The Department of Defense turned off Selectively Availability on May 2, 2000 which reduced GPS uncorrected positional error from approximately 100 meters to 10 meters.
Explanation of Graph Labels:
SPS- Standard Positioning Service- the normal civilian positioning accuracy obtained by using the single frequency C/A code (Coarse/Acquisition).
CEP- Circular Error Probable (horizontal only, 2D)- a statistical statement that describes a 50% confidence level. In other words, 50% of the positions obtained will be within the stated distance from ground truth.
SEP- Spherical Error Probable (horizontal and vertical, 3D)- a statistical statement that describes a 50% confidence level. In other words, 50% of the positions obtained will be within the stated distance from ground truth.
UTC- Universal Time Coordinated- local solar mean time at the Greenwich Meridian. A uniform atomic time system maintained by the U.S. Naval Observatory.
GPS Education Resource
Your GNSS Training Headquarters for GIS and Mapping Applications