Magnetic Inclination Compass

Many migratory birds don't sense magnetic north the way a hand-held compass does. Instead they detect the dip angle between Earth's field lines and gravity — an inclination compass — and steer toward wherever that angle gets steeper. This simulation renders a real geomagnetic dipole field around a 3D globe and flies an instanced flock across it using that exact rule: tan(I) = 2·tan(λ_m). Flip the vertical field component to reproduce the Wiltschkos' landmark reversal experiment, compare against a hypothetical polarity-only compass that fails to reproduce it, dial in sensor noise, and watch the flock lose its bearings in the live-tracked ambiguity zone around the magnetic equator.