Wire sag observation device, wire sag observation program, and wire sag observation method

Abstract

To enable an electric wire sag to be properly adjusted to be a target sag.SOLUTION: A computer 16 carried by an operator 15 comprises a camera and a display. The camera photographs an electric wire 13, which is supported by steel towers 11 and 12 at a distance between them, toward the side of the steel tower 12 from the side of the steel tower 11. The display displays an image taken by the camera. The computer 16 displays collimation and a target position for setting a sag of the electric wire 13 as a target sag on the display in such a manner that they are superimposed on the image. Various pieces of information for setting the sag of the electric wire 13 as the target sag are input into the computer 16. The computer 16 displays the target position based on the collimation on the display, on the basis of the input information, when the collimation is kept in line with a support point H by directing the camera toward the support point H of the electric wire 13 in the steel tower 12.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to an electric wire sag observation device, an electric wire sag observation program, and an electric wire sag observation method.

Background Art

[0002] In facilities where electric wires are supported by a plurality of wire supports spaced apart from each other, when newly installing the facility or replacing the electric wires, in order to set the sag of the electric wires strung across the plurality of wire supports to the target sag, operations such as winding up or paying out the above electric wires are performed. When performing such operations, in Patent Document 1, the above electric wires are wound up or paid out while observing the above electric wires.

[0003] Specifically, a camera for photographing the above electric wires supported by a plurality of wire supports and a display for displaying the video of the above electric wires photographed by the camera are used, and a window for setting the sag of the above electric wires to the target sag is superimposed and displayed on the above video on the display. Then, by winding up or paying out the electric wires so that the above electric wires enter the window, the sag of the above electric wires is adjusted to the sag corresponding to the above window, that is, the target sag.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] As shown in Patent Document 1, when adjusting the sag of an electric wire, if the window is not set appropriately to correspond to the target sag, the sag of the electric wire cannot be adjusted to the target sag. However, in Patent Document 1, the above window is set manually, so it is unlikely that the window can be set appropriately to correspond to the target sag. Therefore, even if the technology of Patent Document 1 is used, it is difficult to appropriately adjust the sag of the electric wire to the target sag. [Means for solving the problem]

[0006] The following describes the means and effects of solving the above problems. The wire sag observation device that solves the above problems comprises a camera, a display, and a control unit. The camera photographs a wire supported by a first wire support and a second wire support, which are spaced apart from each other. The display shows the image of the wire captured by the camera. The control unit overlays a target position for setting the wire sag to a target sag onto the image on the display. The camera is aimed from the first wire support towards the second wire support to photograph the wire. The control unit overlays a target reticle onto the image on the display. The control unit receives information such as the target sag of the wire, the specifications of the wire, the span length between the first and second wire support, the height difference between the support point of the wire on the first wire support and the support point of the wire on the second wire support, and the installation position of the camera on the first wire support. When the control unit directs the camera towards the support point of the wire on the second wire support, thereby aligning the aiming reticle with the support point of the wire on the second wire support, it displays the target position on the display based on the input information, with the aiming reticle as the reference point.

[0007] According to the above configuration, by directing the camera from the first wire support to the support point of the wire on the second wire support, the wire stretched between the first and second wire support is photographed. The display shows the image of the wire captured by the camera, and a reticle is superimposed on the image. When this reticle is aligned with the support point of the wire on the second wire support, a target position for setting the sag of the wire to the target sag is displayed on the display. This target position is based on the reticle and is displayed superimposed on the image. The target position is displayed based on information such as the target sag of the wire, the specifications of the wire, the span length between the first and second wire support, the height difference between the support point of the wire on the first wire support and the support point of the wire on the second wire support, and the camera's installation position on the first wire support. As a result, the target position is appropriately set as the position corresponding to the target sag of the wire. Therefore, by winding up or unwinding the wire so that the wire displayed on the screen is positioned corresponding to the target position, the sag of the wire can be appropriately adjusted to the target sag.

[0008] In the above-described wire sag observation device, the support point of the wire in the second wire support is located at a higher position than the support point of the wire in the first wire support, and the camera is installed at a lower position than the support point of the wire in the first wire support.

[0009] With the above configuration, it becomes easier to see in the image displayed on the screen that the wire is hanging down from the support point of the second wire support. When the reticle displayed on the screen is aligned with the support point of the wire on the second wire support, the target position is displayed below the reticle. This makes it easier to understand the relative position of the wire to the target position.

