On Mon, 2005-07-25 at 15:17, Andy Ross wrote: > I humbly submit that this is yet another area where an Euler (angle) > representation is a bug, not a feature. We have a sane cartesian > coordinate system for the earth. All that's needed is to define one > for the solar system* and then do reasonably trivial conversion.
To be frank, that's close to what's happening anyway. The earth orbits the sun in an ellipse and it is considered to be a 2D system. Trouble is that the earth's orbital velocity isn't constant (as Johann Kepler and Tycho Brahe discovered in the 15th century - or was it the 14th?). Solving where the planet is in its orbit for any given calendar time is tricky. Once you've got that, you then do exactly what Andy says and do a "reasonably trivial conversion" to get the sun's position as seen from the POV of an observer on the planet (or over it) at that calendar time. The hard part is finding the calendar time given a phenomenum (like, say 'sunset'). I outlined that one in my previous post. > The > moon should be even easier, presuming that the moon's orbit passes > through the equatorial plane (it does, doesn't it?). > No. None of the planets share the earth's orbital plane either, but the moon is quite well offset. 18 degrees I think, and its orbital plane precesses w.r.t the earth's quite quickly too. The ancients deserve serious respect for managing to predict the moon's movements and eclipses at all. Steve. _______________________________________________ Flightgear-devel mailing list Flightgear-devel@flightgear.org http://mail.flightgear.org/mailman/listinfo/flightgear-devel 2f585eeea02e2c79d7b1d8c4963bae2d
