17.11.201927.05.2017

Coordinate system (datum) settings in the GPS receiver

As a rule, the parameters of more than 100 coordinate systems are registered in the GPS receiver and it is possible to specify the parameters of the required datum manually. In this article, I will only talk about what you need to do in order to use cards on Psion. You can read more about datums on Morozov's website, in particular - see.

By default, the receiver has a WGS-84 datum. In Russia, Pulkovo 1942 is usually used, maps are most often created in this coordinate system. If the map was printed with a grid of coordinates, then the easiest way to bind it is to the grid, i.e. in Pulkovo coordinates.

The coordinates of the same point in the WGS-84 coordinate system and Pulkovo are different. The RealMaps program does not have coordinate system settings. Therefore, in order to use the map linked to Pulkovo without errors, it is necessary that the GPS receiver transmits coordinates to Psion in the same system in which the maps are linked. To do this, you need to set the Pulkovo parameters in the GPS receiver.

Now your receiver is configured to work with the maps of the Moscow region available on the site.

The above parameters User Datum Setup I successfully tested on the territory of the Moscow region. EtrexSummitUser calculated the optimal parameters for different regions of Russia:

If you will be using gridded maps of these regions, use the appropriate options.

If your region is far from those in the table, you can download (about 25 Kb) and choose the parameters yourself with a minimum error.

The concept of "Datum" is used in geodesy and cartography for the best approximation to the geoid at a given location. The datum is set by shifting the reference ellipsoid along the axes: X, Y, Z, as well as by rotating the Cartesian coordinate system in the plane of the axes by the angle rX, rY, rZ. It is also necessary to know the parameters of the reference ellipsoid a and f, where a- the size of the large axle shaft, f- compression of the ellipsoid.

Most often, datums are encountered in GPS receivers, in GIS systems and in cartography when using any local coordinate network. The transformation of coordinates in such systems from one datum to another can, in general, be performed automatically. Incorrect installation of the datum (or its incorrect conversion) as a result gives horizontal and vertical errors in determining the location from a few to hundreds or even more meters.

List of datums

WGS84 (World Geodetic System 1984). A global datum using a geocentric global ellipsoid calculated from accurate satellite measurements. Used in the GPS system. It is currently accepted as the main one in the USA.
Pulkovo-1942 (SK-42, Coordinate system 1942) Local datum using the Krasovsky ellipsoid, which is closest to the European territory of the USSR. The main (in terms of prevalence) datum in the USSR and the post-Soviet space.
PZ-90 (Parameters of the Earth 1990) Global datum, main (since 2012) in Russian Federation.
NAD-83 (Nord American Datum 1983). Local datum for the North American continent.

In total, several dozen local datums are known for different regions of the Earth. Almost each of them has several modifications.

Links

Wikimedia Foundation. 2010 .

See what "Datum" is in other dictionaries:

- (Latin datum). Same as date. Dictionary of foreign words included in the Russian language. Chudinov A.N., 1910. DATUM lat. datum. Day of the month on letters, official papers. etc. An explanation of 25,000 foreign words that have come into use in ... ... Dictionary of foreign words of the Russian language

datum- (Latin datum) 1. exactly calendar time for a certain time 2. denot in a month (spread redniot bro) 3. signs for a calendar time for a document, letter and word 4. temporary border, temporary moment 5. time for nastanokot, for something, ... ... Macedonian dictionary

Serbian identity card- (Serbian: Lichna karta / Lična karta) is the national identification card used in Serbia. Though the ID card is a primary photo ID, Serbian passport and national Drivers license are used as valid photo IDs for various purposes. It is issued to… … Wikipedia

Extension .tiff, .tif MIME image/tiff Format type geospatial metadata Extended from TIFF GeoTIFF open format metadata that allows you to include georeferenced information in TIFF files. May include a view ... Wikipedia

the date- uh. date f., German Datum, pol. data. 1. A note on a document, letter, etc. about the time (year, month, day) of issuing a document, writing a letter, etc. BAS 2. I am writing to you .. news from various places, and therefore, I confess that I wanted to imitate... Historical Dictionary of Gallicisms of the Russian Language

In order to be able to competently use any GPS receiver, you need to know some of its features. Let's talk a little about the shape of the Earth. We will need this in the future. Earth Shape, Datums. Many of us are used to representing our planet as a sphere. In reality, the shape of the Earth is a complex geometrically irregular figure. If we extend the surface of the waters of the World Ocean under all the continents, then such a surface will be called level. Its main property is that it is perpendicular to the force of gravity at any point. The figure formed by this surface is called the Geoid. It is difficult to use the shape of the geoid for navigation purposes, so it was decided to bring it to a mathematically correct body - ellipsoid of revolution or spheroid. The projected surface of the geoid onto the ellipsoid of revolution is referred to as Reference - Ellipsoesd. Since the distance from the center of the earth to its surface is not the same in different places, certain errors arise in linear distances. Each state, conducting geodetic and cartographic measurements, assigns its own set of parameters and orientation modes for the reference ellipsoid. Such parameters are called geodetic datums(Datum). The datum shifts (orients) the reference ellipsoid relative to a certain reference point (the center of mass of the Earth), setting a more correct orientation relative to the lines of latitude and longitude. Roughly speaking, this is a kind of coordinate grid tied to the reference ellipsoid of a particular place.

