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Subject: Re: Mercator vs. Great Circle Charts
From: Paul Marcuzzo (paulmar@XXX.XXX)
Date: Wed Aug 29 2001 - 12:41:09 EDT
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@XXX.XXX]On Behalf Of Carolyn Seefer
Sent: Wednesday, August 29, 2001 12:24 PM
To: NAVIGATION-L@XXX.XXX
Subject: Re: Mercator vs. Great Circle Charts
In a message dated 8/29/2001 9:05:39 AM Pacific Daylight Time,
navsys@XXX.XXX 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
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