Sag measuring device and measuring method for adjustable catwalk bearing cable based on GNSS (Global Navigation Satellite System) technology

Abstract

The invention discloses a sag measuring device and measuring method for an adjustable catwalk bearing cable based on the GNSS technology, the measuring device comprises the catwalk bearing cable, an upper frame, a lower frame, a pulley block, a sleeve, an adjusting screw rod and the like, a GNSS receiver is installed at the top of the upper frame, and measurement data can be transmitted to a controller in real time; and a universal prism is mounted at the bottom of the upper frame, so that the measurement result of the GNSS method can be checked. The measuring device adjusts the distance between the two pulley blocks to be matched with the size of the catwalk bearing cable through the adjusting screw rod, an instruction is given through the controller, the measuring device slides in the direction of the catwalk bearing cable, and after the measuring device slides to the midspan, the sag of the midspan catwalk bearing cable is calculated according to the elevation transmitted to the controller. According to the invention, the problem that measurement personnel cannot carry out measurement operation on the catwalk bearing cable is effectively solved, and meanwhile, the problems that measurement of the catwalk bearing cable sag by a traditional electro-optical distance measurement method is greatly influenced by atmospheric refraction and a measurement device cannot be reused are solved.

Description

Technical Field

[0001] The invention relates to the technical field of construction measurement of catwalk load-bearing cables, and in particular to an adjustable catwalk load-bearing cable sag measurement device and a measurement method based on GNSS technology. Background Art

[0002] Catwalks are important aerial walkways and work platforms, used for erection, measurement, and cable adjustment of main cable strands. Catwalk load-bearing cables are the main load-bearing components of the catwalk system. When erecting catwalk load-bearing cables, it is necessary to observe the sag at the mid-span of the catwalk load-bearing cables. The mid-span position is usually located above canyons and rivers, and surveyors cannot reach the mid-span position of the catwalk load-bearing cables for measurement. In addition, the sag measurement device of the catwalk load-bearing cables is usually a fixed structure, which cannot adapt to catwalk load-bearing cables of various sizes and cannot be reused.

[0003] In the related art, the catwalk load-bearing cable measurement usually uses a pulley to carry the measuring prism to the middle of the span, and then uses the photoelectric ranging method to measure the prism to calculate the sag of the catwalk load-bearing cable. The Chinese utility model patent application number 202122790189.7 discloses a wireless remote control prism displacement measurement device for catwalk cable erection, which can realize the remote control displacement of the measuring device, but the size of the device is fixed and cannot be reused, and it cannot solve the problem of low measurement accuracy due to atmospheric refraction when measuring the sag of the catwalk load-bearing cable during the day. Summary of the invention

[0004] The first purpose of the present invention is to provide an adjustable catwalk load-bearing cable sag measuring device based on GNSS technology, which can effectively solve the problem of catwalk load-bearing cable sag measurement based on GNSS measurement technology, and adapt to catwalk load-bearing cables of various sizes by adjusting the distance between two pulley blocks, thereby solving the problem that the measuring device cannot be reused.

[0005] The second object of the present invention is to provide a method for measuring the sag of an adjustable catwalk load-bearing cable based on GNSS technology.