World Geodetic System 1984 (WGS–84) or World Geodetic System. Currently, the WGS84 system is controlled by an organization called the US National Geospatial-Intelligence Agency - NGA i.e. US National Geospatial-Intelligence Agency. Initially, the WGS84 system was developed for air navigation purposes. March 3, 1989 Council international organization civil aviation ICAO, approved WGS84 standard (universal) geodetic reference system. The system entered the maritime transport industry after its adoption by the International maritime organization IMO.

At the heart of the orientation process WGS84 lies a three-dimensional system of geocentric coordinates. The reference point starts from the Earth's center of mass. The X axis lies in the plane of the equator and is directed to the meridian accepted by the International Bureau of Time (BIH). The Z axis is directed to the North Pole and coincides with the Earth's axis of rotation. The Y-axis completes the system to the right-hand one (rule right hand) and lies in the plane of the equator between the X-axis at an angle of 90° to the east.

The main parameters of the reference ellipsoid WGS84 include:

It should be remembered that the UKHO (United Kingdom Hydrographic Office) publishes its maps using about a hundred different datums (reference ellipsoids). But the GPS receiver determines the coordinates by default in the WGS84 datum. Looking ahead, most modern GPS receivers have the function of manual (manual) switching of the datum (ie, the receiver's memory contains a huge number of different datums). When transferring coordinates from the receiver to the map, it is necessary to check in advance in which Datum the map was published. To simplify this procedure, since 1982, the UKHO (United Kingdom Hydrographic Office) has added a note to the legend of their charts called “ position" and " Satellite Derived Position". In these paragraphs, we are informed about the Datum in which the map was published. And if it's not WGS84 - how to recalculate the coordinates. Pay special attention to this!

The most commonly known shape of the earth is called " geoid ». This term was proposed in 1873 by the German physicist Johann Benedikt Listing. The definition of the term geoid is based on the fact that any surface of water in a calm state (in a cup, in a bath, in the sea) is a level surface. Water always spreads so that its surface is perpendicular to the direction of gravity. Such a surface is taken as the mathematical surface of the earth, or "sea level ", from which the heights of points are measured earth's surface. The surface of the geoid, in contrast to the physical surface of the earth, is smooth, but very irregular due to the uneven distribution of masses within the planet. As a result, the geoid is more similar in shape not to a ball, but to a pear. The shape of the geoid is very complex and depends on the distribution of masses and densities in the body of the earth.

Determining the exact position of the geoid under the continents is incredibly difficult, since the mathematical expression of the geoid uses the coefficients of spherical harmonics. For example, some geoids use spherical harmonic coefficients for polynomials up to order 360, and the full equation requires more than 60,000 coefficients. To calculate the surface, this is all too complicated. Therefore, a simpler figure is used, but with sufficient accuracy describing the earth.

To simplify mathematical calculations, a more convenient biaxial ellipsoid of revolution is used, while it does not differ much from the shape of the earth. The surfaces of the ellipsoid and geoid differ within 100 meters in one direction or another.

The shape of an ellipse is defined by two radii. A longer radius is called the semi-major axis (usually denoted by the letter a), and a smaller (shorter) radius is called the semi-minor axis (usually denoted by the letter b).

Figure 23. Ellipsoid

The ellipsoid of revolution that best fits the surface of the geoid is called the general earth ellipsoid or earth ellipsoid.

The ellipsoid that best fits the geoid on a limited part of its surface is called a reference ellipsoid (from Latin referens - auxiliary).

An ellipsoid of revolution can be defined either by the semi-major axis, a, and the semi-minor axis, b, or by the magnitude of a and contraction.

Compression is the difference in length between two axes, expressed as a fraction or decimal:

Compression is a small value, so 1/f is typically used instead.

		Major axle (a) , m	1/f
Krassovsky	1940	6 378 245	298.299 738 1
WGS-72	1972	6 378 135	298.26
GRS-80	1979	6 378 137	298,25
	1984	6378137	298.257223563
PZ-90	1990	6 378 136	298.258

In addition to the ellipsoid, geodesy uses such a thing as a datum. Datum (lat. Datum) - a set of parameters used to shift and transform the reference ellipsoid into local geographical coordinates. The term datum is used in geodesy and cartography for the best approximation to the geoid at a given location.

