How did they accurately dig those curved tunnels without emerging out of the mountains at the wrong spot? The surveying has to be 100% spot on.
@坐地球看世界2 жыл бұрын
There are surveyors on the ground, and China's Beidou satellite navigation in space
@syncmaster915n2 жыл бұрын
@@坐地球看世界 I know China has the Beidou nav sat. My question was how did they do it inside a long, curvy tunnel which snakes around. I don't think satellite signal can penetrate mountains, can it?