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Long Range Scanning: The Best Alternative for Large-Scale Projects
 Terrestrial laser scanning is a ground-based laser scanning technique for collecting high-density 3D geospatial data. Its purpose is to enable 3D scanning of very large-scale, complex entities, such as entire buildings, factories, power plants, rooms, landscapes, seagoing vessels, and other structures and locations. Both the inside and the outside of structures can be scanned, as well as natural environments for surveying and design purposes.
Using the highly accurate 3D scan data generated with terrestrial scanning, engineers and designers can create CAD models of actual site conditions by processing the scan data into universally useable CAD models. Terrestrial laser scanning systems are portable and quick to set up, so scanning can be performed in environments where health and safety issues must be considered, such as in a landslide area, or where access is limited, such as on roadways. Inspection or reverse engineering of large vehicles, sculptures, construction projects like bridges, frameworks for large structures or buildings, stadiums, ships, or aircraft, can now be quickly accomplished with this new scanning technology.
Steve DeRemer, General Manager of GKS Inspection Services-Michigan, a global provider of dimensional measurement and terrestrial laser scanning services, has noted a marked increase of customers for terrestrial laser scanning services. “Many of these large-scale scanning applications are one-time projects where the customer can’t justify the substantial cost of buying and learning a new system and its software. As experts in all forms of digitizing, GKS provides its customers with a more cost effective solution; we are a value-added service provider in that we can provide both the equipment and the highly-experienced personnel to run it, very often at less cost than buying the equipment outright.”
The applications are almost limitless in any number of industries, ranging from architecture and engineering to automotive, transportation and energy infrastructure to petrochemical, and anthropological to forensic. For example, “when the blueprints of an old structure are missing or outdated due to repeated remodeling, the terrestrial laser scanner can produce data to accurately retrofit machinery to an existing space, or document the space to plan for new changes,” explained DeRemer. “Having scan data that is so accurate makes planning and retrofitting fixtures and machines to a manufacturing or power-producing site much easier and less expensive.”
How Terrestrial Laser Scanners Work
The new laser scanners often called terrestrial laser scanners or “large-scale” laser scanners, work by projecting a laser beam onto an angled rotating mirror that reflects the beam to the object being scanned, while the entire unit rotates around a vertical axis. Thus the unit scans 360° in a horizontal plane and 320° in a vertical plane. The net effect is that everything the scanner can “see” within a sphere of a 76-meter radius (approximately 250’) can be digitized.
When the beam hits the object being measured the beam is reflected back to the scanner. The distance of the object being measured can be determined by either of two different methods. The first, called “Time of Flight” (TOF), measures the time that it takes the laser beam to “fly” out to the object being digitized and then return to the laser emitter and multiplies this by the speed of light. The second method, called “Phase Shift,” involves projecting constant waves of varying length and measuring the difference, or shift, in the phase of the reflected beam in relation to a reference signal kept at the laser scanner. For example, the terrestrial scanner that GKS uses splits the laser beam into three component parts operating on three different modulation lengths, 76 meters, 9.6 meters, and 1.2 meters. The distance of the reflecting object from the scanner is determined by identifying the location of the reflection on the 1.2 meter cycle. The cycle on which the reflection has occurred is identified through its registration on the longer wavelength cycles. Due to subtle differences, phase shift scanners acquire data faster and are slightly more accurate than TOF scanners.
Terrestrial laser scanners build a 360° data set, or “point cloud,” that records all objects within the range and sight of the laser scanner. Grayscale values are applied to the X, Y, and Z coordinates based on the strength of the returned laser signal. This gives the data the appearance of a black and white photograph. Data registration spheres can be placed within the area to be scanned and the scanner can be repositioned to capture objects out of the original line of sight or out of the original range of the scanner. The individual scans can then be linked together using the registration spheres to complete the 3D point cloud. The software used offers a variety of additional options such as overlaying digital images on the top of the point cloud to provide a color image for enhanced realism.
Laser scanning technology is timesaving, clocking in at 100 times faster than conventional scanners, collecting 8 megapixels of data in less than one minute, so even the largest scan scenario is time efficient. Scene specific 3D measurements can be made directly from the 3D scan data. Non-contact laser scanning means that no detail is omitted or disturbed, which is essential when documenting an accident or crime scene.
The Size of the Object is Unlimited
When utilizing a terrestrial laser scanner, the size of the specimen being scanned is no longer limited to the directional travel of a machine, or the reach of an articulated arm as with conventional laser scanners. Using a large-scale scanner along with registration spheres to allow multiple scan positions greatly increases the scanning volume and layouts that can be digitized. For example, the four exterior sides of a building cannot be digitized from one scanner position due to line of sight, but through the use of reference spheres, data from all four sides of the building can be related back together to form one complete scan. Terrestrial scans can be taken anywhere, at virtually any time. The collected data can be used to create dimensionally accurate 3D CAD models or conventional 2D line drawings such as blueprints or floor plans.
