Positional uncertainty of network RTK observations in a modern datum

T Bernstein,V Janssen

doi:10.1515/jogs-2020-0116

Abstract

Abstract The Geocentric Datum of Australia 2020 (GDA2020) is Australia’s new and much improved national datum. It is based on a single, nationwide least squares network adjustment that rigorously propagates uncertainty. This paper explores three options to include Network Real-Time Kinematic (NRTK) observations and their Positional Uncertainty (PU) in the survey control network of New South Wales (NSW) via the GDA2020 state adjustment. In the first option, PU is empirically estimated based on a dataset of more than 1,500 observations to obtain values that can be uniformly applied to all NRTK observations. In the second option, PU is calculated for each NRTK observation, based on the coordinate quality indicators provided by the Global Navigation Satellite System (GNSS) equipment. Both options continue to treat NRTK observations as point-based position solutions, resulting in poor correlation with surrounding survey control marks. The third option overcomes this issue by utilising the automatically computed GNSS baselines between NRTK observations and their Virtual Reference Station (VRS) to create a connected network that can be adjusted like a static GNSS network. Using a typical urban NRTK survey in Sydney as an example, it is shown that this method offers a rigorous computation of PU, while maintaining the quick and easy nature of NRTK positioning.

Highlights

The Geocentric Datum of Australia 2020 (GDA2020) is Australia’s new and much improved national datum, introduced in October 2017 and adopted in New South Wales (NSW) on 1 January 2020
Positional Uncertainty (PU) is calculated for each Network Real-Time Kinematic (NRTK) observation, based on the coordinate quality indicators provided by the Global Navigation Satellite System (GNSS) equipment
The rst option to incorporate NRTK uncertainties into the GDA2020 state adjustment was to determine an empirical estimate of PU that can be applied to all NRTK observations

Summary

Introduction

The Geocentric Datum of Australia 2020 (GDA2020) is Australia’s new and much improved national datum, introduced in October 2017 and adopted in New South Wales. NSW Spatial Services is accelerating the process of including additional survey marks into the state adjustment in order to improve user access to GDA2020 coordinates and uncertainties (Janssen and McElroy 2020). This paper explores three options to include NRTK observations and their uncertainties in the NSW survey control network via the GDA2020 state adjustment. In an e ort to obtain PU values more tailored to each individual occupation, the reliability of using coordinate quality indicators provided by the GNSS equipment to calculate PU on an occupation-by-occupation basis is explored This computation requires input of the PU of the reference station used, which is generally a Virtual Reference Station (VRS, Landau et al 2002) for NRTK with CORSnetNSW, with the PU of a VRS not yet suitably quanti ed. It is shown that this o ers a rigorous computation of PU, while maintaining the quick and easy nature of NRTK positioning

Empirical estimate of NRTK PU

Minimum Maximum

Mean Median Standard Deviation

Network adjustment using automatic baselines

Findings

Concluding remarks