At present, the most effective method for creating a geodetic network, including geodetic thickening networks, is a method associated with satellite technologies (GL0NASS, GPS). However, this method requires receiving equipment, the high cost of which prevents its widespread use. Therefore, along with highly efficient satellite technologies, traditional methods are also used. It should be noted that when doing geodetic works in enclosed spaces and in cramped conditions, when the observation of a constellation of satellites is impossible or difficult, traditional methods are the only possible ones for solving many problems.
Condensation Geodetic Networks are built using triangulation and polygonometry methods to condense the state geodetic network to the density necessary to create a survey justification for large-scale surveys. Triangulation of the 1st and 2nd categories is developed in open and mountainous areas. Where triangulation of the 1st and 2nd categories is impossible or impractical to perform according to the conditions of the terrain, a polygonometric network of the 4th class, 1st and 2nd categories is developed. It should be noted that polygonometry of the 4th class for large-scale surveys is performed with reduced accuracy compared to the state one.
When creating polygonometry, the whole complex of basic geodetic works is performed: angular and linear measurements, leveling. The angles at the points of polygonometry are measured by the method of a single angle or circular methods with optical theodolites of the type. T1, T2, T5 with a centering accuracy of 1 mm. Heights to all points of polygonometry are transferred by leveling of the IV class or technical. Lines are measured directly: with light range finders, suspended measuring instruments, or indirectly - the lengths of the sides of the stroke are calculated from auxiliary quantities.
When carrying out various national economic, including land management, activities over a large area, topographic maps and plans are needed, compiled on the basis of a network of geodetic points, the planned position of which on the earth's surface is determined in a single coordinate system, and the height - in a single system of heights. At the same time, geodetic points can be only planned or only high-altitude, or both planned and high-altitude.
The network of geodetic points is located on the ground according to the project drawn up for it. Network points are fixed on the ground with special signs.
A geodetic network built over a large area in a single system of coordinates and heights makes it possible to properly organize the work of surveying the terrain. In the presence of such a network, surveys can be carried out independently in different places, which will not cause difficulties in drawing up a general plan or map. In addition, the use of a network of geodetic points leads to a more even distribution of the influence of measurement errors over the territory and provides control over the ongoing geodetic work.
Geodetic networks are built according to the principle of transition from the general to the particular, i.e., first, a rare network of points is built over a large area with very high accuracy, and then this network is condensed sequentially in stages by points, the construction of which is carried out at each stage with less accuracy. There are several such stages of condensation. The density of the geodetic network is carried out in such a way that the result is a network of points of such density (density) and accuracy that these points can serve as a direct support for the upcoming survey.
Planned geodetic networks are built mainly by the methods of triangulation, polygonometry and trilateration.
The triangulation method consists in building a network of triangles in which all the angles of the triangles and at least two sides at different ends of the network are measured (the second side is measured to control the measurement of the first side and establish the quality of the entire network). According to the length of one of the sides and the angles of the triangles, the sides of all Triangles of the network are determined. Knowing the directional angle of one of the sides of the network and the coordinates of one of the points, you can then calculate the coordinates of all points.
The polygonometry method consists in building a network of moves in which all angles and sides are measured. Polygonometric moves differ from theodolite ones in a higher accuracy of measuring angles and lines. This method is usually used in closed areas. The introduction of electromagnetic rangefinders into production makes it expedient to use polygonometry in open areas.
The trilateration method consists in building a network of triangles by measuring all sides of the triangles. In some cases, linear-angular networks are created, which are networks of triangles in which sides and angles are measured (all or in the required combination).
Planned geodetic networks are divided into the state geodetic network; networks of condensation of 1 and 2 categories; filming substantiation - filming network and separate points.
From a geometric point of view, any geodetic network is a group of points fixed on the ground for which plan coordinates (X and Y or B and L) are defined in the accepted two-dimensional coordinate system and H marks in the accepted height system or three coordinates X, Y and Z in the accepted three-dimensional spatial coordinate system.
The geodetic network of Russia was created over many decades; during this time, not only the classification of networks has changed, but also the requirements for the accuracy of measurements in them.
Geodetic networks by purpose and accuracy of construction are divided into three large groups:
- state geodetic networks (GGS);
- geodetic thickening networks (GSN);
- geodetic survey networks.
