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## A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding

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The "Death to the Intercept Method" revisited?
From: Tony Oz
Date: 2017 Sep 1, 10:39 -0700

Hello!

I tried the direct calculation of position - as per the "CELESTIAL NAVIGATION IN THE GPS AGE" by John H. Karl, Chapter 7, the Position without St.Hilaire article.

The formulas are:

cos(D12) = sin(d1) · sin(d2) + cos(d1) · cos(d2) · cos(GHA1−GHA2)
(7.5a)

cos(A) = [ sin(d2) − sin(d1) · cos(D12) ] / [ cos(d1) · sin(D12) ]
(7.5b)

cos(B) = [sin(H2) − cos(D12) · sin(H1) ] / [ sin(D12) · cos(H1) ]
(7.5c)

sin(LatA±B) = sin(d1) · sin(H1) + cos(d1) · cos(H1) · cos(A ± B)
(7.5d)

cos(LHA1) = [sin(H1) − sin(d1) · sin(LatA±B) ] / [ cos(d1) · cos(LatA±B) ]
(7.5e)

Lon = LHA1 − GHA1
(7.5f)

Where the GHAi, di, Hi are the GHA, declination and HObserved of the bodyi respectively.

I guess - the H1 and H2 must correspond to the same moment in time. So in real life I will need either account for the MOB (the movement of body), for the MOA (movement of observer), or do both advancements to the H1 before I may start using the formulas.

So I'm stuck here: I need to know the relative angle between my course T and the azimuth of body1 to be able to obtain the correct value from the V[kn] · cos(Zn - T) · t[hour] formula. (The "V" is my speed, the "t" is the interval between the sights)

Is there a way to do it without any plotting at all? - here (the original "Death..." post) Frank still used some DR and paper graphs.

Thank you in advance.

Regards,

Tony

PS

All the formulas and images are by  John H. Karl. Browse Files

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