The tasks of modern navigation are the selection of the safest and most convenient route for a ship, the use of navigational instruments and devices to determine the direction of travel and the distance covered by a ship at sea (including determination of corrections for the readings of such instruments), the study and selection of the cartographic projections that are most convenient for navigation and their use to solve problems of navigation by analytical and graphic methods, the consideration of the effect of external factors that cause deviation of the ship from the selected route, the determination of the ship’s location on the basis of land reference points and navigation satellites, and the assessment of the accuracy of such determinations. A number of problems of navigation are solved using methods of geodesy, cartography, hydrography, oceanography, and meteorology.
A ship’s voyage between specific points requires the calculation and plotting of its route on maritime navigation charts, and also determination of a course that will ensure that the ship travels along the planned route with consideration for the effect of external disturbances (wind and currents). The nautical mile has been adopted as the fundamental unit for measuring distance at sea, and the degree as the fundamental unit for measuring direction.
The next great revolution in navigation occurred in the 20th cent., when radio signals came into wide use. The development of radar, loran, and radio direction finding during World War II caused fundamental changes in navigational practice; a mariner or pilot today can turn on a Loran or Global Positioning System receiver and determine position and course to within a few yards. Inertial guidance systems, most often used to navigate submarines, aircraft, and spacecraft, allow navigation without contact with a ground base. In such systems, a computer navigates the vehicle with the aid of an inertial navigator device, which consists of a gyroscope to indicate direction and an accelerometer to measure changes in speed and direction. Inertial guidance systems and terrainfollowing radar allow a cruise missile to fly a thousand miles and hit its designated target. The development of navigation satellites beginning in the 1960s led in the 1990s to the U.S.’s Global Positioning System (GPS), which provides location and other information through the reception and interpretation of signals received from satellites; Russia and China have since created similar navigation systems. GPS receivers, which are now incorporated into smartphones and other devices, have made it possible to create navigation systems for vehicles and other forms of transportation.