The eGPS Solutions System

The eGPS Solutions system is based on Trimble technology. Trimble VRS is an integrated system consisting of GPS Hardware, software and communication links.

The links utilize data from permanent reference stations to model errors throughout the coverage area. This model is used to synthesize “virtual” reference stations near the user’s location which then provide a “localized” set of standard format correction messages to the roving receiver.

How The eGPS Solutions System Works

GPS observation data from a set of fixed reference stations is continuously transmitted to the Trimble VRS central server. Here the network processor performs integrity checks on all GPS observables. For every station, quality checks are performed on the data, outliers are rejected and cycle slips are corrected.

ERROR CORRECTION
Once the integrity of the data has been checked, the central server computes ionospheric, tropospheric, and ephemeris errors by analyzing double difference observations. The effect of these errors on any rover working within the network can be modeled so the systematic errors for RTK can be significantly reduced.

VRS GENERATION
To enable the modeling, the rover must provide its approximate position to the central server. This is done via cellular modem using the standard NMEA GGA 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 ionospheric 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 Solutions network is managed by the following Trimble Navigation software packages:

GPS BASE
This software provides for continuous, fully automatic operation of a single base station for post processing, Real Time Kinematic (RTK) or Differential Global Positioning System (DGPS) corrections within a local area.

GPS NET
Designed to connect multiple base stations, this software package expands the GPS base coverage area by managing a network of field base station receivers to provide post processing or Real Time Kinematic (RTK) or Differential Global Positioning System (DGPS) corrections.

RTK NET
This software uses Real Time data streams from the GPS Net software and generates correction modules for high accuracy, Real Time Kinematic (RTK) corrections throughout the network of fixed base stations receivers. The RTK Net is the software that provides the Virtual Reference Station (VRS) broadcast corrections.

View Lonnie Sears, President of eGPS Solutions, demonstrating the easy set-up and operation of the eGPS system.