Hands-on precision paves way for engineering feats

For Chen, 37, who has spent a decade in surveying, the profession's role is widely underestimated.

"Surveying is the only way to turn design coordinates into physical structures on the ground," he said. "Without it, construction loses its spatial benchmark — we cannot achieve precise positioning and alignment across such drastic elevation changes and complex geology."

The Lhasa-Nyingchi section, stretching 403.14 km, was put into operation in 2021. The more geologically extreme Ya'an-Nyingchi section remains under construction, with surveyors continuing to provide measurement support.

For the Hong Kong-Zhuhai-Macao Bridge — a 55-km crossing that opened in October 2018 as one of the world's longest sea links — the fundamental challenge was simple: three jurisdictions, three coordinate systems and one massive structure that had to be built as a single, continuous whole.

"Each place had its own coordinate system and height reference," said Shang Xiaoqi, a surveyor at the First Geodetic Survey Brigade who led the project's precision engineering survey division.

"We can think of the bridge design as a puzzle. Without a unified benchmark for both coordinates and elevation, you simply cannot bring the pieces together or place them in the correct position," Shang said. "The heights won't match, the positions won't align, and the bridge will twist and deform." He described such a scenario as "an engineering disaster".

He took elevation benchmarks as an example, noting that the real danger lies in what surveyors call an "elevation break" — two halves of the bridge, built from opposite shores using different elevation benchmarks, could misalign by tens of centimeters or even meters at the final closure. Such a mismatch would not surface during early foundation work. It would appear at the worst possible moment: when the bridge was supposed to close its final gap.

Before the bridge existed, Shang's team had to transfer elevation data from the Zhuhai side all the way to the Hong Kong side — a task that, with no bridge to walk across, meant routing through Shenzhen. The team measured on foot, crossing the river at the Futian Port border crossing and making its way to Lantau Island.

The total distance was more than 250 km of leveling, measured step by step. Along the route, the team had to cross more than a dozen rivers and sea areas, requiring precision leveling methods to maintain accuracy across the entire line.

"Every observation point and every kilometer mattered," Shang said.