Inspectioneering Journal

Importance of 3D Modeling in High-Definition Remote Visual Measurement Systems

By Charles Janecka, Associate Product Manager at Olympus / Evident Scientific. This article appears in the September/October 2020 issue of Inspectioneering Journal.

How Stereo Measurement Works

Stereo measurement works in a similar way to how human eyes interact with our brains and our environment. We avoid bumping into things when we walk around because our brain is constantly calculating distance, based on triangulation and the parallax from our right and left eyes. For example, when we look at a building and close one eye and then the other (Figure 1), our brain knows that the building has not moved, merely the perspective from each eye, based on its position in relation to the object, has changed. Using these two different perspectives of a static object, measurement becomes possible. Lateral shift is inversely proportional to distance. Therefore, the “Z” distance is inversely proportional to lateral shift. In daily life, our eyes work with our brain to achieve this understanding of how far away various objects are (e.g., a table, a chair, a car, the moon, etc.) and how large or small they are.

Figure 1. Parallax lateral shift – left eye vs. right eye views.
Figure 1. Parallax lateral shift – left eye vs. right eye views.

Applications within Remote Visual Measurement Systems

In terms of remote visual measurement, the parallax determination is calculated in a slightly different way. It does, however, use the same fundamental principles. In remote visual inspection (RVI) equipment, the brain is replaced with a charge-coupled device imaging sensor and a processor. The eyes are replaced with the optical lenses in a tip adaptor. The tip adaptor has two lens systems with a preset offset in their distances to each other. Figure 2 demonstrates how the optical system works in conjunction with the charge-coupled device and processor. The parallax is used to determine the relevant distance of an object, based on the perspective shift across each side of the charge-coupled device.

Figure 2. Parallax of a stereo image on a charge-coupled device.
Figure 2. Parallax of a stereo image on a charge-coupled device.

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