The datum is set by shifting the reference ellipsoid along the axes: X, Y, Z, as well as by rotating the Cartesian coordinate system in the plane of the axes by the angle rX, rY, rZ. It is also necessary to know the parameters of the reference ellipsoid a and f, where a is the size of the semi-major axis, f is the compression of the ellipsoid.

There are two types of datums - geocentric (global) and local. A geocentric datum uses the earth's center of mass as its origin. The origin of the coordinate system for the local datum is shifted relative to the center of the earth. The local datum changes the position of the ellipsoid so that its surface is most closely aligned with the desired area. The local datum should not be used outside the area for which it was designed.

The most widely used datum is the World Geodetic System 1984 (WGS84), which is based on the WGS-84 ellipsoid centered on the earth's center of mass. Also, one of the fairly common datums (used in Russia and some surrounding countries) is Pulkovo-1942 (SK-42), which is based on the Krassovsky ellipsoid, its origin is offset from the center of mass by a distance of about 100 m.

The WGS-84 system is widely used abroad, it is used for almost all data produced in the world, it is also used in almost all navigators. SK-42 is widely used in Russian cartography; all topographic materials of the VTU General Staff of the Russian Federation (Military Topographic Directorate of the General Staff of the Russian Federation) are based on it.

Datum	Description
WGS84 (World Geodetic System 1984)	A global datum using a geocentric global ellipsoid calculated from accurate satellite measurements. Used in the GPS system. It is currently accepted as the main one in the USA.
Pulkovo-1942 (SK-42, Coordinate System 1942)	Local datum using the Krassovsky ellipsoid, as close as possible to the European territory of the USSR. The main (in terms of prevalence) datum in the USSR and the post-Soviet space.
PZ-90 (Parameters of the Earth 1990)	Global datum, main (since 2012) in the Russian Federation (used for the global navigation satellite system GLONASS).
SK-95 (coordinate system 1995)	Local coordinate system, used in Russia (since 2002) for the publication of maps and geodetic works.

We have known since childhood that the earth is round, but at first we did not really understand why the Australians do not fall from it.

From geography, we learned about meridians and parallels and that any point on earth can be accurately indicated by its coordinates - latitude and longitude in degrees, minutes and seconds.

Everything was clear and understandable until we bought a satellite navigator - GPS. The very first attempt to find a point marked by a GPS navigator on the map led to an error of a good hundred meters, despite the declared accuracy of 3-5 meters. It turned out that the meridians and parallels of the Americans are not at all the same as ours. Moreover, almost every country has its own. In order for the coordinates to match, you must specify in which coordinate system they are given. The parameters of this system are set by a set of coefficients, which is called one not entirely clear word "datum" ( datum). It is with this datum that a lot of problems and misunderstandings arise.

The shape of the earth and its mathematical expression.

Until recently, it was not clear to me why there are so many different systems. If you take an arbitrarily crooked land and carefully cut it into slices through the poles and Greenwich, and then from the equator into watermelon slips, then why should it be different? Well, let where it is more convex, the meridians will pass less frequently than in other places. It's just that the map of this place will be a little wider. It doesn't really matter.

The answer turned out to be simple - until recently we did not have a knife of this size. We express coordinates in angular degrees, but we measure the earth in kilometers and meters, forced to crawl along its surface. At the same time, we constantly have to convert meters to degrees and degrees to meters. This is not difficult if you know and mathematically describe what shape the earth has. This is what they did with varying success. earth scientists dating from the fourth century BC.

Let us omit the historical vicissitudes of this process, and move on to times not so distant. The most accurately known shape of the earth is called " geoid". This is not a land with mountains and valleys, but an imaginary surface of the seas and oceans, if it is continued under the continents. On such a land, at any point, gravity is directed strictly perpendicular to its surface.

The geoid is expressed mathematically in terms of the coefficients of the spherical harmonics. For example, geoid Gravity Earth Model EGM 96, uses spherical harmonic coefficients for polynomials up to order 360. For the complete geoid equation EGM 96 more than 60,000 coefficients are required. It is clear that it is too difficult to use all of them to calculate the surface. A simpler figure is needed, but with sufficient accuracy for us to describe the earth.

If we consider the earth as a ball, then we will be mistaken by at least 22 kilometers. If you flatten it a little from the poles and imagine it in the form ellipsoid of revolution(biaxial ellipsoid), then the error will decrease to 150-200 meters. Even greater accuracy can be achieved by squeezing the Earth a little more from the sides. Such a figure is called triaxial ellipsoid.

There is another method to improve accuracy - you can take a simpler (two-axis) ellipsoid, but move and rotate it a little so that it matches the Earth's surface in a given country as much as possible. That's what they usually do.

