Patent Description:
Social infrastructures such as bridges need to be inspected on a regular basis. In addition, in order to inspect a structure efficiently, a crack defect detection method is proposed. In the method, a defect (crack defect) is automatically detected by processing an image acquired by capturing an image of the structure.

For example, <CIT> describes a structure maintenance management service system that acquires information of a captured image of a structure, generates normal-position image information, detects the length of a crack part, and calculates the length of an actual crack part on the basis of a reduced scale of the image information. <CIT> describes a crack information collection method for acquiring a captured image of an inspection target region for a crack in a structure, detecting a crack pixel group from the image, and collecting crack information from positions of a start point, a turning point, and an end point of the pixel group.

An operation for repairing a crack of a structure is performed by covering the crack of the structure with a repair material. Thus, in order to obtain a necessary amount of the repair material, it is necessary to calculate a repair region (repair length) in which repair is to be performed. In a case where a crack of a structure is to be repaired, as illustrated in <CIT> and <CIT>, the repair region is determined on the basis of an image. However, since there are both a crack to be repaired and a crack that does not need to be repaired in the structure, the repair length to be calculated (actual repair length) and a crack detection result have been different from each other.

In "<NPL>), crack growth measurement and analysis of damage mechanisms are disclosed, wherein surface of stainless steel samples coated by different polymeric coating systems are examined using SEM, localization of areas of interest for surface damage analysis in coatings submitted to cavitation is done and linear regression analyses are performed in order to propose models of crack growths. An image processor for a digital image of an object having a crack is disclosed, wherein an area of the image is used to determine the width of a crack on the surface of a concrete structure is disclosed in <CIT>, A repair method for muffle tube wherein a repair length is determined according to the defect type which is obtained by a lasting and tensile creep test is disclosed in <CIT>.

In addition, a crack is repaired by applying, injecting, or filling with (hereinafter referred to as "applying") a repair material. The repair material does not need to be applied exactly on the crack, and the crack is at least included in the area in which the repair material is to be applied. Thus, the repair material is applied on the basis of a curve obtained by blunting an actual crack. Accordingly, the length of the actual crack and the length to be used for repair may be different from each other.

Furthermore, the repair material may be applied on a plurality of cracks continuously even if actual cracks are not continuous. However, since the cracks are recognized as a plurality of cracks in automatic detection, the number of cracks to be repaired (number of times of repair) may be different, and the repair length to be calculated and the repair length to be actually repaired may be different from each other.

In the above manner, if the crack detection result is directly used to determine the repair region, the calculated repair length and the repair length to be actually repaired have been different from each other. As a result, problems have been generated, such as excess or shortage of the repair material to be used, and it has been demanded to know about a more accurate amount of the repair material.

The present invention has been made in view of the above circumstances, and an object thereof is to provide a repair length determination method and a repair length determination apparatus for accurately calculating a region (repair length) in which repair is to be performed in a structure that is a repair target.

In order to achieve the object of the present invention, a repair length determination method according to the present invention comprises the features of claim <NUM>.

According to the present invention, after the image has been acquired and the crack has been detected, by pointing the plurality of points including the two points of the crack and creating the interpolation curve by using the plurality of points, a curve corresponding to the crack can be created. In addition, by setting the interpolation curve as a repair region (repair length) of a crack to be repaired, the repair length to perform repair can be calculated, and an accurate amount of the repair material can be calculated.

According to the invention, by outputting the information of the width of the crack and the length of the interpolation curve corresponding to the width, the repair length corresponding to the width can be checked.

According to claim <NUM>, the repair-target crack and the non-repair-target crack can be recognized on the image.

This feature of claim <NUM> limits the display method of the repair-target crack and the non-repair-target crack, and the repair-target crack and the non-repair-target crack can be distinguished from each other by being displayed by using the line color, the line type, and the line blinking speed corresponding to the crack.

