Unmanned Aerial Vehicles carrying access points or base stations are widely positioned so as to hold line-of-sight links with every ground user at once. The algorithms that do so are evaluated against obstacle information treated as exact, whether that information comes from a surveyed map or, more recently, from onboard vision. This paper analyses what becomes of that requirement when the obstacle information is estimated rather than given, and derives the detection accuracy it implicitly demands. Three results follow. The probability of satisfying the requirement decays geometrically with the number of users, so that a detector accurate enough for one user is not accurate enough for a network. Spatially correlated detection error raises that probability but concentrates failures into systematic blind spots. Relaxing the requirement from all users to ninety per cent of them widens the tolerable detection error by more than an order of magnitude, far beyond what any plausible improvement of the detector could deliver. The requiremen

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