Depending on the need, the raw point cloud data can be exported into a variety of formats, including ASCII, DXF, DWG, IGES, and STEP. The raw scan data can also be optionally post-processed into many other deliverable data file formats including AutoCAD, SolidWorks, Pro/ENGINEER, CATIA, UG, IDEAS, and more.
Applications in the Construction Industry
Terrestrial laser scanning has many applications in the construction industry throughout every stage of the construction lifecycle. 3D models can assist the design process by providing more complete site surveys. They can help during construction by providing more complete and accurate dimensional measurements of the current project status. Also, at the end of the project, a final scan and / or model can serve as archive data, in other words a “time-stamp” of the size and layout of the structure at a given point. This information can prove invaluable during subsequent renovations or repairs.
Civil engineers can use laser scanning to digitize existing and proposed locations for roadways and bridges. With the exact topographical features, they can calculate how much material must be moved, where the best contours are, and many other aspects of infrastructure construction. Laser scanning is much faster than traditional instruments that combine electronic theodilites with electronic distance measuring devices. Also, laser scanning can be used to create complete 3D models as opposed to discrete measurements.
Once construction is underway, laser scans can be used to inspect the work at various intervals, making sure that plans are accurately executed and uncover design flaws before they become costly and time consuming.
Terrestrial laser scanning can improve every phase of the construction lifecycle by having the complete geometry of the construction site, building, or existing landscape described in 3D. Building modifications, upgrades, add-ons, or reconstruction of the assembly at a different location can be accomplished against an as-built condition that is completely documented in 3D.
This technology can also hold information architects or engineers would not know they needed until long after an onsite inspection. The 3D data file of the scan of the site or building allows the construction professionals to get dimensions after the fact and without going back to get more information. This greatly speeds up the project and, most importantly, provides greater reliability that the project will be completed correctly with no surprises when materials and prefabricated components arrive on the job site.
Ongoing Survey Work in Office Tower Construction
A key terrestrial laser scanning application involves performing survey work required to support construction of new office towers. For example, the verticality of concrete elevator cores needs to be monitored on a floor by floor basis after the floors are poured and set. The core thickness and position is also critical to avoid fit problems with horizontal structural steel. The traditional method of performing these measurements is with surveying equipment that utilizes a retro-reflector, usually a two-man job. However, this method cannot detect variations in concrete geometry over its full surface and it can be time-consuming and hazardous.
Laser scanning measurements are far more complete by providing the ability to register scans together and tie them to the building grid. The outside core geometry can be compared to internal geometry to determine core thickness. Thickness variations along the core surface can easily be identified in the model.
Safety Considerations and Compliance
Terrestrial laser scanning is invaluable in conditions that are less than optimal for manual measurement, such as on huge offshore oil rigs and in poorly lit mines or tunnels. The laser scanner can take accurate measurements even in the dark.
Many chemical process plants lack up-to-date site documentation. Compliance with the latest Occupational Safety and Health Administration (OSHA) requirements makes such documentation necessary for most plants. Terrestrial laser scanning provides a fast and relatively inexpensive method to produce accurate drawings.
Laser scanning can document both the indoor and outdoor areas of existing plants. The resulting 3D models can be used for many purposes such as measuring piping in process plants as is required for compliance with safety regulations. In a typical example, a small plant was scanned in 4 days compared to an estimated month that would have been required using manual measurement methods.
For road measurements, laser scanning is also safer, since the need for lane closures is eliminated and no one has to stand in the road with dangerous traffic speeding by. Digital photos may be tied to scans to provide better visualization and enable designers to identify specific attributes. Google’s™ map website uses the same concept when it overlays satellite photos onto street maps.
Offshore oil production facilities provide tremendous dimensional control challenges throughout their entire lifecycle. During construction, tolerances must be closely managed between topsides and hull structures even though they are often built in different facilities. Laser scanning can be used to validate the entire jobsite geometry including locating tie-ins and anchor bolt locations and verify footing dimensions and positions. In the case of damage from a storm, the structures must be rapidly documented to aid in repair or decommissioning.
Laser scanning can be used to provide measurements on land prior to subsea installation which will, when combined with acoustically acquired position data about the installation point, eliminate the need for much deepwater measurement while providing an accurate first-time fit.
