This article is written by Svetlana Golubeva and is being reproduced here.
SUMMARY
In this guide, we take a deeper look into one of the most popular 3D scanning technologies – laser 3D scanning. After reading it, you’ll be familiar with what types of scanners are referred to as “laser,” how they work, where they’re most useful, and what they are used for.
TYPES OF LASER SCANNERS BY TECHNOLOGY – Time of flight, phase shift, triangulation
TYPES OF LASER SCANNERS BY PRODUCT – Handheld, tripod-mounted, desktop
TYPES OF LASER SCANNERS BY RANGE – Short range (up to 5 m), medium range (up to 120 m), long range (up to 2 km)
Today, there are multiple ways and technologies to bring an object from the real world into the digital 3D space. You can do it with various types of 3D scanners: desktop, handheld, or tripod-mounted, industrial or consumer-grade; photo cameras and photogrammetry software; contact-based measuring systems; smartphones or tablets with built-in LiDAR sensors; mobile, terrestrial, airborne systems, and more.
In this article, we’re going to focus on one of the most popular scanning technologies used everywhere from construction and land surveying to forensics and heritage preservation – laser 3D scanning. We’ll see what types of scanners are referred to as “laser,” how each of them work, and where and what those devices are used for.
What is a 3D laser scanner?
When people hear the term “laser 3D scanner,” they might imagine an array of scanning devices, depending on their background and area of expertise. An industrial designer, for example, might picture a portable handheld unit that can capture small to medium objects at a short range, while a construction worker – a tripod-mounted terrestrial scanner for surveying and measuring larger objects such as buildings or entire outdoor areas from the ground. A surveying and mapping technician, on the other hand, would likely picture a car or a drone with a scanning system onboard used for mapping terrain on the go. And all of them would be right, because each of the devices above can correctly be referred to as a 3D laser scanner.
So, what is laser scanning and which devices can be called laser scanners?
To simplify it, laser scanning is a process of capturing precise, three-dimensional information from a real-world object, a group of objects, or an environment, using a laser as a light source. By projecting laser light onto the object, the scanner creates point clouds – millions of precisely measured XYZ points that define the object’s position in space. Some laser scanners allow the option of downloading the model as point clouds, while others automatically convert it into a triangulated mesh, which can then be transformed into a CAD model or a full-colored 3D model if the recording of texture is supported.
A long-range laser scanner being prepared for use on an offshore vessel (Photo courtesy of ASOM)
Unlike the contact-based measuring systems that we reviewed earlier, laser 3D scanners are 100% non-contact and non-destructive active devices that can capture objects made of solid and fragile materials. They can work indoors while some can operate outdoors as well. They can be used in daylight or at night, and can be both stationary and portable. They can be used to scan at a wide range of scales and for a broad range of objects and sites – from very small to very large.
KEY POINT
Non-contact and non-destructive devices, laser scanners capture XYZ coordinates of myriads of points on an object’s surfaces to calculate its dimensions, reconstruct its shape in a 3D environment, and define its position in space – all with astounding accuracy.
Depending on the application, 3D laser scanners can come as standalone devices – portable, handheld, or stationary and tripod-mounted, for example – or as part of a more complex solution such as robotic arms, mobile or airborne laser scanning systems, and more. On the technological side, there are time of flight, phase shift, and triangulation-based laser scanners.
Let’s take a closer look at the most popular types of laser scanners and how they work.
Types of laser scanners
Time of flight
The first type of laser scanners typically used for long-range data acquisition is Time of Flight (TOF). Such 3D scanners work by the same principle as laser range finders work: a laser pulse is sent out onto an object, while a portion of the pulse is reflected from the object’s surface and returns to the scanner. The distance to the object is calculated by the time of the flight of the pulse, using this formula: Distance = (Speed of Light x Time of Flight) / 2). This distance is then used to calculate a coordinate for the tiny section of the surface hit by the laser beam.
How Time of Flight measurement principle works
Time of flight 3D scanners can capture objects over great distances of up to 1,000 meters away. However, their typical working range is 5-300 meters. While TOF systems can measure over long distances, they have the slowest data caption rates – between hundreds and thousands of points per second.
The accuracy of TOF technology is determined by the system’s ability to accurately measure the time of the returning signal. While accuracy specifications vary across different systems, the typical accuracy for a TOF scanner is 4-10 mm. More recent TOF systems also include an additional RGB caption option, either through an internal camera or an external camera set.
Phase shift
Phase shift 3D scanners emit laser light at alternating frequencies and determine the distance to an object by measuring the phase difference between the emitted and reflected signals. Unlike the time of flight scanners, phase shift scanners work at shorter ranges from 80 to 120 meters maximum, with a typical operating range of 1 to 50 meters.
How phase shift measurement principle works
Phase-based 3D scanners are often categorized as the fastest laser scanners, with some systems claiming a caption rate of up to a million points/second. They also have higher accuracy and resolution than TOF scanners. And, like TOF scanners, they include internal or external color capture options.
