GPS - great circle or rhumb

[ghostlymoron]

A question arose last night in the pub. Does a GPS or chart plotter give a great circle(shortest) or rhumb line course. No one was sure. I'm sure someone on the forum will know.

 

[Mark-1]

A question arose last night in the pub. Does a GPS or chart plotter give a great circle(shortest) or rhumb line course. No one was sure. I'm sure someone on the forum will know.

Raymarine Plotters give great circle.

 

[Salty John]

Some do one, some the other. To check what yours is, set a waypoint some large distance due east or west of you and press GOTO. If the course given is exactly 90 degrees or 270 degrees you're getting a rhumb line course, if it's, say, 220 degrees you're getting the initial course for a great circle route.

 

[Skylark]

I thought that they were great circle so I'm now intringued......

 

[alant]

A question arose last night in the pub. Does a GPS or chart plotter give a great circle(shortest) or rhumb line course. No one was sure. I'm sure someone on the forum will know.

These might help

http://www.ybw.com/forums/showthread.php?t=248240&highlight=great+circle+gps

http://www.ybw.com/forums/showthread.php?t=232893&highlight=great+circle+gps

http://www.ybw.com/forums/showthread.php?t=185736&highlight=great+circle+gps

http://www.ybw.com/forums/showthread.php?t=117850&highlight=great+circle+gps

http://www.ybw.com/forums/showthread.php?t=115261&highlight=great+circle+gps

 

[Salty John]

All the manufacturers may have standardised now, but on older sets it could be GC or Rhumb line.

In fact, GC routes were actually a series of rhumb line routes created by the set interjecting a number of waypoints between where you are and your GOTO destination - that still may be the case, the difference in distance would be tiny.

I learned this on a navigation course and I'm dredging it up from memory - I can't locate the course notes, and it was so long ago they were probably written on papyrus!

 

[macd]

Lowrance plotter definitely great circle. Just put in a waypoint near, say, the Aleutians and check out the route.