Geodetic works accompany the construction of any object from the stage of choosing a land plot to the commissioning of a completed structure. This industry has come a long way of development from primitive measuring instruments to modern high-precision equipment capable of real-time determination of the spatial position of the survey point with millimeter precision. We will tell you about the milestones in the development of geodesy and its place on a modern construction site in a series of articles dedicated to this field of human activity..
A bit of history
Since ancient times, humanity has experienced the need to determine the real distances between objects and their spatial position relative to each other. Moreover, the construction of any large-scale structures was impossible without accurate calculations. For example, for the construction of irrigation systems in ancient Egypt in the 6th century BC. used the simplest geodetic surveys, because in order for the channel to go to the river, and not to the thickets with crocodiles, the direction and slope of digging the trench had to be calculated and marked on the ground. This gave impetus to the development of agriculture, and with it the prosperity of the Egyptian state. The ancient Greeks increased the knowledge of the Egyptians, but the science that determines the shape and size of the Earth received wide development with the expansion of trade relations and navigation, when it was required to plot an exact course from one point of the planet to another.
In Russia, the first mentions of distance measurements are dated 1068, when, by order of the Tmutarakan prince Gleb, the width of the Kerch Strait was measured by steps on the ice, a memorial stone about this event is still kept in the Hermitage. Geodesy gained wider development during the “window to Europe” of Peter I, when navigators and travelers needed to have detailed plans of movement on hand. This work was carried out by the officers of the Quartermaster Unit. The war with Napoleon in 1812 revealed the lack of accuracy and provision of cartographic materials, primarily the military, which was the signal for the creation of the Corps of Military Topographers in 1822..
The development of Soviet geodesy began with the signing by VI Lenin on March 15, 1919 of the decree of the Council of People’s Commissars “On the establishment of a higher geodetic administration.” This date will for many years become the date of the professional holiday of surveyors and specialists involved in the industry. In May 1967, the geodetic department will be transformed into the Main Directorate of Geodesy and Cartography (abbreviated as GUGK), which will be directly subordinate to the USSR Council of Ministers, which emphasized the special status of this industry. After the collapse of the Union, the Federal Service of Geodesy and Cartography of Russia was organized, which was subsequently reassigned to the Ministry of Economic Development, and then its functions were transferred to the Federal Service of State Registration, Cadastre and Cartography. So we note with regret that the “golden years” of Russian geodesy as a science fall precisely on the Soviet period.
For high-precision measurements it is necessary to use the same coordinate and height system in order to avoid problems with the “overlay” later. If a survey is being carried out for construction, then the boundary of the work is usually the intersection of the main transport routes and the tie-in points of communications, which should be schematically displayed in the appendix to the terms of reference. Usually, topographic survey of public roads in cities has already been performed in the local coordinate system, the data is stored in archives, and in order to correctly calculate the slopes at the construction site, surveying for construction should be carried out in a similar system.
The beginning of work on a unified coordinate system in our country dates back to 1928, when the proposed by F.N. Krasovsky, the program for the development of a triangulation system – a method for creating a reference geodetic network based on determining coordinates by measuring the angles of triangles, and in class 1 triangulation the length of the sides of these “triangles” reached 25 km. The points whose coordinates were determined by this method were called triangulation points. Then the network of triangles was divided into networks of 2–4 classes, which, respectively, had smaller distances within the line of sight between the points. The fourth grade was divided into 1 st and 2 nd categories, the distance between the points was already 200-500 meters. The coordinates of the points were determined by the polygonometric method, i.e. in addition to angles, with the help of a theodolite, the distances between points were also measured with a measuring tape or optical range finder. It is the points of polygonometry of the 4th class and the points of lattice polygonometry that are mainly used by surveyors for urban work.
