Ground elevation control survey

1. Basic requirements

The ground elevation control network in the survey area can be established by leveling and ranging elevation traverse method. Leveling can be divided into three classes and four classes, and ranging height traverse can replace the fourth class leveling. The survey control network is generally established by leveling method. The selection of scope and grade shall comply with the provisions of Table 4- 17.

Table 4- 17 Selection Requirements for Leveling Grade of Control Network in Survey Area

The primary control network of ground elevation in the survey area should be laid into a ring network, which can also be considered together with plane control. When encryption is carried out, it is laid into a network of attached lines or nodes, and branch lines are only allowed to be laid in mountainous areas. The median elevation error of the weakest point in each leveling network is not more than 2.5cm relative to the starting point.

See table 4- 18 for the main technical requirements of leveling. When calculating the difference between leveling points, L is the route length between leveling points; When calculating the closure difference between loop line and attached route, L is the total length of loop line or horizontal route. L units are all calculated in kilometers. N is the number of stations. The leveling branch line should not be greater than 0/3 of the total length of the attached route.

The technical requirements for leveling observation shall be attached in Table 4- 19.

Table 4- 18 Main Technical Requirements of Leveling

Table 4- 19 technical requirements for leveling observation

The third and fourth grades adopt strict adjustment procedures. When there are more than 20 loops in the leveling route, the total average error per kilometer calculated according to the closure difference of the route (loop) is Mδ≤20 mm, which is calculated according to the formula of urban measurement standard MW =.

The observation order of the third level is back-front-front-back, the fourth level is back-back-front-front, and the contour level is back-back-front-front. Even stations are used for third-class leveling. The original observation value should be printed when using the electronic notebook.

See Appendix D for the third and fourth class leveling records, and Appendix E for other leveling records.

Special circumstances: the local first-,second-and third-class leveling points are basically destroyed. In areas where the mining area is dominated by non-coal open-pit mining rights, the control points made in this field verification only meet the needs of mining rights verification and mining administration management, and the fourth-class leveling or super-leveling can be directly used for elevation fitting without joint leveling. When the accuracy is relaxed to the point where the error is not more than 0.25m in the weakest point elevation, the maximum error is 2 times. In extreme cases, the point where the error is more than 3 times is not used, and the elevation is not provided, which does not exceed110 of the total number of points. These control points are not shared with other departments.

2. Distance measuring elevation traverse

Instead of the fourth level, the photoelectric ranging elevation traverse should be opened and closed on the third level, and its side length is not more than 1 km. The maximum length of the elevation traverse shall not exceed the maximum length of the fourth-class leveling route.

When measuring the side length of elevation traverse, a range finder or total station not lower than level 2 shall be adopted, and the observation shall be made once every 1 and the reading shall be 4 times. The reading difference of 1 is not greater than 10 mm, and each station should read the temperature and pressure values. When using the total station, the meteorological constant can be put on the instrument. The difference between the vertical angle measurement and the index difference is not more than 7 ",and the difference between the opposite observation height difference is not more than 7", and d is the horizontal distance of ranging, in kilometers. The height reading of the instrument is 1mm, and the vertical angle is observed twice. The vertical angle is not greater than 15.

When calculating the height difference, the observation distance should be corrected by adding constant times constant and meteorological correction.

The meteorological correction adopts the parameters and calculation formulas provided by the instrument manufacturer and has been preset. When observing, input temperature and air pressure values, and the instrument will automatically correct. The addition constant and multiplication constant are corrected by the data identified by the instrument.

When each station is set, the one-way observation height difference H between adjacent stations is calculated as follows:

Study on the Technical Method Guide for Field Verification of Mining Rights in China

Where: h is the height difference (m) at both ends of the elevation traverse;

Di is the horizontal distance after meteorological correction (m);

K is the atmospheric refractive index (generally 0. 1 1 ~ 0. 14, if it is inconsistent, the experimental value can be used);

R0 is the average radius of curvature of the earth, which is generally 6369000m. Can be calculated according to latitude and projection plane;

I is the instrument height (m);

V is the height of the target (m);

Zi is the observation vertical angle (").

The median relative observation height difference (h 12) between adjacent stations is calculated as follows:

H 12=(h 1-h2)/2

The elevation difference of leveling points or other fixed points determined by distance measuring elevation traverse should be corrected by adding normal leveling surface, and the calculation method is the same as that of fourth-class leveling.