If we omit the geodesic subtleties, then for us datum is the size of the ellipsoid taken as a basis in a given country(the so-called reference or reference ellipsoid) plus coefficients characterizing its displacement and rotation, for alignment with the territory of a given country.

National coordinate systems

Geodetic subtleties lie in the fact that the datum is determined not by coefficients, but by the coordinates measured on the ground of several dozen reference points evenly distributed throughout the country. Datum parameters are chosen such that all points are displayed on the selected ellipsoid with minimal deviations. I.e, if a geodetic survey of the area was carried out and some maps were compiled, then their datum exists, even if its parameters are not known to anyone.

Usually, some well-known point is chosen as the base point, for example, the center of the hall of the Pulkovo Observatory. Astronomical methods determine its coordinates, the azimuth to some distant object and the distance to it as accurately as possible. This is the reference point of the geodetic system. Then the triangulation method determines the coordinates of other points that form the geodetic network.

The triangulation method is as follows. It is very difficult to measure distances on land covered with mountains and lakes. On the contrary, angles with the help of an optical device - theodolite can be measured simply and very accurately. Knowing the angles and one side of the triangle, you can very easily calculate the remaining two. Consistently building triangles (triangulation moves), you can move far enough, almost without losing accuracy. To be sure, several people come to each point different ways to check if an error has crept into measurements or calculations. By projecting distances and angles onto the selected ellipsoid, we can calculate the geographic coordinates of all the points we need.

As a reference ellipsoid in the USA is used Clark's ellipsoid, calculated in 1880 year. More popular in Europe Bessel ellipsoid 1841 of the year. The same ellipsoid was used for determining coordinates and mapping in Russia until 1946. In other countries and in different years at least two dozen ellipsoids of various shapes and sizes were also used.

Contrary to what is written in many popular articles, all these ellipsoids are biaxial - taking into account only the polar compression of the earth. The first triaxial ellipsoid was calculated in the USSR under the guidance of academician Theodosius Krasovsky in 1940. However, the coordinate system introduced in the USSR in 1946 SK42 and those who followed her SK63 and most modern SK95 use its biaxial version. The triaxial ellipsoid was successfully used to calculate the trajectories of Soviet ballistic missiles.

The differences between ellipsoids and their associated datums are such that a point with the same coordinates, but in different datums, can differ on the ground by a few meters, which is quite acceptable, up to several kilometers, which does not suit us at all.

Local coordinate systems

Even in the most accurate geodetic measurements, errors gradually accumulate, reaching several meters within a country like Russia. In order to slam an atomic bomb on the head of a hated enemy, such accuracy is enough, but two gardeners for half a meter of earth will cut each other's throats. The mayor of a provincial town is interested in the distance from his native Muhosransk to their Paris purely theoretically, but whether a new house will fit between two already built houses and whether it will be necessary to dig up the entire area in search of a gas pipeline are quite pressing questions.

To compile very large-scale maps and plans used in construction and land management, absolute accuracy is not needed, but distances between buildings and structures are needed with centimeter accuracy. As a result, local surveyors "give up" on state system and all measurements are carried out in their own - local. They literally hammer a peg in their city, consider it a starting point and have no problems as long as they do not have to build a bridge across the river separating the two areas. This is where the question of interconnection of local coordinate systems arises, which is solved for a long time and very painfully.

Global coordinate and reference systems.

With the advent of the space age, finally, it was possible to look at the earth from the side, more accurately determine its shape, size and correctly "cut" into parallels and meridians. As a result, an ellipsoid appeared in the USA WGS84 and the common earth coordinate system of the same name, and in the USSR the coordinate system " Land parameters PZ-90", which differ from each other by only half a meter. Europe already has its own system, designed for the still defunct Galileo navigation system.

The reference is considered "International Terrestrial Reference Frame" (ITRF). Its position in the body of the earth is monitored around the clock by satellite measurements of the coordinates of several hundred points around the world. the globe. Its accuracy is such that the coordinates in it are influenced not only by the movements of the continents by several centimeters per year, but also by the melting of glaciers and large earthquakes. Therefore, the parameters of this system are published annually, and the coordinates of points in this system are given with the obligatory indication of the epoch (year) when these coordinates were measured. So, WGS84 tied to the system ITRF era 1984, and PZ-90 respectively to ITRF 1990.

Coordinate systems of satellite navigation systems WGS84 and PZ-90 also remain unchanged. They become more accurate and more convenient to use. WGS84 During its existence, it was thrashed 3 times. Version currently in use WGS84 G1150. True, the changes are so small that users of household GPS navigators may assume that they did not exist.

