# Principle of geographic reference system transformation

Source: Internet
Author: User

1954 the Beijing coordinate system is not established independently based on the theory of elliptical positioning, but uses the krausowski elliptical parameter and passes through the three backbone networks of the Northeast Border, namely Huma, jilalin, and Dongning, through the big geographic network connection with the Soviet Union, we can obtain the longitude and latitude of a trunk three-focal GIS in Beijing and the Earth azimuth to another point through computation. Then, we established the China earth coordinate system, which was named the Beijing Coordinate System in 1954. Therefore, the Beijing Coordinate System in 1954 is actually an extension of the Soviet Coordinate System in 1942. Its origin is not in Beijing, but in polkovo, the Soviet Union. The coordinates of polkovo are
59. 46 '18 ''. 55 (N)
30. 19 '42 ''. 09 (E)
1980 the origin of the national Earth coordinate system is located in Yongle town, Zeyang County, Shaanxi Province. It is called the origin of Xi'an.

1975 International elliptical parameters are used. String 2

The 80 coordinate system has many advantages over the 54 coordinate system, but many of our country's surveying and mapping achievements are based on the 54, which is actually a vivid example of China's science and technology lagging behind, and being forced to be subject to people.

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Let me talk about it now. Different The conversion method of the reference system. String 1

Different geographic reference systems are customized to meet the needs of surveying and drawing in various countries. Generally, a specific frame of reference can only be applied to a specific region. At the same point on the earth, the longitude and latitude are different under different reference systems. In GPS, there are two ways to convert different Earth reference systems. One is to use spatial Cartesian coordinates as a bridge to achieve the purpose of conversion, which is called an indirect method; one is to directly find the correct number of the Earth coordinates, called the correct number method (elliptical variation differential formula ). Neither of these two methods can be clearly stated. It involves many long formulas. I can't enter any mathematical symbols, So I provide reference books:

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Xu Shaoyi, Wu zuyang, Wuhan ing Technology University Press, p294, chapter 13, coordinate system transformation
This book is available in Haidian Emy of Science and Technology Press. This book is actually not very good. If you are interested, you can look at the principles.

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For actual work, understanding the principle is only a small step forward, sometimes even a few steps backward. String 9

In professional GIS software, we can convert the data by clicking the mouse. In the coordinate system dialog box, select translate, and then select new in the pop-up Geography System Transformation to create a conversion. We need to set the conversion method for this conversion. Different conversion methods require us to set different parameters. Obtaining these parameters is a pain point. I do not know the value of 54 to 80. I once consulted the National Basic Geographic Information Center about the conversion parameters. They called it a secret. If you have data to be transferred, they can have GIS. In fact, I am not familiar with the mysteries of this, and I have no important data to translate.

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If we do not have a precise conversion parameter, it is not necessary. We only need to set three offset parameters. The 54 coordinate system can be used to locate the parameter according to the polkov coordinate, which can be obtained. However, the three parameters of 80 are too difficult.

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All in all, to use a computer to convert the earth coordinate system, you only need to specify the conversion method (I think it is enough to use three parameters) and then set three parameters, the longitude and latitude of one coordinate system can be corrected to another coordinate system. String 4

The conversion parameters of local datum to the central coordinate system can be freely downloaded from www.nima.mil/gandg/pubs.html. This is the site of the US National ing and cartography Bureau.

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