Laser-surveying technique can recreate old buildings in a flash

A virtual model of St John's Cathedral has been created with the latest laser surveying technology and the government is considering requiring all buildings to be so recorded before they are demolished.

Ho Puay-peng, of the Chinese University of Hong Kong's department of architecture, and Bruce King, of the department of land surveying at the Hong Kong Polytechnic University, teamed up to create a perfect, 3-D, computer-drawn reproduction of St John's over a 10-week period last summer.

The team used the laser imaging technology to recreate the exact dimensions of the cathedral, and also to produce architectural drawings of the structure.

Dr King said it would have taken them 10 years to do the same thing using conventional technology, rather than the 10 weeks spent on the project last summer.

'It would be a slow, painstaking process, with scaffolding all over the church, both inside and outside,' Dr King said.

'To record these drawings with this accuracy would just not be practical.'

Dr Ho used the example of the site of the Tiger Balm Gardens in Tai Hang, a place where many old Hongkongers used to play as children, which was sold for housing in 1998. 'We can preserve these places forever,' he said.

The chairman of the cathedral's fabric and furnishing committee, Roger Cole, doubts there were ever any proper plans for the church, founded in 1847, but they were needed for future renovations.

'For example, all the windows are different sizes. Once we took one of the shutters on the windows and copied them in China, and when we tried to hang them, none of them fitted,' he said. 'And the images created by the computer are works of art; we could print them to sell as souvenirs to help pay for the upkeep of this beautiful cathedral.'

Antiquities and Monuments Office executive secretary Louis Ng Chi-wa said the department would eventually require developers demolishing old buildings to record their exact dimensions. He could see a day when a virtual record of buildings would be available online. 'The problem now is it's too expensive and still very time-consuming.'