GPS Tracking Errors for Dummies
Another factor that affects satellite tracking errors is their location in orbit. As the satellites are in orbit, there are times when your GPS receiver might have a better grouping of satellites than at other times. For instance, if your receiver was receiving signals from four satellites that were well distributed throughout all directions, your accuracy would be improved. However, if all four satellites that you were receiving were located in the southwest, you would have poor "satellite geometry." This poor distribution of satellite signals would result in an inaccurate reading, if a reading was possible at all.
Satellite geometry can also be affected by buildings, trees, or other objects. It would be possible, for example, to have good satellite geometry from your location if you were on a flat plane, but some of the signals are blocked by objects in the environment, thus creating poor satellite geometry.
Buildings and objects can also create a delay in the acquisition of a signal. The satellite radio signals bounce off of buildings and other large objects, which adds travel time to the signal. This increase in travel time creates an inaccuracy of several feet, but usually only occurs in areas with large buildings.