Improving GPS Positions

These corrections can be applied in real time (requires a connection), or for later post processing.  The best post processing uses a longer time period to provide the corrections, and cannot be done immediately.

Wide Area Augmentation System (WAAS)

WAAS, a regional space-based augmentation system (SBAS) operated by the Federal Aviation Administration (FAA), supports aircraft navigation across North America.

Although designed primarily for aviation users, WAAS is widely available in receivers used by other positioning, navigation, and timing communities.

FAA is committed to providing WAAS service at the performance levels specified in the GPS WAAS Performance Standard. FAA is improving WAAS to take advantage of the future GPS safety-of-life signal to provide even better performance.

The WAAS service is interoperable with other regional SBAS services, including those operated by Japan (MSAS), Europe (EGNOS), and India (GAGAN).

Continuously Operating Reference Stations (CORS)

The U.S. CORS network, managed by the National Oceanic and Atmospheric Administration, archives and distributes GPS data for precise positioning tied to the National Spatial Reference System.

Over 200 private, public, and academic organizations contribute data from almost 2,000 GPS tracking stations to CORS.

The Online Positioning User Service (OPUS) offers free post-processing of GPS data sets to the centimeter level using CORS information. CORS is also being modernized to support real-time users.

Global Differential GPS (GDGPS)

GDGPS is a high accuracy GPS augmentation system developed by the NASA Jet Propulsion Laboratory (JPL) to support the real-time positioning, timing, and determination requirements of NASA science missions.


QZSS uses 3 satellites, 120 apart, with highly inclined, slightly elliptical, geosynchronous orbits. They are not geostationary, but have ground traces which are asymmetrical figure-8 patterns (analemmas). The goal it to have one satellite almost directly overhead (elevation 60 or more) over Japan at all times, to provide GNSS coverage in urban canyons.


Last revision 2/3/2018