Originally Posted by rgleason
I meant convert it to a Track
and then reduce data.
Thanks Tup, those are interesting points, but then you wouldn't use GC routing, just rhumline. I am not so sure my 23 year old autohelm wheelpilot
knows Great Circle.
I was just seeing about O functionality.
Your raymarine autopilot
, however old it may be, if linked to GPS
, does sail a great circle route with a constantly changing heading if you ask it to steer to a destination
waypoint. This applies to any wp even one a very short distance away.
The main difference between GC and RL is that it is impossible for humans and wind
vanes to steer a GC because the bearing will constantly change. Also you need a gnomic projection chart to lay off a GC route and most charts
are mercator hence you end up with a RL.
If you select GC in OCPN all it does is plot a GC route on a mercator chart. The result is a segmented route with a different bearing for each leg.
So using a GC plot on OCPN is only of any use if you intend to sail manually, or by wind vane
to a compass
bearing. I suppose on a very long passage
it would also allow you to make sure that a GC doesn't cause you to hit anything slightly off of the RL.
If you are using a GPS and are intending to ask your AP to steer to a WP then simply enter a single
WP at your destination
and it will by default sail a GC route.