KEY POINT
All laser scanners send out laser light but employ different technologies to interpret inbound signals. Time-of-flight scanners log the time emitted light takes to return once it’s bounced off the surface of an object, phase-shift scanners measure the phase difference between emitted and reflected signals, and triangulation scanners calculate the angle at which an outbound beam returns to the sensor.
Thanks to their high accuracy, phase shift scanners work best for medium-range scanning needs such as large pumps, automobiles, and industrial equipment. Both phase shift and time of flight systems can also be used in terrestrial scanning applications where larger objects or structures of a couple of meters up to multiple kilometers can be surveyed.
Terrestrial TOF and phase-based scanning systems can come as stationary, tripod-mounted equipment, which can be used as-is or mounted onto land-based or aerial vehicles for projects that require information from vast landscapes or inaccessible areas.
Triangulation
The third type of laser-based scanners operates on the principle of triangulation, where laser light is emitted and returned to a specific location on an image sensor array of an inboard camera. To calculate the distance between the object and the 3D scanner, the system uses trigonometric triangulation because the laser source, the sensor, and the target left on the object form a triangle. The distance between the laser source and the sensor is known very precisely, as is the angle between the laser and the sensor. As the laser light bounces off the scanned object, the system can measure the angle at which it is returning to the sensor, and therefore the distance from the laser source to the object’s surface.
How triangulation measurement principle works
Triangulation-based laser scanners work at much shorter ranges (less than 5 meters) than the time of flight or phase shift scanners due to the small dynamic range of the image sensors and decreased accuracy with range. Most triangulation systems also come with an internal RGB capture option.
Commonly, triangulation-based scanners are most suited for scanning smaller objects ranging in size from 1 cm up to 2-3 meters, depending on the manufacturer. As for the form factor, there are stationary, tripod-mounted triangulation scanners. However, this technology meets the most success when used in portable handheld 3D scanners.
Applications of laser scanners
Laser scanners are used in a wide variety of fields, and for a wide variety of applications: from construction and civil engineering to forensics and archeology. As the technology becomes cheaper, lighter, and smaller, more and more industries are getting into laser scanning. Some well-known applications of these devices are listed below.
Reverse engineering
Scanning the undercarriage of a car with short-range laser triangulation 3D scanner
From small mechanical components to massive industrial objects, laser scanners have become an essential technology in the toolkits of professionals involved in product design and development. Once a complicated process that could require days of disassembly, detailed manual measurements, and the painstaking process of examining each part of a product, thanks to laser scanning reverse engineering now takes anywhere from a few minutes for a CAD surface model, to a few hours for a parametric CAD model. The scanners are used to create accurate digital blueprints of parts that have been damaged or deformed, need a redesign but don’t have CAD data available for them. Portable laser scanners with embedded processors are perfect for examining small and medium-sized objects, while medium and long-range devices work best for larger items. Instant creation of CAD models frees up hours if not days of work, which R&D teams can spend on the actual product enhancement.
Quality inspection
Inspecting the pipes with a laser scanner
Another important stage of the manufacturing process and one more area revolutionized by laser scanners is quality inspection. Traditionally dominated by manual, contact-based measuring techniques, thanks to laser scanning quality inspection workflows can now be done way faster, more accurately, and with far more measurable data. This in turn results in fewer iteration loops and faster delivery of products to the customer. Unlike CMMs that can typically acquire dozens of point measurements one at a time, need to be in physical contact with the surface, and require programming for every new part to be examined, laser scanners can capture millions of measurements for various types of objects with a wide range of geometrical complexities in a fraction of the time, and completely contact-free.
KEY POINT
Laser scanners have proved to be effective measuring tools for both industrial production and consumer-level applications: from reverse engineering to quality control, forensics, and self-driving cars.
Short-range laser triangulation scanners that come in the form of portable handheld devices provide flexibility over the types of objects to be inspected, as well as their location. They are great at capturing complex parts that would be impossible to measure by hand or with a moving touch-probe. Thanks to their lightweight design, such devices allow QA managers to be more mobile without being tied to a particular place or area.
Long-range laser scanners are perfect for examining and collecting accurate and measurable data from large objects, and can even be paired with a handheld scanning solution for capturing smaller elements in high detail. The resulting 3D model captured with a laser scanner can be processed in a scan processing software, then converted into a CAD file. At this stage, it can be compared to the original CAD model, and the parts which are in or out of tolerance can be identified.
Forensics
Capturing a crime scene with laser triangulation 3D scanner
Thanks to their capability of capturing large spaces such as room interiors, buildings, and entire sites, laser scanners are becoming the new go-to solution for the accurate documentation and investigation of crime scenes, and reconstruction of accidents. Unlike traditional evidence collection methods such as photo and video cameras, and measuring tapes, laser scanners allow investigators to capture entire crime scenes in their original state, with precise dimensions for every piece of evidence, be it a body, a footprint, or a bullet hole, and do it all in a matter of minutes.
