kChia recently asked ... > > I am curious why do we need to specify elevation in addition to > longitude and latitude. Does this affect the precise apparent > positioning fixing of satellite? What is the error involved comparing say > Sea-level vs someone high up in Colorado.. > It seems to me that specifying the elevation becomes more important the closer a satellite is because of the effect of parallax. Using the astronomy package of Mathematica the following results are obtained, e.g, for 15 NOAA and 12 NOAA for 6/10/99-22.00.00 at 9 deg 11 min E, 51 deg 13 min N and elevations 0 and 2.5 km: Elevation/km Ascension Declination 0.0 12h 15m 40.7s 30° 16´ 06´´ 15 NOAA 2.5 12h 15m 41.4s 30° 15´ 31´´ 0.0 10h 59m 15.7s -39° 40´ 41.6´´ 12 NOAA 2.5 10h 59m 15.7s -39° 40´ 37.2´´ The effect of elevation of the point of observation on the coordinates of an orbiting object which is much further away than those used here vanishes. Peter Ludwig