Geodesy is the science concerned with the exact positioning of points on the surface of the Earth. It also involves the study of variations of the Earth’s gravity, the application of these variations to exact measurements on the Earth, and the study of the exact size and shape of the Earth. These factors were unimportant to early navigators because of the relative inaccuracy of their methods. The precision of today’s navigation systems and the global nature of satellite and other long-range positioning methods demand a more complete understanding of geodesy by the navigator than has ever before been required [3]. I

n mathematics, a geodesic is a generalization of the notion of a "straight line" to "curved spaces". Definition of geodesic depends on the type of "curved space". If the space cares natural metric then geodesics are defined to be (locally) the shortest path between points on the space.

The term "geodesic" comes from geodesy, the science of measuring the size and shape of the Earth; in the original sense, a geodesic was the shortest route between two points on the surface of the earth, namely, a segment of a great circle.