I suppose processing pictures is quite a bit of work, but I have a feeling it shouldn't take a cluster of 16 machines to do that math(although it doesn't hurt). With a little work I bet you could get the work down to the size of a single desktop PC without sacrificing any necessary accuracy. At that point give it 5-10 years and something the size of a mobile phone could do it easily.
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DBeta commented on Aggressive Maneuvers for Autonomous Quadrotor Flight