A completely different situation with the Russian PZ-90. In November 2007, the system was changed and became known as PZ-90.02. Its parameters changed by several meters at once, but on the other hand, it began to almost coincide with ITRF and WGS84. Again, for users of navigators, they can now be considered identical.

Coordinates in global systems are measured not in degrees, but in meters, a three-dimensional Cartesian system familiar to us from school, where the Z axis is directed from the center of the earth to the north pole, the X axis crosses the Greenwich meridian, and the Y axis is directed, as always, sideways.

Maps are not made in global reference systems and their ellipsoids are not reference. Their task is to interconnect different datums different countries and regions and determination of coefficients for accurate conversion of coordinates from one system to any other and vice versa. The exception is WGS84, which, thanks to GPS, has become so popular that making maps based on it is an occupation, although not entirely legal, but very common.

Coordinate transformation.

Convert degree coordinates to Cartesian X, Y, Z.
Rotate and shift the coordinate system to match the new datum
Calculate new coordinates
On the new ellipsoid, determine the new coordinates in degrees.

Recalculation of coordinates in the shifted and rotated system is carried out according to the formulas Helmert transformations (Friedrich Robert Helmert ). The calculations require three parameters for offset, three for rotation angles, and one scale factor. Therefore, this transformation is often called "semiparametric". Converting to degrees will require two more parameters of the ellipsoid - the diameter and the degree of polar compression. Conversion factors are calculated for each country and approved by the relevant normative document. For Russia it GOST R 51794-2001.

We won't count anything. It's too difficult for us. Ordinary satellite navigators do not do this either, but use more simple formulas proposed by Russian scientists M. S. Molodensky. According to these formulas, the coordinates are converted directly from degrees to degrees and require only 3 coefficients to set the datum ( dX, dY, dZ) plus two ellipsoid parameters ( da and df). In the practice of satellite navigation, a set of five coefficients for converting coordinates from WGS-84 to a given coordinate system and are called the datum of this system. These five coefficients will have to be entered into your navigator or navigation program if it does not know the datum you need.

Shift factors for transformation Hemerta and Molodensky generally do not match. The first three parameters of the semparametric transformation cannot be used in Molodensky's formulas. In particular, you should not use receivers and programs, coefficients and the above GOST for input into GPS.

For a map with an unknown datum, it can be calculated by knowing the coordinates of three points in WGS and from the map, as well as the parameters of the ellipsoid on which it is built. There is a free program for this. It is done like this:

Create a custom datum with the parameters of the desired ellipsoid and zero coefficients (as it is done in OziExplorer, described in the last chapter of this article), and bind the map to this datum.
Find three points on the map and write down their coordinates in this datum.
Find the coordinates of the same points in WGS84 by going there with a navigator or by finding them in GoogleEarth.
Convert all coordinates into seconds, multiplying degrees by 3600 and minutes by 60, and enter them into the program.
Change the zeros in the datum to the obtained coefficients, restart OziExplorer and check if the actual points match the points on the map.

To go from WGS84 to Pulkovo 1942 and back, you can calculate these parameters for your region yourself using an excel spreadsheet.

The Molodensky transformation is not accurate, especially if the coordinate systems are rotated relative to each other and is valid only for a limited area. For different countries and their systems, errors can reach 30 meters, but for the datum adopted in Russia and Ukraine Pulkovo-1942 usually do not exceed a few meters. This is quite enough, considering that the SK42 system itself has local deformations of up to 10 meters, and terrain objects on the maps available to us are often plotted with errors from 50 to 100 meters. It should be noted that under the name " Molodensky transformation"As many as three different sets of formulas can be hidden, differing in varying degrees of simplification. Which of the three is used in a given device or program is known only to its developers.

Zero meridians

If you had the patience to read up to this point, then you obviously still remember something from the school geography course. You know for sure that geographic latitude is measured from the equator and is north and south. Meridians are considered to be west and east of the prime meridian or Greenwich, which is located in distant England. But Britain has not always been the mistress of the seas and has never been the leader of world astronomy and geodesy. Therefore, the prime meridian did not originally belong to them.

Initially, everything was much more correct and smarter. In order not to bother with east and west longitude, the zero meridian was placed at the westernmost point of the old world - Ferro Island (El Hierro) Canarian archipelago and tied him to a lonely lighthouse on a deserted rock. As a result, all of Europe ended up in the eastern hemisphere, and America in the western, which was very convenient. It was not convenient that the island was located far in the ocean, and at that time it was almost impossible to accurately measure the distance to it. Then a Solomonic decision was made - to agree that from Ferro to Paris, where at that time there was one of the most modern observatories, in latitude exactly 20 degrees. After that, all meridians were measured from Paris, and on the maps they wrote from Ferro, adding 20 degrees. Subsequently, it turned out that this lighthouse from Paris is 29 minutes or 50 kilometers further, but this did not change anything.

