NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
A less precise position may be more accurate
From: Peter Fogg
Date: 2006 Dec 13, 16:56 +1100
From: Peter Fogg
Date: 2006 Dec 13, 16:56 +1100
The broad thrust of George's argument (see "Position lines, crossing") seems to be that a calculated position is not necessarily the actual position, and one should be aware of as much. Which is a fair enough contention, if not exactly fresh news. Many methods of sight reduction use data expressed to a tenth of a minute of arc, and render a result to the same level of precision. One way of acknowledging the uncertainties of a calculated position, I propose, is to express this rounded off to the nearest minute of arc. The implication is that the position is not necessarily at the intersection of these minute lines of long and lat, but rather may be contained in a rectangle (square at the equator) bounded by the half-way lines to the next whole minutes. Thus a bigger box than that implied by a position expressed to the nearest tenth of a minute. Yes, the actual position may not be contained inside the larger rectangle. But this proposal avoids the spurious and potentially misleading precision of the alternative. And has another advantage of simplicity. There is a good argument that the appropriate level of precision for nav from small boats is to the nearest minute, at best, even if calculations are made using the nearest tenth. This is not much more than another expression of the difference between precision and accuracy. The coarser the expression of position, the more accurate, given the potential for error. --~--~---------~--~----~------------~-------~--~----~ To post to this group, send email to NavList@fer3.com To , send email to NavList-@fer3.com -~----------~----~----~----~------~----~------~--~---