[0010] In the above-described wire sag observation device, the control unit may be configured as follows: The control unit determines the point of contact of a tangent line that touches the wire, whose sag is set to a target sag, and passes through the camera's installation position. The control unit determines a straight line connecting the camera's installation position and the support point of the wire on the second wire support. The control unit determines the length of a line segment that extends from the point of contact to the straight line and is perpendicular to the straight line. The control unit converts the length of the line segment into a distance on the display based on the number of pixels on the display, and displays the target position at a position lowered by that distance from the aiming reticle on the display.

[0011] According to the above configuration, the target position for setting the electric wire to the target sag can be displayed at an appropriate position on the display. The wire sag observation program that solves the above problem takes video from a camera that photographs a wire supported by a first wire support and a second wire support located at a distance from each other, and causes a computer that displays the input video on a display to perform aiming display processing, input processing, and target display processing. The aiming display processing involves displaying a aiming reticle superimposed on the video on the display. The input processing receives information such as the target sag of the wire, the specifications of the wire, the span length between the first and second wire support, the height difference between the support point of the wire on the first wire support and the support point of the wire on the second wire support, and the installation position of the camera on the first wire support. The above target display process displays a target position on the display to adjust the sag of the electric wire to a target sag. When the camera is pointed from the first electric wire support to the support point of the electric wire on the second electric wire support, thereby aligning the aiming reticle with the support point, the target position is superimposed on the image based on the input information, with the aiming reticle as the reference point.

[0012] According to the program described above, by positioning the camera from the first wire support towards the support point of the wire on the second wire support, an image of the wire between the first and second wire support, captured by the camera, is displayed on the screen. A crosshair is displayed on the screen, superimposed on the image. When this crosshair is aligned with the support point of the wire on the second wire support, a target position for setting the wire's sag to a target sag is displayed on the screen. This target position is based on the crosshair and is displayed superimposed on the image. The target position is displayed based on information such as the target sag of the wire, the specifications of the wire, the span length between the first and second wire support, the height difference between the support point of the wire on the first wire support and the support point of the wire on the second wire support, and the camera's installation position on the first wire support. As a result, the target position is appropriately set as the position corresponding to the target sag of the wire. Therefore, by winding up or unwinding the wire so that the wire displayed on the screen is positioned corresponding to the target position, the sag of the wire can be appropriately adjusted to the target sag.

[0013] A method for observing the sag of a power line that solves the above problem uses a camera that photographs a power line supported by a first power line support and a second power line support, which are spaced apart from each other, and a display that shows the image of the power line captured by the camera. The display superimposes a target position on the image to bring the sag of the power line to a target sag. In this method, the power line is photographed by pointing the camera from the first power line support to the second power line support. A targeting reticle is displayed superimposed on the image on the display. Then, when the camera is aimed at the support point of the wire on the second wire support by pointing the camera from the first wire support, the target position is displayed on the display based on the aiming reticle, based on information such as the target sag of the wire, the specifications of the wire, the span length between the first and second wire support, the height difference between the support point of the wire on the first wire support and the support point of the wire on the second wire support, and the camera's installation position on the first wire support.

[0014] According to the above wire sag observation method, by positioning a camera from the first wire support towards the support point of the wire on the second wire support, an image of the wire between the first and second wire support, captured by the camera, is displayed on the display. A reticle is displayed superimposed on the image on the display. When this reticle is aligned with the support point of the wire on the second wire support, a target position for setting the wire sag to a target sag is displayed on the display. This target position is based on the reticle and is displayed superimposed on the image. The target position is displayed based on information such as the target sag of the wire, the specifications of the wire, the span length between the first and second wire support, the height difference between the support point of the wire on the first wire support and the support point of the wire on the second wire support, and the camera's installation position on the first wire support. As a result, the target position is appropriately set as the position corresponding to the target sag of the wire. Therefore, by winding up or unwinding the wire so that the wire displayed on the display corresponds to the target position, the wire can be appropriately adjusted to the target sag. [Brief explanation of the drawing]

