JP2015059768A - Level difference measuring device, level difference measuring method and program - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a level difference measuring device and the like, capable of measuring, accurately with a simple configuration, a level difference occurring on the periphery of a manhole lid.SOLUTION: A level difference measuring device is provided, in which: an image capturing section captures an image of a road 40 and an oval outline therein is detected; a measurement point selecting section divides the oval outline into four areas comprising an upper area, a right area, a lower area and a left area and selects at least one measurement point in each area; a dark area width acquiring section acquires, for the selected measurement point, brightness of a plurality of pixels arranged in a normal direction of the outline and also in a direction from the measurement point toward the inside of the oval, and acquires a width of a dark area from a brightness profile; and a level difference calculating section compares a differential value obtained by subtracting the average dark area width of the right and left areas from the dark area width of the upper area, with a differential value obtained by subtracting the average dark area width of the right and left areas from the dark area width of the lower area, determines whether a lid 50 is rising or sinking with respect to a receiving frame, and outputs a level difference based on the differential values.

Description

  The present invention relates to a step measuring device, a step measuring method, and a program for measuring a step on a road.

  The manhole cover installed on the road can be opened for maintenance of underground water and sewage systems and telecommunications cables. You must not disturb.

  However, due to long-term installation of the manhole, its lid and the receiving frame, the contact surface between the lid and the receiving frame wears out and the lid sinks, or small sand or the like enters from the gap between the lid and the receiving frame. As a result of accumulating on the contact surface, the lid may float. This level difference due to lifting or sinking may cause accidents in automobiles and bicycles. Further, when the lid is lifted from the surface of the receiving frame to form a step, there is a problem that the snow removal blade of the snowplow hits the step and damages the blade and the manhole.

  It is necessary for a person who installs water and sewage and telecommunications cables to manage so that there is no step between the manhole cover and the receiving frame. However, these manhole covers were very numerous and it was very difficult to grasp all the situations.

  On the other hand, an apparatus for discriminating an object existing on a road based on an image taken by a camera mounted on a vehicle traveling on the road has been proposed (for example, Patent Documents 1 and 2).

  The three-dimensional data creation device described in Patent Document 1 is a device that creates three-dimensional data of an object on a road based on continuous stereo images acquired during movement. Image data corresponding to various landmarks, such as manhole covers, is stored as template images from the acquired images, landmarks are identified by pattern recognition on successive images, and the landmarks are tracked. It is described that the data of the three-dimensional coordinates of the landmark is created together with the detection result.

  The object identification device described in Patent Literature 2 receives P-polarized light and S-polarized light having different polarization directions contained in reflected light from an object, captures the respective polarized images, and creates a P-polarized image for each pixel. It has been described that many types of objects can be identified by determining the presence of an object based on a luminance difference value with respect to an S-polarized image. Further, a manhole cover is also identified using an elliptical template for the identified captured image.

JP 2011-80845 A JP 2011-150686 A

  According to the techniques described in Patent Documents 1 and 2, although the presence of a manhole cover can be recognized, it is difficult to accurately measure a step due to the cover rising and sinking. In particular, when a road is photographed with a camera mounted on a vehicle that moves at a speed that does not impede the driving of surrounding cars, the image becomes rough, and only a measurement that can detect the outer shape of the manhole cover can be performed.

  Generally, there is a gap between the actual manhole cover and the receiving frame. For this reason, the portion that appears to be a step on the photographed image includes a gap, and the measurement considering the portion corresponding to the gap has not been performed.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a level difference measuring apparatus and the like that can accurately measure the level difference generated around the manhole cover with a simple configuration.

In order to achieve the above object, a step difference measuring apparatus according to the first aspect of the present invention includes:
A level difference measuring device for measuring a level difference caused by floating or sinking with respect to a receiving frame of a manhole cover on a road,
An image acquisition unit for acquiring a frame image of the road;
A contour detection unit that detects a substantially elliptical contour from the frame image acquired by the image acquisition unit;
The outline of the substantially ellipse detected by the outline detector includes a right area and a left area including an intersection of the outline and the major axis of the substantially ellipse, and an intersection of the outline and the minor axis of the substantially ellipse. A measurement point selection unit that divides into four regions including an upper region and a lower region and selects at least one measurement point in each of the four regions;
The brightness of a plurality of pixels arranged in a direction normal to the contour at the measurement point selected by the measurement point selection unit and in a direction from the measurement point toward the inside or outside of the substantially ellipse is acquired, and the brightness A dark area width acquisition unit that acquires a dark area width that is equal to or less than a predetermined reference;
A correction value calculation unit that calculates a correction value based on the width of the dark region of the right region and the left region;
Based on the first difference value calculated by subtracting the correction value from the dark area width of the upper area, or the second difference value calculated by subtracting the correction value from the dark area width of the lower area , A step calculation unit for calculating the step,
It is characterized by having.

The pixel of the measurement point selected by the measurement point selection unit from the actual size of the outer diameter of the lid or the outer diameter of the receiving frame, which is known in advance, and the number of pixels with the major axis or minor axis of the substantially ellipse of the outline, and It further has an actual size conversion value calculation unit that calculates an actual size conversion value of the surrounding pixels,
The correction value calculation unit is configured to determine a gap between the manhole cover and the receiving frame from the width of the dark region of the right region or the left region and the actual size conversion value calculated by the actual size conversion value calculation unit. Calculating the correction value which is the actual size of the gap width of
The level difference calculation unit subtracts the correction value calculated by the correction value calculation unit from the width of the dark area of the upper area converted into an actual size using the actual size conversion value, thereby calculating the first difference value. The second difference value is calculated by subtracting the correction value calculated by the correction value calculation unit from the dark area width of the lower area that is calculated and converted into the actual size using the actual size conversion value. It may be.

The step calculation unit
If the width of the dark area of the upper area is wider than the width of the dark area of the lower area, it is determined that the manhole cover is sunk more than the receiving frame of the manhole cover, and converted to the actual size And calculating the first difference value as the step,
When the width of the dark area in the upper area is narrower than the width of the dark area in the lower area, it is determined that the manhole cover is floating above the receiving frame of the manhole cover, and converted to the actual size. The second difference value may be calculated as the step.

  The correction value calculation unit may calculate the correction value based on an average value of the dark area width of the right area and the dark area width of the left area.

  The dark area width acquisition unit acquires, as a dark area width, a width of an area that is equal to or less than a reference value determined based on a minimum value of luminance of the plurality of pixels and an average value of luminance of pixels inside the contour. You may make it do.

