Periodic documentation of construction projects improves the accuracy and timeliness of as-built drawings, and new ways of doing so are becoming more practical and more widely used.
Traditionally, original design drawings were “red-lined” manually on paper in the field, but inaccuracies or omissions were common. In the 1980s, with the release of AutoCAD, the process began to include transferring hand-written changes to electronic CAD drawings, but doing so was still only as accurate as the person holding the measuring tape. Now there are two methods to choose from—photogrammetry and LiDAR scanning—to record details throughout the construction process. The results of these methods are as-built plans that show the actual location of wiring, piping and structural components behind the sheet rock.
Ken VanBree, founder of eBuilts, has been doing as-builts for 10 years, since before there was scanning equipment available. Using the as-builts, VanBree says, is an effective way to provide a building owner or manager access to all information he would need through a visual interface.
“Right now obtaining complete as-builts that show pipes and ductwork and everything that is concealed is still an emerging concept. It is typically not a requirement, but it is becoming more common in commercial construction,” VanBree says.
Since VanBree’s primary customers are contractors, eBuilts creates measurable photos and orthophotos and delivers them in a viewer to the contractor or property owner who can then take measurements on the photos to make sure they don’t damage anything behind the walls while making changes during construction or even future repairs.
Today the only way to get mass data of six sides of a room rapidly (four walls, floor and ceiling) is to use photogrammetry or LiDAR. Each technique has advantages and disadvantages for creating electronic as-builts. One big advantage of photogrammetry is that the digital cameras are relatively inexpensive and simple to use, and photogrammetric software such as PhotoModeler and Recap is available to stitch the images together. On the other hand, LiDAR equipment is still fairly expensive, and the point cloud is less intuitive to manage and analyze than a digital image. Visualizing the scanned material is more difficult, and correlating the point clouds requires more skill. Cameras are more efficient when there are obstructions like columns or pipes in the room because scanners must be moved to new scan positions to obtain full coverage. In general, however, scanners are more productive and can document as much as four times the area as compared with the photogrammetric method. Since every project has unique characteristics, both LiDAR and photogrammetry should be considered, while the best answer could be a combination of the two.
In order to compare the two methods, VanBree conducted a test on a residential radiant floor project. The goal was to produce an accurate record of heating tube locations in the floor before gypsum concrete was poured on top. VanBree’s company completed the test using their regular SLR digital cameras to capture images on one floor and using a FARO scanner on another. The assessment showed comparable results; however, LiDAR was faster and more efficient—and only about half the cost of generating an orthophoto.
“LiDAR scanning does give very similar results to close-range photogrammetry in terms of quality and density of points,” says Joe Paiva, founder of Geospatial Associates in St. Louis, Mo. “For the general practitioner, the choice depends on their comfort with technology.” Although many architects and contractors are more willing to test new methods that have potential for saving time and money and improving results, Paiva says many surveyors tend to be somewhat risk averse and are hesitant to use new technology until it is stable and proven.
Government mandates, Paiva says, are partially driving up the demand to accurately map facilities during construction inside and outside. Construction of many buildings, such as VA hospitals, already require accurate mapping, and Paiva believes that in the future many insurance companies and prospective real estate investors will require the data, which would be useful for facility maintenance, emergency response, and renovation projects.
While photogrammetry is better understood and more widely used, Paiva believes that if the price of LiDAR scanners comes down, LiDAR could become the more popular method, paving the way for even safer and more reliable construction data.