INNOVATION May-June 2015

f ea t u r e s

Terrestrial Laser Scanning

Above: Stationary Terrestrial Laser Scanner (TLS) on a tripod. Right: Integrating with positioning sensors,a terrestrial laser scanner (TLS) can be mounted on a mobile platform for dynamic operations to increase coverage efficiency.

George Liu, P.Eng.

The power of three-dimensional (3D) visualization is reaching far beyond the movie theatres. It is increasingly gaining accep- tance in the architectural, engineering and construction industry as an effective tool for design, communication and documenta- tion. As importantly, it is a significant leap since the industry switched from paper drafting to computer aided drafting (CAD) about three decades ago. Terrestrial laser scanning (TLS) collects accurate 3D image data necessary for visualization. The term is synonymous with LiDAR, an acronym for “light detection and ranging.” It uses a coherent laser beam for the rapid acquisition of 3D imaging information from a variety of natural and industrial objects. Cultural heritage sites, buildings, chemical plants, highways, and public infrastructures can all be accurately and efficiently mod- elled and documented with this portable imaging technology. LiDAR has appeared in a number of articles in past Innovation issues, primarily in relation to large scale aerial mapping. That’s not surprising, due to the fact that aerial mapping was the first to adopt LiDAR technology in the late 1980s, around the time the author used prototype GPS technology for positioning an aircraft on LiDAR missions. The terrestrial counterpart lagged until a few

years ago when TLS became smaller in size and faster in captur- ing data. Hardware costs have dropped while imaging resolution continues to improve so that a number of commercially avail- able software can now directly extract features such as windows, walls, pipes, valves, steel beams, etc., from densely populated data points, or the figuratively termed “point cloud.” A small fraction of the architectural, engineering and construction industry has adopted the technology; however, there are many who approach the technology with trepidation and skepticism. What is Terrestrial Laser Scanning (TLS)? TLS makes possible the swift measurement of points by automatically scanning the surrounding area by spinning a laser beam emitter vertically at high speed while slowly rotating the base to capture the entire panoramic image. The most advanced high performance TLS system available today is capable of collecting data up to one million points per second and requires only a few minutes to complete one scan. This is about 10 times faster than just a few years ago. In the resulting dense point cloud, accurate to a few mm’s, objects can be easily identified allowing the creation of 3D models of a wide range of objects.

A historical facade in Vancouver’s Gastown was accurately documented using laser scanning technology. The traditional survey method would have been inefficient due to irregular shaped fixtures and highly detailed ornaments.

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