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navigation例如。I have majored in navigation in ... Maritime college since 2 years ago.
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Navigation is a field of study that focuses on the process of monitoring and controlling the movement of a craft or vehicle from one place to another. The field of navigation includes four general categories: land navigation, marine navigation, aeronautic navigation, and space navigation. It is also the term of art used for the specialized knowledge used by navigators to perform navigation tasks. All navigational techniques involve locating the navigator's position compared to known locations or patterns.Navigation, in a broader sense, can refer to any skill or study that involves the determination of position and direction. In this sense, navigation includes orienteering and pedestrian navigation. For information about different navigation strategies that people use, visit human navigation.The word navigation comes from the word "navgathi" a Sanskrit word. In the European medieval period, navigation was considered part of the set of seven mechanical arts, none of which are used for long voyages across open ocean in Polynesian navigation.LatitudeThe latitude of a place on the Earth's surface is the angular distance north or south of the equator. Latitude is usually expressed in degrees (marked with °) ranging from 0° at the Equator to 90° at the North and South poles. The latitude of the North Pole is 90° N, and the latitude of the South Pole is 90° S. Historically, mariners calculated latitude in the Northern Hemisphere by sighting the North Star Polaris with a sextant and sight reduction tables to take out error for height of eye and atmospheric refraction. Generally, the height of Polaris in degrees of arc above the horizon is the latitude of the observer.LongitudeSimilar to latitude, the longitude of a place on the Earth's surface is the angular distance east or west of the prime meridian or Greenwich meridian.[4] Longitude is usually expressed in degrees (marked with °) ranging from 0° at the Greenwich meridian to 180° east and west. Sydney, for example, has a longitude of about 151° east. New York City has a longitude of about 74° west. For most of history, mariners struggled to determine precise longitude. Longitude can be calculated if the precise time of a sighting is known. The problem was solved initially by using a sextant to take a lunar distance (also called the lunar observation, or lunar for short) that, in conjunction with a nautical almanac, can be used to calculate Greenwich time for determining longitude. Reliable marine chronometers were unavailable until the late 18th century and not affordable until the 19th century.For approximately one hundred years, from about 1767 until about 1850, mariners lacking a chronometer used the method of lunar distances to determine Greenwich time, an important step in finding their longitude. A mariner with a chronometer could check and correct its reading using a lunar determination of Greenwich time.Modern techniqueMost modern navigation relies primarily on positions determined electronically by receivers collecting information from satellites. Most other modern techniques rely on crossing lines of position or LOP. A line of position can refer to two different things: a line on a chart and a line between the observer and an object in real life. A bearing is a measure of the direction to an object. If the navigator measures the direction in real life, the angle can then be drawn on a nautical chart and the navigator will be on that line on the chart.[12]In addition to bearings, navigators also often measure distances to objects. On the chart, a distance produces a circle or arc of position. Circles, arcs, and hyperbolae of positions are often referred to as lines of position.If the navigator draws two lines of position, and they intersect he must be at that position.A fix is the intersection of two or more LOPs.If only one line of position is available, this may be evaluated against the Dead reckoning position to establish an estimated position.Lines (or circles) of position can be derived from a variety of sources:celestial observation (a short segment of the circle of equal altitude, but generally represented as a line),terrestrial range (natural or man made) when two charted points are observed to be in line with each other,compass bearing to a charted object,radar range to a charted object,on certain coastlines, a depth sounding from echo sounder or hand lead line.There are some methods seldom used today such as "dipping a light" to calculate the geographic range from observer to lighthouseMethods of navigation have changed through history. Each new method has enhanced the mariner’s ability to complete his voyage. One of the most important judgments the navigator must make is the best method to use. Some types of navigation are depicted in the table.PilotingPiloting (also called pilotage) involves navigating a vessel in restricted waters and fixing its position as precisely as possible at frequent intervals. More so than in other phases of navigation, proper preparation and attention to detail are important.[16] Procedures vary from vessel to vessel, and between military, commercial, and private vessels.[16]A military navigation team will nearly always consist of several people. A military navigator might have bearing takers stationed at the gyro repeaters on the bridge wings for taking simultaneous bearings, while the civilian navigator must often take and plot them himself. While the military navigator will have a bearing book and someone to record entries for each fix, the civilian navigator will simply pilot the bearings on the chart as they are taken and not record them at all.If the ship is equipped with an ECDIS, it is reasonable for the navigator to simply monitor the progress of the ship along the chosen track, visually ensuring that the ship is proceeding as desired, checking the compass, sounder and other indicators only occasionally.If a pilot is aboard, as is often the case in the most restricted of waters, his judgement can generally be relied upon, further easing the workload. But should the ECDIS fail, the navigator will have to rely on his skill in the manual and time-tested procedures.[16]