According to claim <NUM>, by displaying only the repair-target crack in the filtering step, operations in the subsequent steps are performed with ease.

According to claim <NUM>, by correcting the pointed point to the position of the crack if the pointed position differs from the position of the crack, a more accurate interpolation curve corresponding to the crack can be created.

According to claim <NUM>, by pointing the two points at both ends of the crack and pointing the positions of the plurality of points of the crack therebetween, the operation can be simplified. In addition, by automatic pointing, pointing can be performed under the same conditions, and the interpolation curve can be stably created.

According to claim <NUM>, by outputting the drawing information of the interpolation curve, the interpolation curve can be visually checked. Thus, it is possible to check whether the created interpolation curve corresponds to an actual repair region for a crack to be repaired.

An aspect of the present invention preferably has an output step for outputting, by an output unit, information of a width of the crack and a length of the interpolation curve corresponding to the width.

The repair method for a crack differs according to the width. According to claim <NUM>, by outputting the repair method corresponding to the width, a repair material corresponding to the repair method can be prepared.

According to claim <NUM>, by outputting the data after tilt correction, a more accurate width of the crack and a more accurate repair length can be determined. In addition, the repair position can be checked on the output image.

Claim <NUM> illustrates examples of the interpolation curve. By creating the interpolation curve as a spline curve or a Bezier curve, a curve corresponding to the crack for actually performing repair can be created.

In order to achieve the object of the present invention, a repair length determination apparatus according to the present invention includes the features of claim <NUM>.

The above-described repair length determination apparatus is obtained by developing the repair length determination method as a repair length determination apparatus. The repair length determination apparatus can produce the same effects as the repair length determination method.

In the repair length determination method and the repair length determination apparatus according to the present invention, the plurality of points including both ends of the crack are pointed, and the interpolation curve is created by using the pointed points. By detecting the length of this interpolation curve, the region (repair length) in which repair is to be performed can be accurately calculated.

Now, a repair length determination method and a repair length determination apparatus according to the present invention will be described below in accordance with the attached drawings.

<FIG> is an upward perspective view of a bridge <NUM>, which is a structure. The bridge <NUM> illustrated in <FIG> has a three-dimensional structure of main girders <NUM>, a cross beam <NUM>, a cross frame <NUM>. a lateral frame <NUM>, and a deck slab <NUM> and is constructed by coupling these members by bolts, rivets, welding, or the like. Above the main girder <NUM> and other members, the deck slab <NUM> is disposed, and vehicles and the like travel on the deck slab <NUM>. The deck slab <NUM> is typically made of reinforced concrete. The main girder <NUM> is a member that spans the area between abutments or piers and that supports a load of vehicles and the like on the deck slab <NUM>. The main girder <NUM> has a surface (vertical surface) intersecting with the surface of the deck slab <NUM> (horizontal surface). The cross beam <NUM> is a member that couples the plurality of main girders <NUM> so that the main girders <NUM> support the load. The cross frame <NUM> and the lateral frame <NUM> are members that couple the main girders <NUM> to one another to resist a lateral load caused by wind and earthquake. Although this embodiment describes a case where the bridge <NUM> is a target (structure), the target structure is not limited to a bridge and may be a tunnel, a building, a road, and the like.

<FIG> is a block diagram illustrating a schematic configuration of an image processing system <NUM>. The image processing system <NUM> includes a digital camera <NUM> (an imaging apparatus) and a system main body <NUM> (a repair length determination apparatus). The image processing system <NUM> is a system that calculates, on the basis of an image acquired by capturing an image of a photographic subject, a repair length of a crack that needs to be repaired (details will be described later) and may be applicable to a digital camera, a smartphone, a tablet terminal, a personal computer, or the like. Note that the digital camera <NUM> and the system main body <NUM> may be incorporated in different housings or may be integrated. In addition, the digital camera <NUM> may be incorporated as part of the system main body <NUM>, and the digital camera <NUM> and the system main body <NUM> may constitute a repair length determination apparatus according to the present invention.

