KR101920012B1 - Depth Extraction Apparatus and Method Using Retroreflective Film - Google Patents

Abstract

The present invention relates to an apparatus and a method for measuring a distance using a retroreflective film. A light and dark region is formed on the photographed image of an object to be measured using the retroreflective film having the reflective surface and the non-reflective surface, and the retroreflective film is inclined so that a contrast ratio is clearly displayed at a position corresponding to the focal plane of a camera. Therefore, it is possible to calculate the distance of the object to be measured by detecting the position of a point having the standard contrast ratio. Thus, it is not necessary to irradiate the object to be measured with separate measurement light, and the distance can be sufficiently measured with natural light alone. The apparatus for measuring distance is compact and easy to be used, can obtain more accurate measurement results even in an external environment, and can calculate a position of object image to be measured in real time through analysis of a camera shooting screen. Therefore, the distance to the object can be measured more quickly and conveniently in real time.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a retroreflective film,

The present invention relates to an apparatus and a method for measuring a distance using a retroreflective film. More particularly, the present invention relates to a retroreflective film having a reflective surface and a non-retroreflective surface to form a light and dark region on a photographed image of an object to be measured, It is possible to calculate the distance of the object to be measured by detecting the position of the point having the standard contrast ratio. Accordingly, it is not necessary to irradiate the object to be measured with another measuring light, and the distance can be sufficiently measured with natural light alone , It is possible to miniaturize the device, and it is convenient to use, and more accurate measurement results can be obtained even in an external use environment, and the position of the measurement object image can be calculated in real time through analysis of the camera shooting screen, A retroreflective film that can measure distances more quickly and conveniently in real time Yonghan relates to a distance measuring apparatus and method.

Generally, two representative methods of distance measurement are mainly used for the object to be measured. The first is a method using a pattern light and a photon triangulation method like a Kinect. The second is a method of irradiating an Infra Red (IR) to a subject. A time-of-flight (TOF) ) From the distance. At this time, not only an infrared ray but also a laser may be used.

Recently, the TOF method has been used more and more because of its accuracy and convenience, rather than the method using the pattern light and the optical triangulation method.

The TOF camera irradiates an object with illumination by modulating the near-infrared rays of 850nm band invisible to light at a frequency of several tens of MHz and measures the phase delay of the light coming back from the object with the image sensor, Obtain the distance between the object and the camera at the pixel.

Such a TOF method is very weak or strong because the intensity of infrared rays reflected to surrounding objects is too weak or strong when the measurement is performed in an environment with a large contrast difference or when the reflectance of the surface of surrounding objects is greatly different. Is easily generated.

Particularly, since a separate illumination optical system is necessarily required, there is a problem that it is inconvenient to use in an external environment, the size of the apparatus is increased, and the usability is not good and the accuracy is lowered.

Korean Patent Publication No. 10-2015-0065473

An object of the present invention is to provide a retroreflective film which forms a light and dark region on an image of an object to be measured using a retroreflective film having a reflective surface and a non-reflective surface, The distance of the object to be measured can be calculated by detecting the position of the point having the standard contrast ratio so that the contrast ratio is clearly displayed at the position corresponding to the focal plane of the camera. A distance measuring apparatus and method using a retroreflective film which can measure a distance sufficiently without using light alone and can sufficiently measure the distance, can be miniaturized and is convenient to use, and can obtain more accurate measurement results even in an external environment .

Another object of the present invention is to provide a method and apparatus for measuring the distance of an object to be measured in real time, And to provide a measurement apparatus and method.

It is still another object of the present invention to provide a retroreflective lens capable of more easily and conveniently performing distance calculation on an object to be measured by adjusting an arrangement state of a condenser lens module and a retroreflective film, And an apparatus and a method for measuring a distance using a film.

A condensing lens module for condensing light reflected from an object to form an image of the object to be measured; A reflective surface for retroreflecting the incident image is formed so as to be inclined with respect to an optical axis of the condensing lens module so that an image formed by the condensing lens is retroreflected and re- A retroreflective film on which a non-reflecting surface is formed; A camera for focusing the entire area of the retroreflective film together with the re-reflected image so as to form a focal plane based on the image re-formed by the retroreflective film; And a distance calculating unit for detecting a position of a point having a predetermined reference contrast ratio with respect to a light and dark region generated by the reflective surface and the non-reflective surface of the retroreflective film, A distance measurement device using a retroreflective film is provided.

