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    Re: Assumed positions and plots
    From: Doug Royer
    Date: 2004 Feb 20, 16:49 -0800

    Jim,one more thought on this subject of APs and EPs etc.
    A little experiment if you are interested.
    If you have an A.H. and the conditions are such that you can attempt a round
    of sights and you have the time take a gps reading of your pos.Set up the
    horizon and useing the rules for spaced azimuths shoot 3 altitudes of 3
    objects spaced over a period of time to simulate a real round of sights as
    on a ship so as to obtain a fix.
    Useing the sin-cosine method reduce all the sights and plot the intercepts
    and azimuths on a plotting sheet from the gps(dr)position.
    Turn the sheet over.
    Useing the AP(whole degree)method use H.O. 229 or 249,reduce the same sights
    and plot the corresponding intercept and Zn from each AP on the plotting
    sheet.
    You may also use 1 body and take 3 sights of it over a period of time.
    Explain to me what you see on the plotting sheet.I'm interested in what you
    observe between the 2 methods.
    
    
    Actually,what you quoted from Bowditch '02 in your post today was basically
    what Joel Jacobs quoted yesterday in his post about definitions.
    
    My intent is not to give you a hard time.
    
    
    
    -----Original Message-----
    From: Navigation Mailing List
    [mailto:NAVIGATION-L{at}LISTSERV.WEBKAHUNA.COM]On Behalf Of Royer, Doug
    Sent: Friday, February 20, 2004 10:58
    To: NAVIGATION-L{at}LISTSERV.WEBKAHUNA.COM
    Subject: Assumed positions and plots
    
    
    Jim,I now understand what you are being taught.The course you are takeing
    just seems to use differant terminology than what I'm used to.On that note
    the following:
    1.The method you are useing(being taught)is as good as the method I
    use.You're comfortable useing it.
    2.As Fred stated, in practice, useing the method you are being taught can
    get the plotting sheet or chart rather messy or cluttered.
    3.If you use reduction tables(H.O. 229 or 249)exclusively the AP is
    differant than an EP or DR.As each AP for the round of sights is differant
    due to each  body's LHA being differant.
    4.When plotting the LOPs on the sheet useing an AP(whole degree argument)try
    the following to reduce clutter.
    Instead of marking seperate dr or ep positions corresponding to each cut and
    plotting from such try plotting from each AP.By that I mean in the round of
    sights advance(or retard)each AP instead of each dr.Because the vessel's
    travel distance during the round won't exceed the 30' of arc tolerance
    between the dr and each AP it will not effect accuracy.
    Say you take around of 3 sights starting at 1800.The 2nd sight is at 1812
    and the last is at 1823.Your course is 222* and your speed is 10 kt.The 1st
    AP(1800) is advanced 3.8 mi at 222* and the intercecpt and Zn are plotted
    from there.The 2nd AP(1812) is advanced 2 mi at 222* and plotted from
    there.The 3rd AP(1823) is plotted from it's whole degree position.
    
    
    

       
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