Книга: Radius of curvature: Sphere, Ellipsoid, Radius, Osculating Circle, Oblate, Graph of a Function, Semi-Major Axis, Semi-Minor Axis, Angular Eccentricity

High Quality Content by WIKIPEDIA articles! The distance from the center of a sphere or ellipsoid to its surface is its radius. The equivalent 'surface radius' that is described by radial distances at points along the body's surface is its radius of curvature (more formally, the radius of curvature of a curve at a point is the radius of the osculating circle at that point). With a sphere, the radius of curvature equals the radius. With an oblate ellipsoid (or, more properly, an oblate spheroid), however, not only does it differ from the radius, but it varies, depending on the direction being faced. The extremes are known as the principal radii of curvature.