The measurement tolerance of elevation traverse at each point is shown in Table 4-20.

Table 4-20 Distance Measurement Height Traverse Measurement Tolerance

With the progress of measuring instruments, triangulation method is generally not applicable, and the results of trigonometric leveling used in the original control network are considered reasonable, and those whose accuracy reaches the current standard can be used.

See appendix f for the format of elevation traverse survey manual.

(2) Quasi-geoid refinement

China has CQ G2000 quasi-geoid model. The grid average gravity anomaly resolution in East China, Central China, South China, North China and some provinces and regions has reached 2.5 ′× 2.5 ′ density, and it can also reach 5 ′× 5 ′ in mountainous areas. It can meet the requirements of the field verification of mining rights on the accuracy of control points. It should be noted that the key to using quasi-geoid refinement is to have accurate geodetic height, but the geodetic height of WGS-84 cannot be adjusted by unconstrained adjustment, because the accuracy of ordinary single point positioning is very poor, and the geodetic height error is above 10 meter, while the quasi-geoid model can only know the abnormal height and normal height if it knows the position and geodetic height. Therefore, if we want to do quasi-geoleveling, we must carry out three-dimensional constraint adjustment in WGS-84. If you can't collect the starting point of WGS-84, you can't do it.

(3) Installation elevation

GPS survey is carried out in WGS-84 geocentric coordinate system, and the elevation it provides is geodetic height H, while leveling is based on the leveling origin, which is higher than the average sea level by H.. Because the height of the earth is observed by GPS, in order to determine the normal height, it is necessary to know the abnormal height data. In other words, to know the leveling height and geodetic height of the surrounding points, the normal height of the whole control network can be obtained by using a certain mathematical model. The distance from the quasi-geoid to the reference ellipsoid is called elevation anomaly and recorded as zeta. The relationship between the height of the earth and the normal height can be expressed as: h = hr+zeta. The so-called height fitting method is to use the principle that height anomalies have certain geometric correlation in a small range to solve normal height or height anomalies by mathematical methods.

The elevation anomaly is expressed as the following polynomial:

Zeroth polynomial: zeta ζ= A0

Linear polynomial: zeta = A0+a1db+a2dl.

Quadratic polynomial: zeta = A0+a1db+a2dl+a3db2+a4dl2+a5 dbdl.

(1) Scope of application. The elevation fitting method introduced above is a pure geometric method, so it is generally only suitable for areas with relatively gentle elevation anomalies (such as plain areas), and its fitting accuracy can reach less than one decimeter. The accuracy of this method is limited in areas where the height anomaly changes dramatically (such as mountainous areas), mainly because it is difficult to express the height anomaly characteristics of known points in these areas.

(2) Select a suitable known elevation anomaly point. The so-called known point elevation anomaly is generally obtained by leveling and geodetic height by GPS measurement. In practical work, GPS points are generally arranged on leveling points or leveling points. In order to obtain a good fitting result, it is required to use as many known points as possible, which should be evenly distributed and preferably surround the whole GPS network.

(3) The known points of elevation anomaly. If you want to use the zero-order term for elevation fitting, you need to determine 1 parameters, so you need 1 known points. If we want to use a polynomial to fit the elevation, we need more than three known points to determine three parameters. If we want to use quadratic polynomial for elevation fitting, we need more than 6 known points to determine 6 parameters. We require "elevation fitting, with no less than 6 starting points and a point of 50 square kilometers". These points should be distributed around the survey area, preferably a little in the middle. At least three. The elevation grade of the starting point, the lowest is the contour elevation, and the triangular elevation cannot be used as the starting point.

(4) Special circumstances

The distribution of mining rights in the western region is scattered, with few control points, and some need a mine as a small survey area. It is difficult to check the known points, leveling has no starting point, and only a few control points have high leveling. This problem can be solved by using the detailed baseline solution of unconstrained adjustment. The settlement and displacement of points will cause the change of side length and height difference of control points. The earth height in the detailed solution is wrong, but its height difference is right, and the ratio of baseline side length is right, because the height anomaly values in a small range are equal. Leveling adjustment can be carried out by using the baseline height difference and baseline side length in the detailed calculation of baseline. If it meets the requirements of leveling, it can be proved that the starting point is correct and the normal height of each point can be obtained. This can solve the problem of insufficient starting point inspection and elevation fitting points in small survey area.