The urgent task of the current period is to create a unified classification of all existing and prospective geodetic networks that would meet international standards.
State geodetic network (GGS) is the main geodetic basis for topographic surveys of all scales and must meet the requirements of the national economy and defense of the country when solving the relevant scientific and engineering problems. The planned network is created by the methods of triangulation, polygonometry, trilateration and their combinations; a high-rise network is created by building leveling traverses and geometric leveling networks. The state geodetic network is subdivided into networks of the 1st, 2nd, 3rd and 4th classes, which differ in the accuracy of measuring angles, distances and elevations, the length of the sides of the network and the order of successive development.
State geodetic network of the 1st class, also called astronomical and geodetic network (AGS), is built in the form of polygons with a perimeter of about 800 ... 1000 km, formed by triangulation or polygonometric links no more than 200 km long and located, if possible, along the meridians and parallels.
The state geodetic network of the 2nd class is built in the form of triangulation networks, completely covering the polygons formed by triangulation or polygonometry links with triangles.
Requirements for the accuracy of measuring horizontal angles and distances in triangulation are given in Table 1, in polygonometry - in Table 2.
Table 1. Accuracy of measuring horizontal angles and distances in triangulation.
Table 2. Accuracy of measuring horizontal angles and distances in polygonometry.
| Network class | Wed sq. angle measurement error, arc. min | Relative travel side error | Travel side length, km |
|---|---|---|---|
| 1 | 0,4 | 1:300 000 | >20…25 |
| 2 | 1,0 | 1:250 000 | 7…20 |
| 3 | 1,5 | 1:200 000 | >3 |
| 4 | 2,0 | 1:150 000 | >2 |
In addition, the conditions for the number of sides in the course, the length of the perimeter of the polygons, and some others must be met.
Root-mean-square errors of measurement of excesses per 1 km of travel in leveling passages and networks of classes I, II, III, IY are equal to 0.8; 2.0; 5 and 10 mm, respectively; marginal errors per 1 km of travel are taken equal to 3; 5; 10 and 20 mm respectively.
For topographic surveys, the Instructions of 1966 established the following norms for the density of GGS points:
- for surveys on a scale of 1:25,000 and 1:10,000 - one point per 50 ... 60 km 2;
- for surveys on a scale of 1:5,000 - one point per 20 ... 30 km 2;
- for surveys on a scale of 1:2,000 and larger - one point per 5 ... 15 km 2.
In hard-to-reach areas, the density of GHS points can be reduced, but not more than 1.5 times.
On the territory of cities with at least 100,000 inhabitants or occupying an area within the city limits of at least 50 km 2, the density of GHS points should be increased to one point per 5 ... 15 km 2.
Geodetic Condensation Networks (GCN) are a planned high-altitude substantiation of topographic surveys of scales from 1:5,000 to 1:500, and also serve as the basis for the production of various engineering and geodetic works. They are created by triangulation and polygonometry methods. According to the accuracy of measuring angles and distances, GSS polygonometry is of the 4th class, 1st and 2nd categories (Table 3).
Table 3. Accuracy of measurement of angles and distances of polygonometry of the 4th class, 1st, 2nd category.
It should be emphasized that measurements in the 4th class of GSS polygonometry are performed with a much lower accuracy than in the 4th class of the GHS.
The density of GSS points should be increased to one point per 1 km 2 in the undeveloped area and up to four points per 1 km 2 in the territory of settlements and industrial sites.
The state geodetic network of the 4th class can be considered a transitional type of networks between the GHS and the GSS.
The marks of the GSS points are determined from the leveling of the IV class or from the technical leveling.
Geodetic survey networks serve as a direct basis for topographic surveys of all scales. They are created by all possible geodetic constructions; the density of their points should ensure high quality shooting. Marks of survey network points can be obtained from technical leveling (with a relief section height h ≤ 1 m) or from trigonometric leveling (with a section height h ≥ 1 m).
On the territory of Russia, in addition to the GGS, GSS, GNS (state leveling network), there are other types of geodetic networks:
- fundamental astronomical and geodetic network (FAGS);
- state fundamental gravimetric network (GFGS);
- Doppler geodetic network (DGS);
- space geodetic network (GGS);
- satellite geodetic network of the 1st class (SGS-1);
- satellite differential geodetic network (SDGS).
