Before erecting any structure or object on the ground, it is necessary to perform a survey justification. The survey substantiation includes determining the coordinates of terrain points, calculating elevations, as well as setting the position in the local coordinate system. Such a justification may be based on a theodolite traverse.
Geodetic works
Geodetic work includes many items, including the creation of a survey justification of the area. This work is preceded by the construction of a theodolite traverse with measurements of horizontal angles and side lengths, as well as the calculation of point coordinates.
With the help of a theodolite traverse, you can transfer the coordinates of control points to all other points. This is necessary for the subsequent construction of buildings on this site or the use of the territory for economic purposes.
What is a traverse
Theodolite traverse is a broken line built on the ground with horizontal angles and side lengths measured at it. This data is later used to calculate the coordinates and bearing angles in the calculation sheet.
Building a theodolite traverse consists of two stages. This is:
- Building a polyline on the ground and carrying out field work;
- Mathematical equalization of the move and performing cameral processing of the results.
Both stages are carried out strictly according to the established regulations in compliance with the rules and regulations. The accuracy of building and processing the results ensures the correct operation and subsequent safety of the construction or any other activity on the ground.
Types of traverses
Theodolite traverse is an open or closed polyline. Depending on the form of construction, there are three types of moves:
- Open-loop traverse based on two points with known coordinates and two directional angles.
- An open theodolite traverse based on one starting point and one directional angle - such a traverse is also called a hanging traverse.
- A closed polygonal traverse based on one point and one angle.
All three types have different accuracy of performance. The most preferable construction option will be a polygon, for the measurement control of which there is a separate method. The hanging traverse, tied to only one point of the geodetic network, has the lowest accuracy.
The choice of the type of creation of a theodolite traverse depends on the terrain conditions, the presence of a number of starting points and the type of furtheractivities in the territory.
Preparation for work on the ground
Before performing field work, it is necessary to carry out a preliminary survey of the area using available maps and topographic plans. It includes the study of natural conditions and relief, the search for available points of geodetic justification. It would also not be out of place to find out when the last time geodetic work took place on a given territory and what results were obtained as a result of their implementation.
In addition, it is necessary to select tools for subsequent work, as well as perform their verification to ensure the required accuracy.
Before starting work on a large-scale plan, a possible variant of the location of the points of the theodolite traverse is designed. The next step is to stake them out and check for good visibility.
Making a move
Theodolite traverse is laid on the ground with the obligatory condition of ensuring good visibility between the points. Otherwise, the items are located elsewhere.
The first step is to bind the theodolite traverse to the point of the geodetic network, carried out using a theodolite or total station with high accuracy. Snapping is the definition of the location of the polygon on the ground. The correctness of its execution will have an impact on the determination of all coordinates of the traverse.
Depending on the subsequent appointment, the points are fixed on the ground with temporary or permanent signs. The first ones arewooden stakes driven flush with the ground. In order to keep the exact location of the point, the center is indicated on the stakes. Next to such a temporary sign, as a rule, an identification element is installed - a gatehouse 15-20 centimeters high.
Permanent signs mark points whose location will be necessary for further work for a long time. In this case, more durable materials are used - monoliths or concrete pillars.
For a better orientation, the points of the move are signed: the number is indicated, as well as the distance from the first point.
Field work
After the waypoints have been marked, field work is done. These include taking various measurements and collecting data to solve the traverse calculation sheet.
Inside the theodolite traverse, side lengths and horizontal angles are measured. Work can be carried out using various tools, depending on their availability. At the same time, more modern devices will give more accurate results compared to outdated ones.
All measurements are made twice: forward and backward. The results of the two moves must match or differ by an amount equal to the allowable error. This process, adopted in geodesy, ensures high accuracy of work and reduces the influence of systematic and random errors.
Measuring angles and strokes
Horizontal angles are measured at each vertex using an electronic total station or an optical theodolite. deviceput on one of the points of the move, and on the two neighboring ones they place slats or poles. In this case, it is necessary to ensure that only right or left corners along the course are measured. In order to make it easy to control, in a schematic drawing, an outline of the situation of the area is parallel. An outline is an approximate image of the results of ongoing work, which is necessary for subsequent office calculations.
Angles are measured by the method of receptions, which consists in double control of the measurements. In this case, unacceptable errors are easy to detect using special control formulas. The work is redone until the required accuracy is achieved.
The lengths of the sides of the polygon are measured using laser, light rangefinders or earth tapes. Determine the distance between each two points of the traverse, fixing them in parallel in a specially designated journal.
Office work
A traverse is a polygon or line constructed to determine the coordinates of points that are far from the points of the original network. Thus, the field work is followed by the processing of the obtained results and obtaining the desired values.
Office work is an equally important type of geodetic work, as a result of which it is possible to identify errors made by workers during the construction of the theodolite traverse. In addition, at the stage of processing the results, the influence of systematic errors arising due to inaccurate operation of the device, the effects of weather conditions is excluded.(wind, sun, precipitation, etc.) and incorrect readings by the performer.
According to the results of the work, the theodolite traverse calculation sheet is calculated.
Compiling a traverse statement
The traverse sheet is a table that contains data obtained as a result of field work measurements and office processing calculations. Numerical information about directional angles, increments and coordinates of the starting point and travel points is entered there. There is a separate column for each value.
The initial values are the coordinates and directional angles of the start and end points. All other data is calculated using measured horizontal lengths and angles.
At the beginning of the work, the sum of the measured angles is calculated and the theoretical sum is analytically determined. Their difference will be the discrepancy of the theodolite traverse, calculated by the formula:
fβ=Σβmeas – Σβtheor.
The resulting value must be less than or equal to the allowable residual. It is calculated by the formula:
{fβ}=1’ √n.
If the condition is met, the calculated discrepancy can be distributed equally between all corners with the opposite sign. Then the travel angles can be considered equalized. Corrections are written over existing values and used in subsequent calculations.
The next step in calculating the traverse statement is to find the directional angles of the sides. The left corners along the way are subtracted, and the right ones are added. controlthe correctness of the calculations is to obtain in the end result the first directional direction of the starting point.
Next, the increments along the X and Y axes are calculated in the system of rectangular coordinates. This is necessary for the subsequent location of the traverse points. The increments are calculated as the product of the horizontal distance and the sine or cosine of the corrected directional angle:
∆X=dcosA;
∆Y=dsinA.
The next step is to calculate the discrepancy of the increments similarly to the angular one. If it does not exceed the allowable value, the resulting value is distributed equally with the opposite sign.
The last step is to calculate the coordinates of the traverse sheet. They are obtained as the sum of the coordinates of the previous point and the calculated increment, taking into account the residuals. For the X and Y axes, the values are considered separately, writing in the appropriate columns. The final control is to get the coordinates of the starting point, that is, return to the beginning.
Theodolite traverse in geodetic justification
Constructing a traverse is an important step in creating a survey justification. Geodetic points are usually located at a distance from each other and may not be a sufficient basis for the construction of facilities or other activities.
