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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.
With a local declination of 14°E, a true bearing (i.e. obtained from a map) of 54° is converted to a magnetic bearing (for use in the field) by subtracting declination: 54° – 14° = 40°. If the local declination was 14°W (−14°), it is again subtracted from the true bearing to obtain a magnetic bearing: 54°- (−14°) = 68°.
A magnetic bearing. A magnetic bearing is a type of bearing that supports a load using magnetic levitation. Magnetic bearings support moving parts without physical contact. For instance, they are able to levitate a rotating shaft and permit relative motion with very low friction and no mechanical wear. Magnetic bearings support the highest ...
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]
A drawback to this approach is that magnetic variations change over time, so the charts would need constant revision. [ 12 ] The azimuth compass still had great value in letting the master of a ship determine how far the magnetic compass varied from true north, so he could set a more accurate course while following a line of constant latitude ...
Instruments used to plot a course on a nautical chart. In navigation, the course of a watercraft or aircraft is the cardinal direction in which the craft is to be steered.The course is to be distinguished from the heading, which is the direction where the watercraft's bow or the aircraft's nose is pointed.
Magnetic bearings are observed on the ground from the point under location to two or more features shown on a map of the area. [ 8 ] [ 9 ] Lines of reverse bearings, or lines of position , are then drawn on the map from the known features; two and more lines provide the resection point (the navigator's location). [ 10 ]
In the mathematical discipline of graph theory, the line graph of an undirected graph G is another graph L(G) that represents the adjacencies between edges of G. L(G) is constructed in the following way: for each edge in G, make a vertex in L(G); for every two edges in G that have a vertex in common, make an edge between their corresponding vertices in L(G).