The creation of geodetic networks of any class and category is carried out according to previously developed and approved projects. The project should draw up a network diagram (the layout of network points and their connections), justify the types of centers and signs, determine the volume of measurements and their accuracy, select instruments for measuring angles, distances, elevations, and develop a measurement methodology.
The design of triangulation, trilateration and complex arbitrary networks is usually carried out on a computer using special programs.
Condensation Geodetic Networks are developed on the basis of the state geodetic network and serve to justify large-scale surveys, as well as to conduct engineering and geodetic work at the construction sites of large industrial facilities.
Planned geodetic thickening networks are created in the form of triangulation (triangulation networks) and polygonometry of 1 and 2 categories.
Triangulation 1 digit develops in the form of networks and chains of triangles with a side of 1-5 km, as well as by inserting individual points into a network of a higher class. Angles are measured with root mean square error not more than 5", relative error weekend parties - no more than 1: 50,000.
Triangulation 2 digits is built in the same way as triangulation of the 1st category; in addition, the position of points of the 2nd category can be determined by direct, reverse and combined geodetic serifs. The lengths of the sides of triangles in networks of 2 digits are taken from 0.5 to 3 km, the root mean square error in measuring angles is -10", the relative error of the output sides is no more than 1:20,000.
Polygonometry 1 and 2 digits is created in the form of single passages or systems with nodal points, the lengths of the sides of which are taken on average equal to 0.3 and 0.2 km, respectively. The root mean square error of measuring angles in polygonometry strokes of the 1st category is 5", the relative error of measuring lengths is 1:10,000.
In polygonometry of the 2nd category, the accuracy of angular and linear measurements is 2 times lower compared to polygonometry of the 1st category.
All points of geodetic thickening networks must be given grade IV leveling marks or technical leveling. In mountainous areas, it is allowed to transfer point marks by trigonometric leveling.
The survey substantiation develops from points of state geodetic networks and geodetic networks of condensation. Survey networks are created by building survey triangulation networks, laying theodolite, tacheometric and scale traverses, direct, reverse and combined serifs. With the development of a survey justification, as a rule, the planned and vertical position of the points is simultaneously determined. The heights of survey network points are determined by trigonometric or geometric leveling.
1:1000
1:2000
1:5000
Shooting scale
The number of points per 1 square. km
GEODETIC NETWORKS AND SURVEY NETWORKS
Survey geodetic networks (geodetic survey
justification) are created to condense the geodetic network to a density that ensures topographic surveying.
The density of survey networks is determined by the scale of the survey, the nature of the terrain, as well as the need to provide engineering and geodetic, mine surveying and other works for the purposes of surveying, construction and operation of structures.
A theodolite traverse is a system of points fixed on the ground, the coordinates of which are determined from measurements of horizontal angles and lengths of the sides of the traverse. According to the form and completeness of the initial data, linear-angular moves are divided into the following types:
open traverse - starting points with known coordinates and initial directional angles are at the beginning and at the end of the traverse;
closed traverse - the start and end points of the move are combined; one point of the move has known coordinates and is called the starting point; at this point there must be an initial direction with a known directional angle, and the adjoining angle between this direction and the direction to the second point of the move is measured.
free traverse does not have starting points and starting directional angles either at the beginning or at the end of the move; a hanging linear-angular traverse has a starting point with known coordinates and an initial directional angle only at the beginning of the traverse.
The lengths of the sides between the points of theodolite passages range from 20 to 350m. The maximum allowable stroke length depends on the scale of the survey.
Shooting scale |
Travel length, km |
||
In built-up area |
In an undeveloped area |
||
The angles of rotation at the points of the moves are measured with a theodolite with a mean square error of 0.5' in one step. The discrepancy between the values of the angles in half-points is allowed no more than 0.8 ′. The length of the lines in the moves is measured with rangefinders or tape measures. Each side is measured twice - in the forward and reverse directions. Differences in the measured values are allowed within 1:2000 of the measured line length.
Points of geodetic networks are fixed on the ground by underground centers, which must ensure the invariance of the position and the safety of the point for a long time.
Types of underground centers are established depending on the physical and geographical conditions of the region, the composition of the soil and the depth of seasonal freezing of the soil. For example, the center of the point of the state geodetic network of 1-4 classes of type 1 consists of a reinforced concrete pylon with a section of 16X 16 cm (or an asbestos-cement pipe 14-16 cm filled with concrete) and a concrete anchor. Pylon
cemented into an anchor.
