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Re: Meridional Distances
From: Chuck Taylor
Date: 2002 Sep 17, 19:32 -0700
From: Chuck Taylor
Date: 2002 Sep 17, 19:32 -0700
Peter, In an earlier response I mentioned an error in the formula for Meridional Parts as given in Bowditch 1995. I am happy to report that it (a missing exponent) has been corrected in the online version at http://164.214.12.145/pubs/, and presumably in later printings. At 10:09 AM 9/18/2002 +1000, Peter wrote: >My new (again, new to me) formula for rhumb line goes > >Arctan course = DLON/DMP > >Distance = DMD/cosCourse > >where: >DLON means the difference in longitude expressed in minutes of arc >DMP means the difference in Meridional Parts >DMD means the difference in Meridional Distances The standard formulas for Mercator Sailing, using your notation, are Course = arctan( DLON/DMP ) Distance = DLAT / cos( Course) where DLAT means the difference in latitude in minutes of arc. These formulas are given in paragraph 2417 of Bowditch 1995 and paragraph 1007 of Bowditch 1981 Volume 2. >there is a separate, rather more complicated, formula for when the >course lies close to east or west. The use of a separate formula for when the course lies close to east or west is characteristic of Mid-Latitude Sailing. Like Michael Wescott, I suspect that what you are looking at is some sort of hybrid method. Would you mind giving us a reference that describes the method? I have never heard of a table of Meridional Distances, only Meridional Parts. Chuck Taylor Everett, WA, USA C