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Re: Gnomonic charts and distances
From: Tony Oz
Date: 2018 Aug 6, 02:56 -0700

Dear Robin,

On 2018 Jan 23, 06:42 -0800 you wrote:

Starting at a latitude, longitude L0, λ0 and traveling a distance D(°) on a course C° measured East from North the necessary formulas are:

sin L = sin L0 cos D + cos L0 sin D cos C

sin ( λ - λ0 ) = sin D sin C / cos L

Thank you for the formula.

While making it into my TI-83+ I discovered that as given it works only within the nearest 5400 nm.

To make it work around the globe I had to amend it like that:

λ = λ0 + arcsin(sin(D)sin(C)/cos(L))

if D > 90° then; λ = 180° - (λ0 + arcsin(sin(D)sin(C)/cos(L)))

Now, as far as I can test, - it works for any distance, even for 21600 nm.

Regards,

Tony

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