Leveling is a type of geodetic measurement. Using it, the relative heights of various points on the earth's surface are determined. Such measurements can take such natural objects as rivers, seas, oceans, fields, or other starting points as a conditional level. In fact, leveling is the determination of the value of the excess of the surface of each object over a given (reference) one. Such measurements are required to make an accurate relief of the study area. In the future, these data are used in the preparation of terrain plans, maps, or for solving specific applied problems.
What types of leveling exist?
Such measurements can be carried out by a variety of methods, differing in the equipment or technology used. Consider what are the main types of leveling. The most common are five methods: geometric, trigonometric, barometric, mechanical and hydrostatic measurement of surfaces. Let's get to know each of them in more detail.
Geometric leveling
With this method of measuring the terrain, a special geometric rail and a level device are used. The principle of shooting is to install the staff with strokes and divisions at the required point near the surface under study. Then, using a horizontal line-of-sight beam, the height difference is counted. Geometric leveling is performed according to the principle “from the middle” or “forward”. When measuring by the first method, rails are installed at two points on the surface, the device is between them at an equidistant distance. The result of the survey is the data on the excess of one of the bars above the other. The second method is classic - one device and one rail. These leveling methods are the most common. They found application in the construction of both small objects (houses) and large (bridges).
Trigonometric leveling
With this type of measurement, it is customary to use special goniometer devices, which are called theodolites. Using them, information about the angles of inclination of the beam of the sight, which passes through a pair of predetermined points on the surface, is removed. Trigonometric leveling is widely used in topographic measurements to determine the difference in heights of two objects that are at a considerable distance from each other, but in the zone of optical visibility of the device.
Barometric surface measurement
Barometric leveling is a measurement method based on the dependence of atmospheric air pressure on the height of a point on a defined surface. The reading process is carried out using a barometer. This leveling system should take into account a number of corrections for the real temperature of the air, for its humidity. This method has found application in hard-to-reach areas (for example, in mountainous conditions) during various geographical and geological expeditions.
Mechanical (technical) surface measurement
Technical leveling involves the use of a special device - a leveling machine. Using it, the profile of the studied area is drawn in automatic mode with the help of a friction disk, which records the distance traveled, and an established plumb line, which sets the vertical. Such a device is usually mounted on a vehicle and travels from one detectable point to another. Technical leveling allows you to determine the height difference between the studied objects, the distance between them and the terrain profile, which is fixed on a special photographic tape.
Hydrostatic surface measurement
Hydrostatic leveling is a method based on the principle of action of communicating vessels. Shooting in this way is performed using a hydrostatic device that works with an error of up to two millimeters. Such a level is composed of a pair of glass tubes connected by a hose, this system is filled with water. The measurement process is as follows - the tubes are attached to the rails on which the scale is applied. After this, the planks are installed near the objects under study, the numerical value of the difference of the two levels is marked by tick marks. This design has a significant drawback, namely the limited measurement range, which is determined by the length of the hose.
The described methods of leveling (except mechanical) are very simple and do not require a specific baggage of knowledge from the operator; therefore, they are widely used in construction and other sectors of the national economy.
Measurement Classes
In addition to the measurement methodology, leveling is usually divided into accuracy classes. Each of them corresponds to a certain type and method of information retrieval. Let's consider what leveling classes exist.
- The first class is considered highly accurate. Corresponding to it is the mean square random error of 0.8 millimeters per kilometer and a systematic error of 0.08 mm / km.
- The second class is also considered highly accurate. However, the error here is slightly higher - the standard error is 2.0 mm / km, and the systematic error is 0.2 mm / km.
- Third class. It corresponds to a standard error of 5.0 mm / km, and the systematic error is not taken into account.
- Fourth grade. It corresponds to a standard error of 10.0 mm / km; the system error is also not taken into account.
Depending on the features of the terrain and the objectives of the survey, various methods of conducting data surveying can be used. For example, by polygons, by parallel lines or by leveling a surface by squares. The latter technique is most widely used; it is widely used for data collection from large open areas with a relatively small section height. Let's consider it in more detail.
Square Breakdown
Surface leveling by this method is carried out in order to obtain topographic large-scale plans of flat areas. The smooth position of the control points is determined by laying theodolite moves. And the heights - by the method of geometric measurement using technical levels. The process of data collection can be carried out in two different ways: by laying leveling moves with a gradual breakdown of the widths and squares.
Leveling by squares is carried out by dividing on the ground using a measuring tape and a theodolite (mesh with a cell side of twenty meters) when measured on a scale of 1: 500 and 1: 1000, forty meters - when shooting on a scale of 1: 2000 and a hundred meters at 1: 5000.
At the same time, the situation of the studied territory is fixed and the outline is drawn up. These procedures are performed in the same ways as in theodolite survey. In addition to the cell tops, characteristic terrain objects are fixed on the terrain - plus points: the top and bottom of the hill, the bottom and edges of the pit, points on the lines of the spillway and watershed, and others.
A shooting rationale is created by laying along the outer borders of the grid of squares of leveling and theodolite moves, which are then tied to points of a single state network. The heights of the plus points and the vertices of the cells are determined by the method of geometric leveling. If the length of the side of the square is forty meters or less, then from one station they try to measure all the defined points. The distance from the device to the bar should not exceed 100-150 meters. If the side length of the square is one hundred meters, then the level is placed in the center of each cell. According to the field survey of the area using the square method, a leveling log and measurement outline are compiled.
