By attaching a refractor to the lens of a Video Capture Device (e.g., CCD Video Camera) it is possible to record optical displacements from the original position of any object (tracer particle) within the image plane. If the refractor is physically rotated around the optical axis at high speed, the tracer particles create annular streaks due to the effect caused by the refractor’s circular shift. The perceived displacements are added to the image being recorded by the Video Capture Device (VCD). Additionally, these displacements are directly related to the distance between the VCD and the particle being measured: the magnitude of displacement on the image plane being inversely proportional to the distance between the VCD and point of measurement. Since the radius of each annular streak, of a point being measured, is inversely proportional to its distance from the VCD, it is therefore possible by analyzing these annular streaks, to determine the three dimensional positional information of the point. Thus the radius of the annular streaks on the image plane determines the z coordinate, while the geometric center provides the x and y coordinates. The theory and setup of such a measuring system is subsequently presented, and the measurement of a moving surface, such as moving water, is used to demonstrate a typical application of such a system.

Issue Section:
Technical Papers
Keywords:
CCD image sensors, video cameras, lenses, stereo image processing, flow visualisation
Topics:
Displacement, Fluid measurement, Image processing, Lenses (Optics), Particulate matter, Video cameras, Water, Lasers
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