Saturday, September 4, 2010

Speed sensor with camera and computing based on flies

Found on IEEE Spectrum:

An interesting idea of measuring speed using camera images. The computation is based on how flies measure their speed with vision. It's an alternative to encoders (car speedometer, measuring how fast colored lines change on a spinning wheel), accelerometers (small chips which sense acceleration), or GPS.

The sensor has a camera on it with a lens that gives it 180 degree vision. The images it gets are sent to the processor. Here's the details:

The chip is looking for two variables: temporal frequency (variation of a signal over time in one point) and spatial frequency (variation of a signal such as light intensity in space in one moment). Approximating a division of the temporal frequency by the spatial frequency can yield a remarkably spot-on measure of absolute speed.
Temporal frequency is easy, but spatial frequency is trickier and more computationally expensive. That means it burns a lot of power—anathema to a small, portable sensor.
Vissee’s algorithm lightens the computational load by using methods derived from the fruit-fly brain to filter out any data that does not help the processors calculate speed.

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