Great circle.

[oldbilbo]

.....navigators are unlikely to find charts published on any projection other than a variant of Mercator's projection (normal aspect usually; occasionally transverse). While I routinely used Polar Stereographic and Lambert Conformal Conic, they are not convenient for plotting positions....

This aged nav cannot now remember whether 'orthomorphic' was good or bad, or why. I do recall using Lambert's Conformal sheets extensively during my time with HM Queen's 'force de frappe', for the two Standard Parallels enclosed 'acceptable distortions' between Lincolnshire and the Kola Peninsula, the East Baltic naval ports, and the railway marshalling yards around Minsk, Vilnius and Lodz....

The Herc transport guys trundled regularly down along Italy to Cyprus, then onwards to various places around the Arabian Gulf. For these and other exotic regular destinations, dedicated Transverse Mercator sheets were provided in their dozens.

 

[geem]

I've got 2 GPSs I regularly look at. One is an A65 Raymarine plotter and the .....
I assumed one was showing Great Circle and the other Rhumb Line. But nowhere in the menus, or even the manuals, was I able to select one or the other, or find out which I was being shown.

(Nothing like a long ocean passage for reading manuals cover to cover for the first time)

My east to west route across the Atlantic was on a Garmin 128 that appeared to give a great circle route. You can check what you are doing by doing a goto on the GPS then draw direct route with a straight line on your paper chart, then using the GPS, zoom in and drive along the goto route. Every now and then, plot the lat long off the goto route on the paper chart and compare the difference.

 

[AntarcticPilot]

This aged nav cannot now remember whether 'orthomorphic' was good or bad, or why. I do recall using Lambert's Conformal sheets extensively during my time with HM Queen's 'force de frappe', for the two Standard Parallels enclosed 'acceptable distortions' between Lincolnshire and the Kola Peninsula, the East Baltic naval ports, and the railway marshalling yards around Minsk, Vilnius and Lodz....

The Herc transport guys trundled regularly down along Italy to Cyprus, then onwards to various places around the Arabian Gulf. For these and other exotic regular destinations, dedicated Transverse Mercator sheets were provided in their dozens.

Othomorphic means the same as Conformal; the definition is that the scale is the same in all directions at any point on the map. In practice that means that the map accurately depicts the shape of objects (at least locally - scale distortions mean it doesn't work over long distances), but does not retain the size. Mercator's projection is also conformal. The results of scale distortion can be seen on any wall map where you'll see that Greenland appears to be about the same size as South America on the map. In fact, South America is about 9 times the area of Greenland!

Oh, you'll probably have heard of the Peter's Projection. This is NOT highly regarded by cartographers a) because it's only a special case of a general class of projections (Gall's, invented in the 19th century), b) because it's equal area property is available in many other projections, many better representations of the shape of countries and continents and c) because it looks awful!

 

[oldbilbo]

Overheard two single-handers one evening in Peter's Cafe, Horta, a long time ago....

"Did you sail the Great Circle Route, or did you come straight here...?"

 

[Buck Turgidson]

We tend to use whatever Jeppesen thinks best for the area over which we're flying. Here are a couple of examples:

 

[mjcoon]

Many thanks for all the replies. Can anyone give a simple explanation of why it is shorter to sail in a curve than a straight line? I assume it is due to the way a sphere is plotted on flat charts.
Allan

It is due to the fact that you are sailing on a (rough) sphere, the surface of which is all curved! I suppose a submarine could sometimes travel on a genuine straight line, if it wanted to...

Mike.

 

[oldbilbo]

Oh, you'll probably have heard of the Peter's Projection.

Dunno about that, but I have encountered the Peter Principle rather a lot along the way....


Vide http://en.wikipedia.org/wiki/Peter_Principle