In this case, a separate beam splitter is provided between the focusing lens module and the retroreflective film so as to change the reflection path of the image retroreflected by the retroreflective film, and the camera moves the image changed by the beam splitter And can be arranged to photograph.

The focal plane of the camera may be formed in a direction perpendicular to an optical axis of the condenser lens module based on an image re-formed by the retroreflective film.

The distance measuring module may include a contrast ratio detector for detecting a position of a point having a standard contrast ratio among images of the entire region of the retroreflective film photographed by the camera; And an arithmetic unit operable to calculate a distance to the object using the position of the reference contrast ratio point detected through the contrast ratio detector and the inclination angle of the retroreflective film.

The operation unit may calculate the position of the image formed by the focusing lens module using the position of the reference contrast ratio point detected through the contrast ratio detecting unit and the inclination angle of the retroreflective film, And the distance (b) to the condenser lens module is applied to the lens formula to calculate the distance (a) with respect to the measurement object.

When the distance between the condenser lens module and the retroreflective film is Dn and the distance between the condenser lens module and the retroreflective film is Df, The image of the object may be formed to be positionally adjustable so as to form an image between Dn and Df.

Also, the condensing lens module may be configured such that at least two or more lenses are arranged movably along the optical axis direction.

Also, the retroreflective film may be formed such that a plurality of unit cells having the same shape are in contact with each other, and the reflective surface and the non-reflective surface may be formed in each unit cell.

In addition, the unit cells of the retroreflective film may be formed in a triangular pyramid shape in which three oblique planes are orthogonal to each other and the bottom surface is opened.

According to another aspect of the present invention, there is provided an imaging apparatus comprising: (a) focusing an image of an object to be measured by condensing light reflected from an object to be measured through a condensing lens module; (b) a retroreflective film for retroreflecting an incident image, and a retroreflective film having a non-reflective surface formed on a part of the reflective surface and disposed in a direction inclined with respect to an optical axis of the condensing lens module, Retroreflecting an image formed by the light source; (c) photographing the entire area of the retroreflective film together with the re-formed image by adjusting the focus of the camera so that a focal plane is formed based on the image re-formed by the retroreflective film; (d) detecting a position of a point having a predetermined reference contrast ratio with respect to a light and dark region generated by the reflective surface and the non-reflective surface of the retroreflective film, the image being photographed by the camera; And (e) calculating a distance to the measurement object using the position of the reference contrast ratio point detected through the step (d). .

In this case, if the reference contrast ratio is not detected in the step (d), the arrangement of the condenser lens module may be adjusted and the steps (a) to (d) may be performed again.

According to the present invention, a dark region is formed on a photographed image of an object to be measured by using a retroreflective film having a reflective surface and a non-reflective surface, and the retroreflective film is disposed obliquely, It is possible to calculate the distance of the object to be measured by detecting the position of the point having the standard contrast ratio. Accordingly, it is not necessary to irradiate the object to be measured with a separate measuring light, It is possible to miniaturize the device, which is convenient to use, and it is possible to obtain more accurate measurement results even in an external environment.

In addition, since the position of the object image can be calculated in real time through the analysis of the camera shooting screen, the distance to the object can be measured more quickly and conveniently in real time.

In addition, the arrangement of the condenser lens module and the retroreflective film is adjusted to make the photographing of the measurement object image more convenient, and the distance to the measurement object can be calculated more quickly and conveniently.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic view showing a configuration of a distance measuring apparatus using a retroreflective film according to an embodiment of the present invention;
2 is a functional block diagram functionally showing a configuration of a distance measuring apparatus using a retroreflective film according to an embodiment of the present invention.
3 and 4 are views for explaining a structure of a retroreflective film of a distance measuring apparatus according to an embodiment of the present invention,
5 and 6 are views for explaining the principle of distance measurement of a distance measuring apparatus according to an embodiment of the present invention,
7 is a view showing an actual camera photographed image of the distance measuring apparatus according to an embodiment of the present invention,
FIG. 8 is a view showing an actual photographed image of a retroreflective film changing according to a change of a focus position of a camera according to an embodiment of the present invention;
FIG. 9 is a graph illustrating modulation transfer function values for a camera image according to an exemplary embodiment of the present invention. Referring to FIG.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the drawings, the same reference numerals are used to designate the same or similar components throughout the drawings. In the following description of the present invention, a detailed description of known functions and configurations incorporated herein will be omitted when it may make the subject matter of the present invention rather unclear.

