>Hi Ashley, > >Glad to see that your original description is more or less >confirmed. For others let me warn that the base of the >teepee is in a plane running through the (bary)center of >the earth. It is NOT in a plane tangent to the earth. So >the icecream cone mentioned is not the whole teepee. The >icecream cone is much smaller has a crumbly edge since the >earth is irregular oblate spheroid. >But I have some nagging questions too for Ashley. > >(1) How high is the satelite. It had better be pretty high >or else the satelite will not really be pointing >its beam towards the center of the earth!! >If the satelite is low it will be pointing "down" which >(I guess wildly, nodding to tedd) >may be roughly defined by its visual horizon... > >(2) How do you propose to calculate the coordinates >of your observation point on the earth from latitude, >longitude and elevation above sealevel? I guess >a database is required. Or does one assume that >"sealevel" is a perfect oblate spheroid? > >Cheers > >Laurent S Laurent, (1) The satellite varies anyware from 90Km to 36000Km above the earths surface, depending upon the type of orbit it is in. (2) I am actually using the "earth is a perfect sphere" for the calulations at the moment as I haven't yet come across anything giving me the maths behind the oblate spheroid. I know that there is two different latitudes involved when calculating or dealing this, I think it has something to do with the real latitude involves calculations with the normal to the surface. All the locations are stored in a database giving their name, latitude, longitude and altitude and all the satellites are stored as their special element files and the passed through the orbit propogation function to obtain their X,Y,Z coorindate that is then also converted to a latitude, longitude and altitude. Once again thanks for the help, Regards, Ashley ~)~ ============================================================= Ashley Butterworth Email: macbse@... ============================================================= _________________________________________________________ Do You Yahoo!? Get your free @yahoo.com address at http://mail.yahoo.com