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The cocked hat: formal statements and proofs of the theorems

Published online by Cambridge University Press:  15 February 2021

Imre Bárány ,
William Steiger  and
Sivan Toledo Open the ORCID record for Sivan Toledo [Opens in a new window]
Imre Bárány
Affiliation:
Rényi Institute of Mathematics, 13–15 Reáltanoda Street, Budapest1053Hungary. Department of Mathematics, University College London, Gower Street, LondonWC1E 6BT, UK.
William Steiger
Affiliation:
Department of Computer Science, Rutgers University, 110 Frelinghuysen Road, Piscataway, NJ08854-8019, USA.
Sivan Toledo*
Affiliation:
Blavatnik School of Computer Science, Tel Aviv University, Tel Aviv6997801, Israel
*
*Corresponding author. E-mail: stoledo@mail.tau.ac.il
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Abstract

Navigators have been taught for centuries to estimate the location of their craft on a map from three lines of position, for redundancy. The three lines typically form a triangle, called a cocked hat. How is the location of the craft related to the triangle? For more than 80 years navigators have also been taught that, if each line of position is equally likely to pass to the right and to the left of the true location, then the likelihood that the craft is in the triangle is exactly 1/4. This is stated in numerous reputable sources, but was never stated or proved in a mathematically formal and rigorous fashion. In this paper we prove that the likelihood is indeed 1/4 if we assume that the lines of position always intersect pairwise. We also show that the result does not hold under weaker (and more reasonable) assumptions, and we prove a generalisation to $n$ lines.

Keywords

pilotagestochastic errorhistory
Type
Research Article
Information
The Journal of Navigation , Volume 74 , Issue 3 , May 2021 , pp. 713 - 722
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Copyright
Copyright © The Royal Institute of Navigation 2021

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