FIG. 1 is a view schematically showing a configuration of a distance measuring apparatus using a retroreflective film according to an embodiment of the present invention. FIG. 2 is a view illustrating a configuration of a distance measuring apparatus using a retroreflective film according to an embodiment of the present invention. FIGS. 3 and 4 are views for explaining the structure of a retroreflective film of a distance measuring apparatus according to an embodiment of the present invention, and FIGS. 5 and 6 are views FIG. 3 is a view for explaining the principle of distance measurement of the distance measuring apparatus according to the embodiment. FIG.

A distance measuring apparatus according to an embodiment of the present invention includes a focusing lens module 100, a retroreflective film 200, a beam splitter 500, a camera 300, and a distance measuring module 400 .

The condensing lens module 100 is configured to condense the light reflected from the measurement object 10 to image the image 20 of the measurement object 10 and may be formed of a single lens or a plurality of lens groups. When the lens is formed of a single lens, a convex lens capable of condensing light can be used. In the case of being formed of a plurality of lens groups, various lenses can be used according to the needs of the user, have.

The light collecting lens module 100 according to an embodiment of the present invention may be configured such that at least two or more lenses 110 are arranged to be movable along the optical axis C direction as shown in FIG. The condensing lens module 100 may be configured such that the lens 110 is automatically moved along the optical axis C direction through the separate lens adjusting means 101. Through the movement of the lens 110, The focus position to be condensed can be adjusted. The lens adjusting means 101 may be configured in various ways through various mechanical elements that are not shown in detail but which can move the lens 110 linearly.

The retroreflective film 200 is arranged in a direction inclined with respect to the optical axis C of the condensing lens module 100 in such a manner that the image 20 formed by the condensing lens module 100 is retroreflected and re- . In general, the retroreflective film is a member having various characteristics such that incident light is reflected as it is in the incident direction and is returned. The retroreflective film is formed in various shapes and structures, and is disposed in a direction inclined with respect to the optical axis (C) The incident light is reflected in the incident direction as it is.

The retroreflective film 200 according to an exemplary embodiment of the present invention has a reflective surface 210 that retroreflects an incident image and a non-reflective surface 210 that prevents an incident image from being reflected on a part of the reflective surface 210 220 are formed. An image retroreflected from the retroreflective film 200 by the reflective surface 210 and the non-reflective surface 220 forms a dark region. That is, the image incident on the reflective surface 210 is retroreflected by the reflective surface 210 to appear as a bright region, and the image incident on the non-reflective surface 220 is absorbed without being reflected by the non- And thus, the retroreflected image from the retroreflective film 200 has a dark region.

3 and 4, the retroreflective film 200 is formed in such a manner that a plurality of unit cells 201 having the same shape are in contact with each other, The cell 201 may be configured to form the reflective surface 210 and the non-reflective surface 220.

At this time, each unit cell 201 may be formed as a triangular pyramid having three oblique planes perpendicular to each other as shown in FIG. According to this structure, an image incident on any one of the three oblique planes is sequentially reflected by the remaining two oblique faces, and is reflected again in the incident direction. In this case, according to the geometric shape of the unit cell 201, the image incident on the three oblique planes at three vertexes adjacent to the bottom surface is not refracted on the reflection path but reflected in the other direction, It appears to be reflected. In other words, the triangular-pyramidal unit cell 201 may be formed by merely forming the non-reflecting surface 220 at three vertex portions by the geometric shape without attaching an additional light absorbing member or another reflecting member do.

Therefore, the retroreflected image 20 of the retroreflective film 200 has a dark region formed at each of three vertexes of each unit cell 201 region. Therefore, as shown in FIGS. 7 and 8, A dark region of the shape is formed.

The retroreflective film 200 according to an embodiment of the present invention is disposed in an inclined direction with respect to the optical axis C of the condensing lens module 100. According to this inclined arrangement structure, The contrast ratio of the retroreflective film 200 is clearly displayed only at one point corresponding to the focal plane SF of the display screen 300 and the contrast ratio is blurred as the screen 200 moves away from the point. In the present invention, the distance to the measurement object 10 is measured using the characteristic that the contrast ratio difference appears. The retroreflective film 200 may be provided with an angle adjusting means 201 for adjusting the angle of inclination of the retroreflective film 200 according to an embodiment of the present invention. The angle can be adjusted automatically.

