Global Positioning System Reference
In-Depth Information
FIGURE 7.3. Three-point sextant fix. You have an accurate chart, a sextant, and a
knowledge of geometry, and use these to fix your yacht's position. By measuring
the angle a between reference points A and B , you know that your position is
somewhere on the circle that passes through both these points. Why? The inset
shows a geometrical theorem: all the marked angles are the same and so the ship
must lie somewhere on the circle. (Interested readers can calculate the circle radius
in terms of the angle and the distance AB .) By measuring the angle c between B and
C , you can draw another circle; the yacht's location is the seaward intersection of the
two circles.
check the accuracy of their dead reckoning track by measuring LoPs from
di√erent islands.
Fast-forward to the very near future. You have just won the lottery and
are now retired, living aboard your luxury yacht o√ the coast of Australia.
You want to sail the Great Barrier Reef, but you are aware that these are
 
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