Position resection and intersection: Difference between revisions

Revision as of 04:58, 4 June 2016

Revision as of 00:45, 26 June 2017

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{{Merge to|Snellius–Pothenot problem|date=March 2016}}

'''Resection''' is a method for determining an unknown position (position finding) measuring angles with respect to known positions. Measurements can be made with a [[compass]] and [[topographic map]] (or [[nautical chart]]),<ref>Mooers Jr., Robert L., ''Finding Your Way In The Outdoors'', Outdoor Life Press (1972), {{ISBN |0-943822-41-6}}, pp. 129&ndash;134</ref><ref>Kals, W.S., ''Practical Navigation'', New York: Doubleday & Co. (1972), {{ISBN |0-385-00246-7}}, pp. 43&ndash;49</ref> [[Theodolite]] or with a [[total station]] using known points of a [[Geodetic network]] or landmarks of a map.

==Resection versus intersection==

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==In navigation==

{{broader|Position fixing}}

When resecting or fixing a position, the geometric strength (angular disparity) of the mapped points affects the precision and accuracy of the outcome. Accuracy increases as the angle between the two position lines approaches 90 degrees.<ref>Seidman, David, and Cleveland, Paul, ''The Essential Wilderness Navigator'', Ragged Mountain Press (2001), {{ISBN |0-07-136110-3}}, p. 100</ref> Magnetic bearings are observed on the ground from the point under ___location to two or more features shown on a map of the area.<ref>Mooers, pp. 129&ndash;134</ref><ref>Kals, pp. 43&ndash;49</ref> 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).<ref>Mooers, pp. 129&ndash;134</ref> When three or more lines of position are utilized, the method is often popularly (though erroneously) referred to as [[triangulation]] (in precise terms, using three or more lines of position is still correctly called ''resection'', as angular [[law of tangents]] ([[cotangent|cot]]) calculations are not performed).<ref>Touche, Fred, ''Wilderness Navigation Handbook'', Fred Touche (2004), {{ISBN |978-0-9732527-0-5}}, {{ISBN |0-9732527-0-7}}, pp. 60&ndash;67</ref> When using a map and compass to perform resection, it is important to allow for the difference between the magnetic bearings observed and grid north (or true north) bearings ([[magnetic north|magnetic declination]]) of the map or chart.<ref>Mooers, p. 133</ref>

Resection continues to be employed in land and inshore navigation today, as it is a simple and quick method requiring only an inexpensive magnetic compass and map/chart.<ref>Mooers, pp. 129&ndash;134</ref><ref>Kals, pp. 43&ndash;49</ref><ref>Touche, pp. 60&ndash;67</ref>

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==References==

* Mooers Jr., Robert L., ''Finding Your Way In The Outdoors'', Outdoor Life Press (1972), {{ISBN |0-943822-41-6}}

* Kals, W.S., Practical Navigation, New York: Doubleday & Co. (1972), {{ISBN |0-385-00246-7}}

* Seidman, David, and Cleveland, Paul, ''The Essential Wilderness Navigator'', Ragged Mountain Press (2001), {{ISBN |0-07-136110-3}}

==External links==