Technology Profile

May 1, 2004
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As 3D laser scanners decrease in cost and as accompanying processing software improves, surveyors are taking notice of this new technology. Laser scanning technology is being used to solve certain application projects for more and more surveyors, including topographical surveys (where access and safety may be obstacles) and as-built surveys. Some surveying firms are taking on jobs they previously couldn't have completed with traditional surveying methods. Here is one case study of laser scanning use.

Here a building is shown in the "spotlight effect." The objects in the forefront (the tree) cause shadows on objects in the rear (the building). These are actual holes in the scan data that can be filled in by repositioning the scanner and "shooting" a second scan from a different angle. Scan credit: Optech Inc.

3D Application at the Center for Advanced Spatial Technologies University of Arkansas, Fayetteville

The ability to quickly and accurately map a wide range of surfaces with high levels of precision and accuracy creates new opportunities for surveyors, researchers and engineers who perform as-built surveys, monitor deformations in large structures and reverse-engineer mechanical structures. When integrated with traditional three-dimensional (3D) measuring technologies such as photogrammetry, laser scanning systems enable rapid and effective visualizations of 3D structures.

The ability to analyze the 3D surface elevation and characteristics of large-scale (small area) features is also a critical part of university research in many disciplines. Until recently, however, acquiring these data could only be accomplished with time-consuming surveying or close-range photogrammetric methods. The development of highly accurate terrestrial laser scanning systems such as the Optech ILRIS 3D scanner is revolutionizing research in fields from A (archaeology) to Z (zoology). Researchers affiliated with the Center for Advanced Spatial Technologies (CAST) at the University of Arkansas will be using an Optech system to map detailed rattlesnake habitats, to model the water flow across farm fields, to inventory archaeological mounds, to create architectural records of historic buildings and to provide detailed infrastructure data to support modeling of airborne aerosol distributions in urban environments to predict the effects of possible terrorist attacks.

"In minutes the Optech ILRIS system can produce millimeter-accurate point cloud measurements of surfaces at distances that range from 3 meters to more than 500 meters," says Jack Cothren, project manager for the scanning research at the university. "This provides researchers with a totally new set of data for many different studies."

A rotated view of the same building shows it with no roof. Several scans can be taken of an object and overlayed, a different color representing each different scan. Each individual scan takes approximately 3-5 minutes at an average of 300,000 to 500,000 points per scan. Scan credit: Optech Inc.
A key component of the process is the use of software to process the point clouds. The CAST group uses the PolyWorks software from InnovMetric Software for this purpose. "Point cloud data from the scanner presents many challenges in processing," Cothren says. "The datasets are very large, sometimes in the hundreds of millions of points; there are complex problems of geometry when the scanner is measuring different surfaces in the near and far range, and the data needs to be converted to formats that are useful in other systems." The CAST team is using PolyWorks to process the data and create products that range from surface DEMs, to CAD-based architectural renderings, to volumetric analyses.

The ability of the ILRIS system to both measure large areas and still maintain highly accurate details was important to Angie Smith, a graduate student at CAST. Smith used the system to scan a large cliff face that held a small rock shelter (a shallow cave) that had prehistoric rock art on its walls. "I was able to scan the entire surface of the cliff at centimeter level spacing in five scans, each taking less than 15 minutes. I then scanned the area with the rock art at 0.5 mm spacing at the rock surface. This revealed subtle surface differences created by the prehistoric artists, especially after color digital photographs were draped over the surface." The data was merged in PolyWorks, processed and then used as the basis for complex animation and visualization studies. "I cannot even imagine beginning to do the project with traditional survey techniques," Smith says. "Field data was acquired by the Optech [scanner] in less than one full day and the processing tools in PolyWorks provided automated tools to splice together the different scans, at different resolutions, into one product that could be easily moved into our visualization software, SoftImage."

"The Optech [scanner] is one piece of a series of instruments and software," Cothren says. "While fast and accurate, the data cloud from the scanner provides only relative coordinates. To link these to geographic systems, CAST also acquired a number of Trimble surveying instruments. We can either locate the Optech [scanner] with the Trimble 5700/5800 GPS, or locate targets within the scanning field that are tied back to the proper local reference system with our Trimble 5600." According to Cothren, "determining the scanner location with these instruments allows us to output the data from PolyWorks with precise geographic coordinates."

Acknowledgement: The CAST research was made possible with support from the National Science Foundation Award BCS-0321286.

If you have a case study you'd like highlighted, please send details to brownl@bnpmedia.com.

Manufacturer Information: Optech Incorporated, www.optech.on.ca

InnovMetric Software, www.innovmetric.com

SoftImage, www.softimage.com

Trimble, www.trimble.com

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