Sunday, April 14, 2013

How a Time-of-Flight sensor works

Time-of-Flight, or TOF, sensors measure distance. As such, they are an alternative to triangulation approaches to 3D, as I discussed on April 10th in “Mapping the autobahn in 3D”.

If you look back at that blog post you’ll see a couple of comments regarding the principles behind TOF. Now as we all know, light moves along at quite a lick, so measuring how long it takes to cover a couple of meters would be a challenging task. But TOF sensors aren’t quite that smart. Despite their name, they don’t measure time but rather, phase shift.

It’s still very clever, and if you’re interested in learning more I’d like to refer you to a couple of sources.

First up is an article by German 3D imaging company Metrilus. “Time-of-Flight Cameras” does an excellent job of explaining the basic principles and math.

And then there’s “Image Sensor Technologies for 3D Time-of-flight Range Imaging”, a paper from MESA Imaging (opens as a pdf.) This too covers the math, but it also dives into the details of the various TOF sensors. If you want to become a TOF expert, this is where to start. Just remember, no photons were actually timed during the course of this measurement.

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