The camera 300 may include a camera lens 310 and an image sensor 320 that are configured to capture an image 20 that has been re-formed by the retroreflective film 200. The camera 300 is focused to form a focal plane SF on the basis of the image 20 reconstructed by the retroreflective film 200 and is combined with the refracted reflective film 200 together with the re- As shown in FIG. At this time, the focal plane SF of the camera 300 is formed in a direction perpendicular to the optical axis C of the condensing lens module 100 as shown in FIG.

In this case, it is preferable that the camera lens 310 is formed to have as narrow a depth of field as possible, and similarly, the lens of the condensing lens module 100 also has a narrow depth of field. Although the focus of the lens is determined on only one plane, in real photographs, the phenomenon of gradual blurring increases as the focal plane moves away from it. The limit of the range that is considered to be sufficiently focused is called the depth of field. Accordingly, the camera lens 310 has a narrow depth of field as much as possible, so that the difference in contrast ratio with respect to the focal plane during the retroreflective film photographing is clear, so that the distance calculation can be performed more accurately.

The beam splitter 500 is disposed between the condenser lens module 100 and the retroreflective film 200 so that the reflection path of the image 20 retroreflected by the retroreflective film 200 can be changed. At this time, the camera 300 is arranged to photograph a path-changed image by the beam splitter 500. Through this arrangement, an image can be smoothly photographed through the camera 300 without interfering with the path of the image. 1 and 5, the camera 300 is mounted on the optical axis C of the condensing lens module 100 such that interference with the image path is not generated during photographing of the camera 300 by the beam splitter 500, As shown in Fig. In this case, since the image to be incident on the camera 300 is an image reflected by the beam splitter 500, the photographing direction of the camera 300 is substantially the same as the photographing direction of the condensing lens module 100 The direction of the optical axis C is parallel to the optical axis C. In other words, the photographing direction of the camera 300 becomes the Z-axis direction shown in Fig.

The distance measuring module 400 measures a position of a point having a predetermined reference contrast ratio with respect to a light and dark region generated by the reflective surface and the non-reflective surface of the retroreflective film 200, And calculates the distance to the object 10 to be measured.

The distance measuring module 400 includes a contrast ratio detector 410 for detecting a position of a point having a standard contrast ratio among images 301 of the entire area of the retroreflective film 200 photographed by the camera 300, And an operation unit 420 for calculating the distance to the measurement object 10 using the position of the reference contrast ratio point detected through the detection unit 410 and the tilt angle? Of the retroreflective film 200 . Here, the reference contrast ratio may be a contrast ratio preset by the user, and may be set to a contrast ratio at a point where the contrast ratio is most clearly displayed at a point corresponding to the focal plane of the camera 300 among the areas of the retroreflective film 200.

At this time, the operation unit 420 calculates the position of the image formed by the condensing lens module 100 using the position of the reference contrast ratio point detected through the contrast ratio detector 410 and the tilt angle [theta] of the retroreflective film 200 And calculates the distance a to the measurement object by applying the distance b from the position of the calculated image to the condenser lens module 100 to the lens formula.

That is, the distance measurement module 400 calculates the position of the image formed by the condensing lens module 100 and applies the calculated position to the lens formula to calculate the distance to the measurement object 10.

The distance measurement principle of the distance measuring apparatus using the above-described retroreflective film will be described in more detail.

In the present invention, the distance to the measurement object 10 is calculated using the lens formula. The lens formula is as follows.

Lens formula: 1 / a + 1 / b = 1 / f

Where a is the distance between the lens and the object, b is the imaging position of the image with respect to the object and the distance from the lens, and f is the focal length of the lens.

At this time, the f value can be known through the specification of the condenser lens module 100. When the image position of the measurement object 10 and the distance b between the condenser lens module 100 and the image position are calculated, The distance a value to the target object 10 can be known.

The condensing lens module 100 is configured to adjust the focal length of the image 20 with respect to the measurement object 10 through the lens adjustment unit 101. In this case, The lens module 100 is adjusted such that the image 20 of the measurement object 10 is imaged between Dn and Df shown in FIG. Dn denotes the closest separation distance between the condenser lens module 100 and the retroreflective film 200 and Df denotes the farthest separation distance between the condenser lens module 100 and the retroreflective film 200 do.