[0006] The first object of the present invention is achieved by: An adjustable sag measurement device for a catwalk load-bearing cable based on GNSS technology, characterized in that it includes: a catwalk load-bearing cable, an upper frame, a lower frame, a pulley block, a sleeve, an adjusting screw, a compression spring, a transmission shaft, a receiving system, a power system, a control system, a GNSS receiver, a prism rod, a universal prism, and a controller. The cross-sectional shapes of the upper frame and the lower frame are the same and are both in the shape of "凵". The openings of the upper frame and the lower frame face each other and are mutually nested to form a closed box body. Catwalk load-bearing cable holes for the catwalk load-bearing cable to pass through are provided on the front and rear plates of the lower frame. A sleeve with internal threads is provided in the middle of the box cavity. The two pulley blocks are exactly the same and symmetric left and right. Pulley block shaft holes with the same size as the sleeve are provided in the middle of each pulley block. The two pulley blocks are tightly sleeved into the sleeve from the left and right ends of the sleeve through the pulley block shaft holes, and clamp the catwalk load-bearing cable from the left and right ends. A compression spring is installed in the middle of the sleeve. A nut is provided at the rear of the adjusting screw. The longer screw rods at the inner ends of the two identical adjusting screws are screwed into the sleeve from the left and right ends of the sleeve. The ends of the long ends of the two adjusting screws abut against the left and right ends of the compression spring. The nuts on each adjusting screw abut against the outer side walls of the corresponding pulley blocks from the outside. Transmission shafts are sleeved beside the nuts on the inner sides of the shorter screw rods at the outer ends of each adjusting screw. The end of the shorter screw rod at the outer end of the adjusting screw on the right passes through the corresponding round holes at the upper end of the lower frame and the lower end of the upper frame outward. That is, the two adjusting screws connect the upper frame and the lower frame into one body, and the two adjusting screws and the sleeve are horizontally mounted on the upper frame and the lower frame together. A GNSS receiver is provided on the top of the upper frame. The GNSS receiver can obtain the three-dimensional coordinates of the measurement device at the position where the catwalk load-bearing cable is located in real time and send the real-time three-dimensional coordinates to the controller. The receiving system, the control system, and the power system are respectively fixedly installed on the bottom plate in the lower frame. The receiving system is used to receive the signals transmitted from the controller and transmit the decoded signals to the control system. The power system provides electrical energy for the entire measurement device. The control system can convert electrical energy into kinetic energy and transmit it to the transmission shaft through wires to control the operation of the sleeve, realizing the sliding of the measurement device on the catwalk load-bearing cable. The controller is used to transmit signals to the receiving system, control the sliding actions of the measurement device such as moving forward, backward, and stopping, and can receive the measurement data of the GNSS receiver in real time to realize the real-time display of the sag of the catwalk load-bearing cable. A prism rod is fixedly installed at the bottom of the lower frame, and a universal prism is installed at the end of the prism rod. The measurement data of the GNSS receiver is checked by observing the universal prism through the total station electro-optical distance measurement method to ensure that the erection accuracy of the catwalk load-bearing cable meets the requirements.

[0007] The second object of the present invention is achieved as follows: An adjustable sag measurement method for a catwalk load-bearing cable based on GNSS technology, characterized in that the specific steps are as follows: A. Assemble the measuring device on the catwalk load-bearing cable to be observed: insert two pulley blocks from the left and right ends of the casing to the appropriate position, install a compression spring in the middle of the casing, screw two adjusting screws from the left and right ends of the casing, and the long ends of the two adjusting screws are against the left and right ends of the compression spring, and then adjust the distance between the two pulley blocks to match the size of the catwalk load-bearing cable; install the upper frame and the lower frame, install the GNSS receiver on the top of the upper frame, measure the vertical height h1 from the center of the GNSS receiver to the center of the catwalk load-bearing cable, and input h1 into the controller, fix the receiving system, control system and power system on the bottom plate in the lower frame, and connect them to the casing through the transmission shaft, fix the prism rod at the bottom of the lower frame, install the universal prism at the other end of the prism rod, and measure the vertical height h2 from the center of the universal prism to the center of the catwalk load-bearing cable 1; B. Input the vertical height h1 from the center of the GNSS receiver to the center of the catwalk load-bearing cable into the GNSS receiver, and calculate the average value of the three-dimensional coordinates of the position of the catwalk load-bearing cable obtained by the GNSS receiver in real time for 30 consecutive seconds as the center coordinates of the catwalk load-bearing cable at that position, and obtain the center elevation H1 of the catwalk load-bearing cable at that position; C. Set up a total station at the control point on the shore, measure and input the instrument height, correct the total station with meteorological parameters such as temperature, humidity and air pressure, input the vertical height h2 from the center of the universal prism to the center of the catwalk load-bearing cable in the total station, and calculate the center elevation H2 of the catwalk load-bearing cable based on the vertical angle and slant distance of the universal prism observed by the total station, the vertical height h2 from the center of the universal prism to the center of the catwalk load-bearing cable, the instrument height and the control point elevation; D. When measuring the sag of the catwalk load-bearing cable, it is only necessary to adjust the measuring device to match the size of the catwalk load-bearing cable, issue a command through the controller, and the receiving system transmits the command to the control system after receiving the command. The control system then issues a command to the transmission shaft after processing, and the transmission shaft drives the sleeve and the two pulley blocks to rotate together, so that the measuring device slides along the direction of the catwalk load-bearing cable; E. The GNSS receiver transmits the real-time three-dimensional coordinates to the controller. The controller controls the movement of the measuring device according to the real-time three-dimensional coordinates and determines whether the measuring device slides to the position to be observed in the span. After sliding to the position to be observed, the measuring device stops. F. The verticality of the catwalk load-bearing cable at that location can be obtained according to the real-time three-dimensional coordinates on the controller; G. When the temperature is stable at night, the effect of atmospheric refraction on the measurement accuracy of the photoelectric ranging method can be ignored, and then the sag measurement verification test of the catwalk load-bearing cable using the GNSS method and the photoelectric ranging method can be carried out; H. After three consecutive days of verification, four time periods were selected every day when the temperature was stable at night. The difference between the center elevation H1 of the load-bearing cable 1 observed by the GNSS method and the center elevation H2 of the catwalk load-bearing cable calculated by the photoelectric ranging method was less than ±20mm. According to the requirements of the specification, the relative error of the elevation of each catwalk load-bearing cable in the mid-span was controlled within ±30mm. It can be seen that the verticality measurement accuracy of the catwalk load-bearing cable 1 based on the GNSS method can meet the requirements of the specification.

