NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Mercator vs. Great Circle Charts
From: Dan Hogan
Date: 2001 Aug 29, 7:22 AM
From: Dan Hogan
Date: 2001 Aug 29, 7:22 AM
On 28 Aug 2001, at 22:15, Carolyn Seefer wrote: [Snip personal info] NOTE: These are REALLY basic questions. The answers are available in any navigation text. > > 1. Can true direction be determined in the same manner for all locations on a > Mercator chart? How about on a great circle chart? Mercator -- Yes Great Circle Yes the Great Circle True Course. > 2. How is the compass rose used on each of these charts? To refer to the True Direction using plotting tools. > 3. If I were to draw a straight line between two points (say Tokyo and Cabo > San Lucas) on both a Mercator chart and a great circle chart, would either > straight line represent a great circle? Only on the Great Circle chart. > 4. Given the straight line drawn between Tokyo and Cabo San Lucas (see > above), which chart, the Mercator or the great circle, would give me the > shortest route between these two points? The Great Circle. > 5. Would sailing a great circle course always be the best way to travel > across the ocean, or would ships have to take into consideration unfavorable > winds, currents, or storms that might cause a delay? Depends on the destination and obstacles on the course. Ships use weather routing, small boats use best wind/current and avoiding weather. > 6. Do most large ships today use computer assistance to help them choose the > best course across the ocean? Yes. > I realize that these questions are very basic, but I am hoping you will share > your expertise with a beginner. Thanks so much! Try reading Pub. No. 9, Bowditch; Dutton's Navigation and Piloting or any navigation manual. Dan Hogan WA6PBY C27 "Gacha" dhhogan@verimail.com Nav-L Page: http://www.wa6pby.com