From an object size of about one metre, stitching overlapping scans together is no longer sufficient.
Fringe projection scanners join their individual captures via shared areas. Each of these joins introduces a small error. On a compact component this does not matter — but across an object several metres long the joins accumulate and the result distorts. This mainly affects large, smooth-surfaced objects where the scanner lacks distinctive geometry to orient itself: car bodies, hulls, panelling, tooling.
The remedy is a globally surveyed grid of points. It gives the scanner a fixed reference system to align every individual capture to, instead of merely appending it to the previous one. The join error then no longer accumulates across the component.
The scanner manufacturer's target points are applied to the object. Coded photogrammetric targets and a calibrated scale bar are added. The object is photographed from all directions; the software detects the coded targets automatically, identifies them by their individual pattern and calculates the 3D coordinates of all points in a single common system.
This grid of points is exported and loaded into the scanner software as a reference. The scanner then orients itself on the surveyed points instead of on its own chain of joins.
The maximum length measurement error of the Linearis3D Photogrammetry Standard is 0.1 mm per cubic metre of measuring volume, evaluated in accordance with VDI 2634. The scale bar supplied is DAkkS-calibrated and provides the traceable length reference.
How far a scanner drifts without referencing depends on the individual device — we deliberately do not give a blanket figure for that. What matters is this: with a reference grid of this accuracy it is no longer the chain of joins that determines the dimensional accuracy of the overall scan, but the surveyed field of points.
The reference points are output in open formats. Any scanner whose software can read one of these formats is therefore compatible:
With Artec scanners the interoperability is documented by the manufacturer itself: Artec on integrating Linearis3D photogrammetry. For other makes, please check the documentation of your scanner software to see which of the formats it imports — or ask us and we will look into it with you.
The system is the Linearis3D Photogrammetry Standard and costs from € 4,950 plus VAT. It can be used independently of the scanner and therefore remains usable when you change devices.
We will advise you on which measured values matter — and recommend the right system.
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