Mathematical 3‐Arm Protractor
作者:
W. B. RUHNOW,
期刊:
Navigation
(WILEY Available online 1984)
卷期:
Volume 31,
issue 1
页码: 38-46
ISSN:0028-1522
年代: 1984
DOI:10.1002/j.2161-4296.1984.tb00858.x
出版商: Blackwell Publishing Ltd
数据来源: WILEY
摘要:
ABSTRACTThe mechanical 3‐arm protractor is used to answer (graphically) the question: “Given three positions (landmarks) and two angles, what is present position?”. A marine sextant is typically used to obtain the angles while a 3‐arm protractor is used to determine present position from a chart. However, while the sextant is fairly accurate, the 3‐arm protractor is awkward to use and sacrifices much of the accuracy gained by careful sextant work. Fortunately, the function that the 3‐arm protractor performs graphically can be implemented on a pocket calculator once this function is described mathematically. Thus, savings of time, accuracy, and money may be realized along with the elimination of plotting hardware. The math is presented here along with an example for flat earth calculations. An iterative approach is also presented for spherical earth c
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