Adrian White - Undergraduate Thesis - October 2007  
  School of Surveying and Spatial Information Systems - University of New South Wales

Introduction

Today surveyors and other spatial professionals use GPS for high precision measurements. To achieve the centimetre accuracies they require, they use differential carrier phase positioning by having one set of GPS equipment set up at a known position (the base station) and a second set of GPS equipment at an unknown position (the rover station). The nature of GPS allows the relative distance between the two positions to be measured with high accuracy. When surveyors perform this task in real time where corrections for the position of the base station are used to correct the rover position, it is called Real Time Kinematic (RTK) surveying.

Conventional RTK (Trimble)

However, the biases that are estimated in RTK surveying are distance dependant and once the inter-station distance exceeds 20km, it is difficult to achieve the necessary measurement accuracy. Of late, much interest has been made into using not one, but multiple base stations surrounding the rover station allowing the biases of the area they cover to be modelled and interpolated for an improved estimation of their effect at the rover location, referred to as Network RTK. One particular method of delivering Network RTK solutions is by creating a Virtual Reference Station (VRS) very close to the rover station and then using conventional RTK, with the VRS as the base station, to determine the rover location. Studies have shown that the distance dependant biases are reduced using this approach.

Trimble's Network RTK Solution (Trimble)

In fact, Network RTK has become so popular that organisations have set up networks of permanent GPS receivers, or Continuously Operating Reference Stations (CORS), to deliver improved positioning solutions to the wider spatial community, such as Sydney's CORS network, SydNET. Network RTK allows these stations to be spread at far greater differences while still achieving the required measurement accuracies.

This thesis involved modifying post mission processing Network RTK software to produce Receiver INdependent EXchange (RINEX) files, a standard file format for storing GPS data. The resultant RINEX files were then tested in a variety of ways to determine the performance of the utility.

 

Thesis Supervisors:

Professor Chris Rizos, University of NSW

Thomas Yan, University of NSW

Douglas Kinlyside, NSW Department of Lands

Greg Dickson, NSW Department of Lands