A rotated image obtained by rotating an image around the contour so that the major axis of the approximate ellipse of the contour is horizontal when the major axis of the approximate ellipse detected by the contour detection unit is not horizontal in the frame image An image rotation unit for generating
Based on the actual size conversion value calculated by the actual size conversion value calculation unit, an actual scale at the measurement point is calculated, and an image in which a gauge indicating the actual scale is superimposed on the image generated by the image rotation unit is obtained. You may make it further have the gauge superimposition part to produce | generate.

The image acquired by the image acquisition unit is a stereo image taken with a stereo camera,
The contour indicates when the major axis of the approximate ellipse detected by the contour detector is calculated by three-dimensional measurement based on the stereo image, and the major axis of the approximate ellipse is within a predetermined range. A measurement object determining unit that determines that the manhole cover and the receiving frame are measurement objects;
The level difference calculation unit may output the measurement result of the level difference for the lid and the receiving frame of the manhole that is determined as the measurement target by the measurement target determination unit.

The image acquired by the image acquisition unit is a stereo image taken with a stereo camera,
The height difference in the vertical direction of at least two points inside the fixed distance from the contour detected by the contour detection unit is calculated by three-dimensional measurement based on the stereo image, and the height difference is determined from a predetermined value. If it is larger, it may further include a lid inclination determination unit that determines that the manhole cover 50 is inclined.

The image acquired by the image acquisition unit is a stereo image taken with a stereo camera,
A height difference in the vertical direction of at least one point inside and outside the contour detected by the contour detection unit is calculated by three-dimensional measurement based on the stereo image, and the height difference is calculated with the receiving frame. You may make it further have an outer periphery height difference estimation part estimated as a height difference with the outer periphery of the said receiving frame.

Further, the step measuring method according to the second aspect of the present invention is:
A step measurement method in which a computer measures a step caused by floating or sinking on a receiving frame of a manhole cover on a road,
An image acquisition step for acquiring a frame image of the road;
A contour detecting step for detecting a substantially elliptical contour from the frame image acquired in the image acquiring step;
The outline of the approximate ellipse detected in the outline detection step includes an intersection of a right area and a left area including an intersection of the outline and the major axis of the approximate ellipse, and an intersection of the outline and the minor axis of the approximate ellipse. A measurement point selection step of dividing the upper region and the lower region into four regions and selecting at least one measurement point in each of the four regions;
The brightness of a plurality of pixels arranged in a normal direction of the contour at the measurement point selected in the measurement point selection step and in a direction from the measurement point toward the inside or outside of the substantially ellipse is acquired, and the brightness A dark area width obtaining step of obtaining a dark area width which is equal to or less than a predetermined reference;
A correction value calculating step for calculating a correction value corresponding to the width of the gap between the manhole cover and the receiving frame based on the width of the dark region of the right region and the left region;
Based on the first difference value calculated by subtracting the correction value from the dark area width of the upper area, or the second difference value calculated by subtracting the correction value from the dark area width of the lower area , A step calculating step for calculating the step,
It is characterized by having.

A program according to the third aspect of the present invention is:
To a computer that measures the level difference caused by floating or sinking to the receiving frame of the manhole cover on the road,
An image acquisition procedure for acquiring a frame image of a road;
A contour detection procedure for detecting a substantially elliptical contour from the frame image acquired in the image acquisition procedure;
The outline of the substantially ellipse detected in the outline detection procedure includes a right area and a left area including an intersection of the outline and the major axis of the substantially ellipse, and an intersection of the outline and the minor axis of the substantially ellipse. A measurement point selection procedure that divides into four regions consisting of an upper region and a lower region and selects at least one measurement point in each of the four regions;
The brightness of a plurality of pixels arranged in the normal direction of the contour at the measurement point selected in the measurement point selection procedure and in the direction from the measurement point toward the inside or outside of the substantially ellipse is acquired, and the brightness A dark area width obtaining procedure for obtaining a dark area width that is equal to or less than a predetermined reference;
A correction value calculation procedure for calculating a correction value corresponding to the width of the gap between the manhole cover and the receiving frame based on the width of the dark region of the right region and the left region;
Based on the first difference value calculated by subtracting the correction value from the dark area width of the upper area, or the second difference value calculated by subtracting the correction value from the dark area width of the lower area , A step calculation procedure for calculating the step,
Is executed.

  According to the present invention, it is possible to accurately measure a step generated around the manhole cover with a simple configuration.

It is the figure which showed the block diagram of the level | step difference measuring apparatus which concerns on Embodiment 1. FIG. (A) It is the figure which showed a mode that the road was image | photographed. (B) It is sectional drawing of the lid | cover and receiving frame of a manhole. It is a flowchart which shows a level | step difference measurement process. (A) It is a figure which shows the frame image which an image acquisition part acquires. (B) It is the figure which expanded the lid periphery of the manhole. (A) It is a figure for demonstrating the method to select the measurement point which divides an outline into 4 and measures a brightness | luminance. (B) It is a figure for demonstrating the position which acquires a brightness | luminance profile. It is a figure for demonstrating the acquisition method of a dark region width | variety. (A) It is a figure which shows the state which the cover is sinking with respect to the receiving frame. (B) It is a figure for demonstrating the method of calculating a level | step difference from a dark region width | variety. (A) It is a figure which shows the state which the cover floats with respect to the receiving frame. (B) It is a figure for demonstrating the method of calculating a level | step difference from a dark region width | variety. It is the figure which showed the block diagram of the level | step difference measuring apparatus which concerns on Embodiment 2. FIG. (A) It is a figure which shows the frame image which an image acquisition part acquires. (B) It is the figure which expanded and displayed the gauge around the manhole cover periphery. It is the figure which showed the block diagram of the level | step difference measuring apparatus which concerns on Embodiment 3. FIG.

(Embodiment 1)
Embodiment 1 of the present invention will be described in detail with reference to the drawings.

  The step difference measuring device 10 according to the present embodiment is a device that measures a step generated around the manhole cover 50 installed on the road 40 based on an image obtained by photographing the road 40. As shown in FIG. 1, the level difference measuring apparatus 10 includes a CPU (Central Processing Unit) 11, a communication unit 13, a storage unit 15, and a display unit 17, and receives information from a camera 21 connected to the outside. Measure the step and record it. The camera 21 performs shooting based on a control signal output from the shooting instruction signal generator 22.

