Innovations in the use of laser scanning are bringing a shift in construction management. This article provides an overview of the practice, including types of laser scanning, benefits, progress monitoring, registration, scanning across a project's lifecycle, and more.
Laser Scanning
3D laser scanning is a non-contact, non-destructive technology that digitally captures the shape of physical objects using a line of laser light. In other words, 3D laser scanning is a way to capture a physical object’s exact size and shape into the computer world as a digital three-dimensional representation. Originally applied in the construction and maintenance of industrial plant facilities, laser scanning has since been adopted for many other uses, including building construction and Building Information Modeling (BIM).
Introduction
Before considering the implementation of laser scanners in construction projects, it will be helpful to examine the features and capabilities that apply to conventional construction projects.
Reality capture is one of the most prominent functions of using a 3D laser scanner on your job site. Laser scanning allows for a highly accurate field representation by collecting millions of points within a very short period of time. Those points become intelligent, as they capture the RBG values of the scene collected by the camera of the scanner.
All the features below, along with an extraordinary accuracy, makes laser scanning a great instrument for measurement and controls in the field.
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Types of Scanners
The most common type of laser scanner used in the field of construction is the LiDAR method. LiDAR is a method for measuring distances by illuminating the target with a laser light and measuring each reflection with a sensor.
Differences in the laser return times and wavelengths can be used for making a new digital 3D representation and usually are classified in four main categories shown below. LiDAR scanners can be airborne, stationary terrestrials, mobile terrestrials, and handheld. Each individual type is used for different purposes, needs, and range of accuracy according to the assigned task.
Benefits for General Contractors
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3D laser scanning enables a fast and accurate means of collecting millions of measurable data points in seconds to provide pinpoint accuracy, every time.
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For general contractors, this insight is the single largest benefit of laser scanning. Laser scanning helps lower contractor risks by ensuring as-built drawings are accurate and by exposing any inaccuracies early in the process, before they turn into change orders during construction.
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Data sets are dimensionally accurate, measurable, and shareable, so you can eliminate any guesswork back at the office.
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For detailed MEP installations, you need a high level of accuracy. If your project is complex, involves retrofits, or requires refurbishment, you can capture precise data over the full measurement range.
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The benefits of laser scanning do not stop at preconstruction coordination. Scanning progressively during construction to compare with as-designed models and drawings, provide archival records, and document critical milestones provides tremendous value throughout the construction process as well as to the owner as the building is managed, maintained, and renovated.
Laser Scanning across a Project’s Lifecycle
Design—When it comes to site design, 3D laser scanning is a starting point even sometimes before BIM. Many professionals today are adopting a scan-to-BIM method of design to capture detailed information to kick off and manage the process early.
Construction—Laser scanning helps with construction coordination, specifically in avoiding conflicts between different systems (i.e., HVAC, electrical, plumbing). Data can also be shared between parties to help with any remote coordination.
Operations—Scanning isn’t just performed at the beginning of a project either; it can be done at various other points along the timeline to better document milestones, reduce the necessity of change orders, and pass off work to other trades professionals.
Retrofits and Renovations—Laser scanning captures a very high level of detail, and this helps create a permanent as-built record for both owners and facility managers. In the end, this data can help with building operations, renovations, and future building additions and even demolitions.
Laser Scan Registration
Registration is the process of aligning multiple scans in a parent coordinate system using reference positions common between scans. References are common points between scans that are used to create a “best-fit” alignment. The X,Y, Z coordinate and point name are created on positions like the center of a sphere or planar scan target. The purpose of pairwise registration is to find a common contact surface and optimally align one of the scans relative to another. There are many algorithms for registration of two geometric surfaces that are the alternatives of the well-known Iterative Closest Point (ICP) algorithm.
Laser Scanning Accuracy
The difference of each single range measurement to the mean range value is specified by the Range Noise.
Point Cloud Processing Software
The processing software should be capable of registering the number of laser scans at a time with great accuracy. The noise elimination tools must be incorporated with the software which will help to remove the noise to combine the processed data very accurately.
Benefits of Laser Scanning
Construction Quality Management
Processing millions of closely-spaced points helps in capturing the actual level and member orientation. Feedback from deviation analysis extracted by point cloud facilitates erection and minimizes the overall tolerance of combined structures during the erection stage. It improves coordination and collaboration on the job site, leading to faster and better decision making.
Inspection and Approvals
The overlay of the LOD 400 models versus the collected point cloud creates a composite model that clearly reflects the deviations between as-designed and as-built.
Quantity Estimation
For measuring quantity to maintaining the volume of stockpiles, cut and fill in heavy earthwork industries is difficult. Traditional survey methods are inaccurate and measure up to 80% of original volumes. Measuring a stockpile volume using 3D laser scanning is by far the fastest and safest method available.
Progress Monitoring
Creation of a construction progress model on a timely basis is now easier with laser scanning. It creates a point cloud of each element of a site. The progress models from every span of time create a clear vision of the construction project.
As-Built Preparation
This is the practice of creating a digital representation of existing conditions of the building with its physical and functional characteristics in BIM. The point cloud needs to be imported into a 3D BIM software such as Revit in order to create accurate as-built models.
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Bimal Patwari is a first-generation entrepreneur and founder of Pinnacle Infotech Solutions, the acknowledged global leader in providing innovative BIM solutions. Bimal is recognized for his contribution to the innovative use of BIM technology to improve efficiency and quality and reduce costs and waste. He has received several awards and recognition from government and other industry associations for his entrepreneurship and pioneering contribution to the construction industry.