Solutions based on expensive IMUs [0], SLAM [1], or visual odometry are more realistic than GPS. As a rule, never use GPS for fine-grained control. Even ignorin

Solutions based on expensive IMUs [0], SLAM [1], or visual odometry are more realistic than GPS. As a rule, never use GPS for fine-grained control. Even ignoring accuracy, GPS fails when you lack line-of-sight to GPS satellites, which is extremely dangerous on a quadrotor - how do you safely land a flying chainsaw with no feedback? When finely controlling a platform, you need accurate relative position. The global position is usually unimportant when the platform's position on Earth doesn't matter. Sensors designed for computer vision applications are surprisingly light and small! Board-level cameras can fit in the palm of your hand, and reasonable IMUs are not much bigger than a matchbox. The biggest obstacles today are tradeoffs between performance/weight and performance/battery life. The platform needs algorithms with acceptable results, requiring almost no supporting hardware, and that are robust to the thousands of things that go wrong when trying to sense (noise, errors, resolution, occlusions, etc). Algorithms that fit all of these requirements are very uncommon. In fact, I would not be surprised if there was an Iron Triangle in there somewhere. [0] Inertial Measurement Units: Devices that estimate acceleration (or some other measure of movement). [1] Simultaneous Localization and Mapping. Using stereo vision, lidar, radio ranging, etc. to estimate your position, plus how the environment looks.