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: Steven Tripp
Date: 2001 Aug 29, 8:04 PM
From: Steven Tripp
Date: 2001 Aug 29, 8:04 PM
I have before me DMA #56 Great Circle Sailing Chart of the North Pacific Ocean (a gnomomic chart). 38th ed. Sept 17, 1973 $1.50 !!! > 1. Can true direction be determined in the same manner for all locations on a > Mercator chart? How about on a great circle chart? True direction (true course?) cannot be determined directly on the GC chart. The lines of lat and lon are all distorted. The chart describes an indirect method (below) for determining the GC course in segments. > > 2. How is the compass rose used on each of these charts? The GC chart doesn't have a normal compass rose. Points on the chart are transferred to a course diagram and then that lines is transferred to the compass. This give the course for a segment of the journey. If you don't have a copy of his chart you should get one. It's quite fun to look at. It says at the bottom that when two points differ less than 20� in lon you must use the supplementary method (table-based) which is printed across the bottom of the chart. Steve T.