Portable handheld laser scanners with embedded processors are perfect for capturing standalone items on the go at multiple locations within a day, and can be brought in when higher and more accurate data is needed, e.g. a closer scan of a dead body, a damaged piece of furniture, or close up scan of a footprint left by the criminal. Long-range scanners, on the other hand, are useful for capturing an entire space. By having it placed in the middle of the room where it scans fully automatically, the investigator can engage in other parts of their work, such as talking to witnesses and victims, without a need to control the scanner. The 3D data enables forensic experts to have a fuller and much more detailed picture of a crime scene and build stronger and more decisive cases to present in the courtroom.
Construction (BIM)
3D scanning a warehouse with a tripod-based long-range laser scanner
Another popular application of long and medium-range terrestrial laser scanners, particularly among architects and construction technicians, is 3D capture of buildings and entire construction sites. Such devices allow facility owners or construction project managers to quickly create accurate documentation and 3D visualization of existing buildings and their conditions. They are also used to track the progress of construction and quality inspection of newly constructed projects and compare them with an as-designed model. Laser scanners not only save the time and cost used for manual measurements, they also increase safety conditions when working in unsafe locations. Laser 3D scanners can be used throughout the whole lifecycle of the building, and provide permanent and rich 3D data that can be used for renovation or new building projects, and be accessed anytime.
Archeology
Capturing the skull of a triceratops with a handheld short-range laser scanner (Image by David Cano / 3D Printing Colorado)
Archeology is another area where laser scanners have become indispensable tools for 3D documentation of archaeological excavations, be it a single bone of an extinct animal or an entire ancient city. Portable handheld laser scanners with embedded processors come in handy in fieldwork, and allow archeologists complete autonomy in capturing their discoveries. Thanks to the built-in screen, they can see the results of what they scan in real-time, without carrying an additional laptop or tablet at the same time. Long-range terrestrial and airborne laser scanning systems are successfully applied to map topography, excavations planning, and spot archaeological sites that researchers would never be able to see with the naked eye, thus leaving them hidden.
Laser scanners allow archeologists to collect reliable and high-resolution data much quicker than they’d be able to with other methods such as total stations, GPS devices, or photogrammetry, saving them hundreds of hours of labor during an excavation. Thanks to their non-destructive, contactless nature, they can be used to capture fragile and vulnerable historical pieces in their original state. The data collected can be used for archaeological documentation and for creating virtual-reality models, restoration, preservation, and demonstration of archeological discoveries for the public.
Mobile mapping
An example of a vehicle-borne laser mapping system
One more application of long-range laser scanners is mobile mapping – the process of collecting 3D geospatial data, in other words, where objects are positioned on Earth, from a mobile vehicle either land-based (cars, trains, boats) or airborne (drones, helicopters, or planes). Mobile mapping systems are typically fitted with various navigation and remote sensing technologies such as GNSS, cameras, and LiDAR. The combination of all these technologies allows professionals to visualize, record, measure, and understand environments, whether it’s for road and rail networks management, urban planning, analyzing underwater or underground structures, improving safety in power plant infrastructure, designing digital maps – the list goes on and on.
Artec 3D laser scanners
As we approach the end of our review, it makes sense to at this point look at some real examples of different laser scanners. Here at Artec 3D, we have two types of laser scanners. One is handheld and works best for medium-sized to large objects over short distances (0.35 – 1.2 m) – Artec Leo, while the other one is a phase-shift scanner with an operating range up to 110 meters – Artec Ray.
Artec Leo
Artec Leo is perfect for capturing medium-sized to large objects with up to 0.2 mm resolution and 0.1 mm precision
Artec Leo is a portable, handheld, and versatile triangulation-based structured light laser scanner that remains in a league of its own. All thanks to the built-in computing unit, HD display, Wi-Fi, and a battery that enables scanning and reviewing results in real-time with no other gear (PC or tablet) needed. The scanner can capture up to 35 million points per second and create highly detailed point clouds with 0.1 mm precision and 0.2 mm resolution in a matter of seconds. The large field of view (838 × 488 mm for the furthest range) allows Leo to scan and process quite a variety of object sizes, from small 20-50 cm parts to larger objects or even scenes, from 50 to 200 cm and bigger. Leo utilizes Class 1 VCSEL laser as a light source, which is completely safe for eye exposure, and can be used for scanning both inanimate objects and people. Leo’s design provides complete autonomy and flexibility over the scanning process, which is why its applications go far and wide: from reverse engineering and CAD-based design to healthcare, archeology, forensics, and many more.
Artec Ray
Artec Ray can capture large objects with submillimeter accuracy from up to 110 meters away
Artec Ray is a phase-shift long-range laser scanner designed to capture large and very large objects, such as buildings, airplanes, wind turbines, and the like, with submillimeter accuracy. The scanner has an operating range of 110 meters and can capture up to 208,000 points per second by rotating 360 degrees around itself and vertically with a 270-degrees viewing angle. Unlike many long-range scanners, Ray acquires highly accurate and clean data, which makes it usable for reverse engineering and quality inspection purposes. It comes with a tripod and can work autonomously both indoors and outdoors, thanks to a built-in battery, onboard Wi-Fi, and a mobile app that enables remote control of the scanner. The data captured with Artec Ray can complement more dense and feature-rich scan data acquired with Artec’s handheld scanners.
