On Tue, 1 May 2001, Steve Lelievre wrote: > Gianni wrote: > > As in almost all Web sites, also you take as positive the Longitudes for > > places West of Greenwich.
> > The Explanatory Supplement to the Astronomic Almanac (USNO 1992) at page > > 203 affirms: > > "The geocentric longitude is defined by the angle between the reference > > (or zero) meridian and the meridian of point p, measured EASTWARD > > around the Earth from 0 to 360 deg (IAU, 1983, p.47) " > for our purposes a range -180 to +180 is more convenient than 0 to 360, > especially when trying to visualise what's going on. For instance, in the > > Steve Steve, I agree with your point that -180 to +180 is more convenient, and is also more common usage, I believe. However, if I understood the above correctly, the more significant difference between your convention and that espoused by Gianni, is that you are have positive longitude West of the Prime Meridian, rather than East... Dave 37.3 N 121.9 W