A monumental undertaking

Although authorities conducted a general survey of the ancient barrier with basic information, such as its length and construction period, Li says their program aims to highlight details, such as the complex structure, the location of facilities and the sections with potential risks.

It is not an easy task, because most parts of the Great Wall are located in remote areas. Even with the assistance of the monitoring technology, such as satellites, drones and planes, the team must access these places for closer examination.

"From our images, you can see the lines between the bricks," Li says, adding that every kilometer of the wall requires about 300 high-resolution photos.