Accordingly, the light reflected from the measurement object 10 passes through the condensing lens module 100 and is condensed so that the image 20 is formed at the corresponding position. Then, the reflected light is retroreflected by the retroreflective film 200, The image 20 is re-displayed.

In this state, the entire area of the retroreflective film 200 is photographed together with the re-formed image 20 using the camera 300. At this time, the camera 300 focuses the re- So that the surface is formed. In this case, since the image photographed by the camera 300 photographs the image reflected by the beam splitter 500, the photographing direction of the camera 300 is parallel to the direction of the optical axis C of the condensing lens module 100 Axis direction, and the focal plane SF is in the X-axis direction perpendicular to the optical axis C.

5 and 7, the screen 301 photographed by the camera 300 is obtained by photographing the image 20 of the measurement object 10 with the focal plane SF aligned with the focal plane SF. The contrast 20 of the retroreflective film 200 is clearly visible only at one point E1 of the retroreflective film 200 corresponding to the focal plane SF, As the distance from the point (E2, E3, E4) increases, the contrast ratio gradually becomes blurred.

For example, as shown in FIG. 8, the area of the retroreflective film 200 is divided into five regions and the focal planes SF1, SF2, SF3, SF4, and SF5 are formed to correspond to the respective points, When the entire area of the reflective film 200 is photographed, the contrast ratio appears clearly only at the positions corresponding to the positions of the corresponding focal planes in the photographed image, and the contrast ratio becomes blurred as the positions are further away from the corresponding points. For example, in the image obtained by forming the focal plane at the SF1 point, the contrast ratio is clearly displayed in the E1 region corresponding to the SF1 focal plane, and the contrast ratio is blurred toward the E2, E3, E4 and E5 regions away from the E1 region appear. The same is true for other focal planes.

Since the X-axis direction component appears in the two-dimensional plane on the screen 301 captured by the camera 300, the position of the image 20 re-formed by the retroreflective film 200, The position with respect to the area of the retroreflective film 200 corresponding to the plane SF appears at point X2 in the camera photographing screen 301 and at point X1 in which the contrast ratio is clear.

It is possible to measure the distance on the screen with respect to the distance M from the end of the retroreflective film 200 to the point X1 at which the contrast ratio is clear in the camera shooting screen 301. By using the distance M, The distance b to the image 20 of the measurement object 10 can be obtained.

As shown in FIG. 6, the values of Dn and Df are set according to the initial arrangement state of the condenser lens module 100 and the retroreflective film 200, so that the value b can be obtained by adding K to the Dn value. At this time, the K value can be obtained by multiplying the distance M measured on the camera photographing screen 301 by tan &thetas;.

In summary, if b = Dn + M tan?, And the b value calculated here is substituted into the lens formula, a value can be calculated.

On the other hand, the distance calculation to the X1 point can be more conveniently and easily obtained by deriving the value obtained by converting the contrast ratio at each point in the X-axis direction through the modulation transfer function. FIG. 9 is a graph showing a modulation transfer function (MTF) for the contrast ratio with respect to an X-axis point, and the coordinates of the point at which the modulation transfer function value is the highest can be obtained.

The distance a of the measurement object 10 can be easily measured according to the measurement principle described above. In particular, the distance of the measurement object 10 can be measured in real time by analyzing the camera taken screen in real time.

The condensing lens module 100 is formed such that the position of the image 20 of the measurement object 10 imaged by the condenser lens module 100 appears in a region between Dn and Df. The adjustment operation of the module 100 is incorrect and the image 20 of the measurement object 10 may not be formed in the corresponding section. In this case, when the entire area of the retroreflective film 200 is photographed by the camera 300 while focusing on the image 20 of the measurement object 10, the focal plane SF of the camera 300 is refracted The area having the standard contrast ratio is not displayed on the camera photographing screen 301 because it does not correspond to the film 200. [ That is, the area having a clear contrast ratio does not appear. In this case, the arrangement state of the condensing lens module 100 is adjusted again to photograph the image 20 of the measurement object 10, confirm the reference contrast ratio position on the photographing screen, The arrangement state of the module 100 can be adjusted.