[0015] [Figure 1] This is a schematic diagram showing the equipment used for observing the sag of power lines. [Figure 2] This is a schematic diagram showing the structure of a computer that embodies the wire sag observation device shown in Figure 1. [Figure 3] Figure 2 is a front view showing the display of the computer's screen. [Figure 4] Figure 2 is a front view showing the display of the computer's screen. [Figure 5] These are schematic diagrams illustrating how to determine the target position to be displayed on the displays in Figures 2 and 3. [Figure 6] This figure shows equation (1) used to determine the target position mentioned above. [Figure 7]This is a diagram showing formula (2) used to determine the above target position. [Figure 8] This is a diagram showing formula (3) used to determine the above target position. [Figure 9] This is a diagram showing formula (4) used to determine the above target position. [Figure 10] This is a diagram showing formula (5) used to determine the above target position. [Figure 11] This is a diagram showing formula (6) used to determine the above target position. [Figure 12] This is a schematic diagram for explaining how to determine the target position to be displayed on the displays of FIGS. 2 and 3. MODE FOR CARRYING OUT THE INVENTION

[0016] Hereinafter, an embodiment of a wire sag observation device, a wire sag observation program, and a wire sag observation method will be described with reference to FIGS. 1 to 12. As shown in FIG. 1, in a power transmission facility where a wire 13 is supported by towers 11 and 12 spaced apart from each other, tower 11 serves as a first wire support, and tower 12 serves as a second wire support. When newly installing such a power transmission facility or replacing the wire 13, after the wire 13 is spanned between the towers 11 and 12, the wire 13 is wound up or paid out by a winch 14, so that the sag of the wire 13 is adjusted to the target sag.

[0017] <Wire Sag Observation Device> When adjusting the sag of the wire 13 to the target sag, a wire sag observation device for observing the sag of the wire 13 is used. This device is realized by a computer 16 that can be carried by an operator 15 climbing tower 11. The computer 16 serves as a control unit of the wire sag observation device. As the computer 16, for example, a personal computer such as a notebook type and a tablet type can be adopted, or a portable computer such as a smartphone can be adopted.

[0018] As shown in Figure 2, the computer 16 includes a camera 17, a display 18, a communication unit 21, and a central processing unit 22. The camera 17 is for photographing the power lines 13. The display 18 is capable of displaying images of the power lines 13 captured by the camera 17. The communication unit 21 is for communicating with a display device 20 that can be viewed by the worker 19 operating the winch 14 shown in Figure 1. The central processing unit 22 controls various devices in the computer 16, such as the camera 17, the display 18, and the communication unit 21.

[0019] As shown in Figure 1, worker 15 climbs the tower 11 with a computer 16 to adjust the sag of the power line 13 to a target sag. Once on the tower 11, worker 15 points the camera 17 of the computer 16 towards the tower 12 to photograph the power line 13. At this time, the camera 17 is pointed from the tower 11 towards the tower 12 to photograph the power line 13. The power line 13 is supported by support point L on the tower 11 and by support point H on the tower 12.

[0020] The above-mentioned imaging of the power line 13 by camera 17 is performed with the computer 16 (camera 17) installed at a position lower than the support point L of the power line 13 on the transmission tower 11. Furthermore, the support point H of the power line 13 on transmission tower 12 may be at a higher or lower position than the support point L of the power line 13 on transmission tower 11. Also, support points H and L may be at the same height. In this example, the support point H of the power line 13 on transmission tower 12 is at a higher position than the support point L of the power line 13 on transmission tower 11.

[0021] Figure 3 shows the display 18 of the computer 16. The display 18 in Figure 3 shows the image captured by the camera 17. The computer 16 displays a reticle 23 superimposed on the image on the display 18. The reticle 23 is represented by a horizontal line 24, a vertical line 25, and a circle 26. The circle 26 is centered at the intersection of the horizontal line 24 and the vertical line 25. The center of the circle 26, i.e., the intersection of the horizontal line 24 and the vertical line 25, is the center of the reticle 23. The computer 16 displays a target position 27 on the display 18, superimposed on the image, to set the sag of the power line 13 to a target sag, and extends horizontally.

[0022] The worker 15, having climbed the transmission tower 11, points the camera 17 of the computer 16 at the support point H of the power line 13 on the transmission tower 12, thereby aligning the target reticle 23 on the display 18 with the support point H. When the target reticle 23 is aligned with the support point H, the computer 16 displays the target position 27 on the display 18, based on the target reticle 23. At this time, the target position 27 is displayed such that when the power line 13 is positioned corresponding to the target position 27, the power line 13 will have the target sag.

