NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: V-Correction for Sun?
From: Stan K
Date: 2016 Oct 14, 14:29 -0400
From: Stan K
Date: 2016 Oct 14, 14:29 -0400
Herbert,
Thus the quotation marks around "proprietary algorithm". But the fact is that I know of no other program that even attempts to reproduce the Nautical Almanac values for the hourly GHA of the Sun. Most users are more interested in the accurate values. It is only those people checking their manual reductions using the Nautical Almanac that would be interested in reproducing the Almanac values. Celestial Tools was specifically designed around the needs of United States Power Squadrons students, but it can be used by anyone. Its Sight Reduction tool generally has two modes - the "Accurate" mode and the "NA" mode. Besides the Sun GHA adjustment, the "NA" mode also uses 1200 UT of the middle day of a page for things like v and d values, where the "Accurate" mode uses the date and time of the sight. Neither mode is perfect, but the "NA" mode gets the Almanac values right more often than the "Accurate" mode. And I'll repeat my disclaimer. When asked to develop Celestial Tools, I was given the mandate that it not be perfect - it should help students find errors in their work, not do the work for them. This was very fortunate for me!
Stan
-----Original Message-----
From: Herbert Prinz <NoReply_HerbertPrinz@fer3.com>
To: slk1000 <slk1000@aol.com>
Sent: Fri, Oct 14, 2016 12:17 pm
Subject: [NavList] Re: V-Correction for Sun?
From: Herbert Prinz <NoReply_HerbertPrinz@fer3.com>
To: slk1000 <slk1000@aol.com>
Sent: Fri, Oct 14, 2016 12:17 pm
Subject: [NavList] Re: V-Correction for Sun?
I am not sure whether I should consider myself being addressed by this inquiry or not, but now I am curious: Where is the riddle?
If one wants to interpolate a nearly linear function with slope kt by means of a linear function with slope k0, slightly different from kt, then, in order to minimize the mean interpolation error, the only solution is to pivot the interpolation function on the value at the center of the interpolation interval and adjust the function values at the ends by exactly +/- half the difference between k0 and kt. Naturally, this is what the HMNAO does, because it's the only thing they can do. I can't see where "proprietary" algorithms come into play here, or why HMNAO can't just publish their Fortran program that does all that; so that they may end the kabalistic tradition of keeping the "secret of the calendar", which seems slightly outdated today.
Robin Stuart wrote to Stan K.:
Can you give the details or point me toward previous posts on how the NA makes their adjustments for the GHA of the Sun? This I assume will then explain the background to Herbert's statement concerning what correct the interpolation formula should be,
