Prefer World.frameAt. Without a position, uses world.options.origin.
ReadonlyeastUnit east vector.
ReadonlynorthUnit north vector.
ReadonlyoriginPlanet-centred position of the frame origin on the base sphere (zero on a flat world).
ReadonlyupUnit up vector.
Local height at (x, z): what a (x, z) => y height function should return.
Everything about local (x, z). elevation is converted to local y (curvature included).
Optionalout: WorldSample
A locally flat frame on a world:
xeast,zsouth (three.js convention: −z is north),yup. On a flat world it is the world itself. On a planet it is the tangent plane at a latitude/longitude, accurate for tens of kilometres — enough for grass, forests, rivers and cities. Heights include the planet's curvature drop, so things placed with it sit exactly on the rendered sphere.