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    Re: Problems with AstronavPC
    From: Jim Thompson
    Date: 2004 Feb 16, 17:47 -0400

    Joel,  I think maybe you misunderstood me, which means that I did not
    explain myself well.
    My thinking is that in standard CN we pick an AP (either our DR position or
    a rounded AP position) close to where we think we are, and then reduce the
    sight relative to that AP.
    In the special case I described, the navigator does not need an AP nearby,
    if they have a way to plot a 2,000 mile co-altitude (distance to GP).
    Does that make more sense?
    Jim Thompson
    Outgoing mail scanned by Norton Antivirus
    > -----Original Message-----
    > From: Navigation Mailing List
    > [mailto:NAVIGATION-L@LISTSERV.WEBKAHUNA.COM]On Behalf Of Joel Jacobs
    > I may be plain dumb, but how would you know in advance that the
    > AP is within
    > or without 30NM from the intercept if you hadn't first reduced the sight
    > which requires the selection of an AP. Or is this a misunderstanding of
    > terms? Isn't it that the AP should be within 30 NM of the DR?
    > ----- Original Message -----
    > From: "Jim Thompson" 
    > > I'm new to CN, but isn't the only reason that we try to keep
    > the AP within
    > > 30 NM of the intercept for convenience in plotting?  In theory we don't
    > even
    > > need an AP: with the right tools (electronic would be the only practical
    > > way) we just need the GP of the Body, Azimuth to the GP, and co-altitude
    > > (distance to the LOP from the GP).  In that special case, the
    > intercept is
    > > the co-altitude, which of course tends to be many hundreds or even
    > thousands
    > > of miles away from where we are on the celestial LOP.  All a computer
    > would
    > > have to do is produce data that we need to plot a short segment
    > of the LOP
    > > and the intercept on a large-scale plotting sheet; specificaly
    > a reference
    > > point on the plotting sheet, a bearing line to draw toward or away from
    > that
    > > point, and the distance from that point to the LOP along the
    > bearing line.
    > >
    > > I know -- that "reference point" is the same concept as an AP.  But is
    > there
    > > any other reason why we need to select an AP relatively close
    > to our real
    > > position?
    > >
    > > > -----Original Message-----
    > > > From: Navigation Mailing List
    > > > [mailto:NAVIGATION-L@LISTSERV.WEBKAHUNA.COM]On Behalf Of Aubrey
    > > > O'Callaghan
    > > > I then placed my initial position nowhere near where I was.
    > After about
    > 3
    > > > iterations it converged to my actual position. I was quite
    > surprised as
    > I
    > > > had thought that one's initial guess should be approximately where one
    > is
    > > > (at least within a few degrees).

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