The foregoing description is merely illustrative of the technical idea of the present invention, and various changes and modifications may be made by those skilled in the art without departing from the essential characteristics of the present invention. Therefore, the embodiments disclosed in the present invention are intended to illustrate rather than limit the scope of the present invention, and the scope of the technical idea of the present invention is not limited by these embodiments. The scope of protection of the present invention should be construed according to the following claims, and all technical ideas within the scope of equivalents should be construed as falling within the scope of the present invention.

100: condensing lens module 101: lens adjusting means
200: Retroreflective film 201: Angle adjusting means
300: camera
400: Distance measurement module
410: contrast ratio detection unit 420:
500: beam splitter

Claims (11)

A condensing lens module for condensing the light reflected from the measurement object to image an image of the measurement object;
A reflective surface for retroreflecting the incident image is formed so as to be inclined with respect to an optical axis of the condensing lens module so that an image formed by the condensing lens is retroreflected and re- A retroreflective film on which a non-reflecting surface is formed;
A camera for focusing the entire area of the retroreflective film together with the re-reflected image so as to form a focal plane based on the image re-formed by the retroreflective film; And
A distance measuring unit which detects a position of a point having a predetermined reference contrast ratio with respect to a light and dark region generated by a reflective surface and a non-reflective surface of the retroreflective film, module
And a distance measuring device using the retroreflective film.
The method according to claim 1,
A separate beam splitter is provided between the condenser lens module and the retroreflective film so as to change the reflection path of the image retroreflected by the retroreflective film,
Wherein the camera is arranged to capture an image of a path changed by the beam splitter.
3. The method of claim 2,
Wherein the focal plane of the camera is formed in a direction perpendicular to an optical axis of the condenser lens module based on an image re-formed by the retroreflective film.
The method of claim 3,
The distance measurement module
A contrast ratio detector for detecting a position of a point having a standard contrast ratio among images of the entire area of the retroreflective film photographed by the camera; And
An arithmetic operation unit for calculating a distance to the measurement object using the position of the reference contrast ratio point detected through the contrast ratio detection unit and the inclination angle of the retroreflective film,
And a distance measuring device using the retroreflective film.
5. The method of claim 4,
The operation unit
The position of the image formed by the condenser lens module is calculated using the position of the reference contrast ratio point detected by the contrast ratio detector and the inclination angle of the retroreflective film, and the position of the image from the calculated image position to the condenser lens module And the distance (b) is applied to the lens formula to calculate the distance (a) with respect to the object to be measured.
6. The method according to any one of claims 1 to 5,
Dn is the closest distance between the condensing lens module and the retroreflective film and Df is the farthest distance between the condensing lens module and the retroreflective film.
Wherein the condenser lens module is formed to be position-adjustable so that an image of the measurement object is imaged between Dn and Df.
The method according to claim 6,
Wherein the focusing lens module is configured such that at least two or more lenses are arranged to be movable along the optical axis direction.
6. The method according to any one of claims 1 to 5,
Wherein the retroreflective film is formed such that a plurality of unit cells having the same shape are in contact with each other, and each of the unit cells has the reflective surface and the non-reflective surface.
9. The method of claim 8,
Wherein the unit cell of the retroreflective film is formed in a triangular pyramid shape in which three oblique planes are orthogonal to each other and the bottom surface thereof is opened.
(a) focusing an image of an object to be measured by condensing light reflected from an object to be measured through a condensing lens module;
(b) a retroreflective film for retroreflecting an incident image, and a retroreflective film having a non-reflective surface formed on a part of the reflective surface and disposed in a direction inclined with respect to an optical axis of the condensing lens module, Retroreflecting an image formed by the light source;
(c) photographing the entire area of the retroreflective film together with the re-formed image by adjusting the focus of the camera so that a focal plane is formed based on the image re-formed by the retroreflective film;
(d) detecting a position of a point having a predetermined reference contrast ratio with respect to a light and dark region generated by the reflective surface and the non-reflective surface of the retroreflective film, the image being photographed by the camera; And
(e) calculating a distance to the measurement object using the position of the reference contrast ratio point detected in the step (d)
Wherein the distance measuring method comprises the steps of:
11. The method of claim 10,
If the reference contrast ratio is not detected in the step (d)
Wherein the step (a) to (d) are repeated after adjusting the arrangement state of the condenser lens module.

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