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The foot (standard symbol: ft) [1] [2] is a unit of length in the British imperial and United States customary systems of measurement. The prime symbol, ′, is commonly used to represent the foot. [3] In both customary and imperial units, one foot comprises 12 inches, and one yard comprises three feet.
These are the defining dimensions for NAD 27, but Clarke actually defined his 1866 spheroid as a = 20,926,062 British feet, b = 20,855,121 British feet. The conversion to meters uses Clarke's 1865 inch-meter ratio of 39.370432. The length of a foot or meter at the time could not practically be benchmarked to better than about 0.02 mm. [11]
In many measurement systems based on former English units, the link has remained fixed at 0.66 feet, therefore 0.22 yards or 7.92 inches; it is the absolute length of the yard that has varied. A rare remaining application of the link is in the service of some surveying in the United States, which relates to the definition of the survey foot.
In geodesy, geographic coordinate conversion is defined as translation among different coordinate formats or map projections all referenced to the same geodetic datum. [1] A geographic coordinate transformation is a translation among different geodetic datums. Both geographic coordinate conversion and transformation will be considered in this ...
These efforts are known as "High Accuracy Reference Network" (HARN) or "High Precision GPS Network" (HPGN). In addition, the basic unit of distance used is sometimes feet and sometimes meters. Thus a fully described coordinate system often looks something like: "Washington State Plane North, NAD83 HARN, US Survey feet".
The United States and the Metric System (LC 1136) nist.gov Archive.org; The Metric System in the United States Archived June 11, 2017, at the Wayback Machine; A Metric America: A Decision Whose Time Has Come on nist.gov Archive.org; Metric Conversion Act of 1975 on nist.gov Archive.org; www.us-metric.org—U.S. Metric Association (mirror link)
In the United States, the term statute mile formally refers to the survey mile, [3] but for most purposes, the difference of less than 1 ⁄ 8 inch (3.2 mm) between the survey mile and the international mile (1609.344 metres exactly) is insignificant—one international mile is 0.999 998 US survey miles—so statute mile can be used for either.
The rod, perch, or pole (sometimes also lug) is a surveyor's tool [1] and unit of length of various historical definitions. In British imperial and US customary units, it is defined as 16 + 1 ⁄ 2 feet, equal to exactly 1 ⁄ 320 of a mile, or 5 + 1 ⁄ 2 yards (a quarter of a surveyor's chain), and is exactly 5.0292 meters.