In the middle of the 19th century, Russian surveyors Carl Tenner and Vasily Struve very accurately measured the arc of the earth's meridian, and Fedor Shubert, having loaded several dozen high-precision chronometers with him, he went to check the meridians. As a result, the exact coordinates of several hundred settlements throughout Europe, including the exact coordinates of the Pulkovo Observatory. Since then, all measurements in Russia have been made from Pulkovo, and the coordinates on the maps were written first from Ferro, and then from Pulkovo and Paris, and only at the beginning of the twentieth century did Greenwich appear on the maps.

In order to recalculate the coordinates on old maps to modern Greenwich, you need to add to them or subtract the corresponding difference from them. It is better to take this value exactly as it was considered at the time of the map, for example, from Schubert's book "Expos des travaux astronomiques et geodesiques executes in russie":

At the same time, we must not forget that longitude from Pulkovo can also be east, and it must be added to the longitude of Pulkovo, and west, which must be subtracted. Those who do not remember how many minutes are in a degree or are not able to add decimal-hexadecimal numbers in a column can use the Excel tablet -.

Datums of our Motherland.

Russian empire.

Maps for which it makes sense to speak of a datum appeared in Russia at the beginning of the 19th century. These maps were compiled on the basis of instrumental surveys, which were very accurate for that time, using the form of the earth that best corresponded to the shape of the earth known at that time, Bessel ellipsoid 1841. A degree grid was applied to the maps with the longitude indicated, for later maps - from Pulkovo and Paris, for earlier ones - from Ferro. By the way, the longitude of Ferro Island known at that time was very different from the more accurate values that became known later.

Maps of Mende. Major General A. I. Mende supervised topographic surveys over most of the territory European Russia during 1848-1866 years. Wherein Tverskaya, Ryazan, Tambov and Vladimirskaya provinces were mapped on a scale of 1 verst in 1 inch, Yaroslavskaya- 2 versts in 1 inch, Simbirskaya and Nizhny Novgorod- 3 versts in 1 inch, Penza- on a scale of 8 versts in 1 inch.
A distinctive feature of these cards is that they are made in color. The longitude on them is indicated from the island of Ferro.

Schubert cards. Lieutenant-General Fedor Fedorovich Schubert supervised topographic work in Russia from 1819 to 1843 and, therefore, all maps published in those years were directly related to him. However, Schubert's maps are considered to be only issued in 1848 on 6 sheets. topographic map of Moscow suburbs on a scale of 1 verst in an inch, two-verst map of the Moscow province 1860 on 40 sheets and published from 1821 to 1839, Special map of European Russia on a scale of 10 versts in an inch, projections Bonn and coordinates from Ferro. Three-verst maps of Russia, published later (since 1850), cannot be considered Schubert's maps.

When compiling his maps, Schubert did not pursue the goal of obtaining such a high accuracy, which was characteristic of the triangulations of Tenner and Struve, who at that time were in charge of similar work in Russia. He paid the main attention to the details and reliability of the image on the maps of local objects.

Strelbitsky's maps. In 1865, under the leadership of the Captain of the General Staff, Strelbitsky, work began on the reprinting of Schubert's ten-layouts, which were not very accurate. New Special map of European Russia 10 versts to an inch on 174 sheets, already in the Gaussian conic projection with coordinates from Pulkovo and Paris, was published in 1971, supplemented and republished until 1919.

Military topographic map Russian Empire on a scale of 3 versts per inch began to be published in 1850. Shooting, correction and publication of additional sheets continued until the beginning of the 20th century. These maps are quite detailed and cover the largest area.

How accurate are pre-revolutionary maps? It is impossible to assess the accuracy of maps without knowing their datum and projection parameters. Using them with inappropriate datum parameters and in the wrong projections leads to errors in determining coordinates up to several kilometers. For scientific circles, these maps are, apparently, only of historical interest. Anyway, scientific work devoted to the study of pre-revolutionary maps from the point of view of geodesy, are unknown to me.

Linking maps in the OziExplorer program, taking into account the parameters of their projections on the Bessel ellipsoid with zero transformation parameters, revealed discrepancies between the image of objects on the map and their real position on the ground no more than a kilometer for Strelbitsky's maps and no more than 400 meters for any of the triverstages. Statistical processing of the coordinates of several dozen objects on a three-verst map of the Yekaterinoslav province of 1888 revealed a spread in their values within 300 meters with an average shift of about 200 meters, which made it possible to calculate the datum for this map - Bessel, 3,606,151,407.

Find out whether this displacement is a datum difference or is it a local deformation within a particular region, without processing a large amount of experimental data collected almost over the entire territory of Eastern Europe until it is possible.

