TOP software provides a real-time check of satellite visibility that accounts for the terrain surrounding the GPS receiver.
Communication between the simulator and the TOP computer takes place over an Ethernet link.
The CAST system supplies a list of satellites that are normally visible to the TOP each second.
TOP checks the line-of-sight for each of the proposed satellites with the surrounding terrain database to
TOP returns a visibility status for each of the proposed satellites considering the
terrain obscuration factor. There is no user action required at the TOP, but the user can control the viewpoint
for terrain visualization to get different perspectives on the terrain affecting the test.
Visualization: TOP provides the user of the simulator visual cues on the terrain being simulated in the run.
The terrain is presented in an animated wire-frame view with the observation point relative to the receiver's simulated
location adjustable by the user. This allows the user to simulate terrain effects on the receiver to help quickly
identify performance issues.