How The eGPS Solutions System Works

GPS observation data from a set of fixed reference stations is continuously transmitted to the Trimble or Geo ++ central server. For every station's data set, quality checks are preformed and outliers are rejected and cycleslips are corrected.

Once the integrity of the data has been checked, the central server computes ionospheric, troposphereic, and ephemeris errors by analyzing double-difference solutions or through Kalman filtering. The effect of these errors on any rover working within the network coverage area is then modeled and the systematic errors for RTK are significantly reduced.

To enable the modeling, the rover must provide its approximate position to the central server. This is done via cellular or radio modem using the standard NMEA GAA string. The central server automatically receives this positioning information and performs a geometric displacement to the given location. The software interpolates and applies corrections for ephemeris, tropospheric and ionosoheric errors and generates a "virtual reference station" for that individual rover. The software then produces a set of standard format correction messages as if they were coming from the virtual reference station and transmits them via cellular modem to the rover.

The eGPS Network Data Flow

"Prime Engineering was using a Trimble R8 equipped with eGPS. Our crew chief fell in the creek and he and the equipment were immersed. The GPS equipment was fine but the cell phone died a watery death. We contacted Jeff Little of eGPS to get phone recommendations. Within an hour of the phone failing, Jeff met our party chief at the Verizon store to help us get the right phone and get up and running again.

That is exceptional support.

We at Prime appreciate your timely assistance."

- Greg Wagstaff, RLS
Prime Enginering, Atlanta, GA

"We list the local monuments in our software, set up control and use eGPS to stake out the nearest monument and double-check the accuracy," he says. "We want to get the eGPS value instead of the recorded value. The accuracy is much better."

- Thomas E. Peay, Jr., RLS
Frontline Surveying & Mapping, Inc., Marietta, GA

"Woolpert currently has three 'roving' GPS units collecting cm accuracy positions in the Fulton and Gwinnett county areas. We have found their services to be affordable and highly reliable..You will find their staff knowledgeable and helpful."

- David Wilkins, PLS
Woolpert, Inc., Atlanta, GA