The digital camera <NUM> acquires an image by using an imaging optical system <NUM> including an imaging lens and an imaging element that are not illustrated. Examples of the imaging element include a charge coupled device (CCD) imaging element and a complementary metal-oxide semiconductor (CMOS) imaging element. A color filter of R (red), G (green), or B (blue) is provided on a light-receiving surface of the imaging element, and a color image of the photographic subject can be acquired on the basis of signals of the respective colors. The digital camera <NUM> performs wireless communication with the system main body <NUM> through a wireless communication unit <NUM> and an antenna <NUM>, a captured image is input to an image acquiring unit <NUM>, and processing described later is performed.

The captured image may be an image generated by combining a plurality of separate images that will be described later. In addition, for example, if the size of a panel is small and the digital camera <NUM> can capture an image (entire image) of the deck slab <NUM> including one panel at an appropriate resolution at a single time, the image acquired through single-time image capturing may be used.

The digital camera <NUM> may be, for example, a general-purpose compact digital camera having approximately <NUM> × <NUM> pixels.

The system main body <NUM> is mainly constituted by the image acquiring unit <NUM>. a crack detecting unit <NUM>, a display control unit <NUM>, an operation unit <NUM>, an interpolation curve creating unit <NUM>, a repair length determining unit <NUM>, and an output unit <NUM>. These are connected to one another to transmit and receive necessary information. In addition, the system main body <NUM> performs wireless communication with the digital camera <NUM> through an antenna <NUM> and acquires an image captured by the digital camera <NUM>.

The image acquiring unit <NUM> acquires a captured image of the bridge <NUM> from the digital camera <NUM> (or a recording medium, a network, or the like). The image may be a plurality of images that are obtained by capturing images of the bridge <NUM> separately or may be an image that is acquired through single-time image capturing. If a plurality of images are combined into one image, correspondence points between the images are detected, and a captured image is formed on the basis of the correspondence points between the images.

The crack detecting unit <NUM> extracts and measures a crack in the captured image.

The display control unit <NUM> includes a monitor display unit <NUM> and generally controls display screens for displaying an input image, a detected crack and information of the crack. and information of a created interpolation curve or the like.

The operation unit <NUM> includes a keyboard <NUM> and a mouse <NUM> as an input device and a pointing device. In addition, if the monitor display unit <NUM> has a touch panel, the touch panel and the like are also included. Through such devices and a screen of the monitor display unit <NUM>, a user can perform necessary operations for performing a repair length determination method according to this embodiment (described later). The operations include designation of pointing positions of a crack, input of crack information, and the like.

The interpolation curve creating unit <NUM> creates an interpolation curve from positions pointed through the operation unit <NUM>.

The repair length determining unit <NUM> measures the length of the interpolation curve created by the interpolation curve creating unit <NUM>.

The output unit <NUM> outputs the interpolation curve created by the interpolation curve creating unit <NUM> as drawing data. In addition, the output unit <NUM> also outputs the length of the interpolation curve (repair length) measured by the repair length determining unit <NUM> and information of the interpolation curve and information of a crack detected by the crack detecting unit <NUM> as characters or data in the form of a table. Note that such information may be output as drawing data.

Functions of the units of the system main body <NUM> can be implemented by using various processors. Various processors include, for example, a central processing unit (CPU), which is a general-purpose processor that implements various functions by executing software (program). The above-described various processors also include a programmable logic device (PLD), which is a processor in which the circuit configuration is changeable after manufacture, such as a field programmable gate array (FPGA). The above-described various processors further include a dedicated electric circuit, which is a processor having a circuit configuration that is specially designed to execute specific processing, such as an application specific integrated circuit (ASIC), and the like.

