Abstract: A method for global navigation satellite system (GNSS)-based navigation may include retrieving terrain data for a geographical region and satellite orbit data for a GNSS comprising a plurality of satellites. Then, for of a plurality of time steps in a time period and for each of a plurality of lateral positions in the geographic region, a minimum height at which each satellite is visible from the lateral position at the time step may be determined. Unique combinations of satellites visible from the lateral position at the time step may be identified and error objects indicating GNSS performance quality corresponding to the unique combination of satellites may be generated. Performance quality information may be produced based on the one or more unique combinations of satellites and the respective one or more error objects. At least one aircraft may be operated based on this performance quality information.