Hard surface made of a uniform material, I should think. Or a surface where the mics have been calibrated to it. Otherwise differing speeds of sound through different materials would throw it off if it was, say, half metal and aerogel or something.
As for drawing letters, that's easily accomplished. Remember those virtual keyboards that draw the keys on a surface with a laser and optically detect where your fingers are? Just use cheaper, simpler, audio pickups instead, but still draw on the surface. Perhaps you'd give a laser to each of the audio pickups, so that standing on the surface didn't block a single laser from being able to draw in your shadow.
It also could be useful for mapping situations, e.g. finding various departments or rooms in a hospital.
"Hard surface made of a uniform material, I should think. Or a surface where the mics have been calibrated to it. Otherwise differing speeds of sound through different materials would throw it off if it was, say, half metal and aerogel or something."
Good point. I wonder if you have to tell the software where the mics are located to begin with? If the mics themselves can produce sound, then they might be able to figure out each others' locations, assuming a uniform substrate. Changing the assumed speed of sound in the material would effectively shrink or expand the tablet area, but shouldn't affect calculations of angle, proportional distance, etc.. And you might be able to calibrate even for that, if you could also measure sound speed through the air and compare it to the speed of vibrations in the tablet.
It occurs to me that this idea has already been done in reverse, using sonar/ultrasound/seismic thumping to map out areas of varying sound speed, reflection at interfaces, etc.
Or you could reverse it another way. With four distinct sound emitters in known locations, a simple microphone could act as an acoustic GPS receiver for accurate positioning.
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As for drawing letters, that's easily accomplished. Remember those virtual keyboards that draw the keys on a surface with a laser and optically detect where your fingers are? Just use cheaper, simpler, audio pickups instead, but still draw on the surface. Perhaps you'd give a laser to each of the audio pickups, so that standing on the surface didn't block a single laser from being able to draw in your shadow.
It also could be useful for mapping situations, e.g. finding various departments or rooms in a hospital.
--josh
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Good point. I wonder if you have to tell the software where the mics are located to begin with? If the mics themselves can produce sound, then they might be able to figure out each others' locations, assuming a uniform substrate. Changing the assumed speed of sound in the material would effectively shrink or expand the tablet area, but shouldn't affect calculations of angle, proportional distance, etc.. And you might be able to calibrate even for that, if you could also measure sound speed through the air and compare it to the speed of vibrations in the tablet.
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