Elliptical Wildfire Perimeter Growth & Moisture Extinction

Real wildland fire behavior software doesn't march a grid of cells forward — it tracks the fire's perimeter as a curve and grows it using the Huygens-wavelet elliptical propagation method, because an unobstructed point ignition in uniform wind analytically produces a fire ellipse with the ignition point sitting at one focus. This simulator implements exactly that: the perimeter is a ring of bearings radiating from a single ignition point, each one advancing at a rate set by Anderson's (1983) empirical length-to-breadth ellipse formula and damped locally by Rothermel's moisture coefficient η_M, sampled independently at every bearing against a moist/dry terrain field. Push dead-fuel moisture toward the ~30% moisture-of-extinction threshold for fine fuels and watch stretches of the advancing perimeter stall and dent inward exactly where they meet a damp pocket, while the rest of the ellipse keeps racing downwind — the same physics as the companion 3D grid sim, propagated through a completely different, and more analytically faithful, numerical method.