Four words appear on every 3D scanner specification sheet, and they are routinely used as if they meant the same thing. They do not. Understanding the difference is the difference between buying a scanner that suits your parts and buying one that produces impressive-looking data you cannot certify.
| Concept | Definition | Example |
|---|---|---|
| Accuracy | Closeness to the true value. | A 100.00 mm part measured as 100.01 mm. |
| Precision | Consistency of repeated measurements. | Repeated scans all return 100.01 mm. |
| Resolution | Smallest detectable detail. | The ability to capture a 0.1 mm groove. |
Accuracy
Accuracy measures how closely a measurement matches the actual physical dimension. If a 100.00 mm feature is measured as 100.02 mm, the resulting error is 0.02 mm. It is the figure that matters wherever a measurement has consequences:
- First article inspection (FAI)
- GD&T verification
- Tooling validation
- Casting and machining inspection
- Reverse engineering
- Quality control
Precision
Precision — often called repeatability — describes consistency across multiple scans rather than closeness to truth. Scan a 100.00 mm object five times and get 100.02, 100.02, 100.03, 100.02 and 100.02 mm, and you have excellent precision: a spread of only 0.01 mm. You also have a consistent 0.02 mm offset from the true value. Precision without accuracy means being reliably wrong, which is worse than being obviously wrong, because nothing in the data flags it.
Resolution
Resolution is what lets a scanner capture fine edges, small engravings, surface defects and intricate geometric detail. The critical point: higher resolution does not automatically mean higher accuracy. Resolution governs how much detail is captured; accuracy governs whether the dimensions are correct. Higher resolution also means larger datasets, longer processing and more storage, so the sensible approach is to choose a resolution that matches the inspection tolerance rather than the highest available.
Volumetric accuracy
Volumetric accuracy describes measurement precision across a larger scanning volume, and it is quoted as a formula rather than a single number — because measurement uncertainty accumulates over distance. A typical specification looks like this:
This is why a single-point accuracy figure tells you very little about a 3 m casting or a battery tray. If your parts are measured in metres, the volumetric formula is the number to compare between systems.
Two ways to improve it
- Global markers. Pre-scanning global markers gives the alignment algorithm an absolute spatial reference before point cloud capture begins, rather than letting it rely purely on stitching frames together.
- Video photogrammetry (VPG). SHINING 3D's patented approach reduces preparation time by at least 50% while maintaining volumetric accuracy. It is integrated in the FreeScan Trak ProW, FreeScan Trak Nova, FreeScan Omni, FreeScan Trio and FreeScan UE Pro2.
How the figures are validated
SHINING 3D operates a 1,100 m² ISO/IEC 17025-accredited Accuracy Lab which validates scanners against international standards:
- VDI/VDE 2634 Part 1:2002 — point-by-point probing
- VDI/VDE 2634 Part 2:2012 — area scanning
- VDI/VDE 2634 Part 3:2008 — multiple view systems
- ISO 10360-12:2016 — articulated arm CMMs
- ISO 10360-13:2021 — optical 3D CMMs
Common questions
Does higher resolution mean higher accuracy? No — resolution captures detail while accuracy determines dimensional correctness.
Why does accuracy decrease on larger objects? Measurement uncertainty accumulates over distance, which makes volumetric accuracy increasingly important as parts get bigger.
Which industries require metrology-grade accuracy? Automotive, civil aviation, manufacturing, tooling, heavy industry, energy and quality inspection.
How do you improve accuracy in practice? Proper calibration, stable environmental conditions, optimised scanning workflows, and photogrammetry on large volumes.
Are ISO certifications important? Yes — ISO 10360 and VDI/VDE 2634 provide objective, published methods for evaluating accuracy rather than a manufacturer's own claim.
