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The east north up (ENU) local tangent plane is similar to NED, except for swapping 'down' for 'up' and x for y. Local tangent plane coordinates ( LTP ) are part of a spatial reference system based on the tangent plane defined by the local vertical direction and the Earth's axis of rotation.
The star is the point of interest, the reference plane is the local area (e.g. a circular area with a 5 km radius at sea level) around an observer on Earth's surface, and the reference vector points to true north. The azimuth is the angle between the north vector and the star's vector on the horizontal plane. [2]
32-point compass rose. The points of the compass are a set of horizontal, radially arrayed compass directions (or azimuths) used in navigation and cartography.A compass rose is primarily composed of four cardinal directions—north, east, south, and west—each separated by 90 degrees, and secondarily divided by four ordinal (intercardinal) directions—northeast, southeast, southwest, and ...
Azimuth is measured eastward from the north point (sometimes from the south point) of the horizon; altitude is the angle above the horizon. The horizontal coordinate system is a celestial coordinate system that uses the observer's local horizon as the fundamental plane to define two angles of a spherical coordinate system: altitude and azimuth.
If the reference direction is north (either true north, magnetic north, or grid north), the bearing is termed an absolute bearing. In a contemporary land navigation context, true, magnetic, and grid bearings are always measured in this way, with true north, magnetic north, or grid north being 0° in a 360-degree system. [5]
The North point will then be the point on the limb that is closest to the North celestial pole. Similarly, a line from the center to the South celestial pole will define the South point by its intersection with the limb. The points at right angles to the North and South points are the East and West points.
The Earth-centered, Earth-fixed coordinate system (acronym ECEF), also known as the geocentric coordinate system, is a cartesian spatial reference system that represents locations in the vicinity of the Earth (including its surface, interior, atmosphere, and surrounding outer space) as X, Y, and Z measurements from its center of mass.
1985: Image:BlankMap-World-1985.png – World before the fall of the Soviet Union, the reunification of Germany (including West Berlin), and Yemen, and dissolution of Czechoslovakia and Yugoslavia, and the independence of East Timor and Eritrea. Nominally from 1985. 1990: Image:BlankMap-World-1990.png; 1993: Image:BlankMap-World-1993.png