I've thought about heat sensors, actually.

The faculty I'm working with on this wants a bit more precision than just 'point it at the warm blob over there.' How much precision do you think I can get with those devices?

Ultrasound would work if I only need to pan back and forth. I pulled some nice papers yesterday that talk about localizing a source based on a plane wave arriving at two closely spaced detectors. Depending on the location of the source, the detectors will receive the same signal either in phase, out of phase, or something in the middle.

So the source of a train of pings would be fairly easy to calculate.

If I mount the whole mess fairly close to the ground plane, I can avoid a lot of ambient reflections - similar to how a PZM microphone works.

Unfortunately, it looks like she may want the projector to tilt as well. Which either means moving to a video based system where I can look for a hot spot, or add a second ultrasound sensor pair mounted perpendicular to the first so I can calculate the angle above and below a plane.

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JEC