The function of each unit may be implemented by one processor or may be implemented by a plurality of processors in combination. In addition, a plurality of functions may be implemented by one processor. As a first example for constituting a plurality of functions with one processor, one processor may be constituted by a combination of one or more CPUs and software, and this processor may implement a plurality of functions, as typified by a computer such as a client or a server. As a second example, a processor may be used that implements the functions of the entire system with one integrated circuit (IC) chip, as typified by a system on chip (SoC) or the like. In this manner, various functions are constituted by one or more of the above various processors in terms of hardware configuration. More specifically, the hardware configuration of these various processors is electric circuitry constituted by combining circuit elements such as semiconductor elements.

When the above processor or electric circuitry executes software (program), a processor (computer) readable code of the software to be executed is stored in a non-transitory recording medium such as a read-only memory (ROM), and the processor refers to the software. The code may also be recorded on, instead of the ROM, a non-transitory recording medium such as any magnetooptical recording device or a semiconductor memory. In the processing using software, for example, a random access memory (RAM) is used as a temporary storage area, and for example, data stored in an electronically erasable and programmable read-only memory (EEPROM) is referred to.

Image processing performed by the image processing system <NUM> will be described. <FIG> is a flowchart illustrating a procedure of the image processing (including the steps in the repair length determination method according to the present invention).

First, a plurality of captured images are acquired (step S100; image acquiring step). The plurality of captured images are obtained by the digital camera <NUM> separately capturing images of different portions of the bridge <NUM> (structure). The captured images are images obtained by imaging a crack repair target region. The system main body <NUM> acquires these plurality of captured images through the digital camera <NUM> (the imaging optical system <NUM>, the wireless communication unit <NUM>, the antenna <NUM>, and the antenna <NUM>) and the image acquiring unit <NUM>.

Upon the images being captured, the image acquiring unit <NUM> combines the plurality of captured images into one image. To combine the captured images, information for combination is calculated. For example, correspondence points between the captured images and a homography matrix or the like on the basis of the correspondence points are calculated. Then, the images are combined on the basis of the correspondence points. Note that the step for combining the images can be skipped if the entire region can be captured in one image. The acquired image may be displayed on the monitor display unit <NUM> under control of the display control unit <NUM>. <FIG> illustrates a captured image of the bridge <NUM>. In <FIG>, an entire image <NUM> after combination is illustrated. Cracks <NUM> can be seen in the entire image <NUM>.

From the image acquired in the image acquiring step, cracks are detected (step S102; detection step). Items to measure for crack detection are the position, size, direction, area, shape, and the like and may be set in accordance with conditions such as the type, characteristics, inspection purpose, and the like of the structure. In crack detection, the crack detecting unit <NUM> represents the detection result as a vector, a line segment having a start point and an end point, or a group thereof.

Crack detection may be performed by various methods. For example, a crack detection method described in <CIT> can be employed. This method is a crack detection method having a step for creating a wavelet image and a step for determining a crack region on the basis of the wavelet image. In the step for creating a wavelet image, wavelet coefficients corresponding to two concentrations to be compared are calculated, wavelet coefficients in a case where the two concentrations are changed are calculated to create a wavelet coefficient table, and wavelet transformation is performed on an input image that is obtained by capturing an image of a concrete surface that is a crack detection target. In the step for determining a crack region, a crack region and a non-crack region are determined by comparing the wavelet coefficient of a pixel of interest with a threshold value. The threshold value is a wavelet coefficient corresponding to the average concentration of neighboring pixels within a local region and the concentration of the pixel of interest in the wavelet coefficient table.

In addition, the length of a short side and the length of a long side of a captured image can be input in advance, and the width of a crack can be detected on the basis of a structure that is an image capturing target, an image capturing distance from the digital camera <NUM>, and the number of pixels of the digital camera <NUM>. Furthermore, the width of the crack is preferably detected by using an image after tilt correction. Tilt correction can correct distortion of a building to obtain a photograph as if viewed from the front. In addition, by using the corrected image, the length of the crack and the width of the crack can be measured with higher accuracy.

