A three-dimensional data model has been created for the No 2 terracotta warrior pit of the Qin Dynasty (221-206 BC) in Xi'an, capital of Shaanxi Province.

This is the first time such technology has been used to protect large-scale cultural relics in China, and will pave the way for building a digital information library, experts said during a recent meeting for testing and approving the model by the State Administration of Cultural Heritage in the city.

Long-term deterioration of cultural relics is unavoidable, and many important signs and traces are gradually removed during archaeological excavation work, experts said.

At the same time, traditional archaeological methods such as cartography, photography and written records cannot provide precise information about ruins and relics for future research and demonstration, said Chen Xianqi, an official with Shaanxi Provincial Administration of Cultural Heritage.

In order to preserve the information contained in the No 2 Pit, experts at the Qin Terracotta Warriors and Horses Museum and scientists from Xi'an Siwei Air Survey Remote Sensing Centre began the project in May 2005 to build a digital information library using three-dimensional numerical modelling technology.

The project created a three-dimensional data model for the No 2 Pit the average difference between the pit and the model is less than 2 millimetres, said Wu Yongqi, director of the museum.

The museum, located in Xi'an's Lintong District, opened to the public in October 1979 and became a major tourist hotspot.

The archaeological excavation removed the remains of wooden beams in the Qin pits of the terracotta warriors and horses, Wu said.

There were remnants of wooden beams in three pits of the museum, Wu said, but those in the No 1 and No 3 pits have disappeared with the excavation work and could not be reproduced. "At present, the excavation work is being carried out in the No 2 Pit, where parts of the wooden beams still exist in their entirety, which has great significance for archaeological research," Wu said.

The Qin terracotta warriors and horses were discovered in March 1974, causing a sensation in international archaeological circles. The life-size pottery figures were buried in three pits next to Emperor Qinshihuang's mausoleum, to guard the first feudal emperor of the Qin Dynasty.

Editor: Wing