Uses in Forensics and Liability
Another application for the laser scanner is documenting the scene of a crime or an accident. The high-speed laser scanner quickly collects detailed data of everything that is within range with very minimal intrusion. Nothing is moved or touched by non-contact measurement, so the integrity of the scene is kept intact. The 3D data is then exported to special forensic software for modeling and contouring, creating a realistic view for the investigators to examine visually to determine the sequence of events and possible causes.
Documenting Legacy Structures
With the ever increasing cost of building new structures as well as the decreasing space in which to build them, many businesses and organizations are opting to restore, renovate, or remodel existing historical structures. Usage of terrestrial laser scanning techniques has gained enormous popularity in Europe, where space is often at a premium.
High-speed terrestrial laser scanners can survey the site quickly and more inexpensively than manual survey techniques, creating extremely accurate models from which to work. The business case is compelling because such projects can be estimated more accurately, they take less time to complete, the work is of better quality, and the cost and risk of execution go down. Better documentation of existing locales leads to improved visualization of proposed projects, so public and governmental buy-in is easier for companies to obtain.
A few years ago the GKS team used terrestrial laser scanning to document the existing interior of a church built in the 1950’s. “The original blueprints had been lost long ago, and accurate measurements were needed prior to the start of possible building renovations,” DeRemer explained. Built in the neo-Gothic style, the church had a unique cross-shaped nave. Due to the high vaulted ceiling, massive wooden beams, and wide variety of colors and materials inside the church, obtaining accurate measurements with other types of digitizing equipment would not have been time- or cost-effective.
An entire 360° scan was taken of the interior with GKS’ portable terrestrial scanning system. Through scanning from multiple positions, the entire church interior was scanned within one hour. The results seen in the accompanying pictures are the result of the laser scanning process and are not based on the use of any sort of camera; the image is made of the hundreds of thousands of individual X, Y, and Z data points collected by the laser scanner.
The laser also records the light value of the objects it scans and assigns a grayscale value to each collected data point, so the image looks like a black-and-white digital photograph. Through the optional attachment of a digital camera, the scanner can assign true color values to the points rather than the standard grayscale to make the resulting image even more true to life. However, the colorized set of point data is fully measureable.
Photo 1: This image shows one entire 360° scan taken with the LS-880. The distorted view is due to the 360° spherical scan being stretched and flattened out for viewing purposes. This is similar in nature to “peeling” the spherical map from a globe in order to produce a flat map. While the image resembles a simple black and white photograph, it is actually made up of the hundreds of thousands of individual X, Y, Z data points collected by the LS-880.
 Photo 2: This image shows a partial scan. The distortion is again due to the “flattening” effect mentioned above. Note that this data, as well as that in photo 1, is a result of the laser scanning process, and is not based on the use of any sort of camera. The laser actually records the light value of the objects it scans and assigns a grayscale value to each collected data point.
Photo 3: This image shows the color version of the same scan data as in photo number 2. Through the optional attachment of a digital camera, the LS-880 can assign true color values to the points rather than the standard grayscale value. Again, while this image appears to be a digital photograph, it is actually a colorized set of point data that is fully measurable.
Photo 4: This image shows just some of the raw 3D points within the Faro software. Through scanning from multiple positions, the entire church interior was scanned within one hour.
Above 4 photos and data used w/ permission, and with thanks to St. Paul’s LCMS, New Boston, MI.
Future of Terrestrial Laser Scanning
According to DeRemer, “This new terrestrial laser scanning technology is helping our company serve our growing list of customers needing on-site services.” The laser’s high speed reduces both the time expenditure and the cost of a large-scale measurement or surveying project. High density data insures complete and accurate replication into the digital format for design and engineering calculations. The amazingly realistic 3D models provide confidence that the visualization created corresponds to the actual existing conditions. “Terrestrial laser scanning can bring a huge scanning project down to a workable scale for our customers,” added DeRemer.
About GKS Inspection Services
GKS Inspection Services has been a leading provider of dimensional measurement services, 3D laser scanning services, and terrestrial laser scanning for over 25 years. The company’s Plymouth, MI lab (in the Detroit area) is accredited by the A2LA for Mechanical Testing and Calibration. It provides 3D laser scanning and engineering services, as well as unbiased third-party inspection services that the company was founded on. The Michigan lab features numerous CMM’s, vision systems, 3D laser scanners, surface analyzers, and other inspection equipment. GKS also has branch offices in Minneapolis, Toledo, India, and Korea. The company’s expert metrologists and engineers are experienced in automotive and many other manufacturing industries.
For more information about how GKS Inspection Services can improve your manufactured product, save you money, and decrease your development time, contact Steve DeRemer, by phone (734-582-9600) or email.
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