/kloc-What areas did China investigate in the 20th century and what achievements did it make?

The investigation area extends from Hami, Xinjiang in the northwest to Sichuan, Guizhou, Yunnan and Tibet in the southwest, and all the way to the source of the Ganges River. 17 17, the world's highest peak, Mount Qomolangma, was discovered by surveyors in China, and this peak was first marked on the imperial map in the early Qing Dynasty. This is before Effie, a British surveyor from Indian Survey Bureau, began to measure this peak in 1852 135 years. Northeast China goes deep into Heilongjiang and Liaodong. Southeast to Fujian, Taiwan Province Province and Hainan Island. The longitude and latitude points measured are all ***64 1 except Tibet, which are almost all over the vast territory of China. The measurement methods include astronomical survey and geodetic triangulation. At that time, latitude was mainly determined by the high arc of the sun at noon. However, due to the inconvenience of night measurement and the inaccuracy of instruments, the latitude determination method of Polaris is rarely used in practice. At that time, the longitude was mainly measured by the eclipse longitude method, that is, the longitude was calculated by observing the time difference of eclipses in different places. Sometimes it is difficult to use the observation of eclipse. "A series of triangles are measured by careful calculation of the triangle control network, and the coordinates of each point are calculated by the plane triangle. Measuring the included angle with a telescope, first accurately measuring the baseline, then calculating by triangulation, from near to far, or using known mapping points for reverse survey ... so that the newly measured map has considerable accuracy and has become a basic work of China's geographical map industry. "

Since then, in the 21st and 24th years of Qianlong (1756, 1759), the Turpan area in Xinjiang and the Kaidu River basin, as well as the vast area south of Balkhash Lake in the former Soviet Union from Hami to now, have been re-surveyed. The survey was conducted with Chinese surveyors as the technical backbone.