NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Bowditch
From: Noel Casey
Date: 2001 Jan 29, 5:59 AM
From: Noel Casey
Date: 2001 Jan 29, 5:59 AM
This is a well known limitation of the arctangent(x,y) function as being ambiguous for angles greater than 90 deg. The function Arctangent2(x,y) resolves the issue. I don't know if the VAX compiler handled that. In excel spreadsheet there is the atan and atan2 functions, with the atan2 function being preferable in all cases. > -----Original Message----- > From- Roger M. Derby [SMTP:derbyrm@SEIDATA.COM] > Sent: Friday, January 26, 2001 7:45 PM > To: NAVIGATION-L@LISTSERV.WEBKAHUNA.COM > Subject: Re: Bowditch [was Re: Hi (WAS: RE: ping)] > > Just a word of caution that I'm sure is unnecessary. When I was > programming > a VAX to do great-circle calculations (path length and departure) using > the > equations from Bowditch, I got some very strange results. These turned > out > to be caused by the machine's math library making different assumptions > about quadrant than was used by Bowditch. I finally made up a table of > entries for two points a few nm apart using paths that hit all four > quadrents and the four cardinal points and then checking against > "reasonable" answers. Had to add several IF-THENs before Singapore was a > long way from the Lizard and in the correct direction. > > Roger > * ** *** ** * ** *** ** * ** *** ** * This email and any files transmitted with it are confidential and intended solely for the use of the individual or entity to whom they are addressed. If you have received this email in error please notify the system manager. This message has been scanned for viruses. * ** *** ** * ** *** ** * ** *** ** *