Improving cadastral infrastructure with RTK GPS in Australia

Cadastral surveying is primarily concerned with the process of gathering evidence in the form of position information that is used to define the location of objects or land boundaries for the purposes of identifying ownership and/or the value of land parcels. The advent of Global Navigation Satellite Systems (GNSS), such as the Global Positioning System (GPS), has revolutionised the way 3-dimensional positions are determined and GPS surveying techniques, particularly Real Time Kinematic (RTK), are increasingly being adopted by cadastral surveyors. Due to the size of the Australian continent, the density of established (i.e. valid) survey marks varies considerably across the country, and there are areas where a higher density of established marks is desired. This paper presents a methodology for using RTK GPS observations to improve the existing cadastral survey control infrastructure, based on an extensive survey covering Junee Shire Council in NSW carried out as part of the Geospatial Alliance Project (GAP). A large number of already established survey marks were occupied, facilitating an investigation of the accuracy achieved with the RTK GPS technique. Comparison of the RTK-derived positions of the established marks against their published values showed an accuracy (RMS) of 11 mm in the horizontal and 34 mm in the vertical component (1). The relative accuracy of the RTK GPS results was investigated by performing bearing and grid distance calculations between a subset of established marks. Of particular interest were short distances routinely encountered by cadastral surveyors, i.e. less than 300 m, and it was shown that the results agreed very well with the values derived from the state’s survey control database (SCIMS), easily meeting accuracy specifications and NSW survey regulation requirements. Of the 128 unestablished marks (Class U) surveyed, 55% permitted upgrade to established mark status with a classification of C, while the quality of the remaining marks was updated to Class D or E. Ground observations obtained from Deposited Plans (DPs) provided valuable additional information for the adjustment. The results show that the RTK GPS technique is well suited to improving survey control infrastructure for cadastral surveyors as well as having the potential to detect erroneous DP information