  The camera 21 is provided in the vehicle 2 that travels on the road 40 as shown in FIG. For example, the camera 21 is horizontally provided on the upper surface of the vehicle 2 and photographs the front of the vehicle 2. The optical axis of the camera 21 may be directed slightly downward so that a range closer to the vehicle 2 on the road in the traveling direction of the vehicle 2 can be captured.

  The manhole cover 50 where the level difference that is the object of measurement closes the manhole opening 51 for maintenance such as water and sewage and telecommunications cables buried underground, and is made of metal such as iron or concrete. The The manhole cover 50 has a diameter determined by the equipment to be maintained.

  As shown in the sectional view of FIG. 2B, a receiving frame 52 made of metal is provided on the outer periphery of the opening 51 of the manhole. The receiving frame 52 includes a lower support portion 521 that supports the lid 50 from below. The outer periphery of the receiving frame 52 is fixed to the manhole body and the surrounding asphalt.

  When the manhole cover 50 is fitted into the receiving frame 52, the surface of the cover 50, the surface of the receiving frame 52, and the road surface on the outer periphery of the receiving frame 52 are flat, and there is no step. . However, as the manhole, the lid 50 and the receiving frame 52 are used over a long period of time, the contact surface between the receiving frame and the lid wears down, or the lid sinks, or a small stone enters between the receiving frame and the lid, and the contact surface between the receiving frame and the lid The lid may float up. These steps are measured with high accuracy, and if a step exceeding a predetermined reference value occurs, repair work must be performed.

  The level difference measuring apparatus 10 according to the present embodiment measures a level difference inside the receiving frame 52 that is generated when the surface of the lid 50 is lifted or sinks from the surface of the receiving frame 52.

  The imaging instruction signal generation unit 22 transmits an instruction signal for instructing the camera 21 to take an image at regular time intervals when detecting an operation input instructing the user to start imaging. For example, when the user performs an operation input indicating that shooting is started 50 times per second, the shooting instruction signal generation unit 22 is set to 0.020 seconds and 0.040 seconds based on 0.000 seconds per second on the hour. An instruction signal is transmitted to the camera 21 every second and 1/50 second. Upon receiving the instruction signal, the camera 21 takes a picture at the timing when the instruction signal is received, and stores the acquired image data in a built-in frame memory.

  As shown in FIG. 1, the imaging instruction signal generation unit 22 includes a GPS (Global Positioning System) antenna 221 and receives a radio wave signal transmitted from the GPS satellite 20 by the GPS antenna 221. The shooting instruction signal generator 24 obtains the current time and position information based on the radio wave signal from the GPS satellite 20 when outputting an instruction signal for instructing the camera 21 to take a picture, and the information and position of the current time in the instruction signal Include information. As a result, the camera 21 can obtain the shooting time information and the shooting location position information from the shooting instruction signal generator 22.

  The communication unit 13 of the level difference measuring device 10 receives image data captured by the camera 21. This image data also includes the shooting time acquired from the shooting instruction signal generator 22 and the position information of the shooting location.

  The storage unit 15 is a large-capacity storage device, and stores image data received by the communication unit 13 and step data measured by the processing of the CPU 11. The storage unit 15 also stores a program executed by the CPU 11. The display unit 17 is a display for outputting information such as images and characters, and displays an image indicated by image data received by the communication unit 13, an image subjected to image processing, a measurement result of a step, and the like.

  As shown in FIG. 1, the CPU 11 executes the program stored in the storage unit 15, thereby causing the image acquisition unit 111, the contour detection unit 112, the measurement point selection unit 113, the dark area width acquisition unit 114, and the actual size. The conversion value calculation unit 115, the gap width calculation unit 116, the step calculation unit 117, and the time / position acquisition unit 118 function as functional units.

  The image acquisition unit 111 selects an image for one frame from the image data received by the communication unit 13 from the camera 21, acquires the image, and outputs it to the contour detection unit 112.

  The contour detection unit 112 searches for and detects an elliptical contour 55 from the image input from the image acquisition unit 111. That is, the contour 55 of the manhole cover 50 displayed as an ellipse on the image is detected. Then, the peripheral image of the detected elliptical manhole cover 50 is enlarged, and the enlarged image is displayed on the display unit 17. Here, the enlarged image is displayed by rotating the image around the detected ellipse contour so that the major axis of the ellipse is in the horizontal direction of the image or the minor axis of the ellipse is in the vertical direction of the image. You may let them.

  The measurement point selection unit 113 measures the width of a dark area where the luminance is low due to a gap and a step between the manhole cover 50 and the receiving frame 52 in the elliptical contour 55 detected by the contour detection unit 112. Select 4 or more points.

  The dark area width acquisition unit 114 acquires the luminance of a plurality of pixels arranged in the normal direction of the contour 55 at the measurement point selected by the measurement point selection unit 113 and in the direction from the measurement point toward the inside of the ellipse. , Get the width of dark area with low brightness.

  The actual size converted value calculation unit 115 calculates the pixel of the measurement point selected by the measurement point selection unit 113 from the known actual size of the outer diameter of the receiving frame 52 and the number of pixels of the ellipse diameter or minor diameter of the contour 55. And the actual size conversion value of the surrounding pixels is calculated.

  The gap width calculation unit 116 calculates the width of the gap between the manhole cover 50 and the receiving frame 52 based on the dark area width acquired by the dark area width acquisition unit 114 at each measurement point. When calculating the width of the gap, the actual size of the gap is calculated using the actual size converted value calculated by the actual size converted value calculation unit 115.

  The level difference calculation unit 117 is configured so that the manhole cover 50 and the receiving frame 52 are based on the dark area width acquired by the dark area width acquisition unit 114 at each measurement point and the gap width calculated by the gap width calculation unit 116. The step between is calculated. When calculating the step, the actual size converted value calculated by the actual size converted value calculation unit 115 is used to calculate the actual size of the step. The calculation result of the step is displayed on the display unit 17 and stored in the storage unit 15.

  When the image acquisition unit 111 acquires an image for one frame from the image data received from the camera 21 by the communication unit 13, the time / position acquisition unit 118 captures information on the imaging time of the image and the position of the shooting location. Information is acquired, stored in the storage unit 15 together with the image, and displayed on the display unit 17.

  The level difference measurement process executed by the CPU 11 of the level difference measuring apparatus 10 configured as described above will be described in detail with reference to the flowchart of FIG.

