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: Paul Marcuzzo
Date: 2001 Aug 29, 10:41 AM
From: Paul Marcuzzo
Date: 2001 Aug 29, 10:41 AM
Wow, this is the liveliest this list has been in months ! Carolyn never assume that the compass roses are all the same on the chart. The outer ring will be but the inner variation may change, sometimes significantly due to some geophysical anomaly. Also some charts are printed at an angle to better fit the paper and North isn't "straight up" on the chart. There are several here along the west coast Florida that are that way. Good luck with your class Fair Winds ! Paul Speranza - Lagoon 410 Punta Gorda, FL to dock - N 26? 53.471' W 082? 03.515' to Corona Locker - N 26? 53.472' W 082? 03.516' -----Original Message----- From Navigation Mailing List [mailto:NAVIGATION-L@LISTSERV.WEBKAHUNA.COM]On Behalf Of Carolyn Seefer Sent: Wednesday, August 29, 2001 12:24 PM To: NAVIGATION-L@LISTSERV.WEBKAHUNA.COM Subject: Re: Mercator vs. Great Circle Charts In a message dated 8/29/2001 9:05:39 AM Pacific Daylight Time, navsys@PINEFIELDS.COM writes: The question is unclear to me. What is meant by "true direction"? Is this the course to be steered or just a bearing? My guess is that "true direction" in this case means if one can gauge N-S-E-W just by looking at the chart. When I look at the Mercator chart, it seems as though I can tell directions accurately, and all compass roses on the chart are identical. With the great circle chart, on the other hand, the distortion seems to also distort the actual directions. Just by looking at the chart, I can't actually determine what is "true North." It seems that adjustments would have to be made. Again, I'm new to all of this! By the way, thanks for pointing me to the NIMA publications online. I've already started reading Chapter 3 of the Bowditch text. This is very helpful; Bowditch hasn't been mentioned in class yet. Carolyn Seefer