From mboxrd@z Thu Jan 1 00:00:00 1970 Path: news.gmane.org!not-for-mail From: Barry Margolin Newsgroups: gmane.emacs.help Subject: Re: distance from Easter Island to Chile Date: Sun, 20 Apr 2014 03:01:36 -0400 Organization: A noiseless patient Spider Message-ID: References: <87mwfguasr.fsf@nl106-137-194.student.uu.se> NNTP-Posting-Host: plane.gmane.org X-Trace: ger.gmane.org 1397977525 15992 80.91.229.3 (20 Apr 2014 07:05:25 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Sun, 20 Apr 2014 07:05:25 +0000 (UTC) To: help-gnu-emacs@gnu.org Original-X-From: help-gnu-emacs-bounces+geh-help-gnu-emacs=m.gmane.org@gnu.org Sun Apr 20 09:05:19 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 1WbloU-0003oI-SY for geh-help-gnu-emacs@m.gmane.org; Sun, 20 Apr 2014 09:05:18 +0200 Original-Received: from localhost ([::1]:44634 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1WbloU-0008IE-Db for geh-help-gnu-emacs@m.gmane.org; Sun, 20 Apr 2014 03:05:18 -0400 Original-Path: usenet.stanford.edu!news.kjsl.com!feeder.erje.net!eu.feeder.erje.net!eternal-september.org!feeder.eternal-september.org!news.eternal-september.org!barmar.motzarella.org!.POSTED!not-for-mail Original-Newsgroups: gnu.emacs.help Original-Lines: 31 Injection-Info: barmar.motzarella.org; posting-host="2be9e9f5dd9af768b8861af71b85fc28"; logging-data="735"; mail-complaints-to="abuse@eternal-september.org"; posting-account="U2FsdGVkX18GZ9r3D7hGiN/kk2Ys22tY" User-Agent: MT-NewsWatcher/3.5.3b3 (Intel Mac OS X) Cancel-Lock: sha1:ZteNfjwOkg+3jnJFf23l9dAej3s= Original-Xref: usenet.stanford.edu gnu.emacs.help:204984 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:97249 Archived-At: In article , Eli Zaretskii wrote: > > From: Emanuel Berg > > Date: Sun, 20 Apr 2014 02:03:32 +0200 > > > > (defun distance (l1-r f1-r l2-r f2-r) > > (interactive) > > (let ((l1 (degrees-to-radians l1-r)) > > (f1 (degrees-to-radians f1-r)) > > (l2 (degrees-to-radians l2-r)) > > (f2 (degrees-to-radians f2-r)) ) > > (* 2 6378.1 ; Earth's radius > > (asin > > (sqrt > > (+ (sin2 (/ (- f2 f1) 2)) > > (* (cos f2) (cos f1) (sin2 (/ (- l2 l1) 2))) )))))) > > This is inaccurate (Earth is not a sphere). How accurate does your input have to be for that to be a significant? I.e. if you're calculating the distance between two cities, and each city is 5 miles wide, the distance is +/- 10 miles depending on where in the two cities you decide to get the coordinates from. So if the error in the formula is 2 miles, it's less than the inaccuracy in the input, so the formula should be good enough. -- Barry Margolin, barmar@alum.mit.edu Arlington, MA *** PLEASE post questions in newsgroups, not directly to me ***