3D scanning method replaces optical instruments with water

An international team of researchers have carried out detailed 3D scans of objects, simply by dipping them in a water tank gradually and measuring the displacement of the water. This allows for the scanning of hidden features which optical devices are unable to capture.

3D shapes tend to be scanned with optical devices such as laser scanners or cameras. These sample the visible surface of the object to create a digital reconstruction. However, these methods are often noisy and incomplete, mostly leaving some parts of an object hidden to the scanner’s line of sight.

Researchers from Tel-Aviv University, Shandong University, Ben-Gurion University and the University of British Columbia, have developed an entirely new approach to 3D scanning. Their technique is based on an ancient scientific breakthrough: Archimedes’ Principle of fluid displacement.

Approaching the problem of 3D reconstruction using this principle turns modelling surface reconstruction into a problem of volumetrics.

As liquid can penetrate cavities, there is no “line of sight restriction” which optical instruments suffer. As water treats all impermeable liquids similarly, transparent and high-gloss materials do not present a visibility problem as they do for optical techniques.

The new method computes the volume of an object and compares it with its surface. The researchers describe using a robot arm to gradually submerge objects into a water tank. By dipping the objects along an axis, the researchers could measure the changing displacement of the liquid, and turn these measurements into a set of thin volume slices of the shape, much like in a computerised tomography (CT) scan. Dipping the object at various angles allowed them to capture the full geometry of the object, including its hidden parts.

3D scan of a cat statue

Courtesy of ACM SIGGRAPH 2017

Image credit: Courtesy of ACM SIGGRAPH 2017

This approach is inexpensive, and capable of generating a whole 3D shape at low computational cost. Unlike CT scans, they can be carried out anywhere and without the need for bulky and expensive equipment.

The researchers were able to accurately reconstruct even the hidden parts of objects which 3D laser scanners often fail to capture and they demonstrated the efficacy of their technique by producing accurate scans of various objects, including a hand curled into a fist, and a DNA double helix model.

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