(JJ Sinclair) wrote in message ...
Navigational question for the day;
One minute of latitude = 1 nautical mile. At what point on the earth does 1
minute of longatude = 1 nautical mile?
JJ Sinclair

8-9 degrees north or south LAT where EW radius of curvature = NS
radius of curvature.

With screwy "geodetic" latitude that gps uses, FAI 6371km sphere
errors are even worse than if using geocentric latitude on ellipsoid.
I think pythagorean theorum with scale factors below would match
ellipsoid better than sphere does for gliding distances.

Someone please check these equations. The instrument display makers
may want to use an ellipsoid some day:

dist = pi/180*[delta Lat or Long in deg]*radius of curvature

radius of curvature NS:
a^2*b^2/(a^2*cos^2(Lat)+b^2*sin^2(Lat))^(3/2)

radius of curvature EW:
a^2/sqrt(a^2+b^2*tan^2(Lat))

Jonathan

p.s. check my equations against tiny EW or NS distances at various
lats using the FAI java calculator.