Unless you have a precise map of all the weed locations, precise location in absolute world coordinates doesn't seem too important. You'd need fairly precise an

Unless you have a precise map of all the weed locations, precise location in absolute world coordinates doesn't seem too important. You'd need fairly precise and accurate relative positioning from tank to drone and drone to weed, though. Drone to weed could be done via camera (you need to detect the weed anyway), but tank to drone would likely be a difficult engineering problem. A flying drone seems like the wrong way to solve the problem, though. For a drone close enough to the ground to reliably detect weeds, you'd likely need a multi-rotor, a slow flying fixed wing aircraft, or a blimp. A multirotor has a huge energy penalty, and a fixed wing aircraft or blimp loses the practical gains vs. just using a tractor of some sort.