Alex is correct, pictures are essential to get this correct, I just wish PPrune made this easier!
Over the Earth GCs are shortest routes with changing direction and RLs are of constant direction. GCs ALWAYS lie polar side of RLs. However it is easier to draw them as Alex described.
The other thing to spot in the first example N45 W014 12 to N45 E012 48 is the two latitudes are the same this means that the RL must either be 270 or 090 as in this case as you are going from W to E.
Then you are into convergency = Ch Long * Sine Mean Lat. Two different hemispheres means add them to get 37 degrees Ch Long * Sine 45 = 26 degrees. The angle between your RL of 090 and the GC is HALF convergency = 13 (conversion angle). RL of 090 - 13 gives you INITIAL GC track (at W014 12) of 077 and FINAL GC track (at E012 48) of 103.
As said much easier with diagram.
Last edited by RichardH; 28th November 2014 at 05:24.