The cracks detected in the detection step are mapped in the image acquired in the image acquiring step, and the image is displayed (step S <NUM>; display step). The image in which the measurement results are mapped is, as illustrated in <FIG>, displayed on the monitor display unit <NUM> under control of the display control unit <NUM>. With the mapping, positions of the cracks can be indicated, and also widths of the cracks can be displayed. In addition, characters. figures, symbols, or the like associated with the measurement results can be displayed on a screen. The displayed characters, figures, symbols, or the like may be selected by an operation through the operation unit <NUM> (the keyboard <NUM> and/or the mouse <NUM>), and in accordance with the selection, the detection results and measurement results are displayed on the monitor display unit <NUM> of the display control unit <NUM>. The characters, figures, symbols, or the like may simplify or emphasize actual cracks or may be displayed in different forms in accordance with sizes (widths) or the like of the cracks. In <FIG>, a repair-target crack 22A (a crack with a width of <NUM> or more) that needs to be repaired is displayed by a thick line, a non-repair-target crack 22B (a crack with a width of less than <NUM>) that does not need to be repaired is displayed by a thin line. Although the lines with two types of thickness are used for display in accordance with the width of the crack in <FIG>, lines with three or more types of thickness may also be used in accordance with the width of the crack. In addition, as a method for displaying a crack in accordance with the width of the crack, a line type (e.g., a straight line, a broken line, or a chain line), a line color, a line blinking speed, or a combination thereof may be used for display. Furthermore, by setting to display a non-repair-target crack to be transparent, only a repair-target crack can be displayed without performing the subsequent filtering step. By using the above display method, the repair-target crack and the non-repair-target crack can be displayed to be distinguishable from each other.

Filtering may be performed to delete the non-repair-target crack from the image displayed on the monitor display unit <NUM> in the display step by the display control unit <NUM> (step S106; filtering step). The filtering step may be performed as necessary, and may not be performed if the non-repair-target crack does not disturb the subsequent operation even if being displayed. The filtering is performed by pressing a "filtering" button <NUM> illustrated in <FIG>. By performing the filtering step, as illustrated in <FIG>, the non-repair-target crack can be deleted from display.

Subsequently, in response to an instruction from a user through the operation unit <NUM> (the keyboard <NUM> and the mouse <NUM>), a plurality of points in the repair-target crack 22A displayed on the monitor display unit <NUM> are pointed (step S108; pointing step).

In the pointing step, by the user pointing a plurality of points through the operation unit <NUM>, control points for controlling an interpolation curve to be created in the subsequent interpolation curve creating step are selected. A point can be pointed, as illustrated in <FIG>, by the user selecting a pointer <NUM> displayed on the monitor display unit <NUM> through the operation unit <NUM>.

As illustrated in <FIG> and <FIG>, the cracks <NUM> are composed of a plurality of substantially straight cracks with different widths that are continuously connected. In <FIG>, the cracks <NUM> have in a zigzag shape. Crack repair is performed in such a manner that the plurality of cracks become a continuous smooth curve. When the cracks are only detected, as illustrated in <FIG>, shapes of actual cracks are displayed, and thus, the displayed cracks differ from a region in which repair is to be performed. Accordingly, by using points that are pointed through the operation unit <NUM> in the pointing step, an interpolation curve corresponding to the repair region assumed by the user is created.

As the plurality of points to be pointed, a plurality of points including two points (i.e., a start point and an end point) at both ends of the repair-target crack 22A are selected. Positions are pointed in such a manner that an interpolation curve to be created in the subsequent step is formed near an actual crack. For example, as illustrated in <FIG>. positions where the direction of a crack changes can be pointed. Also, positions from the start point to the end point can be pointed at equal intervals.

