How come the satellites trajectories aren ellipses ?
Actual GPS satellites orbits are indeed ellipses but in an absolute frame of reference, i.e whose axes are not moving wrt to, say, some distant stars. But, GPS3D displays stuff in an earthbound frame of reference (i.e. the frame rotates along with the planet). In that frame of reference, the satellite’s trajectories are not at all ellipses. They look like a horse’s saddle. See http://www.mgix.com/gps3d/orbits.jpg to see a plot.
