Jay Gischer (gischer++at++knex.engr.sgi.com)
Mon, 8 Feb 1999 09:31:44 -0800 (PST)
> But seriously, there is a nice consistency
> resulting from the choice of signs to be such that
> the primitive rotations h,p,r take +x to +y,
> +y to +z, and +z to +x respectively.
> That makes it possible for me to actually get the directions right
> without having to consult a book each time (but maybe I'm just weird).
Since Heading increases in a clockwise direction (from N to E),
this is consistent with common navigation in the Western Hemisphere,
with +X being West and +Y being North. But in the Eastern Hemisphere,
+X is East...
To complicate matters further, in the Northern hemisphere +Y is North,
but in the Southern Hemisphere +Y is South. So on two separate
quarters the earth the coordinate system is right-handed:
(+X = N, +Y = W) (N.America) or (+X = S, +Y = E) (S.Africa)
and on the other two quarters it's left-handed:
(+X = N, +Y = E) (Most of Europe) or (+X = S, +Y = W) (Australia, S. America)
There, now doesn't that brighten your day?
-j
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