In addition, in a case where a crack is to be repaired by filling the crack with a repair material or injecting a repair material, positions to be filled with the repair material or to which the repair material is to be injected can be pointed. By pointing the positions to be filled with the repair material or to which the repair material is to be injected, a crack can be reliably repaired at the positions. Since the crack can be filled with the repair material or the repair material can be injected at <NUM> intervals, for example, the positions can also be pointed at <NUM> intervals.

The number of positions to be pointed is not limited to a particular number and can be set as appropriate in accordance with the shape of a crack and an interpolation curve to be created. However, if a large number of positions are pointed, the length of an actual crack that is displayed does not differ from the length of the interpolation curve, and, at least, the interpolation curve may not correspond to the position of the actual crack, and some portions may not be repaired.

In addition, as illustrated in <FIG>, cracks may include a non-repair-target crack <NUM> (with a width of <NUM>) in continuous cracks. In automatic detection, as illustrated in <FIG>, such cracks are detected as two cracks, a crack 23C and a crack 23C, and regarded as different cracks. In such a case, an end of one of the cracks may be pointed as a start point, an end of the other of the cracks may be pointed as an end point, and a plurality of points therebetween may be pointed, so that the two cracks may be interpolated by one interpolation curve. Also in a case where two or more cracks are preferably repaired continuously, the cracks may be interpolated by one interpolation curve by pointing an end of one of the cracks as a start point, an end of another one of the cracks as an end point, and a plurality of points therebetween.

Note that for a branching crack, an interpolation curve is created for two cracks that are one crack and another one crack starting from a branching point.

Intermediate points other than the two points at both ends of a crack may all be pointed by a user through the operation unit <NUM>, or after the two points at both ends have been pointed, a position of a point or positions of a plurality of points between the two points at both ends may be automatically pointed. As a method for automatic pointing, positions may be pointed at equal intervals from one of the ends, or connecting portions (portions with different widths) or the like of a plurality of cracks may be automatically pointed. In addition, automatic pointing and pointing through the operation unit <NUM> may be combined. After automatic pointing, for example, if part of a crack is apart from the pointed positions and the crack is also apart from an interpolation curve to be subsequently created, the pointed positions may be increased or changed by an operation through the operation unit <NUM>, so that the interpolation curve may be approximated to the crack.

In addition, the operation unit <NUM> may correct a position pointed by a user to a position of a crack near the pointed position. If there is an error between the position of a crack and the pointed position, by correcting the pointed position, an interpolation curve approximated to the actual crack can be created.

After the cracks displayed on the monitor display unit <NUM> have been pointed, interpolation curves are created by using the pointed points (step S110; interpolation curve creating step). The created interpolation curves correspond to repair regions where the repair material is to be actually applied. In <FIG>, interpolation curves <NUM> and <NUM> are displayed in the entire image <NUM>. The interpolation curves are created by pressing an "obtain spline" button <NUM>.

As an interpolation curve, a spline curve or a Bezier curve can be used. The spline curve is a smooth curve in which a plurality of pointed points (control points) control passing points of the curve. The pointed points may or may not pass through the spline curve. As a spline curve, a quadratic spline curve is defined by coordinates of two control points and a control point in front of them. Points other than both ends do not pass through designated control points, but pass though the midpoint of a line segment connecting two adjacent control points. In addition, a cubic spline curve is defined by coordinates of two control points and control points in front of and behind them. Also in the cubic spline curve, points other than both ends do not pass through designated control points.

A Bezier curve is an (N-<NUM>)-th-order curve obtained from N control points. In a Bezier curve, a line segment connecting a start point and a first control point is the tangent of the curve at the start point, and a line segment connecting a second control point and an end point is the tangent of the curve at the end point. The Bezier curve passes through designated control points.

Although the pointing step and the interpolation curve creating step are illustrated as different steps in the flowchart in <FIG>, the interpolation curve creating step may be performed concurrently in the pointing step. If the interpolation curve can be created between previously pointed points during pointing in the pointing step, the interpolation curve can be created while pointing is being performed.

