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The Universal Transverse Mercator (UTM) is a map projection system for assigning coordinates to locations on the surface of the Earth.Like the traditional method of latitude and longitude, it is a horizontal position representation, which means it ignores altitude and treats the earth surface as a perfect ellipsoid.
Consider a point on the globe of radius R with longitude λ and latitude φ. If φ is increased by an infinitesimal amount, dφ, the point moves R dφ along a meridian of the globe of radius R, so the corresponding change in y, dy, must be hR dφ = R sec φ dφ. Therefore y′(φ) = R sec φ.
(On the sphere it depends on both latitude and longitude.) The scale is true on the central meridian. • The projection is reasonably accurate near the equator. Scale at an angular distance of 5° (in latitude) away from the equator is less than 0.4% greater than scale at the equator, and is about 1.54% greater at an angular distance of 10°. •
In surveying, bearings can be referenced to true north, magnetic north, grid north (the Y axis of a map projection), or a previous map, which is often a historical magnetic north. [ citation needed ] If navigating by gyrocompass , the reference direction is true north , in which case the terms true bearing and geodetic bearing are used.
A geographic coordinate system (GCS) is a spherical or geodetic coordinate system for measuring and communicating positions directly on Earth as latitude and longitude. [1] It is the simplest, oldest and most widely used of the various spatial reference systems that are in use, and forms the basis for most others.
The Military Grid Reference System (MGRS) [1] is the geocoordinate standard used by NATO militaries for locating points on Earth. The MGRS is derived from the Universal Transverse Mercator (UTM) grid system and the Universal Polar Stereographic (UPS) grid system, but uses a different labeling convention.
Informally, specifying a geographic location usually means giving the location's latitude and longitude. The numerical values for latitude and longitude can occur in a number of different units or formats: [2] sexagesimal degree: degrees, minutes, and seconds : 40° 26′ 46″ N 79° 58′ 56″ W
Geodetic latitude and geocentric latitude have different definitions. Geodetic latitude is defined as the angle between the equatorial plane and the surface normal at a point on the ellipsoid, whereas geocentric latitude is defined as the angle between the equatorial plane and a radial line connecting the centre of the ellipsoid to a point on the surface (see figure).