Bah! Just when I thought I had it figured out! Oh well, at least now I get it. Thanks for that Phil. Very helpful.
Cheers, Phil. ----- Original Message ----- From: "Phil Scadden" <[EMAIL PROTECTED]> To: "NZ Borland Developers Group - Delphi List" <[EMAIL PROTECTED]> Sent: Thursday, April 22, 2004 10:19 AM Subject: Re: Fw: [DUG] Converting some code from C > > Actually, as you pointed out, a rhumb line is the straight line, but if you > > follow a constant bearing (eg, make sure that you are heading 20deg at all > > times) then you will not be following a straight line (although it's all > > relative to the projection you use) because of the curvature of the earth > > No, that is not correct. A rhumb line is not a straight line, it a line of > constant bearing (a loxadrome) when traversing a sphere. The idea of a > rhumb line as "a straight line" comes from the use of a mercator > projection. This projection is the favourite of navigators because of its > property of showing a rhumblines as straight lines. If you always head 20 > degrees, you are followinging a rhumbline by definition. If you follow > a great-circle path on the earth, then you are changing your bearing > constantly. Since this isnt really practical for all but the most > sophisicated of navigation, great-circles navigation is usually by a series > of rhumblines approximating the great circle. > > > Thanks for the rhumb line calculation - I will try it later and see if it > > works. As it turns out, it's the calculation that I was after anyway - I > > mistakenly asked for the wrong formula. Rhumb line *is* what I want. I was > > going to implement the great circle bearing version with incremental rumb > > line segments. I'll let you know if the formula checks out. > > Okay, you figured it out. Just be aware that the formula has limitations on > the ellipsoid but you probably have limitations with the accuracy of > distance too if this is for navigation. > > ---------------------------------------------------------- > Phil Scadden, Institute of Geological and Nuclear Sciences > 764 Cumberland St, Private Bag 1930, Dunedin, New Zealand > Ph +64 3 4799663, fax +64 3 477 5232 > > _______________________________________________ > Delphi mailing list > [EMAIL PROTECTED] > http://ns3.123.co.nz/mailman/listinfo/delphi > _______________________________________________ Delphi mailing list [EMAIL PROTECTED] http://ns3.123.co.nz/mailman/listinfo/delphi
