NavList:

In fact I have used tree different criterions over time:

·       0 <= L <= 360º (W to E)        
·       -180º(W) <= L <= +180º(E)      
·       -180º(E) <= L <= +180º(W)

and I prefer the –W/+E convention.

The equation for LHA becomes: LHA = GHA+L or LHA = GHA-L

Why I prefer the –W/+E convention, because I use a Cartesian and spherical coordinate System:

Right-handed orthonormal basis , and coordinates.

        Origin: O, is the centre of the Earth.

Axes:

·       Z: from O to the North Pole.
·       X: from O to the Greenwich meridian, included in the Earth’s equatorial plane.
·       Y: defined by

       
One can uses a time based convention or takes a Right-handed reference frame or another…

I have books from UK, USA, France and Spain that use the –W/+E convention, most of them written by navigators, now and then.

Also the IAU has changed its criterion recently.

Obviously, the convention of signs must be in accordance with the equations.

The world of conventions. Why in some countries people drive in left lane?

I don’t know what a ºF, a yard, a pound is? I know what a pint is because I like beer :-), I have in my mind the international system of units, … conventions, more or less successful, but conventions.

Andrés

-----Mensaje original-----
De: NavList@fer3.com [mailto:NavList@fer3.com] En nombre de George Huxtable
Enviado el: miércoles, 11 de junio de 2008 15:30
Para: NavList@fer3.com
Asunto: [NavList 5399] Re: 3-Star Fix - "Canned Survival Problem"

Additionally (and this is a separate matter) Andres' program appears to

treat all longitudes as Easterly, so that a Westerly longitude is shown as

negative. To me, this seems somewhat perverse, though I am aware that many

programs (particularly for astronomy) do so. We navigators work in hour

angles (GHA and LHA) for our positions of bodies in the sky, and those hour

angles are always measured Westwards, so that they always increase with

time. An hour angle is nothing else but the longitude of the body, measured

Westerly from Greenwich, 0 to 360. Why don't we measure our geographical

longitudes exactly the same way, so that we simply difference the longitudes

to get local hour angle? Meeus is an astronomer who sets us a sensible

example. It seems madness to measure hour-angles as positive Westwards, and

longitudes as positive Eastwards. Can anyone really justify it?

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