The base of the center should be located below the depth of seasonal soil freezing at least 0.5 m and at least 1.3 m from the ground surface. In the upper part of the sign at the ground level, a cast-iron mark is concreted with an indication of the point to which the coordinates of the point refer. At 1 - 1.5 m from the center, an identification pole with a security plate is installed.
FIXING AND MARKING ON THE TERRAIN OF POINTS OF THE GEODETIC NETWORK
Points of the high-altitude geodetic network are fixed ground benchmarks, wall benchmarks and stamps. The ground benchmark in the upper part has a cast-iron mark; the mark of the benchmark refers to the top point of the hemispherical protrusion of the brand.
The height of the wall benchmark is determined for the upper face of the protrusion, and the heights of the marks are determined for the center of the hole made in the disk. A security plate cast from cast iron serves as an external design for the wall benchmark. It is fixed in the wall of a building or structure next to the wall benchmark or above it.
Most of the shooting network points are fixed with temporary signs, which are wooden stakes or metal tubes at least 40-50 cm long, which are hammered flush with the ground, the center of the temporary wooden sign is a nail driven into the upper end of the stake. To facilitate the search for such a sign, a gatehouse 30 cm high is clogged next to it.
Currently, the most effective method for creating a geodetic network, including geodetic thickening networks, is the method associated with satellite technologies (GL0NASS, GPS). However, this method requires receiving equipment, the high cost of which prevents its widespread use. Therefore, along with highly efficient satellite technologies, traditional methods are also used. It should be noted that when performing geodetic work indoors and in cramped conditions, when the observation of a constellation of satellites is impossible or difficult, traditional methods are the only possible ones for solving many problems. Let us dwell on the traditional methods of thickening the geodetic network in more detail.
Condensation geodetic networks are built using triangulation and polygonometry methods to condense the state geodetic network to the density required to create a survey justification for large-scale surveys. Triangulation of the 1st and 2nd categories is developed in open and mountainous areas. Where triangulation of the 1st and 2nd categories is impossible or impractical to perform according to the conditions of the terrain, a polygonometric network of the 4th class, 1st and 2nd categories is developed. It should be noted that polygonometry of the 4th class for large-scale surveys is performed with reduced accuracy compared to the state one.
The characteristics of triangulation of the 1st and 2nd category and polygonometry of the 4th class, 1st and 2nd categories are shown in Table 1.
When creating polygonometry, the whole complex of basic geodetic works is performed: angular and linear measurements, leveling. The angles at the points of polygonometry are measured by the method of a single angle or circular methods with optical theodolites of the type. T1, T2, T5 with a centering accuracy of 1 mm. Heights to all points of polygonometry are transferred by leveling of the IV class or technical. Lines are measured directly: by light-range numbers, suspended measuring instruments, or indirectly - the lengths of the sides of the stroke are calculated from auxiliary quantities.
When carrying out various national economic, including land management, activities over a large area, topographic maps and plans are needed, compiled on the basis of a network of geodetic points, the planned position of which on the earth's surface is determined in a single coordinate system, and the height - in a single system of heights. In this case, geodetic points can be only planned or only high-altitude, or simultaneously - planned and high-altitude.
The network of geodetic points is located on the ground according to the project drawn up for it. Network points are fixed on the ground with special signs.
A geodetic network built over a large area in a single system of coordinates and heights makes it possible to properly organize the work of surveying the terrain. In the presence of such a network, surveys can be carried out independently in different places, which will not cause difficulties in drawing up a general plan or map. In addition, the use of a network of geodetic points leads to a more even distribution of the influence of measurement errors over the territory and provides control over the ongoing geodetic work.
Geodetic networks are built according to the principle of transition from the general to the particular, i.e., first, a rare network of points is built over a large area with very high accuracy, and then this network is condensed sequentially in stages by points, the construction of which is carried out at each stage with less accuracy. There are several such stages of condensation. The density of the geodetic network is carried out in such a way that the result is a network of points of such density (density) and accuracy that these points can serve as a direct support for the upcoming survey.
Planned geodetic networks are built mainly by the methods of triangulation, polygonometry and trilateration.