After an interpolation curve has been created, the length of this interpolation curve is measured (step S112; repair length determining step). By creating the interpolation curve, this interpolation curve can be regarded as the positions at which a crack is to be actually repaired. By measuring the length of the interpolation curve, this length of the interpolation curve can be determined as the repair length. The repair length can also be obtained on the basis of the length of the short side and the length of the long side of the captured image.

The interpolation curve can be output as drawing information as necessary. In addition, crack information, for example, the width of the crack and the length of the interpolation curve corresponding to the width may be output. Furthermore, a repair method corresponding to the width of the crack may be output (step S1 <NUM>; output step). At least the length of the interpolation curve is calculated as the repair length in this embodiment, and the above information is not necessary output.

As a method for outputting drawing information of the interpolation curve, interpolation curves illustrated in <FIG> can be output as a computer-aided design (CAD) diagram in the form of a drawing exchange format (dxf) file. As the drawing information, information of the width of the crack and the length of the interpolation curve (repair length) or the like can also be output. The drawing information can be output by pressing a "dxf output" button <NUM> illustrated in <FIG>.

In a case where the width of the crack, the length of the interpolation curve, and the repair method are output, a comma separated value (CSV) file can be output as table information. In a case where a CSV file is output, as illustrated in <FIG>, detected cracks may be denoted by numbers (No.), and widths of cracks corresponding to the numbers and lengths of interpolation curves may be output. The width of a crack may be a maximum value or an average value of widths of the crack and may be determined as appropriate in accordance with necessary information.

In addition, the interpolation curves may be sorted according to the width of a crack among repair-target cracks, and a group of interpolation curves corresponding to the width of the crack may be output (<FIG>). In <FIG>, a first group corresponds to a crack width of greater than or equal to <NUM> and less than <NUM>, a second group corresponds to a crack width of greater than or equal to <NUM> and less than <NUM>, and a third group corresponds to a crack width of greater than or equal to <NUM>. Note that cracks with a width of less than <NUM> are non-repair-target cracks. In addition, as interpolation curve information, total lengths of interpolation curve groups are output. By outputting the total lengths of interpolation curve groups, a material necessary for repair or the like can be checked.

Furthermore, a repair method corresponding to the width of a crack may also be displayed. Cracks are repaired differently according to the width of the crack. A crack with a small width is repaired by a surface coating method, that is, a method for covering only a crack part with a covering material. A crack with a large width is repaired by a method for injecting a repair material into the cracks. Since the repair method differs according to the width of the crack in this manner, by outputting information of the repair method, the repair material can be prepared with ease even if there are cracks with different widths.

As data to be output in the output step, data after tilt correction is preferably output. By displaying cracks and interpolation curves in an image that is subjected to tilt correction. it is possible to display and check the interpolation curves in an image that is close to an actual structure, and thus, the amount of a repair material and the like can be checked before repair.

Claim 1:
A repair length determination method comprising:
an image acquiring step for acquiring, by an image acquiring unit (<NUM>), an image (<NUM>) obtained by imaging a crack repair target region in a structure;
a detection step for detecting, by a crack detecting unit (<NUM>), a crack (<NUM>,<NUM>,23C) from the acquired image;
a display step for displaying, by a display control unit (<NUM>), the crack detected in the detection step; and
a pointing step for pointing a plurality of points including two points at both ends of the crack in response to an instruction from a user, through an operation unit (<NUM>);
characterized by an interpolation curve creating step for creating, by an interpolation curve creating unit (<NUM>), an interpolation curve (<NUM>,<NUM>) by using the points pointed in the pointing step;
a repair length determining step for detecting, by a repair length determining unit (<NUM>), a length of the interpolation curve and determining the length of the interpolation curve as the repair length; and
an output step for outputting, by an output unit (<NUM>), information of a width of the crack and a length of the interpolation curve corresponding to the width, as well as information of a repair method corresponding to the width.