[0023] Computer 16 transmits the image displayed on display 18 to the display device 20 shown in Figure 1 via the communication unit 21. The display device 20 displays the same image as the one displayed on computer 16's display 18 by displaying the image transmitted from computer 16. The worker 19 operating the winch 14 operates the winch 14 while looking at the image displayed on the display device 20 so that the electric wire 13 is positioned corresponding to the target position 27. That is, the worker 19 winds up and unwinds the electric wire 13 with the winch 14 so that the electric wire 13 is positioned corresponding to the target position 27 as shown in Figure 4. As a result, the sag of the electric wire 13 becomes the target sag.

[0024] Next, we will explain in detail the target position 27 displayed on the display 18 when the aiming reticle 23 on the display 18 is aligned with the support point H of the power line 13 on the transmission tower 12. The computer 16 receives the following information to determine the target position 27: the target sag d of the power line 13, the specifications of the power line 13, the span length S between the tower 11 and the tower 12, the height difference h between the support point L of the power line 13 on tower 11 and the support point H of the power line 13 on tower 12, and the installation position A of the camera 17 on tower 11. Based on the above information received, the computer 16 displays the target position 27 on the display 18, with the aiming reticle 23 as the reference point.

[0025] As shown in Figure 5, the target sag d of the power line 13 is the target value of the distance (sag) the power line 13 is lowered relative to the straight line L1 connecting support point L and support point H, near the midpoint between tower 11 and tower 12. The specifications of the power line 13 are the horizontal tension T acting on the power line 13 and the weight W of the power line 13. The installation position A of the camera 17 on tower 11 is the coordinates of the worker 15 when the support point L is the origin, the horizontal direction is the x-axis and the vertical direction is the y-axis, more specifically the coordinates (a,b) of the computer 16 held by the worker 15.

[0026] When the sag of the electric wire 13 shown in Figure 5 is defined as the target sag d, the horizontal sag dL of the electric wire 13 with respect to the support point L is expressed by the distance between the horizontal plane passing through the support point L and position D. The pressure at position D is (n, dL). The x-coordinate n of position D can be calculated by equation (1) shown in Figure 6. The horizontal sag dL, which is the y-coordinate of position D, can be calculated by equation (2) shown in Figure 7. Equation (1) also uses the catenary number C. This catenary number C can be calculated by equation (3) shown in Figure 8. In equation (3), g is the acceleration due to gravity.

[0027] The target position 27 (Figures 3 and 4) for setting the sag of the electric wire 13 to the target sag is the position corresponding to point B when the electric wire 13 is viewed from the camera 17 installation position A in Figure 5, with the sag set to the target sag d. This point B is the point of contact between the electric wire 13 and the tangent L2, which is in contact with the electric wire 13 and passes through installation position A. The tangent L2 is expressed by equation (4) shown in Figure 9. The slope k in equation (4) can be calculated by equation (5) shown in Figure 10. The coordinates (xB, yB) of point B can be expressed by equation (6) shown in Figure 11.

[0028] Computer 16 determines the coordinates (xB, yB) of point B on the tangent line L2. Computer 16 determines the straight line L3 shown in Figure 12, which connects the installation position A and the support point H, and further determines the length of the perpendicular line segment L4 extending from point B to line L3. Computer 16 converts the length of line segment L4 into a distance on the display 18 based on the number of pixels on the display 18, and displays the target position 27 at a position lower than the aiming reticle 23 on the display 18 by the above distance. As a result, the target position 27 is displayed on the display 18, for example, as shown in Figures 3 and 4.

[0029] <Power line sag observation program> Next, I will explain the wire sag observation program. The wire sag observation program is designed to cause computer 16 to perform targeting display processing, input processing, and target display processing.

[0030] The above targeting display process displays the targeting reticle 23 on the display 18, superimposed on the image captured by the camera 17. The input process described above receives the information mentioned above. This information includes the target sag d of the power line 13, the specifications of the power line 13, the span length S between tower 11 and tower 12, the height difference h between the support point L of the power line 13 on tower 11 and the support point H of the power line 13 on tower 12, and the installation position A of the camera 17 on tower 11.

[0031] The above target display process displays the target position 27 on the display 18 to adjust the power line 13 to the target sag. Specifically, when the camera 17 is pointed from the tower 11 to the support point H of the power line 13 on the tower 12, the aiming reticle 23 is aligned with the support point H, and the target position 27, based on the input information, is superimposed on the image.

