From mboxrd@z Thu Jan 1 00:00:00 1970 Path: news.gmane.org!not-for-mail From: Emanuel Berg Newsgroups: gmane.emacs.help Subject: Re: distance from Easter Island to Chile Date: Mon, 21 Apr 2014 03:40:06 +0200 Organization: Aioe.org NNTP Server Message-ID: <8761m3tq89.fsf@nl106-137-194.student.uu.se> References: <87mwfguasr.fsf@nl106-137-194.student.uu.se> <87mwfg823s.fsf@nl106-137-194.student.uu.se> NNTP-Posting-Host: plane.gmane.org Mime-Version: 1.0 Content-Type: text/plain X-Trace: ger.gmane.org 1398044727 32132 80.91.229.3 (21 Apr 2014 01:45:27 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Mon, 21 Apr 2014 01:45:27 +0000 (UTC) To: help-gnu-emacs@gnu.org Original-X-From: help-gnu-emacs-bounces+geh-help-gnu-emacs=m.gmane.org@gnu.org Mon Apr 21 03:45:23 2014 Return-path: Envelope-to: geh-help-gnu-emacs@m.gmane.org Original-Received: from lists.gnu.org ([208.118.235.17]) by plane.gmane.org with esmtp (Exim 4.69) (envelope-from ) id 1Wc3IN-00077W-7p for geh-help-gnu-emacs@m.gmane.org; Mon, 21 Apr 2014 03:45:19 +0200 Original-Received: from localhost ([::1]:47196 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Wc3IM-0001OU-OU for geh-help-gnu-emacs@m.gmane.org; Sun, 20 Apr 2014 21:45:18 -0400 Original-Path: usenet.stanford.edu!goblin2!goblin.stu.neva.ru!aioe.org!.POSTED!not-for-mail Original-Newsgroups: gnu.emacs.help Original-Lines: 45 Original-NNTP-Posting-Host: VVbyYd/iFZoeWNmD9i++cQ.user.speranza.aioe.org Original-X-Complaints-To: abuse@aioe.org User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/24.3 (gnu/linux) X-Notice: Filtered by postfilter v. 0.8.2 Cancel-Lock: sha1:uX3oEUOED4i7xR06lxqKyFHwvsc= Mail-Copies-To: never Original-Xref: usenet.stanford.edu gnu.emacs.help:205014 X-BeenThere: help-gnu-emacs@gnu.org X-Mailman-Version: 2.1.14 Precedence: list List-Id: Users list for the GNU Emacs text editor List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: help-gnu-emacs-bounces+geh-help-gnu-emacs=m.gmane.org@gnu.org Original-Sender: help-gnu-emacs-bounces+geh-help-gnu-emacs=m.gmane.org@gnu.org Xref: news.gmane.org gmane.emacs.help:97279 Archived-At: 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