# NavList:

## A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding

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Re: Mileage of rhumb line compared to mileage of great circle
From: Gary LaPook
Date: 2011 Jun 5, 12:00 -0700
 I knew that you had to use Meridional parts for this computation so you need to carry Bowditch next to your calculator and it is hard to put in your pocket. Like I said, it is a lot easier to calculate the GC (you should be able to remember the formulas in your head since they the same ones you use for computing altitude and azimuth) than the RL course. So I rest my case for a second time.gl --- On Sun, 6/5/11, Dave Walden wrote:From: Dave Walden Subject: [NavList] Re: Mileage of rhumb line compared to mileage of great circleTo: NavList@fer3.comDate: Sunday, June 5, 2011, 7:28 AMThe "MY" refered to below is the "Meridional Parts" function. Table 5 in my 1962 Bowditch, Table 3 in 1918, and Table VI (Latitudes Croissantes in French) in Friocourt, and in many other collections of tables.>>That is trickier, but still not a rocket science.>>tan(TC)=(lon2-lon1)/(MY(lat2)-MY(lat1))>>where MY(lat) is Y coordinate in mercator projection>>MY(lat)=ln(tan(45+lat/2))>>nsg----------------------------------------------------------------NavList message boards and member settings: www.fer3.com/NavListMembers may optionally receive posts by email.To cancel email delivery, send a message to NoMail[at]fer3.com----------------------------------------------------------------
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