[0032] <Method for observing wire sag> Next, we will explain the method for observing wire sag. In the wire sag observation method, the camera 17 and display 18 of the computer 16 are used to display an image of the wire 13 taken by the camera 17 on the display 18, and a target position 27 for adjusting the wire 13's sag to a target sag is superimposed on the image.

[0033] Specifically, the camera 17 of the computer 16 is pointed from tower 11 to tower 12 to photograph the power lines 13. The target reticle 23 is displayed on the display 18, superimposed on the image captured by the camera 17. Then, the camera 17 is pointed from tower 12 to the support point H of the power lines 13 on tower 12, thereby aligning the target reticle 23 with the support point H. At this time, based on the information input to the computer 16, the target position 27, based on the target reticle, is displayed on the display 18, superimposed on the image of the power lines 13 captured by the camera 17.

[0034] The above information includes the target sag d of the power line 13, the specifications of the power line 13, the span length S between tower 11 and tower 12, the height difference h between the support point L of the power line 13 on tower 11 and the support point H of the power line 13 on tower 12, and the installation position A of the camera 17 on tower 11.

[0035] According to the embodiment described in detail above, the following effects and advantages can be obtained. (1) When adjusting the sag of the power line 13 stretched between towers 11 and 12 to the target sag, the following procedure is performed. Specifically, the worker 15 takes a picture with the computer 16's camera 17 from tower 11 toward the support point H of the power line 13 on tower 12. As a result, the image of the power line 13 between towers 11 and 12, captured by the camera 17, is displayed on the computer 16's display 18. Furthermore, a targeting reticle 23 is displayed on the display 18 overlaid on that image.

[0036] Furthermore, various pieces of information are input into the worker's computer 16 to set the sag of the power line 13 to a target sag. This information includes the target sag d of the power line 13, the specifications of the power line 13, the span length S between tower 11 and tower 12, the height difference h between the support point L of the power line 13 on tower 11 and the support point H of the power line 13 on tower 12, and the installation position A of the camera 17 on tower 11.

[0037] When the aiming reticle 23 on the display 18 is aligned with the support point H of the power line 13 on the transmission tower 12, the display 18 displays a target position 27 for setting the sag of the power line 13 to the target sag, based on the information input to the computer 16. This target position 27 is based on the aiming reticle and is displayed superimposed on the image displayed on the display 18. At this time, the target position 27 is displayed on the display 18 based on the information above, and is therefore appropriately set as the position corresponding to the target sag of the power line 13.

[0038] Therefore, by winding up or unwinding the electric wire 13 with the winch 14 so that the electric wire 13 displayed on the display 18 is positioned corresponding to the target position 27, the slack of the electric wire 13 can be appropriately adjusted to the target slack.

[0039] (2) The support point H of the power line 13 on the transmission tower 12 is located higher than the support point L of the power line 13 on the transmission tower 11. The camera 17 of the computer 16 held by the worker 15 is positioned lower than the support point L of the power line 13 on the transmission tower 11. The worker 15 then points the camera 17 of the computer 16 towards the support point H of the transmission tower 12, thereby aligning the reticle 23 displayed on the computer 16's display 18 with the support point H of the transmission tower 12.

[0040] In this case, the image displayed on the display 18 makes it easier to see that the power line 13 is hanging down from the support point H of the transmission tower 12. When the reticle 23 displayed on the display 18 is aligned with the support point H of the power line 13 on the transmission tower 12, the target position 27 is displayed below the reticle 23. This makes it easier to understand the relative position of the power line 13 with respect to the target position 27.

[0041] (3) The computer 16 displays the target position 27 on the display 18 as follows: The computer 16 determines the coordinates of point B, which is the point of contact between the tangent line L2, which is tangent to the power line 13 with a target sag and passes through the camera 17 installation position A, and the power line 13. The computer 16 determines the straight line L3 connecting the camera 17 installation position A and the support point H of the power line 13 on the transmission tower 12. The computer 16 determines the length of the line segment L4 that extends from point B to the straight line L3 and is perpendicular to the straight line L3. The computer 16 converts the length of the line segment L4 into a distance on the display 18 based on the number of pixels on the display 18, and displays the target position 27 at a position lower than the aiming reticle 23 on the display 18 by the amount of the distance. This makes it possible to display the target position 27 for setting the sag of the power line 13 to the target sag at an appropriate position on the display 18.

