NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Bowditch
From: Roger M. Derby
Date: 2001 Jan 29, 18:07 EST
From: Roger M. Derby
Date: 2001 Jan 29, 18:07 EST
It was quite doable. It's just that I was born of Friday the 13th and computers are inherently evil. They will find the wrong answer if there is any ambiguity available. (Try testing a floating point number for zero as a loop terminator. I had to test for less than 10E-32 since the series never quite converged due to truncation errors.) Roger ----- Original Message ----- From: "Casey. Noel" <Noel.Casey@XXX.XXX> To: <NAVIGATION-L@XXX.XXX> Sent: Monday, January 29, 2001 7:58 AM Subject: Re: [NAV-L] Bowditch > 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@XXX.XXX] > > Sent: Friday, January 26, 2001 7:45 PM > > To: NAVIGATION-L@XXX.XXX > > 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. > > * ** *** ** * ** *** ** * ** *** ** * > >