A Brief Tutorial
Scanning Technologies at a Glance
RE Technology Comparison Chart ...Dozens of companies make three dimensional digitizers and scanners, and it’s a frequently changing cast of characters. Instruments are available to digitize objects from microscopic in size to entire construction projects or large portions of oil refineries. Data acquisition speeds range from a few points per minute using manual technologies, to more than a million points per second. Prices range from a couple of thousand dollars to hundreds of thousands of dollars. To a great extent this situation reflects the wide range of applications that are presented to this class of devices. But the very exuberance of engineering approaches may also be indicative of an immature market and technology base. Rapid prototyping is another field that exhibits a similarly wide range of technologies, and perhaps it is not a coincidence that reverse engineering may be considered reverse-rapid prototyping.
Digitizers have numerous specifications, but there are just three key ones: volume, accuracy and speed. Volume is self-explanatory, but it should be noted that for most technologies it’s not actually much of a limitation. That’s because it’s possible to stitch together numerous scans using RE software to accommodate objects that are much larger than the available scanning volume. The tradeoff is time and accuracy, however. 
Accuracy and resolution are related, but not the same. Accuracy refers to how precisely the measurements correspond to dimensional standards. Resolution specifies the smallest increment of distance or volume that the instrument can measure. It’s possible for an instrument to have high resolution and be inaccurate, and vice versa. Some manufacturers specify one value and not the other, and each uses its own terminology and conditions. Different specifications can apply to each axis of measurement, as well. Accuracy and resolution are the main "weasel clauses" in most digitizer specs. If they are critical to your application, it may be necessary to get further data from the manufacturer or perform certification testing. Speed is frequently given in points/second. Here again, there is great variation among manufacturers in terminology and conditions. Some manufacturers supply essentially anecdotal specifications or no information at all. Nevertheless, it’s usually possible to at least get an idea of the regimen the instrument falls into. A Brief Tutorial
Mechanical Touch-probe Systems
RE Technology Comparison Chart ... An important basic distinction among digitizing technologies is between contacting and non-contacting instruments. Contacting digitizers, or touch-probes, are often very accurate over a wide measurement volume, and some instruments in this class are among the most affordable devices available. There are contact digitizers that are positioned manually to yield a single measurement at a time, or may be scanned across a surface to produce a series of measurements. There are also touch probe instruments available which can automatically scan an object using a variety of mechanical drive means. Contact instruments are often in the form of an articulated arm that allows for multiple degrees of freedom of movement. The position of each section of the arm is determined by encoders, glass scales, or in the case of the more inexpensive devices, by potentiometers mounted in each joint. Other mechanical arrangements besides arms are also used.
On the down-side, contacting devices can distort soft objects such as auto upholstery, and are too slow to digitize parts of human bodies, or may require much labor to scan complex curved surfaces. On the other hand, they are not affected by the color of a surface or if it is transparent or reflective, the way laser and other light-based systems may be. And while slow, they may actually be the fastest way to digitize simple surfaces where just a few data points need be gathered. Manually positioned devices can also make it easier to get at hard to digitize areas of an object such as narrow slots or pockets.
Laser-based Systems
RE Technology Comparison Chart ...Line and Spot Scanners / TriangulationThe two major classes of non-contact scanners are those based on laser technology and those based on some form of non-coherent, white, or broadband light source. Laser scanners most often use straightforward geometric triangulation to determine the surface coordinates of objects. A laser line is scanned on the target object and individual sensors image the line, usually simultaneously from each side of the line. Where the laser line's image falls on each sensor, most often a CCD array, is easily determined and the rules of trigonometry are then applied to calculate the position of the target surface at each point on the laser line. The simplicity of the technique and its ability to fairly quickly digitize a substantial volume with good accuracy and resolution have made laser line scanners a popular choice. Products are supplied both as complete systems, and as self-contained measuring heads for mounting to standard touch-probe arms or in other ways, including customized mechanical fixtures for specialized applications.