Log and outline leveling by squares
The journal contains data on the size of the side of the cell, the binding of the coordinate grid to theodolite moves (geodetic substantiation). In addition, the reference to the terrain objects - lakes, hills and so on. It should also be noted from which positions the leveling of the area was carried out. In the outline are recorded the results of shooting each of the squares. At the top and plus point of each cell, the counts from the black side of the bar (in meters), as well as the calculated heights, are indicated. This calculation is performed on the instrument horizon. The height of the vertices of the cells is defined as the difference between the horizon of the tool at the station and the reference on the staff.
In order to control the surface measurement process for two cell vertices, leveling is performed from two different stations. The preparation of a plan for the obtained data on the acquisition of surface data begins with fixing on the tablet the coordinates of the points of the unified state geodetic network, survey justification objects (leveling and theodolite moves), plus points, vertices of squares and the situation.
Application Method
When leveling the territory by applying theodolite and leveling passages broken down into diameters, the passages are laid along the natural characteristic lines of the given area, for example, along overflows or watersheds. In such work, the widths and pickets should be broken down every forty meters when shooting on a scale of 1: 2000 and after twenty meters when shooting on a scale of 1: 1000 and 1: 500. At the inflection points of the slopes, plus objects are noted. In the process of breaking pickets, one should fix the situation and draw up an outline. Leveling records are made in the journal. It marks the serial numbers of the pickets, counts along the red and black sides of the rails, the distance of the plus objects from the nearest pickets. Based on the results of leveling, a topographic plan of the territory, transverse and longitudinal terrain profiles are compiled.
It is advisable to measure the surface in areas of the proposed site for landscaping and vertical layout of the territory. An example is the landscape design of the area surrounding any architectural monument, or landscape gardening zone.
What is a level?
To conduct a geometric measurement of the terrain, which is widely used in construction, levels of various designs are used. These devices, according to their operating principle, are usually divided into: electronic, laser, hydrostatic and optical-mechanical. All levels are equipped with a telescope rotating in a horizontal plane. The modern design of such a measuring device provides automatic compensation for exposure to the working position of the visual axis.
Leveling history
The first information that reached modern man about leveling refers to the first century BC, namely, the construction of irrigation canals in ancient Greece and Rome. Historical documents mention a water meter. Its invention and use is associated with the names of the ancient Greek scholar Geron of Alexandria and the Roman architect Mark Vitruvius. The impetus for the development of these measuring instruments and methods of leveling was the creation of a telescope, a barometer, a cylindrical level and a gradation grid in telescopes. These inventions relate to the 16-17th centuries, they allowed to develop a system for accurate shooting of the earth's surface.
In Russia, during the time of Peter the Great, an optical workshop was founded, where, among other things, levels were also produced, only then they were called spirit levels with a pipe. The development of levels in the workshop was carried out by I. E. Belyaev. In the same period, the first measuring instruments appeared, which were based on barometers. At the beginning of the nineteenth century, the first trigonometric levels appeared, with their help very large-scale work was carried out to determine the difference in levels of the Azov and Black Seas, and the height of Mount Elbrus was measured. The use of geometric instruments was recorded in the mid-nineteenth century. So, in 1847 they were used in the construction of the Suez Canal. In our country, geometric leveling of the surface was used in the construction of water and land roads. The beginning of the creation of the national state network is considered to be 1871. Then work began on fixing and installing points, which served as the basis for topographic surveys.
Leveling application
The result of leveling is the creation of a single reference geodetic network, which serves as the basis for conducting topographic measurements of the terrain or various geodetic measurements. Shooting is widely used for research and scientific purposes: when studying the globe, the movement of the earth's crust, to record fluctuations in the level of seas and oceans.
Leveling is also used to solve various applied problems that are associated with the construction of various objects, laying communication lines, utilities, etc. For example, terrain measurement is necessary to carry out the transfer of design decisions in height, in addition, during installation work on the installation of building structures . When solving such problems, the data obtained by the geodesy service is always used. Also, directly to solve various highly specialized tasks, automatic information retrieval systems are used. Such tasks include, for example, repair and construction of the roadway. The sensors included in the automatic leveling device are installed on railway cars, cars, as a result of which a ready-made profile of the studied area is obtained in the shortest possible time.
Modern technologies
Today, due to the unusually rapid development of science and technology, various technical know-how is used to level the surface.
- Laser The basis of their work is the reading of terrain parameters using a laser scanning device.
- Ultrasonic The main element of such a device is an ultrasonic sensor emitting waves .
- GNSS technology, which is associated with obtaining information about current coordinates using satellite communications. Such equipment provides a very high leveling accuracy.
To ensure the efficient processing of a large number of information streams obtained in the process of applying the above know-how, it is necessary to have appropriate special software that will perform tasks related to the storage, management, visualization and processing of data.
Modern leveling systems in road construction
In modern pavement construction, automated systems are widely used. They allow you to control road construction equipment, given its current position. At the same time, the automatic leveling of the route is highly accurate, which significantly improves the quality of the produced roadbed, as well as reduces the construction time. Such devices installed on pavers, road milling cutters, bulldozers, allow to eliminate damage and defects of the old coating when laying a new layer. These levels control the transverse slope of the road, perform it according to the parameters precisely specified by the project. Modern surface measurement systems for road construction equipment are divided into several types, depending on the technology used.
- Ultrasonic devices with a different number of sensors.
- Laser removal systems.
- The device is based on GPS satellite technology.
- Three-dimensional system operating on the principle of a total station.
If necessary, depending on the complexity and peculiarity of the work being carried out, one or another technology of automatic leveling can be used.