[0008] In order to solve the problem of low measurement accuracy caused by atmospheric refraction when measuring the verticality of the catwalk load-bearing cables during the day by the photoelectric ranging method, the present invention combines the pulley with the GNSS (Global Navigation Satellite System) measurement technology to realize the real-time measurement of the catwalk load-bearing cables by GNSS technology. However, it is also necessary to verify the accuracy of the GNSS measurement technology. At the same time, to ensure that the measuring device slides smoothly on the catwalk load-bearing cables, the weight of the GNSS receiver above the catwalk load-bearing cables should not exceed the weight below the catwalk load-bearing cables.

[0009] After verification, the measurement accuracy of domestic GNSS receivers is constantly improving, and the trend of lightweight is obvious. At present, the plane measurement accuracy of domestic GNSS receivers can reach 8mm±0.5ppm, and the elevation measurement accuracy can reach 15mm±0.5ppm. The measurement accuracy of GNSS receivers is much higher than the vertical measurement accuracy of catwalk load-bearing cables. For example: the size of the Beidou Haida series domestic GNSS receiver is about 13.2cm×6.7cm, and the built-in radio including built-in batteries and band antenna weighs less than 0.7kg.

[0010] Compared with the prior art, the advantages of the present invention are: 1. The controller controls the measuring device to slide to the mid-span position on the catwalk load-bearing cable. The GNSS receiver can obtain the three-dimensional coordinates of the position of the measuring device on the catwalk load-bearing cable in real time and transmit the three-dimensional coordinates to the controller. The controller displays the verticality of the catwalk load-bearing cable in real time according to the three-dimensional coordinates. The universal prism at the bottom of the measuring device is observed by the photoelectric ranging method of the total station to obtain the verticality of the catwalk load-bearing cable where the measuring device is located. The real-time data of the GNSS receiver is checked to ensure that the erection accuracy of the catwalk load-bearing cable meets the requirements; 2. Two pulley blocks and two adjusting screws are respectively provided at both ends of the casing. The adjusting screw combined with the compression spring can control the distance between the two pulley blocks, so that the adjustable measuring device can adapt to the sag measurement of catwalk load-bearing cables of different sizes, solving the problem that the traditional measuring device cannot be reused; 3. The GNSS method is used to measure the sag of the catwalk load-bearing cables. The sag measurement accuracy of the catwalk load-bearing cables can meet the requirements of the specifications. Compared with the traditional photoelectric ranging method for measuring the sag of the catwalk load-bearing cables, the observation window period is increased and the waiting time for measurement is reduced; 4. When the environment is stable at night, the photoelectric ranging method can be used to observe the verticality of the catwalk load-bearing cables to verify the verticality results of the catwalk load-bearing cables observed by the GNSS method, which greatly improves the accuracy.

