A 3d scanner records an object’s shape as digital points, and its technology falls into 2 categories: contact and non-contact. Non-contact scanners use lasers, projected light patterns, photographs or pulse timing.
The choice of scanner decides what a model can capture, so it shapes the whole workflow of 3d modeling that follows.
Contact versus non-contact scanning
Wikipedia’s entry on 3D scanning states that “3D scan technologies can be split in 2 categories: contact and non-contact.” Contact scanners physically touch the part. A coordinate measuring machine (CMM) moves a touch probe along the surface and records the probe’s position at each step, building a point set from direct measurement rather than from reflected light.
Non-contact scanners are further divided into active and passive types. Active scanners emit light or radiation and read the reflection. Passive scanners, such as photogrammetry rigs, use only ambient light and ordinary cameras. Contact methods are slow and risk marking soft or fragile objects, but the Aniwaa scanning guide credits them with precision and the ability to scan transparent or reflective surfaces that defeat optical methods.
That last point matters in practice. The same Wikipedia entry warns that optical technology may struggle with dark, shiny, reflective or transparent objects. A glass bottle or a polished metal part is a good reason to look at a contact probe, a spray-on scanning powder, or a different optical method altogether.
Laser triangulation scanners
Laser triangulation reaches an accuracy “on the order of tens of micrometers” according to Wikipedia, which makes it one of the most precise handheld and desktop approaches. The scanner shines a laser dot or line on the subject, and a camera looks for where it lands. The laser emitter, the camera and the dot form a triangle, and simple trigonometry gives the distance.
The trade-off is range. Wikipedia notes that triangulation range finders are usually limited to a few meters for reasonably sized devices. That suits small and medium objects such as machine parts, figurines, dental models and tooling, but not buildings or terrain.
Aniwaa lists the strengths as high resolution and accuracy. The downside it names is sensitivity to surface properties, since very shiny, transparent or dark surfaces are particularly problematic. Scanner operators therefore often dust glossy parts with a matte coating before scanning.
- 3D scan technologies split into contact and non-contact: 2 categories
- Triangulation accuracy: tens of micrometers
- Triangulation range: a few meters
- ToF scan rate: 10,000 to 100,000 points per second
- ToF scan duration: millions of samples can take minutes
Structured light scanners
Structured light is the most common technology in desktop and handheld scanners sold for design and hobby work, and it was named by Aniwaa for its speed and resolution. A projector casts a pattern of stripes or a grid onto the object, and a camera measures how that pattern deforms across the surface.
Because the scanner captures a whole patch of the surface at once instead of tracing a single line, a single capture can be quick. Aniwaa also notes that the light is non-harmful, so it can be used for 3D body scanning, which a strong laser would not suit.
Structured light still depends on controlled lighting. Strong ambient light can wash out the projected pattern, and the same dark or shiny surfaces that trouble lasers can disturb it too. For a step-by-step walk-through of capturing a part, see the guide on how to 3d scan an object.
Photogrammetry from photographs
Photogrammetry needs no special scanner at all, only a camera and software, which is why Aniwaa highlights its acquisition speed and its ability to pick up colors and textures. It analyses several photographs of a static subject, taken from different viewpoints, and automatically detects the pixels that correspond to one physical point.
The software, built on computer vision and computational geometry, reconstructs the 3D positions of those points. Aniwaa cautions that a very powerful computer is required to run the algorithms. The processing step, not the shooting, is usually the bottleneck for large image sets.
Photogrammetry is passive, so it avoids lasers and projectors. It works for outdoor objects too large for a desktop scanner, though plain, glossy or moving subjects give the software few features to match. The result is a mesh with a colored texture, which is useful for game assets and heritage records.
Time-of-flight and LiDAR scanners
Typical time-of-flight 3D laser scanners can measure 10,000 to 100,000 points every second, according to Wikipedia. These scanners send out a laser pulse and time how long the reflection takes to return, which gives distance directly. A lidar scanner of this kind may be used to scan buildings and rock formations.
The trade-off runs opposite to triangulation. Time-of-flight scanners reach much farther, but their accuracy is lower than the tens of micrometers that triangulation achieves. Wikipedia adds that a high-resolution scan requiring millions of samples can take minutes for some time-of-flight scanners, while a low-resolution scan takes less than a second.
These devices fit surveying, architecture and site documentation. Once any scan is captured, the point cloud is usually cleaned and converted to a mesh in modeling software, and options such as free cad software can handle the follow-up measurement and redesign work.
Choosing between the types
Object size is the first filter. Triangulation reaches roughly a few meters at tens of micrometers of accuracy, while time-of-flight covers sites and buildings at lower precision. Structured light sits between the two for small and medium objects, and photogrammetry covers any size if the computer can process the images.
Surface is the second filter. Dark, shiny or transparent items favor a contact probe or a matte coating, and textured, colorful items favor photogrammetry or structured light with color capture. Budget and software skill form the third filter, since photogrammetry needs only a camera while a CMM is a fixed laboratory instrument.
Frequently asked questions
What is the most accurate type of 3d scanner?
What is the most accurate type of 3d scanner?
Contact probes and laser triangulation are the most precise; Wikipedia puts triangulation accuracy on the order of tens of micrometers, and Aniwaa credits contact scanning with precision.
Which 3d scanner suits large buildings?
Which 3d scanner suits large buildings?
Time-of-flight lidar, which Wikipedia says may be used to scan buildings and rock formations, with typical rates of 10,000 to 100,000 points every second.
Can a camera alone work as a 3d scanner?
Can a camera alone work as a 3d scanner?
Yes. Photogrammetry rebuilds a subject from photographs taken at different viewpoints, according to Aniwaa, though it needs a very powerful computer for processing.
Why do shiny objects scan badly?
Why do shiny objects scan badly?
Aniwaa says very shiny, transparent or dark surfaces are particularly problematic for laser triangulation, and Wikipedia says the same of optical technology in general.
