Laser Scanning Reduces Rework Costs

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Each day provides new opportunities for innovative applications of technology. Pushing the envelope in construction through creative architectural and engineering design is the place where innovative concepts meet reality. The best solutions arise from difficult tasks. It is both an invigorating and challenging time for individuals and companies that design and build today’s state-of-the-art projects.

Children’s of Alabama operates the third largest pediatric medical facility in the United States. Located in Birmingham, Alabama, Children’s recently completed construction of the Benjamin Russell Hospital for Children. This graceful 720,000-square-foot expansion project is Alabama’s first Leadership in Energy and Environmental Design (LEED)-certified hospital building under LEED vv2.2 for New Construction and the largest LEED-certified project in the state to date.

Unique and innovative architecture brings with it a multitude of challenges for the building contractor. Dixie Acoustical Contractorsa Birmingham-based company with 47 years of experience in the installation of acoustical tile, sound proofing, and metal studswas engaged to install a 12,000-square-foot ceiling in the main lobby. The architectural design required that one common grid pattern of panels be used to transition through and connect multiple lobby spaces, corridors, and rooms. An installation with rectilinear spaces would be fairly easy, but the lobby was designed with constantly flowing curvilinear walls and soffits.

The graceful architectural design required Dixie to rethink traditional methodology in order to fall within acceptable fabrication design error tolerances. It was quite obvious that conventional on-site measurements of the constructed walls would be time consuming, unproductive, and introduce the costly risk of human error. Dixie decided to consult with a local expert in engineering and surveyingWalter Schoel Engineering Co., Inc. (WSE)to see if a better methodology could be utilized.

With 125 years of professional service history in engineering and surveying, WSE was a logical choice to take on the challenge and provide the information required by Dixie for this sophisticated installation. WSE’s business model centers on superseding competitive firms in the adoption and implementation of leading edge technology for surveying and mapping. The company’s proactive stance on technology has been a critical factor in the firm’s longevity and in its planning for future growth and success.

In 2010, just as laser scanning began to emerge as a new technology, WSE created a new department to provide enhanced services for their clients. To ensure that this new business venture had the best chance for success, a Topcon GLS-1500 was purchased from local dealer Earl Dudley, Inc. With a scan rate of 30,000 points per second and a range of up to 1,100 feet (330m), WSE determined this would be a definite advantage for their new venture.

Jeff Yerby, one of Dixie’s estimators, contacted WSE to see what could be done to expedite the work of onsite measurement. Initially, Yerby thought that a total station might be a solution. WSE’s staff explained how laser scanning could exponentially reduce the time required for measurement, as well as provide infinitely more detail with a 3D point cloud model.

WSE’s crews completed the necessary scans in less than three days, an impressive accomplishment in efficiency and productivity considering the onsite working conditions. The survey work was done during the closeout phase of the project, with literally hundreds of subcontractors moving in and out of the workspaces. The GLS-1500 could not always be positioned at an optimal location for multiple scan registrations due to equipment obstructions on the ground; narrow corridors required the use of a tilt bracket to obtain the coverage required.

The GLS-1500 is operated from a notebook computer with Topcon’s ScanMasterTM software. ScanMaster can also be used in the office for registering multiple scans and other point cloud analyses. WSE further processed the data with Carlson, AutoCAD, and MicroStation software to produce 2D drawings that depicted the as-built positions of walls and relevant obstructions. These deliverables were turned over to Dixie Acoustical for the shop fabrication of the grid system and ceiling panels.

Dixie’s fabricator is located in Canada, which added an additional concern. If any of the panels or frames had to be redone, shipping time would add days of delay. However, WSE’s drawings functioned perfectly and no time was lost on adjustments. The fabricator and Yerby talked back and forth, verifying and double-checking measurements numerous times during the process. Once completed, three trailer loads of frames and panels were shipped to the job site.

New technology always claims to have theoretical benefits, but its real value is proven in field applications. In a ceiling tile installation, the typical rework cost due to measurement inaccuracies ranges from seven to 12 percent of the total contract cost. WSE made a detailed analysis after the project and determined that the actual rework cost for the project was less than one percent. Again, laser scanning proved its true value in meeting the demands for intricate architectural construction.