[0011] The present invention is based on GNSS measurement technology, which effectively solves the problem that surveyors cannot go to the catwalk load-bearing cables to perform measurement operations. At the same time, it solves the problem that the vertical measurement of the catwalk load-bearing cables using the traditional photoelectric ranging method is greatly affected by atmospheric refraction and the measuring device cannot be reused. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 Schematic diagram of the appearance structure of the measuring device in this embodiment; Figure 2 is a schematic diagram of the elevation structure of the measuring device in this embodiment; Figure 3 This is a schematic diagram of the structure of the pulley block, sleeve and compression spring in this embodiment; Figure 4 Schematic diagram of the structure of the adjusting screw and the compression spring in this embodiment. DETAILED DESCRIPTION

[0013] The present invention is further described in detail below with reference to the accompanying drawings and embodiments.

[0014] A sag measurement device for an adjustable catwalk load-bearing cable based on GNSS technology, comprising: a catwalk load-bearing cable 1, an upper frame 2, a lower frame 3, pulley blocks 4, a sleeve 5, adjusting screws 6, compression springs 7, a transmission shaft 8, a receiving system 9, a power system 10, a control system 11, a GNSS receiver 12, a prism rod 13, a universal prism 14, and a controller 15. The cross-sectional shapes of the upper frame 2 and the lower frame 3 are the same and are both in the shape of "凵". The openings of the upper frame 2 and the lower frame 3 face each other and are mutually embedded to form a closed box body. Catwalk load-bearing cable holes 31 for the catwalk load-bearing cable 1 to pass through are provided on the front and rear plates of the lower frame 3. A sleeve 5 with internal threads is provided in the middle of the cavity 16. The two pulley blocks 4 are exactly the same and symmetric left and right. Pulley block shaft holes 41 with the same size as the sleeve 5 are provided in the middle of each pulley block 4. The two pulley blocks 4 are tightly sleeved into the sleeve 5 from the left and right ends of the sleeve 5 through the pulley block shaft holes 41 and clamp the catwalk load-bearing cable 1 from the left and right ends. A compression spring 7 is installed in the middle of the sleeve 5. A nut 61 is provided at the rear of the adjusting screw 6. The longer screw rods 62 at the inner ends of the two identical adjusting screws 6 are screwed into the sleeve 5 from the left and right ends of the sleeve 5. The ends of the longer screw rods 62 of the two adjusting screws 6 abut against the left and right ends of the compression spring 7. The nut 61 on each adjusting screw 6 abuts against the outer side wall of the corresponding pulley block 4 from the outside. A transmission shaft 8 is sleeved on the inner side of the shorter screw rod 63 at the outer end of each adjusting screw 6 and beside the nut 61. The end of the shorter screw rod 63 at the outer end of the adjusting screw 6 on the right passes through the corresponding round holes at the upper end of the lower frame 3 and the lower end of the upper frame 2 outwards, that is, the two adjusting screws 6 connect the upper frame 2 and the lower frame 3 into one body, and the two adjusting screws 6 and the sleeve 5 are horizontally mounted on the upper frame 2 and the lower frame 3 together. A GNSS receiver 12 is provided on the top of the upper frame 2. The GNSS receiver 12 can obtain the three-dimensional coordinates of the measurement device at the position where the catwalk load-bearing cable 1 is located in real time and send the real-time three-dimensional coordinates to the controller 15. The receiving system 9, the control system 11, and the power system 10 are respectively fixedly installed on the bottom plate in the lower frame 3. The receiving system 9 is used to receive the signals transmitted from the controller 15 and transmit the signals to the control system 11 after decoding. The power system 10 provides electrical energy for the entire measurement device. The control system 11 can convert electrical energy into kinetic energy and transmit it to the transmission shaft 8 through wires to control the operation of the sleeve 5, realizing the sliding of the measurement device on the catwalk load-bearing cable 1. The controller 15 is used to transmit signals to the receiving system 9, control the sliding actions such as the forward, backward, and stop of the measurement device, and can receive the measurement data of the GNSS receiver 12 in real time, realizing the real-time display of the sag of the catwalk load-bearing cable 1. A prism rod 13 is fixedly installed at the bottom of the lower frame 3. A universal prism 14 is installed at the end of the prism rod 13. The universal prism 14 is observed by the total station electro-optical distance measurement method to check the measurement data of the GNSS receiver 12 to ensure that the erection accuracy of the catwalk load-bearing cable 1 meets the requirements.

