Next message: Peter Fogg: "Re: Azimuth and Declination formulae"
Robert Eno wrote:
> Essentially, the Grid reference system for northing tells you how many
> meters one is from the equator.
It's close, but not quite exact. An object on a UTM zone's central
meridian becomes a little smaller when projected onto the grid. An
object at the edge of a zone expands a little. The maximum scale error
is about 1 in 1000.
Directions are distorted too. Meridians (except the central meridian of
the zone) are curves on the UTM grid.
So if you follow a course of grid north from the equator to 4000 km
northing, the track made good on the real world follows a constantly
changing true course, and is not exactly 4000 km. This is true whether
you assume the "real world" is a sphere or an ellipsoid.