Laser and other light-based systems may be affected by the color of a surface or if it is transparent or reflective. As more experience has been gained over the years, however, users have become adept at work-arounds for surface problems which may cause errors. One must also be appropriately safety conscious when using any laser source. Even though most lasers used for scanning are rated well below any harmful threshold, reflections on curved surfaces and other inadvertent events can result in a potentially harmful focused beam.
Dual-Capability SystemsMany companies that make contact digitizing instruments, as well as many of those that make laser scanners, provide turnkey products that have both of these quite complementary capabilities. Broad areas can be quickly scanned using a laser device mounted on the arm, and features which might be geometrically problematic for the laser can be contact-probed. Some companies provide instruments which can carry both a contact probe and a laser head simultaneously.
A few companies provide color laser scanning technology. Arius 3D uses a multiplexed arrangement of red, green and blue lasers to simultaneously gather color and geometric data. The company mainly offers scanning services, however, rather than selling equipment. Other companies such as Minolta and Cyberware use laser scanning to gather surface measurements and combine that data with color video information gathered separately. Most color scanners use structured white light or broadband sources. See that section.
Other Types of Laser SystemsSeveral additional laser technologies are also utilized, including time of flight, optical radar and laser tracking. In general, these methods offer good accuracy combined with the capability of making measurements from a long distance away from the subject - in some cases tens of meters. This so-called "stand-off" distance is important for applications such as digitizing large machinery, buildings, and the like, which represent a large fraction of the applications for these technologies.
Time of flight systems measure how long it takes for light emitted by a laser to return to a sensor located near its source. Optical radar systems are similar in operation, and both are analogous to standard radar systems which measure the return-time of a radio wave. Time of flight and radar systems don't usually require retroreflectors mounted on the object to be measured and can operate at very high rates to quickly capture entire scenes or objects. In contrast, laser trackers look for a signal in their field of view from a retroreflector placed or held on the object. The main advantage these systems offer is high precision over a large working volume and a frequent use is for aligning large pieces of machinery or verifying as-built dimensions of large objects.
Other Types of Tracking Systems Directory of Commercial Providers of this Technology ...In addition to laser-based tracking systems, a number of companies make LED-based and other types of tracking systems, such as magnetic trackers. These technologies generally have smaller working envelopes than laser-based systems and may not be quite as accurate. They're most frequently used in human and other types of motion studies, but are also useful for reverse engineering. A probe with one or more LED's is touched or attached to the object to be digitized. Sensors, most often utilizing CCD chips in a dual camera arrangement, image the LED's in their field of view. As with laser scanners, trigonometry is then used to calculate the position of the probe on the surface of the object. Encoding schemes based on high-speed modulation of the light emitted by the LED's allow some instruments to simultaneously track the position of hundreds of LED's.
Magnetic trackers offer the added benefit of being able to digitize points on objects that are not within a direct line of sight. Instead of an LED probe, these systems use a small wire coil as a target. One company that makes magnetic trackers, Polhemus, combines this technology with laser scanning. The result is a system that has many of the same features as laser scanners mounted on mechanical arms, while providing very great freedom of movement.
In RE applications, these systems provide good accuracy over a substantial volume and moderate speeds. They aren't affected by surface quality or color. On the down-side, they require a contacting probe or marker and can be slow to digitize complex surfaces.
A Brief Tutorial
Structured-light or Broadband-source Systems
RE Technology Comparison Chart ... Numerous instruments are available that use one form or another of structured-light to measure the geometry of an object. Most use white light, but some use other broadband sources. Perhaps the simplest to understand are those that project a pattern of lines on an object to be digitized. The pattern is distorted by the object’s three-dimensional nature, and the deviation from the original pattern is translated into a surface measurement at each point in the field of view of the instrument. Triangulation is used to calculate the surface data and nearly all systems use CCD cameras for sensing.
