The approximate expression is not limited to this, and may be an expression in which a higher-order polynomial or function is combined.

The correction formula or the coefficients (a, b, c) of the correction formula generated in the preparation step are stored in the correction formula storage section 16 in the TOF apparatus 1 in fig. 1. Then, in the actual measurement step, the distance correction unit 15 corrects the distance data x calculated by the distance calculation unit 14 into distance correction data y using a correction formula. As a result, even in a multipath environment, it is possible to correct a distance error with respect to an object and to track a moving path of a person with high accuracy.

According to the preparation procedure for generating the correction formula described above, as a method of measuring a distance error caused by a multipath phenomenon, data in a multipath-free state and data in a multipath state can be acquired in one measurement. That is, the operator only has to stick the reflective tape on the floor surface, and a series of preparation works for generating the correction formula can be automatically performed by a dedicated program, which greatly reduces the burden on the operator.

Fig. 7 is a flowchart showing a sequence for generating a correction expression in this embodiment. As preparation for generating the correction formula, the operator sets the TOF apparatus 1 in an actual use environment in a state where the reflection tape is stuck on the floor surface in the measurement direction. Hereinafter, the description will be given using reference numerals in fig. 4.

S101: the TOF device 1 is operated and a measurement range 50 comprising the reflection band 5 is started for distance and brightness measurements. The measurement range 50 is, for example, Y — Y1(2m) to Yn (8m), and the measurement interval Δ Y is, for example, 1 m. Distance data is acquired for each pixel of the two-dimensional sensor 12a of the light receiving section, and luminance data at each pixel position is acquired.

S102: the measurement window 51 is moved to the start position of the measurement range 50 (Y — Y1). This is done by selecting the reading position of the two-dimensional sensor 12 a. The measurement window 51 is sized as follows: a width Yw (± 1cm) in the Y direction, and a width Xw (± 0.5m) in the X direction.

S103: the luminance data at the current measurement position is read, and the irradiation light intensity of the light emitting section 11 is adjusted so that the luminance level falls within a prescribed range. Therefore, for example, the light reflected from the region 51a of the reflection band 5 may be monitored and adjusted by the light emission control section 13.

S104: distance data and brightness data within the measurement window 51 are acquired. That is, each pixel included in the range of the width Yw in the Y direction and the range of the width Xw in the X direction is acquired.

S105: from the distribution of the luminance data within the measurement window 51, for each pixel comprised therein, the separation is: a pixel group that detects the inner side of the reflection band and exhibits high luminance, and a pixel group that detects the outer side of the reflection band and exhibits low luminance.

S106: the distance data of the high-luminance pixel group is averaged into la (y) among the acquired distance data, and is stored in the memory of the correction expression generating unit 18.

S107: the distance data of the low-luminance pixel group is averaged to lb (y) in the acquired distance data, and is stored in the memory of the correction expression generating unit 18.

S108: the position of the measurement window 51 is moved by a measurement interval Δ Y (═ 1m) (Y ═ Y + Δ Y).

S109: it is determined whether the position Y of the measurement window 51 exceeds the end position Yn (═ 8m) of the measurement range 50. If so, the step proceeds to S110. If Not (NO), the step returns to S103, and the above processing is repeated.

S110: la (Y) and lb (Y) found in S106 and S107 are read from the memory, and it is determined whether the difference between the two at the same position Y is smaller than the threshold at all positions Y. The threshold value is, for example, 3%. If less than the threshold (yes), the step proceeds to S111, and if greater than or equal to the threshold (no), the step proceeds to S112.

S111: and judging that the measurement error is at a level which can be ignored, and the multipath influence does not exist, and not correcting the measurement value.

S112: according to the relationship between La (Y) and Lb (Y), a correction formula for converting the measured value Lb (Y) into the measured value La (Y) is generated. The correction formula is automatically generated by a known method such as the least square method.

S113: the generated correction formula (e.g., y ═ ax)²+ bx + c) or coefficients (a, b, c) thereof are stored in the correction formula storage section 16.

This completes the preparatory steps for generating the correction formula. Thereafter, the distance correction unit 15 corrects the measured distance value obtained in the measurement step using the correction formula, and outputs the corrected value.

The above description describes one TOF apparatus, but when a plurality of TOF apparatuses are provided, a reflection band may be used to generate a correction formula for each TOF apparatus.

As described above, in the preparation step of the present embodiment, as a method for measuring a distance error due to a multipath phenomenon, an operator can acquire data in a multipath-free state and data in a multipath-containing state by only sticking the reflection tape to the floor surface by one measurement. Thus, the correction formula can be automatically generated, and the workload and the working time of the operator can be greatly reduced.