THE CALCULATION OF SEARCH AREAS RELATING TO D.F. FIXES
ADMIRALTY RESEARCH LAB TEDDINGTON (UNITED KINGDOM)
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When bearings on a target are taken from a number of stations it is not sufficient to plot the bearings and estimate the best point for the target. It is common practice to calculate the dimensions of a rectangular region which has a 90 probability that the target lies inside it, in order to estimate the precision of the fix. Various methods have been produced for doing this, and the method described in references has been programmed for a number of computers. The method is extremely tedious to compute by hand and it is not clear from the formulae employed how the various parameters of the fix, namely, the number of stations, the variance of the bearings, the distance from the station and the angle subtended by the wing stations at the target, affect the size and shape of the region. It is important, when the disposition of the stations and the requirements for new apparatus are being studied to consider the way in which various factors affect the size and shape of the region, since this vitally affects the performance of the system in practice. Formulae are produced to enable the size and shape of the search region for certain theoretical arrangements to be quickly deduced, and the way in which each parameter affects the dimensions of this region is discussed. A comparison of the results obtained using the formulae given with those obtained using the method described in references is given in the appendix.
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