Coordinate system 1932 (SK-32).

The introduction of a new coordinate system in the Soviet Union was due not only and not so much to the results of large-scale and more accurate geodetic measurements, but to the transition to new types of cartographic projections and a new coordinate notation system. Now the coordinates of geodetic points were no longer expressed in degrees, but in meters according to the system Gaussian- the distance from the equator along the X axis and from the nearest meridian of the six-degree zone along the Y axis. New maps were compiled and published already in a more progressive and accurate Gauss-Kruger projection and are currently known under the name " Maps of the General Staff of the Red Army". There was also a harmonious and convenient system for designating sheets of maps of various scales, which is still used today.

Maps of the General Staff of the Red Army built on the Bessel ellipsoid at scales of 1, 2 and 5 kilometers per centimeter. Their datum is most likely known, but not published anywhere. Checking their accuracy on the example of several maps of the north-west of Ukraine at a scale of 1:50000 when referenced in a datum Bessel,3,0,0,0 showed that in terms of accuracy they are no worse than similar cards in SK-42.

Coordinate system 1942 (SK-42).

Extensive and more accurate geodetic measurements taken in prewar years under the guidance of academician Krasovsky, showed that the Bessel ellipsoid is completely unsuitable for displaying such vast spaces as the territory of the USSR. As a result, a more accurate ellipsoid was adopted as the reference ellipsoid Krasovsky 1940 and a new coordinate system SK-42 officially approved in 1946. From that moment, the titanic work began on a more accurate triangulation of the country's territory and the compilation detailed maps throughout its territory. This work was completed only 30 years later, and we still use its results and, I think, will use it for a long time to come.

Datum cards in SK-42, used in GPS navigators and the program OziExplorer entitled " Pulkovo 1942", usually uses the values recommended by the ITU ( dX=28, dY=-130, dZ=-95, da=-108, df= +0.004808).

1963 coordinate system (SK-63).

The brainchild of the cold war system SK-63 owes its appearance not to surveyors, but to Soviet counterintelligence officers. The idea was simple. If all cards are SK-42 move and rotate a little, then within the same map it will be possible to safely build houses and roads and not make it very secret. But the evil enemy, not knowing the deeply classified shift and turn coefficients, will no longer be able to aim his missiles from one map to another. In fact, every card in SK-63 is a map in a local coordinate system with its own, secret datum. True, they did not become less secret than the previous ones. I have never gotten my hands on these.

In a few years, satellite intelligence has become so successful that maps for targeting missiles are no longer needed. Yes, and terribly secret coefficients by this time, of course, had already been stolen. SK-63 canceled and returned old, good SK-42.

SK-95 system

The advent of satellite navigation made it possible to make more accurate measurements and to check the previously considered very accurate geodetic network of Russia. It turned out that many regions are depicted on maps with an unacceptable error, and Kamchatka generally "left" as much as 10 meters. As a result, everything was accurately re-measured and not by several dozen, but by several hundred points, and a new coordinate system was adopted. SK-95, already tied to PZ-90, and together with it to WGS-84 and to ITRF.

Since the center of the hall of the Pulkovo Observatory is still considered the base point of the new system, the inhabitants of European Russia, Ukraine and Belarus need not worry. On their territory, it does not differ from the SK-42.

When will the cards be available? new system unknown. I think - never. While it will be implemented, the whole world will switch to anything global, even to the same WGS84.

SKU 2000.

The first own Ukrainian coordinate system became a "tough response to the evil Muscovites" for the adoption of the SK-95. In addition to high-profile statements in the mass press, I found nothing about her. Deep digging on the Internet confirmed me in a purely personal opinion that behind it, apart from political slogans and the desire of Ukrainian scientists to achieve at least some kind of funding, nothing is worth it. I think that her fate is even more sad.

As a result, everything that I wrote here about coordinate systems, you can safely forget. To use satellite navigation, one is enough WGS-84. To work with maps, you will need a datum available in any navigator and in any program. Pulkovo 1942. And only black diggers will have to use their brains and figure out custom datums and tricky projections.

Coordinates and datums in satellite navigators.

The main and only task of any GPS receiver, as well as GONASS, by the way, is to constantly determine the current coordinates of the place where it is located. He doesn't do anything else, and he shouldn't. All other functions: calculating speeds, distances, directions, recording points and tracks, displaying a map and laying routes - this is the merit of a computer built into it or connected to it and a smart program.

In order not to have problems - remember once and for all: All GPS navigators perform all calculations in their native WGS-84 system. In the same system, they store points, tracks and routes in their memory. In it, it is customary to transfer coordinates to computers and other devices and save data to files. The coordinates of roads, settlements, mountains and lakes in the map loaded into the navigator are also stored in WGS, regardless of the system in which this map was built. GLONASS receivers do the same, but in their PZ-90.

