What Is a Resection?

The resection refers to setting up a station only at the point to be determined, observing a horizontal angle A to two known control points, and calculating the coordinates of the point to be determined, which is called the resection. Rendezvous surveying is a commonly used method for encrypting control points. It can set up stations on several known control points and observe the direction or distance to the to-be-determined point, or set stations on the to-be-determined point to observe the direction or distance Distance, and then calculate the coordinates of the point to be determined. The commonly used methods of resection are forward resection, rear rendezvous, side rendezvous, and free standing method.

As shown in the figure below, the coordinates of the three points A, B, and C are known.

The following formulas are used for the RBF:

In actual measurement, a total station is generally used to measure the three direction angles PA, PB, and PC. Calculate the following six variables based on these three orientation angles, and then substitute the above formula to calculate the coordinates of point P.

The total station measures three direction angles PA, PB and PC. The formula for calculating the P coordinate of a point based on these three directional angles is as follows: ^[1]

When point P is on the circumcircle of triangle ABC, , , will remain unchanged. In this way, the coordinates of point P will be infinite-any point on the circumscribed circle can be point P. At this time, when using the calculation formula to calculate the P coordinate of the point, an invalid solution may be obtained by dividing by zero.

When the point P is close to the circumscribed circle, a small observation error will cause a large deviation of the position of the point P. Therefore, the circumscribed circle of the triangle ABC is called a dangerous circle. During the resection, point P should be avoided to be close to the circle of danger.

Assume that the error in the observation of the horizontal azimuth is

, Then:

The positioning accuracy of point P is:

The orientation accuracy is:

In the above two formulas

Calculated according to the following formula

Note: When point P is on the circle of danger

Will be equal to zero, so the positioning accuracy and orientation accuracy will be infinite. ^[2]

The Zhengzhou-Xi'an (hereinafter referred to as Zhengxi) railway passenger dedicated line is one of the first three high-standard passenger dedicated lines under construction at a speed of 350 km / h. The track structure is an integral ballastless track. In order to meet the requirements of high smoothness, high comfort, high safety and maintenance-free, the relevant technical standards have reached today's international advanced level. The new Weinan elevated station of the Zhengzhou-Xi'an Passenger Dedicated Line (DIK415 + 547.6 DIK417 + 507.07) is located on the northern edge of the urban planning area of Weinan, on the south side of the Weihe Embankment and on the southwest side of the Weihe Shawang Highway Bridge. The design of the station adopts the viaduct structure, which is the first case in China.

Limitations of General Stakeout Methods in the Resection

After the establishment of a two-level control network (CP, CP), the Weinan elevated vehicle on the Zhengxi Passenger Dedicated Line

Figure 1 Schematic diagram of free standing stake out platform

The following construction survey work of the station bridge surface mainly includes: re-controlling the control network on a regular basis, stakeout of bored piles, stakeout sideline, stakeout pier, stakeout sideline, stakeout of cast-in-situ beam midline, adjustment of suspended irrigation formwork, deformation (Sedimentation) monitoring and so on. The methods for measuring and setting the plane position of general engineering buildings include: Cartesian coordinate method, polar coordinate method, angle intersection method, distance intersection method and so on. With the development of science and technology, measuring instruments are becoming more and more advanced, and the application of total stations in the field of engineering construction has become very popular. Generally, the surveying and setting of the plane position of buildings generally uses the total station polar coordinate method for stakeout. However, in order to avoid damage to the control points during construction and better protect the control points, the control network of linear engineering generally runs along the line and is arranged on both sides of the line. The control point of the wire is 100m to 200m from the center of the line. As shown in Figure 1, A, B, and C are control points. When it is necessary to stake out the edge of the platform in the foundation pit, if the polar coordinate method is used, then the instruments are installed at points A and B, and the foundation pit cannot be seen. At the four corners of the bearing platform, support wires need to be set up. Set up the instrument near the foundation pit, and then look back at point A or B, and then stake out the four points of P1, P2, P3, and P4. In this way, the source of error and work intensity are increased. In addition, the branch wire points are not checked, and the branch wire points set near the foundation pit are often destroyed, and the protection is not strong.

Introduction to Stakeout Method

(1) Stakeout method of measuring side and rendezvous

The Lewei TCA1800 total station is used for the construction and stakeout of the new Weinan station on the Zhengxi Passenger Dedicated Line. The angle measurement accuracy is 1 , and the distance measurement accuracy is 1ppm + 2ppm. The LeicaTC series total station has a rear intersection in its own program (free Setting method). The specific steps are as follows: level the instrument at any point P select the resection program enter any point P point name enter the information of known point A (point name, coordinate value) back to the known point A And ranging turn right backsight of known point A and ranging enter information of known point B (point name, coordinate value) turn left backsight of known point B and ranging turn right backsight of known point B and Ranging Set P point as the measuring station Measure or stake out the point.

(2) Accuracy analysis of point setting out

The formula for point stakeout accuracy analysis is:

Through accuracy analysis, we can find that: 1) When = 90 °, the accuracy of the rendezvous is the best; 2) When the length of the rendezvous is 3 or more, the accuracy can be guaranteed. The steps in this article only mention the situation of backsighting two known points. The Leica TCA1800 total station can backsight several at the same time, and up to 10 known points can be backsighted to increase observation conditions and improve accuracy.

Resection research conclusions

The advantages of the free set-up construction and setting-out by distance measurement and resection method are as follows:

1) Freely set up stations are not restricted by known points. It is especially prominent in the work of setting out the sidelines of the foundation in the foundation pit, the sidelines of the staking slab, adjusting the suspension irrigation formwork, the staking out of the pier, and the sizing of the cast-in-place beam.

2) No need to center the instrument, only the total station needs to be leveled, saving time and labor intensity;

3) The arrangement of branch wires is reduced, and the lofting accuracy is improved to a certain extent. With the increase of engineering difficulty, engineering and technical personnel should not only pay attention to the accuracy of control measurement, but also pay attention to the improvement of stakeout accuracy. ^[3]