  First, the image acquisition unit 111 selects and acquires an image for one frame from the image data received by the communication unit 13 from the camera 21 (step S101). The contour detection unit 112 searches for an elliptical contour 55 from the image acquired by the image acquisition unit 111, and when it cannot be detected (step S102: No), selects and acquires an image of another frame. When the ellipse can be detected (step S102: Yes), an image obtained by enlarging the peripheral image of the detected ellipse outline 55 is displayed on the display unit 17 (step S103).

  The detection of the outline 55 of the ellipse is performed by converting the entire frame image into a monochrome gray when the image is color, and then smoothing and binarizing the image as it is when the image is monochrome gray. 52 is extracted as an area, the edge of the area is detected, and an elliptical contour 55 is detected from the edge information.

  For example, when the image acquisition unit 111 acquires a frame image as illustrated in FIG. 4A, the contour detection unit 112 detects an elliptical contour 55 indicating the outer periphery of the receiving frame 52. Then, an image obtained by enlarging the peripheral image of the elliptical contour 55 as shown in FIG. 4B is displayed on the display unit 17 (step S103).

Next, the measurement point selection unit 113 selects a measurement point for measuring the width of the dark region (step S104). More specifically, as shown in FIG. 5A, the contour 55 detected by the contour detection unit 112 is divided into four regions, an upper region A, a right region B, a lower region C, and a left region D. At least one measurement point is selected. The upper area A is an area including the upper point on the screen among the intersection points of the contour 55 and the major axis 551 of the ellipse, and the right area B is the right side of the intersection of the contour 55 and the minor axis 552 of the ellipse on the screen. The lower region C is a region including the lower point on the screen among the intersections of the contour 55 and the major axis 551 of the ellipse, and the left region D is the minor axis 552 of the contour 55 and the ellipse. This is the area that includes the point on the left side of the screen. In the present embodiment, three equidistant points including respective intersections in each region are selected as measurement points (upper region A: a ₁ , a ₂ , a ₃ , right region B: b ₁ , b ₂ , b ₃ , lower region C: c ₁ , c ₂ , c ₃ , left region D: d ₁ , d ₂ , d ₃ ).

  Next, the actual size conversion value calculation unit 115 calculates the actual size conversion value of the pixel at the measurement point selected by the measurement point selection unit 113 and its surrounding pixels (step S105). Specifically, the pixel of the measurement point selected by the measurement point selection unit 113 and the surrounding pixels are selected from the known actual size M of the outer diameter of the receiving frame 52 and the number N of the ellipse major axis of the contour 55. An actual size conversion value T that is an actual size per pixel is calculated. In the vicinity of the intersection between the contour 55 and the long axis 551, the actual size conversion value T is as shown in Equation (1). Here, to simplify the description, it is assumed that the image of the manhole cover 55 is located near the center in the horizontal direction of the image.

  T = M / N (1)

On the other hand, except near the intersection of the contour 55 and the long axis 551, the distance (depth value) Z _S from the camera 21 to the actual position on the lid 55 corresponding to the measurement point and the lid corresponding to the center of the ellipse from the camera 21 it is necessary to correct based on the distance (depth value) Z _C to the actual position on 55. The actual size converted value T after correction other than the vicinity of the intersection between the contour 55 and the long axis 551 is expressed by Equation (2).

T = M / N × Z _S / Z _C (2)

Next, the dark area width acquisition unit 114 is arranged in the normal direction of the contour 55 at each measurement point and in the direction from each measurement point toward the inside of the ellipse (the direction of the arrow in FIG. 5B). Get the brightness of the pixel. The luminance profile includes a dark region where the luminance is low as shown in FIG. This dark region is a portion that appears dark due to a gap or a step between the manhole cover 50 and the receiving frame 52. The width of this dark area is calculated (step S106). More specifically, the minimum luminance value L _min in the luminance profile of each point and the average luminance value L _ave of the pixels inside the contour 55 are acquired, and the threshold value L _th represented by the expression (3) is calculated. To do. Then the luminance profile, to obtain the width P of the range equal to or less than the threshold value L _th as a dark area width.

L _th = kL _ave + (1−k) L _min (0 <k <1) (3)

  Here, since three measurement points are selected in each of the areas A to D, the average value of the dark area width acquired for each of the three points is obtained.

  When the surface of the manhole cover 50 and the surface of the receiving frame 52 are flush with each other, the dark area width obtained in step S106 is only the dark region due to the gap between the cover 50 and the receiving frame 52. Is displayed. On the other hand, when there is a deviation between the surface of the lid 50 and the surface of the receiving frame 52, not only the gap between the lid 50 and the receiving frame 52 but also the portion caused by the step between the lid 50 and the receiving frame 52 is a dark region. Is displayed.

  Here, since the dark areas of the right area B and the left area D are considered to represent almost the gap between the manhole cover 50 and the receiving frame 52, the dark areas of the right area B and the left area D are based on the dark area width. The gap dz is calculated (step S107). Specifically, the right gap is calculated by multiplying the number of pixels of the dark area width of the right area B by the actual size conversion value of the measurement point of the right area B, and the left area D is calculated by the number of pixels of the dark area width of the left area D. The left gap is calculated by multiplying the actual size converted value of the measurement point of B. Then, an average value of the right gap and the left gap is calculated as the gap dz.

  Next, a step is calculated based on the actual size conversion value obtained in step S105, the dark area widths of the upper area A and the lower area C obtained in step S106, and the gap width obtained in step S107.

  When the dark area width of the upper area A is wider than the dark area width of the lower area C (step S108: (i)), the manhole cover 50 is located with respect to the receiving frame 52 as shown in FIG. Since it can be determined that the object is sinking, a step that is a sinking amount is calculated (step S109). The step calculation method will be described in detail with reference to FIG. On the image plane F, an image having a length s ′ corresponding to the step s between the manhole cover 50 and the receiving frame 52 is projected, and an image having a length t ′ corresponding to the gap dz between the manhole cover 50 and the receiving frame 52. Is projected. Assuming that the actual size of the image of length t ′ is t, Equation (4) is obtained. Here, the angle θ is expressed as in Expression (5) using the height y of the camera 21 and the distance (depth value) z from the camera 21 to the side surface of the lid 55. Here, the downward angle of the camera is 0 degree.

t = dz · tan θ (4)
θ = atan (y / z) (5)

  Since the dark area of the upper area A corresponds to the sum of the step s between the manhole cover 50 and the receiving frame 52 and t corresponding to the gap, the upper area A corresponds to the number of pixels of the dark area width of the upper area A. The level difference s is calculated by subtracting t from the value obtained by multiplying the actual size conversion value at the measurement point.

