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    Re: Mercator vs. Great Circle Charts
    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 !
    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
      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,
      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,
      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
      Bowditch hasn't been mentioned in class yet.
      Carolyn Seefer

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