When polar coordinates (r,θ) are used to parameterize the plane, centred on the origin, then the first fundamental form is
More generally, at a point on a surface, there is a unique locally defined geodesic in each given tangent direction. Using geodesic polars, so that coordinates (r,θ) are assigned to the point distance r along the geodesic in direction θ, the first fundamental form has E = 1, F = 0, as above.