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    Re: Cannot dispense with the assumed position at sea
    From: Jim Thompson
    Date: 2004 Feb 20, 11:51 -0400

    I have been keeping an eye on that.  I still think that none of us have been
    re-inventing definitions, merely speaking from our varying schools of
    thought and traditions of practice (or learning, in my case):
    
    Bowditch 2002:
    
    "Assumed Position: A point at which a craft is assumed to be located,
    particularly one used as a preliminary to establishing certain navigational
    data, as that point on the surface of the earth for which the computed
    altitude is determined in the solution of a celestial observation, also
    called CHOSEN POSITION."
    
    "Assumed longitude [or latitude]: The longitude [or latitude] at which an
    observer is assumed to be located for an observation or computation, as the
    longitude [or latitude] of an assumed position or the longitude [or
    latitude] used for determining the latitude by meridian altitude [or if
    latitude then longitude of timed sight]. Also called CHOSEN LONGITUDE [or
    LATITUDE]."
    
    "Dead reckoning: Determining the position of a vessel by adding to the last
    fix the ship?s course and speed for a given time. The position so obtained
    is called a DEAD RECKONING POSITION. Comparison of the dead reckoning
    position with the fix for the same time indicates the sum of currents,
    winds, and other forces acting on the vessel during the intervening period."
    
    "Estimated position: The most probable position of a craft determined from
    incomplete data or data of questionable accuracy. Such a position might be
    determined by applying a correction to the dead reckoning position, as for
    estimated current; by plotting a line of soundings; or by plotting lines of
    position of questionable accuracy. If no better information is available, a
    dead reckoning position is an estimated position, but the expression
    estimated position is not customarily used in this case. The distinction
    between an estimated position and a fix or running fix is a matter of
    judgment. See also  MOST PROBABLE POSITION."
    
    Dutton's 2004 does not have a glossary, but discusses,
    - AP positions in articles 2002, 2504, 2603, 2016, 2605, 2606, 2607, and
    2608; and
    - EP positions in articles 103, 901, 1222, 1209, 1517; and
    - DR positions in a variety of those and other articles.
    
    Dutton's does not mention using EP on a celestial LOP, and points out the
    traditional difference between EP and DR this way:
    - DR uses assumptions to deduce a position.
    - EP uses observations of natural forces to refine a DR position, but not
    including those natural elements that would make the position a "fix".
    So it would not be inconsistent to use a celestial LOP to refine a DR
    position by dropping a perpendicular from the LOP to the DR position.
    
    The Nautical Almanac does not define AP.
    
    Jim Thompson
    jim2@jimthompson.net
    www.jimthompson.net
    Outgoing mail scanned by Norton Antivirus
    -----------------------------------------
    
    > -----Original Message-----
    > From: Navigation Mailing List
    > [mailto:NAVIGATION-L@LISTSERV.WEBKAHUNA.COM]On Behalf Of Joel Jacobs
    >
    > 2. Why, at least for those in this country, is there a need to construe
    > definitions that are different from those found in the standard U.S.
    > published navigation texts of which most list members are aware.
    > 3. I have sold mine, but I recall the tables such as HO 214, 229, and 249
    > also had sections with definitions. The Nautical Almanac had definitions.
    >
    > I realize many changes have taken place, but are none of these sources
    > satisfactory?
    > Should we ignore Bowditch as another example?
    
    
    

       
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