NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
NavPac
From: Peter Fogg
Date: 2005 Jan 7, 13:16 +1100
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