[0015] A method for measuring the sag of an adjustable catwalk load-bearing cable based on GNSS technology, the specific steps are as follows: A. Assemble the measuring device on the catwalk load-bearing cable 1 to be observed: insert the two pulley blocks 4 from the left and right ends of the sleeve 5 to the appropriate position, install the compression spring 7 in the middle of the sleeve 5, screw in the two adjusting screws 6 from the left and right ends of the sleeve 5, and the ends of the long ends 62 of the two adjusting screws 6 are against the left and right ends of the compression spring 7, and then adjust the distance between the two pulley blocks 4 to match the size of the catwalk load-bearing cable 1; if the adjusting screw 6 is screwed in, the compression spring 7 is squeezed, and the distance between the two pulley blocks 4 becomes smaller, which is suitable for the sag measurement of the catwalk load-bearing cable 1 of a smaller size; if the adjusting screw 6 is screwed out, the compression spring 7 is loosened, and the distance between the two pulley blocks 4 becomes larger, which is suitable for the sag measurement of the catwalk load-bearing cable 1 of a smaller size. The verticality of the load-bearing cable 1 of the larger catwalk should be measured; the upper frame 2 and the lower frame 3 are installed, the GNSS receiver 12 is installed on the top of the upper frame 2, the vertical height h1 from the center of the GNSS receiver 12 to the center of the catwalk load-bearing cable 1 is measured, and h1 is input into the controller 15, the receiving system 9, the control system 11 and the power system 10 are fixedly installed on the bottom plate in the lower frame 3, and connected to the sleeve 5 through the transmission shaft 8, the prism rod 13 is fixedly installed at the bottom of the lower frame 3, the universal prism 14 is installed at the other end of the prism rod 13, and the vertical height h2 from the center of the universal prism 14 to the center of the catwalk load-bearing cable 1 is measured; B. Input the vertical height h1 from the center of the GNSS receiver 12 to the center of the catwalk load-bearing cable 1 into the GNSS receiver 12, calculate the average value of the three-dimensional coordinates of the position of the catwalk load-bearing cable 1 obtained by the GNSS receiver 12 in real time for 30 consecutive seconds, and use it as the center coordinate of the catwalk load-bearing cable 1 at that position, and obtain the center elevation H1 of the catwalk load-bearing cable 1 at that position; C. Set up a total station at a control point on the shore, measure and input the instrument height, correct the total station for meteorological parameters such as temperature, humidity and air pressure, input the vertical height h2 from the center of the universal prism 14 to the center of the catwalk load-bearing cable 1 in the total station, and calculate the center elevation H2 of the catwalk load-bearing cable 1 based on the vertical angle and slant distance of the universal prism 14 observed by the total station, the vertical height h2 from the center of the universal prism 14 to the center of the catwalk load-bearing cable 1, the instrument height and the control point elevation; D. When measuring the sag of the catwalk load-bearing cable 1, it is only necessary to adjust the measuring device to match the size of the catwalk load-bearing cable 1, and issue a command through the controller 15. After receiving the command and decoding the signal, the receiving system 9 transmits it to the control system 11. After processing, the control system 11 issues a command to the transmission shaft 8, and the transmission shaft 8 drives the sleeve 5 and the two pulley blocks 4 to rotate together, so that the measuring device slides along the direction of the catwalk load-bearing cable 1; E. The GNSS receiver 12 transmits the real-time three-dimensional coordinates to the controller 15. The controller 15 controls the movement of the measuring device according to the real-time three-dimensional coordinates to determine whether the measuring device slides to the position to be observed in the span. After sliding to the position to be observed, the measuring device stops; F. The sag of the catwalk load-bearing cable 1 at that position can be obtained according to the real-time three-dimensional coordinates on the controller 15; G. When the temperature is stable at night, the effect of atmospheric refraction on the measurement accuracy of the photoelectric ranging method can be ignored, and then the sag measurement verification test of the catwalk load-bearing cable using the GNSS method and the photoelectric ranging method can be carried out; H. After three consecutive days of verification, four time periods were selected every day when the temperature was stable at night. The difference between the center elevation H1 of the catwalk load-bearing cable 1 observed by the GNSS method and the center elevation H2 of the catwalk load-bearing cable 1 calculated by the photoelectric ranging method was less than ±20mm. According to the requirements of the specification, the relative error of the elevation of each catwalk load-bearing cable 1 in the mid-span was controlled within ±30mm. It can be seen that the verticality measurement accuracy of the catwalk load-bearing cable 1 based on the GNSS method can meet the requirements of the specification.

