> 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
