Back in 1982, a Japanese physicist came up with an interesting idea for creating three-dimensional virtual models of real objects using a single camera. The process, known as profilometry, involves projecting a pattern of parallel lines onto the object and photographing it.
The three-dimensional object will distort these parallel lines in a specific way. It is then a relatively straightforward task for a computer to use these distortions to determine the shape. And photographing the object as it rotates allows the computer to build a 360-degree model.
This process is fast, cheap, and easy to perform but it has one significant disadvantage. While it works well for objects that are largely spherical, it does not work well for more complex shapes that contain depressions and discontinuities, for example where the object is made up of more than one different part.
The reason is that the pattern of distortions is not unique in these more complex objects. So it is impossible for the computer to derive the original three-dimensional shape.
Today, Manuel Servin and pals at the Centro de Investigaciones en Optica in Mexico reveal a remarkably simple solution to this problem that allows a computer to capture a three-dimensional model of a complex shape with a single camera.
The new approach is straightforward. The original process required a projector to beam a pattern of parallel lines onto the object at an angle to the camera. The new process adds a second projector at the same angle on the other side of the camera.
The process of recording an image involves projecting the pattern of parallel lines from one angle, taking a photograph, then projecting the pattern of parallel lines from the other side of the camera and taking a photograph. Finally, the object is rotated through small angle and the process begins again.
The advantage of this technique is that the parallel lines beamed from different angles are bent in different ways by discontinuities on the surface of the object. And a computer can use this information to reconstruct the original three-dimensional shape more or less exactly.
Servin and co have tested this approach on the particularly complex shape of a plastic human skull and the results are impressive. Not only does the technique record depressions as well as mounds but it also accurately records discontinuities in the structure, where the jaw separates from the skull, for example.
That is a handy addition to the virtual modelling toolbox. With a simple and easy way to record almost any three-dimensional object, it should become much easier for anyone to create virtual copies and, indeed, real ones using 3-D printing techniques.
Ref: arxiv.org/abs/1408.6463: Co-Phased 360-Degree Profilometry Of Discontinuous Solids With 2-Projectors And 1-Camera
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