Lidar, the secrets of Angkor Wat and Autodesk

A new technology we’re hearing a lot about is lidar – light detection and ranging. Used to examine the surface of the Earth, you may have also seen it in operation on the Beeb’s recent Jungle Atlantis: Death Of Angkor Wat’s Megacity, where lidar technology has revealed the original city of Angkor. And the same technology can be used in architecture too, even linking up with Autodesk…

What is lidar technology?

Lidar is a remote sensing method that uses light in the form of a pulsed laser to measure ranges, or variable distances, to Earth. When these pulses are combined with other data recorded from the air, you can generate precise 3D information about the shape of the Earth and its surface over broad areas.

The lidar instrument itself consists of a laser, a scanner, and a specialised GPS receiver, usually on board a plane or chopper. There are two types: topographic and bathymetric. Topographic lidar typically uses a near-infrared laser to map the land, while bathymetric lidar uses water-penetrating green light to also measure seafloor and riverbed elevations.

How is it used?

You may have seen lidar employed on a recent BBC documentary production, Jungle Atlantis: Death Of Angkor Wat’s Megacity. In the programme, you saw how an international team of archaeologists and scientists have used lidar technology to discover the secrets of the forgotten Cambodian Khmer civilisation. The lidar device was mounted on a helicopter criss-crossing the countryside, firing a million laser beams every four seconds through the jungle canopy, recording minute variations in ground surface topography.

The archaeologists found undocumented cityscapes etched on to the forest floor, with temples, highways and elaborate waterways spreading across the landscape. “You have this kind of sudden eureka moment where you bring the data up on screen the first time and there it is – this ancient city very clearly in front of you,” said Dr Damian Evans to the BBC.

How can we use it?

The potential for lidar in architecture is massive too. Replacing photos with the laser pulses and automated calculations of lidar point cloud data means it’s accurate, as well as fast and cheap (providing you have access to your own aircraft…) – it virtually places you on your target site without having to leave the office.

There’s actually been support for lidar data in Autodesk products for some time now, and you’ll find an end-to-end solution in AutoCAD, AutoCAD Labs, AutoCAD Civil 3D, Map 3D and Navisworks products. Here’s a great tutorial that outlines a simplified process of bringing large lidar data sets into Civil 3D and then modifying that information into clean and manageable surfaces.

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