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A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Obtain a fix when you don't have an clear AP?
From: Stan K
Date: 2015 Jan 11, 10:11 -0500
From: Stan K
Date: 2015 Jan 11, 10:11 -0500
Andres,
WOW! Your analysis hurt my brain, but it is interesting in that the solution agrees with what I proposed as an alternate solution in my previous message, the one using the Nautical Almanac values of the Sun's altitude corrections rather than the values calculated by Celestial Tools.
I realize that there may be several "correct" solutions to this type of problem, depending on who you are trying to please, that is whether you are trying to aim a missile at a target or merely taking a Power Squadrons course. What I would like to do, though, is reconcile the differences between Greg's answer, obtained using Pilot Navigator 6.9 and deemed correct by the maker of the video, and yours (my alternate answer). What parameter(s) were different in the Pilot Navigator solution? Did it have something to do with the algorithm (mathematical or graphical) used to calculate the fix. (I avoided using a fix-calculating algorithm from an initial AP by adjusting the AP latitude and longitude until I got zero-length intercepts for both sights. FYI, using the AP that you used, 47ºN, 122ºW, the algorithm used in Celestial Tools calculated a fix at 47º28.8'N, 122º13.8'W, close but no cigar.)
On the other hand, how did the maker of the video determine the "correct" answer. Was it by GPS or off a map? How do we know that his two sights were "perfect"? Well, what the maker of the video considers the correct answer is not really relevant to the problem I am trying to solve - the cause of the discrepancies between the answers.
Stan
-----Original Message-----
From: Andrés Ruiz <NoReply_AndresRuiz@fer3.com>
To: slk1000 <slk1000@aol.com>
Sent: Sun, Jan 11, 2015 6:51 am
Subject: [NavList] Re: Obtain a fix when you don't have an clear AP?
From: Andrés Ruiz <NoReply_AndresRuiz@fer3.com>
To: slk1000 <slk1000@aol.com>
Sent: Sun, Jan 11, 2015 6:51 am
Subject: [NavList] Re: Obtain a fix when you don't have an clear AP?
Stan, do not worry about the discrepancies.
If full correction is used for Hs to Ho: oblateness, augmentation,...
And the correct UT1 is taken into account:
The solutions is:
47º 28.9' N
122º 14.0' W
by vector solution and by MSH LoPs after 2 iterations if AP(47N, 122W)
20/02/2010
17:26:26 UT1
Be = 47.000000 º = 47º 0.0'
Le = -122.000000 º = -122º 0.0'
ALMANAQUE NAUTICO - NAUTICAL ALMANAC
Sun
GHA = 78.183753 º = 78º 11.0'
Dec = -10.773904 º = -10º 46.4'
SD = 16.174109 '
HP = 0.148219 '
CORRECCION DE LA ALTURA - ALTITUDE CORRECTION
Limb: upper
Ref: Artificial Horizon
Hs = 40.3033 º = 40º 18.2'
ie = 0.0000 '
heas = 0.0000 m
T = 10.0000 ºC
P = 1010.0000 hPa
Hoi = 20.1517 º
dip = 0.0000 º
Ha = 20.1517 º = 20º 9.1'
R = 0.0441 º
OB = -0.00000612 º
HP = 0.0025 º
PA = 0.00231297 º
SD = -0.2696 º
Aug = -0.00000400 º
SDag = -16.174349 '
Ho = 19.8403 = 19º 50.4'
21/02/2010
00:16:02 UT1
Be = 43.316667 º = 43º 19.0'
Le = -2.000000 º = -2º 0.0'
ALMANAQUE NAUTICO - NAUTICAL ALMANAC
Sun
GHA = 180.591654 º = 180º 35.5'
Dec = -10.671327 º = -10º 40.3'
SD = 16.173132 '
HP = 0.148210 '
CORRECCION DE LA ALTURA - ALTITUDE CORRECTION
Limb: lower
Ref: Artificial Horizon
Hs = 24.0733 º = 24º 4.4'
ie = 0.0000 '
heas = 0.0000 m
T = 10.0000 ºC
P = 1010.0000 hPa
Hoi = 12.0367 º
dip = 0.0000 º
Ha = 12.0367 º = 12º 2.2'
R = 0.0742 º
OB = -0.00000209 º
HP = 0.0025 º
PA = 0.00241376 º
SD = 0.2696 º
Aug = 0.00000242 º
SDag = 16.173278 '
Ho = 12.2345 = 12º 14.1'
solution and by MSH LoPs if AP(47N, 122W)
best regards
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