[0042] The above embodiment can also be modified as follows, for example. The above embodiment and the following modifications can be combined and implemented to the extent that they do not contradict each other technically. The computer 16 does not necessarily have to have the camera 17 integrated, as is the case with personal computers such as notebooks and tablets, and portable computers such as smartphones; the camera 17 may be a separate unit.

[0043] Instead of worker 19 operating the winch 14 while looking at the display device 20, worker 15, who has a computer 16, may communicate instructions regarding the operation of the winch 14 to worker 19 via voice call or other means while looking at the display 18. In this case, worker 19 operates the winch 14 according to the instructions from worker 15.

[0044] • Worker 15 does not necessarily need to climb the tower 11. For example, worker 15 may not climb the tower 11, but instead photograph the power lines 13 with a camera 17 from the base of the tower 11. [Explanation of Symbols]

[0045] 11, 12… transmission towers 13...Electric wire 14…Winch 15…Worker 16… Computer 17…Camera 18…Display 19…Worker 20…Display device 21... Communications Department 22…Central Processing Unit 23... Aim 24…Horizontal line 25...Plumb line 26... yen 27…Target position

Claims

1. It comprises a camera, a display, and a control unit. The camera photographs a wire supported by a first wire support and a second wire support, which are spaced apart from each other. The display shows the image of the power line captured by the camera, In a wire sag observation device, the control unit displays a target position for adjusting the sag of the wire to a target sag on the display, superimposed on the image. The camera is directed from the first wire support to the second wire support to photograph the wire. The control unit displays a targeting reticle superimposed on the image on the display, while receiving information such as the target sag of the electric wire, the specifications of the electric wire, the span length between the first electric wire support and the second electric wire support, the height difference between the support point of the electric wire on the first electric wire support and the support point of the electric wire on the second electric wire support, and the installation position of the camera on the first electric wire support. When the camera is pointed towards the support point of the electric wire on the second electric wire support to align the targeting reticle with the support point of the electric wire on the second electric wire support, the control unit displays the target position based on the targeting reticle on the display based on the input information.

2. The support point of the electric wire in the second electric wire support is located at a higher position than the support point of the electric wire in the first electric wire support. The wire sag observation device according to claim 1, wherein the camera is installed at a position lower than the support point of the wire on the first wire support.

3. The wire sag observation device according to claim 2, wherein the control unit determines the point of contact of a tangent to the wire that is in contact with the wire and passes through the installation position of the camera, determines a straight line connecting the installation position of the camera and the support point of the wire on the second wire support, determines the length of a line segment that extends from the point of contact to the straight line and is perpendicular to the straight line, converts the length of the line segment into a distance on the display based on the number of pixels on the display, and displays the target position on the display at a position lowered by the distance from the aiming point.

4. A wire sag observation program that causes a computer to perform aiming display processing, input processing, and target display processing, which receives video from a camera that photographs a wire supported by a first wire support and a second wire support that are spaced apart from each other, and displays the input video on a display, The aforementioned targeting display process involves displaying a target on the display overlaid on the image, The input processing receives information such as the target sag of the electric wire, the specifications of the electric wire, the span length between the first electric wire support and the second electric wire support, the height difference between the support point of the electric wire on the first electric wire support and the support point of the electric wire on the second electric wire support, and the installation position of the camera on the first electric wire support. The target display process displays a target position on the display for adjusting the sag of the electric wire to a target sag, and the electric wire sag observation program displays the target position based on the input information superimposed on the image when the camera is aimed at the support point of the electric wire on the second electric wire support by pointing the camera from the first electric wire support to the support point of the electric wire.

5. A method for observing the sag of an electric wire, comprising a camera that photographs an electric wire supported by a first electric wire support and a second electric wire support separated by a distance from each other, and a display that displays the image of the electric wire captured by the camera, wherein a target position for adjusting the sag of the electric wire to a target sag is superimposed on the image on the display, The electric wire is photographed by directing the camera from the first electric wire support to the second electric wire support. A crosshair is displayed on the aforementioned display, superimposed on the aforementioned image. A method for observing wire sag, wherein when the camera is directed from the first wire support to the support point of the wire on the second wire support to align the aiming reticle with the support point, the target position based on the aiming reticle is displayed on the display based on information such as the target sag of the wire, the specifications of the wire, the span length between the first wire support and the second wire support, the height difference between the support point of the wire on the first wire support and the support point of the wire on the second wire support, and the installation position of the camera on the first wire support.

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