Gps for Cadastral Surveying – Practical Considerations

GPS technology, in particular real-time kinematic (RTK) GPS, has matured to the stage where it has become another tool for the professional surveyor. Commercial products offer user-friendly hardware/software and suggest techniques that can improve productivity at a high accuracy. Government services such as SCIMS in NSW and AUSPOS (Geoscience Australia) support improved GPS positioning and surveying for the user community. However, even though some professional surveyors have embraced GPS survey methods into their businesses, mainly for a range of engineering and topographic detail tasks, many practitioners are still reluctant to invest in the technology. This has been due to a number of reasons such as prohibitive cost, a lapsed understanding of geodesy, confusion about GPS surveying capabilities and best practice techniques, uncertainty over how to best utilise existing GPS services and infrastructure, lack of time/resources to invest into GPS surveying training, and for the cadastral surveyor uncertainty over what is acceptable practice to satisfy current survey regulations in their particular state or territory. This last point is of particular importance because if a professional surveyor can justify using RTK-GPS for engineering, detail and cadastral surveying then suddenly RTK-GPS does indeed become “just another tool” like the ubiquitous total station. This paper seeks to investigate a number of practical issues faced by the cadastral surveyor using RTK-GPS. A brief introduction on how RTK GPS works is presented followed by a range of issues including the impact of GPS errors for the cadastral surveyor, initialisation, radio links, marks under trees and future GNSS augmentations. Survey regulations differ between states and impact on acceptable practices. As the author lives in NSW, this paper will have a NSW flavour. As State Governments increasingly encourage professional surveyors to provide at least MGA control (and sometimes even MGA coordinates) on modern cadastral surveys, RTK-GPS, being a high precision coordinate generator, seems and obvious tool to use (in favourable conditions). It is hoped that this paper will encourage professional surveyors to trial GPS and/or use it more effectively.