---Ruben Velasco <heston@arrakis.es> wrote: > When you enter your local altitude to a tracking software like Iridflar, > Stsplus, Trakstar... should you enter the metres above the sea level or > above the WGS-84 model? For example, I'm writing this from a place > "oficially" at 9 meters "Above Sea Level". But the sea level stardard > we use here is actually several metres higher than, say, that of the > Indian Ocean near Sri Lanka. In other words, the Earth is not a perfect > spheroid, etc, etc (you already know the story :) Technically, you are right, you would want to enter your altitude relative to the spheroid model being used by the program. The whole purpose of entering altitude is to refine the vector being calculated from the earth's center to the observer and thereby calculate sight lines from the observer to the satellite. Programs ask for altitude/elevation/height (I'll use all three so I won't restart a thread about the 'proper' use of those terms) above mean sea level is that the common number end users have access to. You're also right that the difference between the sea level datum and the spheroid datum makes no practical difference: your 30 meter 'error' relative to a 6378 km earth radius is one part in 200,000. __________________________________________________ Jim Varney 121.398W 38.458N 8m Sacramento, CA (Sorry. I am not the "Voice of Slinky Dog.") jamesv@softcom.net, sat_watcher@rocketmail.com _________________________________________________________ DO YOU YAHOO!? Get your free @yahoo.com address at http://mail.yahoo.com