  On the other hand, when the dark area width of the upper area A is narrower than the dark area width of the lower area C (step S108: (ii)), the manhole cover 50 is located with respect to the receiving frame 52 as shown in FIG. Since it can be determined that the vehicle is floating, a step calculation value that is a floating amount is calculated (step S110). The step calculation method will be described in detail with reference to FIG. 8B. On the image plane F, an image having a length s ′ with respect to the step s between the manhole cover 50 and the receiving frame 52 is projected, and the manhole cover 50 is projected. And an image having a length t ′ with respect to the gap dz between the receiving frames 52 is projected. t is obtained in the same manner as in step S109.

  Since the dark area of the lower area C corresponds to the sum of the step s between the manhole cover 50 and the receiving frame 52 and t corresponding to the gap, the measurement of the lower area C corresponds to the number of pixels of the dark area width of the lower area C. The level difference s is calculated by subtracting t from the value obtained by multiplying the actual size conversion value at the point.

When the dark area width of the upper area A and the dark area width of the lower area C are substantially the same (step S108)
: (Iii)), the step is determined to be about 0 (step S111).

  The steps calculated in steps S109 to 111 are stored in the storage unit 15 together with the frame image used for the step calculation, the location information of the shooting location, and the shooting time, displayed on the display unit 17 (step S112), and the process ends.

  As described above, in this embodiment, the outline of an ellipse is detected from an image obtained by photographing a road, and the outline of the ellipse is divided into four areas including an upper area A, a right area B, a lower area C, and a left area D. Divide and select at least one measurement point in each area, obtain the luminance of multiple pixels arranged in the normal direction of the contour at the measurement point and in the direction from the measurement point toward the inside of the ellipse, and a luminance profile The dark area width is obtained from the above, the dark area width of the upper area A is compared with the dark area width of the lower area C, and it is determined whether the lid 50 is floating or sinking with respect to the receiving frame 52, and the upper area The calculated value of the step is output by subtracting the average value of the dark area widths of the right area B and the left area D from one of the dark area width of the A area and the dark area width of the lower area C. Thereby, a level | step difference can be accurately measured easily with a simple structure.

(Embodiment 2)
The second embodiment of the present invention will be described in detail with reference to FIGS.

  The step difference measuring device 30 according to the present embodiment is a device that measures a step generated around the manhole cover 50 installed on the road 40 based on an image obtained by photographing the road 40 as in the first embodiment. However, this embodiment is different from the first embodiment in that it has a function of rotating and enlarging an image and superimposing and displaying an actual scale gauge.

  As shown in FIG. 9, the step difference measuring device 30 includes a CPU (Central Processing Unit) 31, a communication unit 13, a storage unit 15, and a display unit 17, and information received from an externally connected camera 21. Measure the step and record it. The camera 21 performs shooting based on a control signal output from the shooting instruction signal generator 22. The configurations of the camera 21 and the shooting instruction signal generator 22 are the same as those in the first embodiment.

  The CPU 31 has the same image acquisition unit 111, contour detection unit 112, measurement point selection unit 113, dark area width acquisition unit 114, actual size converted value calculation unit 115, gap width calculation unit 116, step calculation unit as in the first embodiment. 117, in addition to the time / position acquisition unit 118, an image rotation unit 311 and a gauge superimposing unit 312 are further provided.

  The image rotation unit 311 creates an enlarged image by rotating around the measurement point of the image, and the gauge superimposing unit 312 displays an image in which an actual scale gauge is superimposed on the enlarged image.

  For example, a case where the image acquired by the image acquisition unit 111 is an image as illustrated in FIG. The contour detection unit 112 detects an elliptical contour 55 in a region near the upper right end. In the region near the edge of the image, since the image is distorted, the long axis of the ellipse rotates from the horizontal direction and is displayed in a further distorted state. Therefore, it is necessary to detect the contour of the ellipse without depending on the major axis direction, and it is also necessary to detect a shape that deviates from an accurate ellipse within a predetermined range.

  First, the measurement point selection unit 113 selects an intersection between the contour 55 and the major axis 551 and the minor axis 552 of the ellipse as a measurement point.

  When the contour detection unit 112 detects the contour 55 in which the major axis direction is not horizontal and the ellipse is distorted, the image rotation unit 311 corrects the distortion when enlarging the image around the measurement point, and An image as shown in FIG. 4 (b) rotated so that the axial direction is horizontal is generated.

  For the enlarged image generated by the image rotation unit 311, the gauge superimposing unit 312 generates an image in which a gauge (scale) with the selected measurement point as a reference position is superimposed, as shown in FIG. It is displayed on the display unit 17. Here, the gauge indicates an actual scale at each measurement point of the contour 55 based on the actual size converted value calculated by the actual size converted value calculation unit 115.

  In the image displayed on the display unit 17, by inputting a numerical value visually measured by the user at the left and right measurement points, the gap width calculation unit 116 can calculate the gap width based on the input value. In addition, by inputting a numerical value visually measured by the user at the upper and lower measurement points, the level difference calculation unit 117 can calculate the level difference in consideration of the gap width based on the input value.

  As described above, in the present embodiment, when the contour detection unit 112 detects the contour 55 in a state where the major axis direction is not horizontal and the ellipse is distorted, the image rotation unit 311 detects the periphery of the contour 55. When the image is enlarged, the distortion is corrected and the image is rotated so that the major axis direction is horizontal, and the gauge superimposing unit 312 generates an image in which the gauges with the measurement point as a reference position are superimposed. Thereby, even if an ellipse is detected in any region of the image, the step can be visually observed in a state where the major axis direction of the ellipse is horizontal, and the step can be measured using a gauge.

(Embodiment 3)
A third embodiment of the present invention will be described in detail with reference to FIG.

  The level difference measuring device 60 according to the present embodiment is a device that measures the level difference generated around the manhole cover 50 installed on the road 40 based on an image obtained by photographing the road 40 as in the first embodiment. However, the image used for the step measurement is different from the first embodiment in that the image is taken by a stereo camera.

  As shown in FIG. 10, the level difference measuring device 60 includes a CPU (Central Processing Unit) 61, a communication unit 13, a storage unit 15 and a display unit 17. Two steps are measured based on information received from the camera 24 and recorded. The first camera 23 and the second camera 24 shoot simultaneously based on the control signal output from the shooting instruction signal generator 22.

