Virtual reference station (VRS) in South Africa

Abstract

This project seeks to investigate and report on the performance of the South African Virtual Reference Station (VRS) concept as an extension of the Global Positioning System (GPS) Real-Time-Kinematic (RTK) survey technique. Using this investigation, it is hoped to provide reliable and valid information on the accuracy, precision and reliability of the VRS survey technique. VRS addresses many of the limitations faced by the classic RTK technique. The past few years has seen many countries install permanent reference station networks to spatially model the biases for a given region. The Chief Directorate: Survey and Mapping has developed two permanent reference station networks called the Gauteng VRS network and Western Cape VRS network. Both these networks operate using Trimble’s VRS hardware and software. Classic RTK technique enables surveyors to carry out centimetre level positioning activities. The accuracy of classic RTK has been well documented. However, the accuracy, precision and reliability of the VRS network, here in South Africa, have yet to be proven. The reliability of the Gauteng VRS network is assessed by carrying out detailed testing of determining the performance of the accuracy, precision, initialisation times and its coverage extent. Several test sites located within, on, and outside of, the network are selected and several measurements are collected, processed and collated at each test site. The results indicate that the Gauteng VRS system is at least comparable to the classic RTK technique in the areas of accuracy, precision and initialisation times, and demonstrated greater robustness of the coverage extents of the system. The results of the test will be of interest to existing and potential users of GPS for positioning activities and will benefit them as an aid to making an informed decision.