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Re: distance from Easter Island to Chile
From: |
Emanuel Berg |
Subject: |
Re: distance from Easter Island to Chile |
Date: |
Mon, 21 Apr 2014 03:40:06 +0200 |
User-agent: |
Gnus/5.13 (Gnus v5.13) Emacs/24.3 (gnu/linux) |
giacomo.boffi@gmail.com writes:
>> I get an answer of 4301.199
>
> me too
I get that too. We all get the same result - it is a
function that maps input (in a deterministic way) to
output. Provided the implementation is correct that's
what you get with the Haversine method.
> (progn
> (defun d2r (x) (/ (* pi x) 180))
> (defun spherical-law-of-cosines (p1 p2)
> "http://en.wikipedia.org/wiki/Great-circle_distance#Formulas"
> (let ((lat1 (car p1)) (lon1 (cadr p1))
> (lat2 (car p2)) (lon2 (cadr p2)))
> (acos (+ (* (sin lat1) (sin lat2))
> (* (cos lat1) (cos lat2) (cos (- lon2 lon1)))))))
>
> (setq santiago (mapcar 'd2r '(33.4500 70.6667)))
> (setq easter_i (mapcar 'd2r '(27.1167 109.3667)))
> (insert (format "\nEaster Island to Santiago distance is%8.2f km."
> (* (spherical-law-of-cosines
> santiago easter_i) 6378.1))))
That's uncanny close to the Googled distance! - that
means the Earth is very, very spherical, I take it?
This is so exact it *could* be used in those "school
essays" (in which I told not to use the Haversine
method) - one is even tempted to suspect that this
formula is what they used - possibly adding or
subtracting some (empirical) constant?
Awesome stuff!
Comment: There is already a d2r (degrees-to-radians).
I'll definitely add this to my distance.el - keep this
up, and we will soon have an Emacs GIS library...
--
underground experts united:
http://user.it.uu.se/~embe8573
- distance from Easter Island to Chile, Emanuel Berg, 2014/04/19
- Re: distance from Easter Island to Chile, Frank Stutzman, 2014/04/20
- Re: distance from Easter Island to Chile, Emanuel Berg, 2014/04/20
- Re: distance from Easter Island to Chile, giacomo . boffi, 2014/04/20
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- Re: distance from Easter Island to Chile,
Emanuel Berg <=
- Re: distance from Easter Island to Chile, Emanuel Berg, 2014/04/20
- Re: distance from Easter Island to Chile, giacomo . boffi, 2014/04/21
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- Re: distance from Easter Island to Chile, Emanuel Berg, 2014/04/21
- Re: distance from Easter Island to Chile, Emanuel Berg, 2014/04/21
- Re: distance from Easter Island to Chile, Emanuel Berg, 2014/04/22
- Message not available
- Re: distance from Easter Island to Chile, Emanuel Berg, 2014/04/20
Re: distance from Easter Island to Chile, Barry Margolin, 2014/04/20
Re: distance from Easter Island to Chile, Eli Zaretskii, 2014/04/20
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