  The first camera 23 and the second camera 24 are provided in the vehicle 2 that travels on the road 40 as shown in FIG. For example, the first camera 23 and the second camera 24 are horizontally provided on the upper surface of the vehicle 2 and photograph the front of the vehicle 2. The first camera 23 and the second camera 24 capture images with optical axes that are substantially parallel to each other or slightly inward so that the manhole cover 50 to be imaged can be simultaneously captured. Further, the optical axes of the second camera 23 and the second camera 24 may be directed slightly downward so that a range closer to the vehicle 2 than the road in the traveling direction of the vehicle 2 can be captured.

  The CPU 61 includes an image acquisition unit 111, a contour detection unit 112, a measurement point selection unit 113, a dark area width acquisition unit 114, an actual size converted value calculation unit 115, and a gap width calculation unit that have the same configuration and functions as those of the first embodiment. 116, a level difference calculation unit 117, and a time / position acquisition unit 118, a three-dimensional coordinate acquisition unit 611, and a point-to-point distance calculation unit 612 are provided.

  The three-dimensional coordinate acquisition unit 611 acquires three-dimensional coordinates of locations indicated by mutually corresponding measurement points in the two images captured by the first camera 23 and the second camera 24 at the same time. Here, the acquisition of the three-dimensional coordinates is performed by a method of calculating the three-dimensional coordinates using the principle of triangulation from a conventional stereo image.

  The two-point distance calculation unit 612 calculates the distance between two points based on the three-dimensional coordinates of two or more measurement points acquired by the three-dimensional coordinate acquisition unit 611.

  The level difference measuring device 60 of the present embodiment calculates the level difference between the manhole cover 50 and the receiving frame 52 by the same method as in the first embodiment, and variously obtains three-dimensional coordinates based on the stereo image. Evaluate.

  For example, when the three-dimensional coordinate acquisition unit 611 acquires three-dimensional coordinates of two intersection points between the ellipse contour 55 detected by the contour detection unit 112 and the major axis of the ellipse, the two-point distance calculation unit 612 The actual size of the major axis of the ellipse can be calculated. The actual size of the major axis corresponds to the outer diameter of the manhole receiving frame 52. In many cases, the manhole cover 50 and the receiving frame 52 have different outer diameters depending on applications such as water and sewage systems and telecommunication cables. Therefore, by measuring the outer diameter of the receiving frame 52, the manhole cover 50 to be measured can be selected. In this case, the result may be output only for the selected manhole cover 50. Here, the distance calculation unit 612 between two points also functions as a measurement target determination unit.

  When the 3D coordinate acquisition unit 611 acquires 3D coordinates of at least two points inside the fixed distance from the elliptical contour 55 detected by the contour detection unit 112, the distance calculation unit 612 between the two points A difference in coordinates in the vertical direction between the two points on the lid 50 can be calculated. If the difference in coordinates in the vertical direction is larger than a predetermined value, it can be determined that the manhole cover 50 is tilted. Here, the distance calculation unit 612 between two points also functions as a lid inclination determination unit. The two points for acquiring the three-dimensional coordinates may be arbitrary points. For example, the three-dimensional coordinates at a position inside a certain distance from the two intersections of the ellipse contour 55 and the major axis of the ellipse are acquired.

  When the three-dimensional coordinate acquisition unit 611 acquires three-dimensional coordinates of at least one point inside and outside the elliptical contour 55 detected by the contour detection unit 112, the two-point distance calculation unit 612 receives A difference in coordinates in the vertical direction between a point on the surface of the frame 52 and a point on the road surface outside the receiving frame 52 can be calculated. Since the difference in coordinates in the vertical direction indicates a height difference between the surface of the receiving frame 52 and the outer road surface, the height difference can be measured. That is, the two-point distance calculation unit 612 also functions as a height estimation unit for the receiving frame 52 and its outer periphery.

  When the three-dimensional coordinate acquisition unit 611 performs three-dimensional measurement of the contour 55 detected by the contour detection unit 112 and calculates the major axis of the ellipse, the receiving frame used by the actual size conversion value calculation unit 115 uses the major axis. You may use as an actual size of 52 outer diameters.

  Further, the three-dimensional coordinate acquisition unit 611 calculates the three-dimensional position of the measurement point selected by the measurement point selection unit 113 with high accuracy and uses it as the three-dimensional position information of the measurement point used by the actual size converted value calculation unit 115. May be.

  When the contour detected by the contour detection unit 112 is two of the outer periphery of the manhole cover 50 and the receiving frame 52, the three-dimensional coordinate acquisition unit 611 acquires three-dimensional information of two ellipses, The step may be calculated based on the difference.

  As described above, in the present embodiment, the steps between the manhole cover 50 and the receiving frame 52 are measured based on the images taken by the first camera 23 and the second camera 24 constituting the stereo camera. At the same time, the three-dimensional coordinate acquisition unit 611 acquires the three-dimensional coordinates around the contour 55, and the two-point distance calculation unit 612 calculates the distance between the two points from which the three-dimensional coordinates have been acquired. As a result, various evaluations such as the outer diameter of the receiving frame 52, the inclination of the manhole cover 50, and the height difference between the receiving frame 52 and the outer periphery thereof are possible.

  As described above, the present invention detects a substantially elliptical contour from an image of a road, and intersects the right region and the left region including the intersection of the contour and the major axis of the substantially elliptical shape with the contour and the minor axis of the substantially elliptical shape. Is divided into four areas consisting of an upper area and a lower area, and at least one measurement point in each area is selected, the direction of the normal of the contour at the measurement point, and the inside or outside of the approximate ellipse from the measurement point The brightness of a plurality of pixels arranged in the direction toward the center is acquired, the width of a dark area whose brightness is equal to or less than a predetermined reference is acquired, and the manhole cover indicated by the substantially ellipse is based on the width of the dark area of each area It was determined that there was a float or sink with respect to the receiving frame, and the level difference was calculated. Thereby, it becomes possible to measure the level | step difference which arose around the manhole cover correctly with a simple structure.

  In addition, this invention is not limited to the said embodiment, Of course, the various change in the range which does not deviate from the summary of this invention is possible.

  For example, although the contour detected by the contour detection unit 112 is divided into four regions and the luminance profile of one or more measurement points is acquired in each region, it may be divided into five or more regions.