Several variations are available including systems that project moire patterns or fringes, structured-color light patterns, and polarized-light interferometry. Specifications and applications greatly overlap, but structured-light systems have two strong advantages compared to laser-based systems: They’re very fast and can digitize hundreds of thousands to millions of points per second - and they don’t use a laser. These two features have resulted in making them strongly favored for digitizing human beings. A wide selection of application-specific instruments is available for digitizing complete human bodies, and for more specialized needs such as faces, teeth, feet, breasts, etc. A few manufacturers of broadband-source systems provide color capability, but laser scanners that provide color information from ancillary video sources, such as those made by Minolta and Cyberware, are also strong contenders in the body-scanning field.
On the down-side, broadband-source systems are, in general, somewhat less accurate than laser systems and are for the most part limited to smaller scanning volumes, typically a cubic meter or less. This may not be a strong limitation, however, since scans can be merged to completely cover very large objects, although it may take considerable time and effort to do so.
A Brief Tutorial
Seeing Inside - Internal Viewing Technologies
RE Technology Comparison Chart ... There are times when more data is required than can be viewed only from the outside of an object or a part. For example, it may be necessary to verify that a part with complicated internal features has been manufactured correctly, or to survey a fossil’s internal features. Touch and light-based systems may be applicable to some portions of the problem, but may require destruction of the object for complete data gathering. This is acceptable in some situations, but certainly not for others where a valuable or irreplaceable object is involved.
There are, however, additional instrumentation choices available which address the problem of internal viewing. Non-destructive systems based on X-ray computed tomography are made by several companies. These work in an analogous fashion to their medical counterparts, beaming an X-ray from many directions and calculating resulting interior point density. Some systems offer resolutions in the few mil range while accommodating objects as large or larger than 16 inches. The instruments can be large, expensive and require specialized knowledge to use, however.
An alternative is offered by CGI, Inc. The company produces a destructive system based on a CNC milling machine combined with optical data-gathering using a CCD camera. CGI calls their technology cross-sectional scanning (CSS). A part or other object is embedded in a contrasting color plastic matrix material. Subsequently, this part and matrix combination is then shaved by the miller and scanned layer by layer until data for the complete object has been acquired. The obvious disadvantage is the destruction of the object, but the machinery is straightforward in concept and use, especially for manufacturers who are familiar with machine tools. The technique can also be comparatively fast and very precise. Destruction of a part is often quite acceptable for quality control and similar applications
A Brief Tutorial
3D Metrology Systems for Manufacturing
RE Technology Comparison Chart ...Every scanning and digitizing technology is used as a solution to a machine vision (MV) problem in one way or another. The applications are extremely varied and include: automated inspection and quality control; automobile manufacturing from auto bodies to tires and other components; lumber and wood products; metals production - and just about any other high-volume industry. Simple problems can readily be solved with off-the-shelf components and software. Uncomplicated requirements, such as measuring the profile or selected specific dimensions of a fabricated part, frequently can be met with automated laser scanning or touch-probe technologies and don’t require much, if any, outside assistance.
However, most digitizing equipment manufacturers offer help and experience in adapting their technologies to MV problems, and a number of them specialize exclusively in more sophisticated applications. These companies don’t especially address reverse engineering applications at all. For the most part, MV-oriented companies tend to offer solutions based on structured-light and related technologies that produce a lot of data quickly. That’s because many of the more complex requirements are for high-speed inspection applications that require limited depth of field.
Scanners for Very Large Objects
and Surveying Applications
RE Technology Comparison Chart ...Virtually all technologies that are used for scanning very large objects, such as large machinery and fabricated parts, vehicles, aircraft, buildings, construction and archaeological sites, mines and industrial plants, use lasers. The two basic choices are those that can survey an entire scene in a single sweep and those that are based on some form of laser tracking. The former offers faster data collection, while the latter offers greater accuracy. As in all other scanning situations, specifications overlap.
A few companies provide color laser scanning technology. For example, Minolta and 3rdTech, Inc. use laser scanning to make surface measurements and combine that data with color video information gathered separately. The choice of technology is largely driven by the specific application.
