Article: 3873 of rec.aviation.piloting Newsgroups: rec.aviation.piloting Path: newshost.ncd.com!ncd.com!olivea!nntp.msstate.edu!emory!europa.eng.gtefsd.com!howland.reston.ans.net!vixen.cso.uiuc.edu!newsrelay.iastate.edu!newsxfer.itd.umich.edu!ncar!csn!col.hp.com!news.dtc.hp.com!hpscit.sc.hp.com!cupnews0.cup.hp.com!mtc From: mtc@cup.hp.com (Mark Cousins) Subject: Re: Great Circle Equations? Sender: news@cupnews0.cup.hp.com (News Admin) Message-ID: Date: Thu, 31 Mar 1994 22:43:52 GMT References: <2ndmmo$4sq@darkstar.UCSC.EDU> Nntp-Posting-Host: hptacmc.cup.hp.com Organization: Hewlett-Packard X-Newsreader: TIN [version 1.2 PL1.4] Lines: 44 In article <2ndmmo$4sq@darkstar.UCSC.EDU>, Brian Matthew Aljian (smythe@cats.ucsc.edu) wrote: >Could someone please post the great circle equation(s)? I'm interested >in doing some great circle distance calculations between airports. >[I suppose I could derive the equations... but hey, who has the time? :-)] From an article by Robert Grove (I wonder what happened to him?) a few years ago: RG> Definitions- RG> LAT1- Latitude of origin in degrees RG> LON1- Longitude of origin in degrees RG> LAT2- Latitude of destination in degrees RG> LON2- Longitude of destination in degrees RG> DLo- LON2-LON1 RG> R- 3438 nm. The nominal radius of the curvature of the earth in nautical RG> miles. RG> RG> Initial great-circle course angle (C in degrees) RG> RG> C=arctan[sin(DLo) / (cos(LAT1)tan(LAT2) - sin(LAT1)cos(DLo))] RG> RG> Great-circle distance (D in nautical miles): RG> RG> D = ((PI*R)/180) arccos [sin(LAT1)sin(LAT2) + cos(LAT1)cos(LAT2)cos(DLo)] RG> RG> There are other ways as well. One source for further information is: RG> RTCA/DO-194 November 17, 1986 RG> RG> This is available from: RG> Radio Technical Commission for Aeronautics RG> One McPherson Square RG> 1425 K Street, N.W., Suite 500 RG> Washington, D.C. 20005 I've used this in a C program and it seems to work fine. I'll send you the source if you want; email me. Mark -- Mark Cousins Hewlett-Packard Co. mtc@cup.hp.com HP-UX VAB programs 19055 Pruneridge Ave., MS 46TU2 (408) 447-4659 Cupertino, CA 95014 FAX: (408) 447-4364