  In addition, the luminance profile of the measurement point is acquired for pixels inside the measurement point, but the contour 55 detected by the contour detection unit 112 may indicate the outer periphery of the manhole cover 50. You may make it measure the inner side and outer side of.

  Further, when the actual size conversion value is obtained, it is calculated from the ratio of the known actual size of the outer diameter of the receiving frame 52 and the major axis of the ellipse of the contour 55. The contour 55 is the outer periphery of the manhole cover 50. In this case, the actual size conversion value may be obtained from the ratio of the known actual diameter of the lid 50 and the major axis of the ellipse of the contour 55 in that case.

  Further, the level difference is calculated by subtracting the average value of the dark area widths of the right area B and the left area D from the dark area width of the upper area A, but the dark area of the right area B is calculated from the dark area width of the upper area A. The step may be calculated by subtracting either the width or the dark area width of the left area. The number of luminance measurement points can be reduced, and the processing amount of the CPU 11 can be reduced.

  In addition, the actual size conversion value calculation unit 115 calculates the actual size conversion value based on the ratio of the known actual size of the outer diameter of the receiving frame 52 and the number of pixels of the major axis of the ellipse of the contour 55. The method may be used. For example, when the internal parameters of the camera 21 (focal length, image center, image sensor actual size) are known, the three-dimensional position / posture of the lid 50 relative to the camera 21 can be easily obtained using the internal parameters. It is. Using the position / orientation, the three-dimensional position of the measurement point selected by the measurement point selection unit 113 is calculated more accurately. Based on the three-dimensional position, the pixel of the measurement point and the surrounding pixels are calculated. The actual size can be obtained.

  As another calculation method of the actual size conversion value, when the internal parameters (focal length, image center, pixel actual size) and external parameters (height and downward angle with respect to the road surface) of the camera 21 are known, the internal parameters and the external The three-dimensional position / posture of the lid 50 with respect to the camera 21 may be accurately obtained using parameters. Using the position / orientation, the three-dimensional position of the measurement point selected by the measurement point selection unit 113 is more accurately calculated, and based on the three-dimensional position, the pixel of the measurement point and one pixel of its surrounding pixels The actual size can be obtained.

  The actual size conversion value can be approximated by the depth value when the lid 50 is far from the camera 21 even when the lid 50 is positioned to the left or right in the image. Therefore, a more accurate actual size conversion value can be acquired by replacing the depth value with a three-dimensional distance based on the three-dimensional position.

  In addition, the measurement points are measured in the contour 55 detected by the contour detection unit 112, the dark area width is acquired and the level difference is obtained, but the contour detection unit 112 knows the internal parameters and the external parameters of the camera 21. If the contour 55 cannot be detected, an ellipse may be projected on the image from the actual size of the diameter of the manhole known in advance using the internal parameters and the external parameters. At this time, an ellipse projected to the center position designated by the center position designation unit may be determined as the contour 55, having a center position designation unit for designating the center position of the manhole in the frame image.

  In addition, the gap width calculation unit 116 calculates the gap size of the actual size using the actual size conversion value, and calculates the step based on the calculated value. However, the gap width calculation unit 116 calculates the dark area width of the right area B and the dark area width of the left area D. On the basis of this, a correction value before actual size conversion may be calculated, and the correction value may be subtracted from the dark area width of the upper area A or the dark area width of the lower area C to obtain a value corresponding to the step.

  Further, when obtaining the dark area width, the threshold value is determined based on the minimum value of the luminance profile of the pixels arranged inside the ellipse from the measurement point and the average value of the luminance values of the pixels inside the contour 55, and is equal to or less than the threshold value. Although the area is determined to be a dark area, the threshold value may be a predetermined value, or may be set by another method such as using either the minimum value or the average value as a reference.

  Further, by executing a program of processing executed by the CPUs 11, 31, 61 on an information terminal such as an existing computer, the information terminal can also function as the step difference measuring devices 10, 30, 60 according to the present invention. It is.

  Such a program distribution method is arbitrary, for example, a computer-readable recording medium such as a CD-ROM (Compact Disc Read-Only Memory), a DVD (Digital Versatile Disc), an MO (Magneto Optical Disc), or a memory card. It may be stored and distributed in the network, or distributed via a communication network such as the Internet.

10, 30, 60 ... Step difference measuring device 11, 31, 61 ... CPU
DESCRIPTION OF SYMBOLS 111 ... Image acquisition part 112 ... Contour detection part 113 ... Measurement point selection part 114 ... Dark area width acquisition part 115 ... Actual size conversion value calculation part 116 ... Gap width calculation part 117 ... Step difference calculation part 118 ... Time and position acquisition part 13 ... Communication unit 15 ... Storage unit 17 ... Display unit 2 ... Vehicle 20 ... GPS satellite 21 ... Camera 22 ... Shooting instruction signal generation unit 221 ... GPS antenna 23 ... First camera 24 ... Second camera 311 ... Image rotation unit 312 ... Gauge Superimposition unit 611 ... 3D coordinate acquisition unit 612 ... Distance between two points calculation unit 40 ... Road 50 ... Lid 51 ... Opening part 52 ... Receiving frame 521 ... Lower support part 55 ... Contour 551 ... Long axis 552 ... Short axis

Claims (11)