A Brief Tutorial
RE Scanner & Digitizer
Technology Comparison Chart
This is by no means a complete listing. There are many more instruments available in each technology category and from each vendor, and from many additional vendors, as well. Entries were selected to illustrate the general specifications of a technology, or to show the upper and lower bounds of a vendor's offerings. Use the commercial directory pages to explore categories of interest in depth.
| Technology | Representative Vendor | Model | Volume | Accuracy | Color ? | Speed | Price Range |
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| Mechanical Arm | Faro Technologies | FaroArm - Advantage | 4 feet | 0.001 inches | Not Applic | Manual operations | $19,900 |
| Mechanical Arm | Faro Technologies | FaroArm - Platinum | 12 feet | 0.005 inches | Not Applic | Manual operations | - |
| Mechanical Arm | Immersion | MicroScribe G2 | 50 inches (1.27 m) | 0.015 inches (0.38 mm) | Not Applic | Manual operations | $3,495 |
| Mechanical Arm | Immersion | MicroScribe G2LX | 66 inches (1.67 m) | 0.012 inches (0.30 mm) | Not Applic | Manual operations | $5,495 |
| Guided Probe | Roland DGA Corp. | PIX-4 | 6 x 4 x 2.4 inches | Minimum scan pitch of 0.002 inches | Not Applic | No info provided | $1,995 |
| Guided Probe | Roland DGA Corp. | PIX-30 | 12 x 8 x 2.4 inches | Minimum scan pitch of 0.002 inches | Not Applic | No info provided | $3,495 |
| Strengths | accuracy; low-cost instruments avail.; measures deep slots, pockets; not affected by color or transparency | ||||||
| Weaknesses | manual operation; slow for complex surfaces; can distort soft objects | ||||||
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| Technology | Representative Vendor | Model | Volume | Accuracy | Color ? | Speed | Price Range |
| | |||||||
| Laser Meas. Head | Laser Design, Inc. | RPS-120 | Not Applic., Measuring head; 3.5 inches stand-off distance | +/- 0.00025 in acc.; 0.001 in resolution | No | 14,400 points / sec | - |
| Laser Meas. Head | Laser Design, Inc. | RPS-450 | Not Applic. Measuring head; 7.83 inches stand-off distance | +/- 0.001 in acc.; 0.0037 in resolution | No | 14,400 points / sec | - |
| Laser Meas. Head | KREON Technologies | KLS 51 | Not Applic. Measuring head; Mtd to Arm or Mach tool / Triangulation angle 30 deg | resolution 42 microns | No | Up to 20 000 points/sec | - |
| Laser Meas. Head | KREON Technologies | KLS 171 | Not Applic. Measuring head; Mtd to Arm or Mach tool / Triangulation angle 30 deg | resolution 120 microns | No | Up to 20 000 points/sec | - |
| Laser Scanner / Aux. Video | Cyberware | Model 15 Desktop Scanner | 9.84 (X) x 5.91 (min Y) x 2.95 (Z) inches | Resol: X,Y: 0.012; Z: 0.002 to 0.008 (inches) | Yes | 14,580 points / sec. | - |
| Laser Scanner / Aux. Video | Cyberware | Model Shop 3D Scanner 3030RGB/MS | 39 (X) x 10.25 (min Y) x 11.82 (Z) inches | Resol: X: 0.01 to 0.04;Y: 0.028; Z: 0.004 min (inches) | Yes | 4,580 points / sec. | - |
| Laser Scanner / Aux. Video | Cyberware | Whole Body 4 color 3D Scaner | Cylindrical FOV; Depth: 47 inches; Height: 79 inches | Resol: X: 0.19;Y: 0.08; Z: 0.019 min (inches) | Yes | 60,000 points / sec. | - |
| Laser Scanner / Aux. Video | Minolta | Vivid 700 | 2.8 x 2.8 to 43.3 x 43.3 inches | 200 X 200 X 256 points (x,y,z resol.) | Yes | 160,000 points in 0.6 sec. | - |