But drastic reduction in rework cost is only the beginning of the story. Measurements at one-inch intervals allowed the fabricator to cut frames and panels to an extreme high degree of precision. Out of the three truckloads of materials, only 10 or 12 pieces did not fit. From an installation contractor’s perspective, this degree of accuracy turns a nearly impossible job into a manageable reality. Repeated actual field metrics such as this will continue to build confidence in laser scanning technology.

Adam Arrington, Earl Dudley vice president, maintains a keen interest in the projects of his customers. Fully aware of WSE’s project for Dixie Acoustical and its inherent challenges, Arrington said, "The Topcon GLS-1500, with its precise scan technology, allowed Schoel Engineering to create the highly accurate as-built data needed to ensure precise 3D dimensioning that this project demanded."

Laser scanning has already proven itself to be a primary source of highly accurate location data for BIM applications. More importantly, the time and cost savings to trade-specific contractors result in a quick return-on-investment for the instrument and software. Scanned 3D data totally eliminates human error that is always a given in conventional measurements. In addition, the speed with which required measurements can be obtained far exceeds the capabilities of other measurement technologies, such as the total station.

Jeff Yerby is now a believer. "There is absolutely no way that this job could have been done without laser scanning," he said. He also made a comment that should be of keen interest to manufacturers and service providers whose livelihoods depend on this superior means of measurement: "Lack of contractor’s awareness about laser scanning technology is the only reason it isn’t more widely used."

WSE will be one of the first end-users of Topcon’s new GLS-2000 laser scanner. Features of the new instrument include a scan range of 1,150 feet (350m), survey-grade accuracy and integrated twin cameras. The compact size and an expanded field-of-view make it an easy-to-use solution for any survey or construction application. Details for the new scanner can be found here.

Richard Rybka consults with Topcon Positioning Systems as an Applications Journalist.

A Disciplined Workflow

To get the precise results that made the Childrens Hospital project a success, a disciplined workflow must be followed. Wade Ward, LSIT, is WSE’s laser scanning specialist. He worked on the project and explains how the survey was completed:

"To begin the project, the site was walked to get a better understanding of exactly how this scanning information needed to be collected. Once a plan was established the scanning began. A total of 21 setups were used to collect a total of 35 scans. When using Topcon ScanMasterTM software, the field data collected is saved as an .sdf (Topcon ScanMaster Database Files) file. Each file was about 1240 KB. The data was collected in three days.

Scanning and target positions were set as the scanning progressed throughout the building. Some scanning setups utilized the occupy/back sight method for registration while other setups utilized a tilt bracket and therefore utilized a resection method for registration. For QA/QC reasons extra target scans were made no matter what the registration method was. When using occupy/back sight only one target scan is needed. We collected two target scans. When registering using resection methods three target scans are need. We collected four. Once these scan/ targeting positions were established coordinates could be assigned to these points by running site control.

Site control was established using WSE’s standard surveying practices (turning two sets of double angles, sighting prisms mounted on tribrachs and tripods on the back sights and foresights, running a closed traverse, and establishing elevations by running a level loop. A digital level and a total station were used on this project. This traverse information was then post processed using Carlson Surveying Software and adjusted to provide the most accurate site control possible.

This site control was then imported into ScanMaster to register the scans onto the common coordinate system. Once registered the scans are in their native .cl3 file type. They then had to be written to a file type we could use in AutoCAD. The .las file type was used to export point clouds from ScanMaster so drafting could be done in AutoCAD.

Multiple .las point clouds were created using slicing tools in ScanMaster. Slices were made at different heights in various areas to ensure all the information we needed to accurately draft the soffit was included. Some clouds were east corridor, south corridor, north room and restroom. They ranged in size from 7800kb to 586kb.

These .las files were then indexed to a .pcg file using AutoCAD. The.pcg file was used in AutoCAD to create the complex geometry of the curvilinear soffit. This geometry was created by using thin slices and segments of data while also utilizing a best fit from points command in AutoCAD. This function will consider all data points, i.e. point cloud data, to best fit the geometry to the data. This process was repeated along every soffit surface within the area of interest.

Once done, this geometry was then imported into MicroStation, WSE’s primary CAD platform, per the client’s request. The final deliverable was a 2D CAD file and printed exhibit."

A 3.849Mb PDF of this article as it appeared in the magazine complete with images is available by clicking HERE