A level difference measuring device for measuring a level difference caused by floating or sinking with respect to a receiving frame of a manhole cover on a road,
An image acquisition unit for acquiring a frame image of the road;
A contour detection unit that detects a substantially elliptical contour from the frame image acquired by the image acquisition unit;
The outline of the substantially ellipse detected by the outline detector includes a right area and a left area including an intersection of the outline and the major axis of the substantially ellipse, and an intersection of the outline and the minor axis of the substantially ellipse. A measurement point selection unit that divides into four regions including an upper region and a lower region and selects at least one measurement point in each of the four regions;
The brightness of a plurality of pixels arranged in a direction normal to the contour at the measurement point selected by the measurement point selection unit and in a direction from the measurement point toward the inside or outside of the substantially ellipse is acquired, and the brightness A dark area width acquisition unit that acquires a dark area width that is equal to or less than a predetermined reference;
A correction value calculation unit that calculates a correction value based on the width of the dark region of the right region and the left region;
Based on the first difference value calculated by subtracting the correction value from the dark area width of the upper area, or the second difference value calculated by subtracting the correction value from the dark area width of the lower area , A step calculation unit for calculating the step,
A step difference measuring apparatus comprising: The pixel of the measurement point selected by the measurement point selection unit from the actual size of the outer diameter of the lid or the outer diameter of the receiving frame, which is known in advance, and the number of pixels with the major axis or minor axis of the substantially ellipse of the outline, and It further has an actual size conversion value calculation unit that calculates an actual size conversion value of the surrounding pixels,
The correction value calculation unit is configured to determine a gap between the manhole cover and the receiving frame from the width of the dark region of the right region or the left region and the actual size conversion value calculated by the actual size conversion value calculation unit. Calculating the correction value which is the actual size of the gap width of
The level difference calculation unit subtracts the correction value calculated by the correction value calculation unit from the width of the dark area of the upper area converted into an actual size using the actual size conversion value, thereby calculating the first difference value. Calculating and calculating the second difference value by subtracting the correction value calculated by the correction value calculation unit from the width of the dark area of the lower area converted into an actual size using the actual size converted value;
The level | step difference measuring apparatus of Claim 1 characterized by the above-mentioned. The step calculation unit
If the width of the dark area of the upper area is wider than the width of the dark area of the lower area, it is determined that the manhole cover is sunk more than the receiving frame of the manhole cover, and converted to the actual size And calculating the first difference value as the step,
When the width of the dark area in the upper area is narrower than the width of the dark area in the lower area, it is determined that the manhole cover is floating above the receiving frame of the manhole cover, and converted to the actual size. Calculating the second difference value as the step,
The level | step difference measuring apparatus of Claim 1 or 2 characterized by the above-mentioned. The correction value calculating unit calculates the correction value based on an average value of the dark area width of the right area and the dark area width of the left area;
The level | step difference measuring apparatus of any one of Claim 1 thru | or 3 characterized by the above-mentioned. The dark area width acquisition unit acquires, as a dark area width, a width of an area that is equal to or less than a reference value determined based on a minimum value of luminance of the plurality of pixels and an average value of luminance of pixels inside the contour. To
The level | step difference measuring apparatus of any one of Claims 1 thru | or 4 characterized by the above-mentioned. A rotated image obtained by rotating an image around the contour so that the major axis of the approximate ellipse of the contour is horizontal when the major axis of the approximate ellipse detected by the contour detection unit is not horizontal in the frame image An image rotation unit for generating
Based on the actual size conversion value calculated by the actual size conversion value calculation unit, an actual scale at the measurement point is calculated, and an image in which a gauge indicating the actual scale is superimposed on the image generated by the image rotation unit is obtained. A gauge superimposing unit to be generated,
The step difference measuring device according to any one of claims 1 to 5, wherein The image acquired by the image acquisition unit is a stereo image taken with a stereo camera,
The contour indicates when the major axis of the approximate ellipse detected by the contour detector is calculated by three-dimensional measurement based on the stereo image, and the major axis of the approximate ellipse is within a predetermined range. A measurement object determining unit that determines that the manhole cover and the receiving frame are measurement objects;
The step calculation unit outputs the measurement result of the step for the lid of the manhole and the receiving frame that the measurement target determination unit has determined to be a measurement target.
The level | step difference measuring apparatus of any one of Claim 1 thru | or 6 characterized by the above-mentioned. The image acquired by the image acquisition unit is a stereo image taken with a stereo camera,
The height difference in the vertical direction of at least two points inside the fixed distance from the contour detected by the contour detection unit is calculated by three-dimensional measurement based on the stereo image, and the height difference is determined from a predetermined value. In the case of being large, it further includes a lid inclination determination unit that determines that the manhole cover 50 is inclined.
The step difference measuring device according to any one of claims 1 to 7, wherein The image acquired by the image acquisition unit is a stereo image taken with a stereo camera,
A height difference in the vertical direction of at least one point inside and outside the contour detected by the contour detection unit is calculated by three-dimensional measurement based on the stereo image, and the height difference is calculated with the receiving frame. An outer periphery height difference estimating unit for estimating the height difference from the outer periphery of the receiving frame;
The step difference measuring apparatus according to any one of claims 1 to 8, wherein A step measurement method in which a computer measures a step caused by floating or sinking on a receiving frame of a manhole cover on a road,
An image acquisition step for acquiring a frame image of the road;
A contour detecting step for detecting a substantially elliptical contour from the frame image acquired in the image acquiring step;
The outline of the approximate ellipse detected in the outline detection step includes an intersection of a right area and a left area including an intersection of the outline and the major axis of the approximate ellipse, and an intersection of the outline and the minor axis of the approximate ellipse. A measurement point selection step of dividing the upper region and the lower region into four regions and selecting at least one measurement point in each of the four regions;
The brightness of a plurality of pixels arranged in a normal direction of the contour at the measurement point selected in the measurement point selection step and in a direction from the measurement point toward the inside or outside of the substantially ellipse is acquired, and the brightness A dark area width obtaining step of obtaining a dark area width which is equal to or less than a predetermined reference;
A correction value calculating step for calculating a correction value corresponding to the width of the gap between the manhole cover and the receiving frame based on the width of the dark region of the right region and the left region;
Based on the first difference value calculated by subtracting the correction value from the dark area width of the upper area, or the second difference value calculated by subtracting the correction value from the dark area width of the lower area , A step calculating step for calculating the step,
A step difference measuring method characterized by comprising: To a computer that measures the level difference caused by floating or sinking to the receiving frame of the manhole cover on the road,
An image acquisition procedure for acquiring a frame image of a road;
A contour detection procedure for detecting a substantially elliptical contour from the frame image acquired in the image acquisition procedure;
The outline of the substantially ellipse detected in the outline detection procedure includes a right area and a left area including an intersection of the outline and the major axis of the substantially ellipse, and an intersection of the outline and the minor axis of the substantially ellipse. A measurement point selection procedure that divides into four regions consisting of an upper region and a lower region and selects at least one measurement point in each of the four regions;
The brightness of a plurality of pixels arranged in the normal direction of the contour at the measurement point selected in the measurement point selection procedure and in the direction from the measurement point toward the inside or outside of the substantially ellipse is acquired, and the brightness A dark area width obtaining procedure for obtaining a dark area width that is equal to or less than a predetermined reference;
A correction value calculation procedure for calculating a correction value corresponding to the width of the gap between the manhole cover and the receiving frame based on the width of the dark region of the right region and the left region;
Based on the first difference value calculated by subtracting the correction value from the dark area width of the upper area, or the second difference value calculated by subtracting the correction value from the dark area width of the lower area , A step calculation procedure for calculating the step,
A program for running

Images