In order to calculate the coordinates of the main points in the "geodetic network", it is necessary to choose a point as the starting point, which is the geodetic origin, also known as the geodetic datum. Usually, a medium point in the national geodetic network is selected as the origin, and the astronomical latitude, longitude and astronomical azimuth from it to another point are measured with high accuracy. According to the method of "reference ellipsoid" positioning, the geodetic latitude and longitude, geodetic height and geodetic azimuth to another point are obtained. These data are called "geodetic datum".
In the early days of the founding of the People's Republic of China, China did not have its own geodetic origin, but adopted the geodetic coordinate system with the former Soviet Bolkov Observatory as the coordinate origin, which was extremely disproportionate to China's construction and development. China adopted the Beijing coordinate system of 1954, with Leningrad in the former Soviet Union as the origin and Krasovsky ellipsoid as the reference ellipsoid. Ellipsoid is far away from China, which has large calculation error and many disadvantages, and it is difficult to meet the needs of China's high-tech development. Therefore, the relevant state departments decided to establish an independent geodetic coordinate system.
Starting from 1975, the relevant departments organized manpower, collected and analyzed a large amount of data, and conducted on-the-spot investigation and comprehensive analysis on topography, geology, geotectonics, astronomy, gravity and geodesy of several cities according to the requirements of "origin", and finally determined that the origin of China geodesy was Beiliu Village, Yongle Town, Jingyang County, Shaanxi Province.
The specific location is 34 32 ′ 27.00 ″ north latitude, 0/08 55 ′ 25.00 ″ east longitude and 417.20m above sea level. ..
The reason why the geodetic origin is located in Yongle Town, Jingyang County is explained in the Report on the Selection of Geodetic Origin of the People's Republic of China: "In order to make all aspects of geodetic data calculate evenly, it is best to locate the geodetic origin in the middle of Chinese mainland."
Shijisi Village, Yongle Town, Jingyang County, Shaanxi Province, is indeed in the middle of Chinese mainland. It is 880km to the north, 2500km to the northeast, 0/000km to the east, 0/750km to the south, 2250km to the southwest, 2930km to the west and 2500km to the northwest of China. At the same time, the geological conditions here are also ideal:
First, the geographical location is in the middle of China's territory;
Second, the geological structure is stable;
Third, the underground material is stable;
Fourth, all sides are transparent, and there is no big shelter, which is convenient for observation;
5. It is close to Xi 'an, with convenient transportation, which is convenient for surveying and mapping workers to carry out their work.
Geologically, the birthplace of the country is located in the hinterland of Guanzhong, 800 miles from Qinchuan, and the underground is silted loess, so it is relatively stable. In addition, there are no mineral resources in the place where the earth originated, and there has never been a major flood in history. Therefore, it is unlikely to be threatened by artificial excavation and flood. It is basically safe and stable to set the origin of the earth here. The terrain of Lanzhou is relatively narrow, and the geographical position of Zhengzhou is slightly to the east. Wuhan was flooded because of the Yangtze River. Considering these aspects, it abandoned the construction of the origin of the earth in Lanzhou, Zhengzhou and Wuhan.
After the completion of Origin of People's Republic of China (PRC), relevant experts found that the ultra-long baseline of 1000 km in the Western Han Dynasty in China passed through here. The building baseline measured more than 2000 years ago is basically consistent with the origin of People's Republic of China (PRC) and China, with a difference of only 2 seconds longitude (60 meters). This coincidence in the history of ancient and modern surveying has deeply touched the archaeological and surveying circles.