In construction, there's a direct correlation between the quality of a plan and the ultimate quality of a project. That's why a good plan can be worth its weight in gold.
But all too often—especially in construction—there are major discrepancies between design assumptions and actual site conditions. That pressure to get accurate descriptive data of the site, structure, or system is pushing an increasing number of Building Teams to take a harder look at advanced site surveying methods.
Historically, surveying methods that involve advanced optics or high-resolution photography, field workers, and lots of time have been the only option to grab all that relevant project data.
In the past several years, scanning with lasers has had a major impact on job site surveying.
Cyra Systems (which was acquired by Leica Geosystems, Norcross, Ga.) helped popularize the use of lasers in the 1990s with its Cyrax System, a tripod-mounted 3-D laser scanner attached to a computer equipped with processing software. The laser scanner gathered 3-D point clouds and created 3-D surface geometry of complex structures and sites. As the technology evolved, specialized scan-reading software was replaced with an add-on program called Cloudworx that allowed users to import that data into CAD programs such as Autodesk's AutoCAD and Bentley's MicroStation.
Dayton, Ohio-based Trimble Engineering and Construction Group and Optech Inc., Toronto, are among the other major suppliers of 3-D laser scanners to the construction industry.
In the past, applying 3-D laser scanning techniques on a project involved hiring one of a handful of specialized surveying firms that owned this cutting-edge equipment. The biggest consumers of the technology were the firms that either owned or constructed process and power plants, such as Chevron and Bechtel.
Today, a growing number of AEC firms are adding 3-D laser scanning to their arsenal, in what is called high-definition surveying. These systems have increased in speed and accuracy while dropping in price. At the same time, improvements to the process and technology have shortened the learning curve, allowing a greater number of construction firms to embrace laser scanning.
Firms are using laser scanners for a variety of applications, including large-scale construction projects, topographic surveys, and large monitoring or deformation-monitoring surveys. Other common applications include urban planning, complex as-built surveys, and large-volume determination surveys.
Deliverables from a surveyor using a 3-D laser scanner include 3-D solid models, 2-D/3-D plan views, digital terrain models, 3-D flyovers and virtual walkthroughs, and 2-D/3-D as-built quantity takeoffs.
Geoff Jacobs, SVP of strategic marketing with Leica Geosystems, says 3-D laser scanners are especially applicable for projects that involve critical geometry, such as steel column verticality, base plate locations, tie points, elevation consistency of concrete forms, and new concrete pours.
“High-definition surveying for quality assurance in new building construction has been one of the best-kept secrets in the business,” says Jacobs.
Other popular applications include historic building modifications; construction engineering, where scaffolding or sheet piles may need to be designed and built; and redevelopment proposals, where the high-definition surveys are used to capture existing buildings and streetscapes for the purpose of creating compelling marketing proposals for developer clients.
How 3-D laser scanning works
Laser scanners automatically rotate, giving a 360-degree view of the target. As the device rotates, it emits a spray of pulses similar to the pattern of a paint sprayer. The resulting “point cloud” represents the 3-D area that can be scanned in high-definition by the device.
A typical laser can scan from one to 250 meters at 4-6mm accuracy. At 50 meters, for example, a laser can create a 3-D model precise down to 2mm.
These devices are getting faster too. In October, Leica Geosystems announced a no-cost firmware enhancement to its scanner line that produces the same high-definition data at up to 80% faster.
The company is also working to make data more accessible to AEC firms. In November, Leica released two point-cloud software modules designed to open the value of rich, as-built point-cloud data to the AEC industry. One free program, Leica TruView, is designed for lay professionals who want to view and measure detailed laser scan point clouds. The program publishes as-built or topographic point clouds and images in a user-friendly, panoramic viewing format.
Trimble's new RealWorks Survey office software allows users to manipulate and manage large scan files to produce 2-D and 3-D deliverables. The software also supports data collected using GPS techniques, allowing users to coordinate and combine data from a surveying job in a single project file that can be exported to design software such as AutoCAD and MicroStation.