3D VISION


Isak du Preez integrating Axiscan’s software with the first full-scale machine


gengineer and the software is where the complexity lies;


the machines themselves are relatively simple. Trough his company, Axiscan, du Preez provides the pattern and the software to decode it, while the large scanning machines are built or commissioned by his customers according to the requirements of the application. Ultimately, Axiscan’s software accepts camera video as input and produces a 3D mesh of the surface as output. Te 3D mesh contains one


vertex per camera pixel; its lateral density is limited only by the camera resolution. In addition, the system is self- calibrating, with the software automatically calculating each camera’s position from its direct view of the encoded scene. Te early scanners built for


assessing hail damage on cars used security cameras, which are less than ideal as they compress video. ‘Tis is the last thing you want,’ du Preez said. ‘You want the pixels as independent as possible for this.


A 3D scan showing the curvature of a car windscreen ‘But it still worked,’ he added,


saying dent reconstruction from different cameras was consistent with each other down to approximately 1µm. ‘Considering the low camera specifications, the video compression, and the generally uncontrolled environmental conditions, this level of repeatability from the software is encouraging.’ He continued: ‘Te hardware


specifications in this project are extremely relaxed. I don’t think we’re anywhere near the ceiling of attainable accuracy yet.’


Precision in the infrared Most metal sheets that go into building a car scatter light a lot more than exhibiting specular reflection. It’s normally only after the car has been painted that it becomes reflective. But rougher surface types can still resemble a mirror when imaged in the longwave infrared. If automakers could detect defects before the expensive step of painting the car it would add a lot of value. Attempts at infrared


deflectometry in the past have usually involved moving a pattern made up of heated elements in a complex motion with many degrees of freedom, and this still only encodes a planar scene. Te technology has been difficult to engineer because of the lack of off-the- shelf infrared displays and because thermal elements only change temperature slowly. Du Preez thinks Latitude


Isak du Preez’s first prototype scanner, built in 2016 from hardware store materials


8 IMAGING AND MACHINE VISION EUROPE DECEMBER 2021/JANUARY 2022


Code Scanning Deflectometry might be ideal for working in


‘I don’t think we’re anywhere near the ceiling of attainable accuracy yet’


the infrared because it already relies on a moving scene generator, and encodes large curved surfaces. Te camera just needs to be changed to an infrared camera, and the pattern switched to a thermally emissive pattern painted on a heated arch. Testing this potential is one of the aims of a collaboration with a research lab at BMW. At the moment, du Preez’s


software takes about seven minutes to produce the 3D result, but that’s running on a single threaded CPU. He expects with parallel processing to cut that down to 15 seconds or less, which would fit within the natural cycle time of the movement of the arch. Du Preez hopes that Latitude


Code Scanning Deflectometry will bring the precision of deflectometry to many new applications, and the interest from BMW and others will only help refine the technique. He said Latitude Code Scanning Deflectometry is not quite as accurate as interferometry, nor as versatile as structured light scanning, but that the combination of precision and versatility, while also being cost effective, suggests the approach has promise. ‘Tere’s a lot to explore,’ he said. O


@imveurope | www.imveurope.com


Isak du Preez


Isak du Preez


Isak du Preez/Axiscan


Isak du Preez/Axiscan


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