The first high-precision coordinate system on the territory of the USSR is considered to be the coordinate and altitude system of 1942 (SK-42), approved in April 1946, and the water level in the instrumental chamber of the Kronstadt port (zero of the Kronstadt footstock), adopted in 1913, was used as zero in height. This moment is still used by some “experts” when shooting in a conventional system of coordinates and heights, taking the edge of any reservoir as zero in height.
The measured state of affairs in the industry was violated by GRU Colonel Oleg Penkovsky, who, out of the kindness of his heart, sold, among other things, cartographic materials in SK-42 to the Western special services. The Soviet government, prone to paranoia, gave the command to adjust the coordinate system so that the enemy could not use secret maps to launch a nuclear strike, and a new coordinate system was born – SK-63, which was a distorted version of SK-42. From this system, urban polygonometry developed, which, in turn, was a distorted version of the SK-63. Wanting to confuse enemies, the functionaries themselves got confused as a result. In SK-63, huge arrays of maps were made, the land cadastre is partly maintained, and at the junctions of the map zones, large overlays and inconsistencies are possible. SK-63 was canceled by the Decree of the Central Committee of the CPSU and the Council of Ministers of the USSR in March 1987, but continued to be used in the future “as an exception.”.
Currently in Russia for the needs of space geodesy there is a spatial coordinate system PZ-90.02, which in turn is an analogue of WGS84 – a single coordinate system for the entire planet, and for geodetic and cartographic work they use the geodetic coordinate system of 2011 (GSK-2011), a derivative from its predecessors – SK-95 and SK-63. As you understand, the differences between coordinate systems and the loss of accuracy during the transition from one system to another do not add overall accuracy to the performed topographic and geodetic works. At the construction site, for ease of use, a breakdown is made in a conditional coordinate system that has a connection with local or regional systems, because the numerical values of coordinates in state systems can reach seven-digit numbers in meters, excluding centimeters and millimeters.
Tools and equipment used for the production of work
Along with the accumulation of knowledge about the shape and size of the Earth by mankind, the tools with which he performed geodetic work changed. Initially they were:
- Theodolite – This instrument is the main surveying instrument used to measure horizontal and vertical angles. Structurally, the theodolite consists of a horizontal and vertical circle, which is also called a “limb” and has divisions for taking readings, and a rotating part – “alidade”, on which the telescope is fixed. This tool is indispensable for engineering, geodetic and astronomical work.
- The level is an optical-mechanical instrument that allows you to determine the difference in heights of points on the earth’s surface. The difference between the numbers that are visible in the level on two vertical bars with divisions is equal to the difference in heights of the points at which the bars are installed – wooden beams 3-4 meters high with divisions for reading.
- Level is an indispensable control tool for every builder. This is a device with a glass ampoule filled with liquid for determining the horizontal surface and measuring small angles of inclination.
- Kipregel – this tool is used when performing topographic surveys and allows you to graphically build the situation right in the field, measuring angles, distances and elevations. Used in conjunction with a beaker – a field drawing table.
- Pantometer – used to be used for surveying swamps and forests in cases where high accuracy of measurements was not required.
- Measuring tape – usually a steel tape with a scale for measuring the horizontal distance of points.
- Rangefinder is a device for determining the distance between points; in construction, its function is successfully performed by a laser tape measure.
- Boussol – this tool allowed to determine the magnetic bearing on the ground.
- Length gauge – the tool used in mine surveying made it possible to measure distances using a flexible thread and a measuring block.
Naturally, progress does not stand still, and the “veterans” are being replaced by modern geodetic equipment, with which only specialists can work. However, knowing the basics of science, it is not necessary to call surveyors for all types of work, you can perform some simple operations yourself without the help of complex tools and expensive software..
Having a 20-meter tape measure on the farm, you can easily break the axes of the country house or calculate the approximate area of the site, and with the help of simple devices it is even possible to perform a simplified geodetic survey of the site for individual construction.
The following articles from our cycle on geodesy and its role on a construction site will tell you about the features of the choice of geodetic equipment and the possibility of independent solution of the simplest geodetic problems..