[0016] Although the present invention is disclosed as above, the present invention is not limited thereto. Any person skilled in the art can make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the scope defined by the claims.

Claims

1. A sag measurement device for an adjustable catwalk load-bearing cable based on GNSS technology, characterized in that: Including: The catwalk load-bearing cable, upper frame, lower frame, pulley block, sleeve, adjusting screw, compression spring, transmission shaft, receiving system, power system, control system, GNSS receiver, prism rod, universal prism, controller. The cross-sectional shapes of the upper frame and the lower frame are the same and are both in the shape of "凵". The openings of the upper frame and the lower frame face each other and are fitted together to form a closed box body. Catwalk load-bearing cable holes for the catwalk load-bearing cable to pass through are provided on the front and rear plates of the lower frame. A sleeve with internal threads is provided in the middle of the cavity of the box. The two pulley blocks are identical and symmetric left and right. Pulley block shaft holes with the same size as the sleeve are provided in the middle of each pulley block. The two pulley blocks are tightly sleeved into the sleeve from the left and right ends of the sleeve through the pulley block shaft holes and clamp the catwalk load-bearing cable from the left and right ends. A compression spring is installed in the middle of the sleeve. A nut is provided at the rear of the adjusting screw. The longer screws at the inner ends of the two identical adjusting screws are screwed into the sleeve from the left and right ends of the sleeve. The ends of the long ends of the two adjusting screws abut against the left and right ends of the compression spring. The nut on each adjusting screw abuts against the outer wall of the corresponding pulley block from the outside. A transmission shaft is sleeved on the inner side of the shorter screw at the outer end of each adjusting screw and beside the nut. The end of the shorter screw at the outer end of the adjusting screw on the right passes through the corresponding round holes at the upper end of the lower frame and the lower end of the upper frame. That is, the two adjusting screws connect the upper frame and the lower frame into one body, and the two adjusting screws and the sleeve are horizontally mounted on the upper frame and the lower frame together. A GNSS receiver is provided on the top of the upper frame. The GNSS receiver can obtain the three-dimensional coordinates of the measuring device at the position where the catwalk load-bearing cable is located in real time and send the real-time three-dimensional coordinates to the controller. The receiving system, control system and power system are respectively fixedly installed on the bottom plate in the lower frame. The receiving system is used to receive the signals transmitted from the controller, decode the signals and transmit them to the control system. The power system provides electrical energy for the entire measuring device. The control system can convert electrical energy into kinetic energy and transmit it to the transmission shaft through wires to control the operation of the sleeve, realizing the sliding of the measuring device on the catwalk load-bearing cable. The controller is used to transmit signals to the receiving system, control the sliding actions such as the forward, backward and stop of the measuring device, and can receive the measurement data of the GNSS receiver in real time, realizing the real-time display of the sag of the catwalk load-bearing cable. A prism rod is fixedly installed at the bottom of the lower frame. A universal prism is installed at the end of the prism rod. The universal prism is observed by the total station electro-optical distance measurement method to check the measurement data of the GNSS receiver to ensure that the erection accuracy of the catwalk load-bearing cable meets the requirements.

