A Curve is a 1-dimensional geometric object usually stored as a sequence of Points, with the subtype of Curve specifying the form of the interpolation between Points. This specification defines only one subclass of Curve, LineString, which uses linear interpolation between Points. A Curve is a 1-dimensional geometric object that is the homeomorphic image of a real, closed, interval. A Curve is simple if it does not pass through the same Point twice with the possible exception of the two end points. A Curve is closed if its start Point is equal to its end Point. The boundary of a closed Curve is empty. A Curve that is simple and closed is a Ring. The boundary of a non-closed Curve consists of its two end Points. A Curve is defined as topologically closed, that is, it contains its endpoints f(a) and f(b).