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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.
Also known as the Rectangular Survey System, it was created by the Land Ordinance of 1785 to survey land ceded to the United States by the Treaty of Paris in 1783, following the end of the American Revolution. Beginning with the Seven Ranges in present-day Ohio, the PLSS has been used as the primary survey method in the United States.
Local attraction at a place can be detected by observing bearings from both ends of the line in the area. If fore bearing and back bearing of a line differ exactly by 180°, there is no local attraction at either station. But if this difference is not equal to 180°, then local attraction exists there either at one or both ends of the line. [3]
The surveyors start from an old reference mark or known position and place a network of reference marks covering the survey area. They then measure bearings and distances between the reference marks, and to the target features. Most traverses form a loop pattern or link between two prior reference marks so the surveyor can check their measurements.
Compass surveying is a type of surveying in which the directions of surveying lines are determined with a magnetic compass, and the length of the surveying lines are measured with a tape or chain or laser range finder. [2] The compass is generally used to run a traverse line. The compass calculates bearings of lines with respect to magnetic needle.
In surveying, free stationing (also known as resection) is a method of determining a location of one unknown point in relation to known points. [1] There is a zero point of reference called a total station. The instrument can be freely positioned so that all survey points are at a suitable sight from the instrument.
A bearing compass, is a nautical instrument used to determine the bearing of observed objects. (Bearing: angle formed by the north and the visual to a certain object in the sea or ashore). Used in navigation to determine the angle between the direction of an object and the magnetic north or, indirectly relative to another reference point.
absolute bearing The bearing of an object in relation to north: either true bearing, using the geographical or true north, or magnetic bearing, using magnetic north. See also bearing and relative bearing. accommodation ladder A portable flight of steps down a ship's side. accommodation ship. Also accommodation hull.