2. A method for measuring the sag of an adjustable catwalk load-bearing cable based on GNSS technology, characterized in that: The specific steps are as follows: A. Assemble the measuring device on the catwalk load-bearing cable to be observed: insert two pulley blocks from the left and right ends of the casing to the appropriate position, install a compression spring in the middle of the casing, screw two adjusting screws from the left and right ends of the casing, and the long ends of the two adjusting screws are against the left and right ends of the compression spring, and then adjust the distance between the two pulley blocks to match the size of the catwalk load-bearing cable; install the upper frame and the lower frame, install the GNSS receiver on the top of the upper frame, measure the vertical height h1 from the center of the GNSS receiver to the center of the catwalk load-bearing cable, and input h1 into the controller, fix the receiving system, control system and power system on the bottom plate in the lower frame, and connect them to the casing through the transmission shaft, fix the prism rod at the bottom of the lower frame, install the universal prism at the other end of the prism rod, and measure the vertical height h2 from the center of the universal prism to the center of the catwalk load-bearing cable 1; B. Input the vertical height h1 from the center of the GNSS receiver to the center of the catwalk load-bearing cable into the GNSS receiver, and calculate the average value of the three-dimensional coordinates of the position of the catwalk load-bearing cable obtained by the GNSS receiver in real time for 30 consecutive seconds as the center coordinates of the catwalk load-bearing cable at that position, and obtain the center elevation H1 of the catwalk load-bearing cable at that position; C. Set up a total station at the control point on the shore, measure and input the instrument height, correct the total station with meteorological parameters such as temperature, humidity and air pressure, input the vertical height h2 from the center of the universal prism to the center of the catwalk load-bearing cable in the total station, and calculate the center elevation H2 of the catwalk load-bearing cable based on the vertical angle and slant distance of the universal prism observed by the total station, the vertical height h2 from the center of the universal prism to the center of the catwalk load-bearing cable, the instrument height and the control point elevation; D. When measuring the sag of the catwalk load-bearing cable, it is only necessary to adjust the measuring device to match the size of the catwalk load-bearing cable, issue a command through the controller, and the receiving system transmits the command to the control system after receiving the command. The control system then issues a command to the transmission shaft after processing, and the transmission shaft drives the sleeve and the two pulley blocks to rotate together, so that the measuring device slides along the direction of the catwalk load-bearing cable; E. The GNSS receiver transmits the real-time three-dimensional coordinates to the controller. The controller controls the movement of the measuring device according to the real-time three-dimensional coordinates and determines whether the measuring device slides to the position to be observed in the span. After sliding to the position to be observed, the measuring device stops. F. The verticality of the catwalk load-bearing cable at that location can be obtained according to the real-time three-dimensional coordinates on the controller; G. When the temperature is stable at night, the effect of atmospheric refraction on the measurement accuracy of the photoelectric ranging method can be ignored, and then the sag measurement verification test of the catwalk load-bearing cable using the GNSS method and the photoelectric ranging method can be carried out; H. After three consecutive days of verification, four time periods were selected every day when the temperature was stable at night. The difference between the center elevation H1 of the load-bearing cable 1 observed by the GNSS method and the center elevation H2 of the catwalk load-bearing cable calculated by the photoelectric ranging method was less than ±20mm. According to the requirements of the specification, the relative error of the elevation of each catwalk load-bearing cable in the mid-span was controlled within ±30mm. It can be seen that the verticality measurement accuracy of the catwalk load-bearing cable 1 based on the GNSS method can meet the requirements of the specification.

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