The triangulation method consists in building a network of triangles in which all the angles of the triangles and at least two sides at different ends of the network are measured (the second side is measured to control the measurement of the first side and establish the quality of the entire network). According to the length of one of the sides and the angles of the triangles, the sides of all Triangles of the network are determined. Knowing the directional angle of one of the sides of the network and the coordinates of one of the points, you can then calculate the coordinates of all points.
The polygonometry method consists in building a network of moves in which all angles and sides are measured. Polygonometric moves differ from theodolite ones in a higher accuracy of measuring angles and lines. This method is usually used in closed areas. The introduction of electromagnetic rangefinders into production makes it expedient to use polygonometry in open areas.
The trilateration method consists in building a network of triangles by measuring all sides of the triangles. In some cases, linear-angular networks are created, which are networks of triangles in which sides and angles are measured (all or in the required combination
Filming networks
A survey geodetic base is a network of points that are used as stations when surveying a terrain situation. The density of such points and the method of their construction depend on the scale and survey technique, as well as on the nature of the terrain. The initial data for the construction of the survey geodetic base are the points and sides of the reference networks. When mapping small areas, the survey network can develop independently. In any case, the density of the survey network should be sufficient for the survey of the area on a given scale. The marginal error in determining the coordinates of the survey base points relative to the initial points should not exceed 0.2 mm on the survey scale, i.e. 10, 20, 40, 100 cm in scales 1:500, 1:1000, 1:2000, 1:5000 respectively. for unfavorable terrain conditions (forested or pitted surface), these tolerances increase one and a half times.
The construction of the survey network is carried out by laying theodolite, leveling, theodolite-leveling, theodolite-height, tacheometric, scale passages, micro-triangulation rows and quadrangles without diagonals, as well as various geodesic serifs. In survey networks, the coordinate values are calculated with an accuracy of 0.01 m (in the course of trigonometric leveling).
The points of the survey network are fixed on the ground, usually by temporary centers.
Geodetic thickening networks are developed where further thickening of the state geodetic network is required (in populated areas, at large construction sites, etc.). Usually such networks are called geodetic networks of local importance.
Geodetic thickening networks, as well as state networks, can be planned and high-rise. Planned concentration networks are subdivided into networks of the 1st and 2nd category, created by the methods of triangulation, polygonometry and trilateration, and high-altitude (leveling) networks are developed by the method of geometric leveling III and IV classes, as well as technical leveling moves. High-rise networks are discussed in more detail in Sect. 7 Leveling.
Geodetic planned thickening networks of the 1st and 2nd categories are based on the points of the state geodetic network of the 1st-4th classes. In accordance with the principle of transition from general to particular, geodetic networks of condensation have shorter sides and less accuracy than state networks. The main indicators characterizing the size and accuracy of geodetic thickening networks are given in Table 8.2.
Like points of state geodetic networks, points of density networks are fixed by permanent signs, consisting of an underground center and an external sign.
T a b l e 8.2 - Characterization of networks of condensation
8.5 Modern concept of development
planned state geodetic networks
Currently, to build state geodetic networks, they use satellite measurement methods. For this, two satellite systems are mainly used: the Russian system GLONASS (Global Navigation Satellite System) and the NAVSTAR GPS system (navigation system for determining distance and time, the global system positioning) developed in the USA.
In the satellite method, instead of fixed points of the geodetic network with known coordinates, mobile satellites are used, the coordinates of which can be calculated at any time.
The concept of the state satellite network provides for the construction of a three-level network:
1 - fundamental astronomical-geodesic;
2 - high-precision astronomical-geodesic;
3 - satellite geodesic of the 1st class.
The fundamental astronomical geodetic network should consist of geodetic points with average distances between them of 700–800 km. Some of these points should become astronomical observatories equipped with radio telescopes and satellite receivers of GPS-GLONASS systems. The mutual position of these points will be determined with an error of 1–2 cm.
The high-precision astronomical-geodesic network should replace the 1st class triangulation links and represent constructions of uniform accuracy with distances between adjacent points of 150–300 km. The mutual position of these points will be determined by satellite methods with an error of 2–3 cm.
The satellite geodetic network of the 1st class should replace the triangulation of the 1st and 2nd classes with average distances between points of 30–35 km and an RMS error of the relative position of 1–2 cm.
The construction of such a network is supposed to be carried out within the next ten years.