| Laser Scanner / Aux. Video | Minolta | Vivid 910 | 111 x 84 x 40 mm (tele lens) to 1200 x 903 x 400 mm (wide lens) | +/- 0.008 mm acc.; +/- 0.008 mm prec. | Yes | 307,000 pixels in 2.5 secs using Fine mode and tele. lens | - |
| Laser Scanner | Nextec | Table Top Hawk | Linear travel: 240 mm (9.4 inch); Scanning range: +/- 5 mm (+/-0.2 inch) | Resolution: 1 micron; Total measuring accuracy: 10 microns (1 sigma) | No | 40 points per sec | - |
| Laser Scanner / Aux. Video | Riegl | LMS-Z210i | 4 to 400 m range x 80 deg vert x 360 deg Rot. | 5 mm resol.; +/- 15 mm accuracy (averaged) or +/- 25 mm single shot | Yes, Optional | 12,000 points / sec; up to 15 deg / sec for horiz scan | - |
| Laser Scanner | Riegl | LMS-Z420i | 2 to 800 m range x 80 deg vert x 360 deg Rot. | 5 mm resol.; +/- 5 mm accuracy (averaged) or +/- 10 mm single shot | No | 12,000 points / sec; up to 15 deg / sec for horiz scan | - |
| Laser Scanner | Roland DGA Corp. | LPX-250 | 10 in (dia.) x 16 in (ht.) | 0.008 inches resol. | No | No info provided | $9,995 |
| Laser Scanner | ShapeGrabber | LM600 System | 600 x 160 x 165 mm | Accuracies to 0.03 mm | No | 15,000 to 100,000+ points/sec | - |
| Strengths | non-contacting; fast digitizing of substantial volumes; good accuracy and resolution; color capability available | ||||||
| Weaknesses | possible limitations for colored or transparent surfaces; laser cautions apply | ||||||
| | |||||||
| Technology | Representative Vendor | Model | Volume | Accuracy | Color ? | Speed | Price Range |
| | |||||||
| Laser time of flight | Callidus Precision Systems GmbH | CT900 | 1.6 m W x 1.4 m H | 50 microns resolution on axis of turntable; 70 microns at far end of meas range | No | 4000 points / sec | - |
| Laser time of flight | Callidus Precision Systems GmbH | CT180 | 350 mm W x 375 mm H | 25 at near end to 70 microns at far end of meas range | No | 4000 points / sec | - |
| Laser tracking | Automated Precision, Inc. | Smart Trak 6D | 40 m range | Static acc: 0.001 inches at 16 ft | No | Up to 2000 meas / second tracking a moving target | - |
| Strengths | non-contacting; fast digitizing of substantial volumes; good accuracy and resolution; trackers are very precise; large stand-off distance for large objects | ||||||
| Weaknesses | possible limitations for colored or transparent surfaces; trackers are fairly slow and may req targets; laser cautions apply | ||||||
| | |||||||
| Technology | Representative Vendor | Model | Volume | Accuracy | Color ? | Speed | Price Range |
| | |||||||
| LED-based tracking | Boulder Innovation Group, Inc. | 3D Creator | 1 m Sphere | 0.2 mm mean volumetric acc | No | 300 points / second | - |
| LED-based tracking | Metronor | Solo Measurement System | 10.5 m range | 0.02 to 0.1 mm meas. uncertanty | No | Manual operations | - |
| Magnetic tracking | Northern Digital | Aurora | 500 mm cubic volume | 1.3 mm rms; 2.1 mm to 95% confid. level | No | 22 to 45 points / sec depending on number of sensor coils | - |
| Strengths | can digitize hidden points in some cases; can be used to track motion of many points simult.; magnetic devices can meas outside line of sight; not affected by color, transparency or surface quality | ||||||
| Weaknesses | requires targets or contacting probes; smaller volumes; lower accuracy; slow for complex surfaces | ||||||
