Rule #1: Remember to convert from magnetic bearings to true bearings, i.e., add any eastern deviation or subtract any western deviation before inputting the bearings.
Rule #2: All arguments are in decimal degrees, with north latitude and west longitude being positive.
The example button inputs values from the original case that caused me to consider this problem. I was in my boat in Rosario Strait (San Juan Islands of Washington State) and took two bearings moments apart of Mount Baker (10785') and Mount Rainier (14441'). I wanted to know where I was from the known location of these two magnificient mountains.
So, in this example, point X is Mt. Baker (latitude N48°46'39", longitude W121°48'43") and I measured it at 50° from magnetic north. The deviation here is 18°47' East, so I added this to 50° to get my first bearing. Point Y is Mt. Rainier (latitude N46°51'10", longitude W121°45'31") and I measured it at 140° from north. I added the same correction for magnetic deviation to obtain its true bearing.
My best guess at the position where I took these measurements is N48°30.647' and W122°45.082'. This program calculates N48°32.0' and W122°44.8', for an error of 1.37 nmi, not too bad. I measured my bearings with the compass that is built into a pair of Fujinon 7x50 binoculars. I wonder if the elevation of these mountains should be included in this calculation for better accuracy?
The formulas for this are from Ed Williams' Aviation Formulary, to whom many thanks!
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Created: 5 Aug 2003 Modified: 5 Aug 2003