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    NavPac
    From: Peter Fogg
    Date: 2005 Jan 7, 13:16 +1100

    HM Nautical Almanac Office, who also publishes 'The Nautical Almanac' in the
    UK, has a navigational software package known as 'Nav-Pac and Compact Data'.
    
    It comes out every 5 years; the 2006/2010 version contains data for 1986 -
    2010. The interface presents a set of functions:
    
    CALCULATE RISE AND SET TIMES OF NAVIGATIONAL BODIES
            Times of rise, set and meridian passage. Also civil, nautical and
    astronomical twilight as zone or UT.
    
    FIND LOCATIONS OF NAVIGATIONAL BODIES
            Tabulates and plots altitudes and azimuths of bodies selected for
    given time, date and location. The plot looks like a star map with the
    bodies and data alongside.
            The set of 7 best bodies are indicated. Apparently this selection is
    the same as would be chosen using HO 249.
    
    CALCULATE GREAT CIRCLE/RHUMB LINE ROUTE
            Positions to courses and vice-versa, including dates, times and
    speeds. One detail I especially like is that dates and times are displayed
    both in UT and Zone Time, so you can use either, or swap between them,
    hopefully avoiding any confusion. For great circles the legs can be as short
    as 0.1nm, although only the first 99 legs are displayed. An alternative is
    to nominate meridians of longitude for course changes.
    
    CALCULATE POSITION FROM SIGHTS
            From time to time there are postings on this List that indicate a
    desire to squeeze the utmost in accuracy and/or precision from sights made.
    This product could be a boon for that endeavour. The calculated intercept is
    displayed to 4 decimal places (eg, -2.5687 nm) and the azimuth to the
    nearest tenth of a minute of arc (eg, 124d 52.9'). Temperature and pressure
    can be entered (or left as default settings) and the parallax, refraction,
    and semi-diameter factors are displayed. The almanac data used, to the
    nearest tenth of a minute of arc, is also displayed. Thus the software can
    also be useful as a check for manual methods. A maximum of 15 sights can be
    entered for a fix.
            This leads to a 'Position Line Plot Form' which can be zoomed in and
    out, the default setting is a 20 nm square with the fix in the centre and
    the DR off to one side. A 95% confidence ellipse is shown as a default
    setting. Position lines are shown in different colours for different bodies
    (stars, planets, etc).
    
    
    CONSULT ALMANAC
            The usual suspects, 57 stars plus Polaris and Octantis and Aries.
    
    The software encourages the keeping of an electronic log, with fixes being
    saved and results used for subsequent calculations.
    
    In the book that accompanies the CD (included as a PDF file within the
    software) all of this takes less than a third of the book to explain,
    together with examples. The rest is data to enable those who like to roll
    their own to program a calculator or computer - another subject that came up
    here recently.
    
    'The main tables contain monthly polynomial coefficients ... daily
    polynomial coefficients ... and monthly Chebyshev coefficients ... and five
    yearly coefficients ...'
    
    'Astronomers and navigators will also find the package useful because the
    CD-ROM contains the compact astronomical data in ASCII format, so that they
    will be able to read the data directly into a PC ...'
    
    There are pages and pages of formulae, and whole chapters of, for example,
    Chebyshev coefficients.
    
    Also: '... a chapter from "The Admiralty Manual of Navigation" on the
    practical aspects of sight reduction ... is included...' (as a PDF file)
    
    (tell 'em the price, son!)
    Navigation Pac retails for 40 British pounds through www.tso.co.uk/bookshop
    and possibly elsewhere. ISBN 0 11 887331 8
    
    
    

       
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