| | |||||||
| Technology | Representative Vendor | Model | Volume | Accuracy | Color ? | Speed | Price Range |
| | |||||||
| Arm-mounted structured white light scanners | GOM mbH | ATOS II | 5 x 4 x 4 to 67 x 53 x 53 inches | 0.003 to 0.039 inches | No | 1.3 million points in 7 secs. | - |
| Arm-mounted structured white light scanners | GOM mbH | ATOS III | 6 x 6 x 4 to 80 x 80 x 80 inches | 0.003 to 0.040 inches | No | 4 million points in 8 secs. | - |
| Moire white light pattern | Inspeck | 3D Mega Capturor II / Small Field | 401 x 321 mm | X & Y: 0.3 mm; Z: 0.4 mm resol. | Yes | 1.3 million points in 0.7 sec. | - |
| Moire white light pattern | Inspeck | 3D Mega Capturor II / Large Field | 1140 x 910 mm | X & Y: 0.9 mm; Z: 1.0 mm resol. | Yes | 1.3 million points in 0.7 sec. | - |
| Moire white light pattern | Inspeck | Capturor II / Small Field | 352 x 264 mm | X & Y: 0.6 mm; Z: 0.5 mm resol. | Yes | 0.3 million points in 0.4 sec. | - |
| Moire white light pattern | Inspeck | Capturor II / Large Field | 1195 x 896 mm | X & Y: 1.9 mm; Z: 1.0 mm resol. | Yes | 0.3 million points in 0.4 sec. | - |
| Projected white light patterns | Genex Technologies, Inc. | Rainbow 3D Camera | Several customizable models offered with capacities from approximately a 3 inch cube to more than a 10 inch cube. | Accuracy to 25 microns (0.001 in) | Yes | Captures 768 X 576 pixel image (442,368 pixels) in < 1 sec. | - |
| Moire-coded white light triangulation | Steinbichler Optotechnik GmbH | Comet | Not specified; 2 million points per view | Accuracy to +/- 20 microns | No | Not speciied | - |
| Strengths | very fast; color available; no laser safety precautions | ||||||
| Weaknesses | somewhat lower accuracy | ||||||
| | |||||||
| Technology | Representative Vendor | Model | Volume | Accuracy | Color ? | Speed | Price Range |
| | |||||||
| X-ray computed tomography | Aracor | Konoscope 160/200 | 200 mm dia | 1024 X 1024 X 1024 pixel image; 0.4 mm resol; 0.04 mm acc. | Not Applic | No info provided | - |
| X-ray computed tomography | Aracor | ICT 2500 | 2500 mm dia | 2048 X 2048 pixels; 3mm resol; 0.25 mm acc. | Not Applic | No info provided | - |
| X-ray computed tomography | Bio-Imaging Research (BIR) | Actis 600/450 | 600 mm dia; unlimited height | 20 line pairs/ mm max spatial resol; density resol: 0.1%; can detect 150 micron flaw, 200 micron void and 10 micron crack. | Not Applic | 14 min for scanning 600 mm dia object | - |
| X-ray computed tomography | HYTEC Sensors & Imaging Group, Inc. | Flash CT | 16 inches in height; cross sectional area undefined | 0.005 inches resolution | Not Applic | 200 MB / minute of volume data | - |
| Destructive / Cross-sectional Scanning | CGI, Inc. | CSS-300 | 7 x 5 x 9 inches | +/- 0.0008 inches (0.0005 to 0.010 inches layer thickness) | No | 2 to 3 hours | - |
| Destructive / Cross-sectional Scanning | CGI, Inc. | CSS-3000 | 14 x 16 x 15 inches | +/- 0.0008 inches (0.0005 to 0.010 inches layer thickness) | No | No info provided | - |
| Strengths | Internal viewing and sample preservation for CT | ||||||
| Weaknesses | radiation safety; sample destruction for CSS; can be slow | ||||||
| Technology | Representative Vendor | Model | Volume | Accuracy | Color ? | Speed | |
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