The radius of curvature, expressed by ρ: ρ, is the reciprocal of the curvature in meters. Curvature, expressed by Kappa:κ, is a measure of geometric roughness. For different geometric shapes, flatness has different meanings.

For plane curves? The curvature of c and p at a point is equal to the reciprocal of the radius of an intimate circle, which is a vector pointing to the center of the circle. Its size can be measured by diopter, and 1 diopter is equal to every meter 1 (radian). The radius of this osculating circle is the radius of curvature.

The smaller the radius of the osculating circle, the greater the curvature; So when the curve is close to a straight line, the curvature is close to zero, and when the curve turns sharply, the curvature is very large.

The curvature of a straight line is 0 everywhere; The curvature of a circle with radius r is 1/r everywhere.