Even if your GPS receiver can transmit data in a system other than WGS-84, and the program can receive such data, never do this. At best, you will lose accuracy on two extra conversions, and at worst, your points will "leave" by 150 meters and you will be asking for a long time on the forums why.

To use the navigator, you do not need any other datums other than WGS-84 at all. In this system, you can store coordinates, send them to friends, publish them on the Internet. At such coordinates, the rescue service of any country will quickly find you, despite the fact that they may have adopted a different system. You may need another datum only if you have a paper map in a different coordinate system, and you want to find the current point on this map or enter the coordinates of the point determined from the map into the navigator. For this, and only for this, you need to change the datum in the navigator.

Changing the datum setting in the navigator in no way changes the way it works. It calculates, stores and transmits everything, as before in WGS-84, and only when the coordinates need to be shown on the screen, it counts them into the system you need. The coordinates entered by you from the keyboard, it, first of all, converts to WGS and then acts with them as usual.

Most navigators have a whole list of datums to choose from. If, unfortunately, this list does not contain exactly the datum that you need - do not despair. There's a datum called " user" or "custom". Select it and manually enter the coefficients to convert WGS-84 to the datum you need. Where to get these coefficients is a separate question.

If you have changed the datum in the navigator, in order to avoid problems, warn everyone to whom you are trying to send some coordinates in one way or another that they are not in WGS-84.

Coordinate display formats

This question is not related to datums, but can also be a source of serious problems.
In geography lessons, we were taught that coordinates are given in angular degrees, minutes and seconds. Many, but, oddly enough, not all, still remember that there are 60 minutes in a degree and 60 seconds in a minute. Satellite navigators are so accurate that arcseconds are also shown with decimal fractions after the decimal point. For example, the coordinates of the famous Dzhur-Dzhur waterfall in Crimea will be shown as follows:
44°48"19.44"N 34°27"35.52"E
more like this
44 48 19.44N 34 27 35.52E

This format is indicated in the literature and in the settings of navigators as DD MM SS.SS- degrees (degrees), minutes (minutes) seconds (seconds). But he is not the only one. In satellite navigation, a different format is more often used - DD MM.MMMM(degrees and minutes with decimals). The same waterfall in this format:
44°48.3240"N 34°27.5920"E

Many programs and Excel spreadsheets need the coordinates in degrees as an ordinary real number - DD.DDDDDD. Very often, in this format, coordinates are written to files and transmitted over cables. Like this:
44.805400N 34.459867E
or even so
44.805400,34.459867

If you are able to multiply and divide by 60, then there is nothing complicated here. The main thing is not to confuse and not confuse others.

If such transformations have to be made frequently, then you can use a completely free program.

In all navigators, you can select at least any of the three listed formats. Often there is also a display of coordinates in meters UTM or User Grid. Such coordinates are very convenient when working with paper maps. Therefore, we will talk about it where we talk about cards.

Datums in OziExplorer.

Program OziExplorer became very popular because it can work with raster (scanned) maps. At the same time, it can work with maps of various countries, built in various datums and made in many different projections.

In order to take advantage new card, you need to load the picture with the map into the program, specify the datum and projection of the map to the program, and then indicate several points on the map with known coordinates. This very simple process, called map linking or calibration, is described in detail in many detailed instructions scattered all over the Internet. At the same time, almost every new user of this program at least once encounters a situation where the entire map moves to the side or when the points loaded from the navigator are not at all where they should be on the map. Most often, these situations are caused by errors in setting up datums.

Datums in the OziExplorer program are configured or selected in as many as six places. At the same time, Ozi himself performs all actions and calculations in WGS84, correctly recalculating coordinates to other systems, if necessary.

Initially, OziExplorer is set up correctly, but not understanding how it works with datums forces the user to change settings and, as a result, constantly get problems with coordinate mismatches.
So, let's list six OziExplorer datums and see what they affect:

Map Datum- set in the first tab of the map calibration window. This datum must correspond to the datum in which this map is made. Rather, it is a datum in which it is more convenient for you to enter the coordinates of the calibration points marked with the cursor from the keyboard.

If you calibrate using real points loaded from a file, then the datum in which they were measured or saved to the file does not have to match the datum of the linked map at all. Ozi himself will recalculate everything and show the coordinates already in the desired datum.

If you made a mistake with the datum when linking the map, then the whole map will be shifted relative to the terrain by the difference in datums. In this case, all degree and kilometer grids will exactly match the grids on the map. The difference between Pulkovo 1942 and WGS84 for Ukraine is about 125 meters with an offset to the southwest (azimuth 260). If only this card moved to such a distance, you obviously overdid it with the datum when linking this particular card.