Mercator Sailing: Course and Distance

[Gene222]

(08-30-2018 11:59 PM)Gene222 Wrote:  I am still hung up on 180 meridian crossings, or maybe not. I ran my program to calculate the course and distance of a 180 degree meridian polar crossing.
Pt1: Lat 80 N, Long 45 E
Pt2: Lat 80 N, Long 135 W
The program gave me a course of 270 deg and a distance of 1875.7814 nm, which does not make any sense to me.

I see what I am doing wrong. The course is 270 (due west) on a Mercator map. I was looking a polar map. I guess starpath.com online Mercator calculator was right. EDIT 8/30/18. The path on the Mercator map is a straight line at 270 degrees. The path on a polar map is a semi-circle. I guess this is why they have Great Circle Sailing. I still have errors in my program. The Latitude difference for the above problem is 600' and the Meridional parts for point 1 and 2 are not the same. My procedure for East-West courses needs to be cleaned up, which should be easy to do. Lastly, I am using an eccentricity of 0.081819190842622 for the WGS84 ellipsoid from the Department of Defense World Geodetic System 1984, National Imagery and Mapping Agency, 3rd Ed, Amendment 1, Jan 2000.