EDMCAL: Processing EDM calibrations in NSW
The Surveyor General of New South Wales is a verifying authority under the National Measurement Act 1960 and responsible for ensuring that surveyors use verified measuring equipment. According to the Surveying and Spatial Information Regulation 2012, surveyors are required to verify their Electronic Distance Measurement (EDM) equipment in relation to an Australian standard of measurement of length at least once a year. For this purpose, Land and Property Information (LPI) provides and maintains several EDM baselines across the state. LPI is currently in the process of improving this infrastructure by upgrading existing baselines and building new baselines for the calibration of EDM instruments. This paper presents the current status of EDM baseline infrastructure in NSW and outlines the data processing performed by LPI in regards to EDM calibrations. The EDMCAL software currently employed by LPI is described and compared to a spreadsheet calculation generated by the University of New South Wales. Finally, LPI’s new online EDM baseline booking system is introduced. This online system should now be used by surveyors to book access to all EDM baselines in NSW in order to allow efficient and effective use of existing and future baseline infrastructure.
Best practice: Performing EDM calibrations in NSW
The Surveyor General of New South Wales is a verifying authority for reference standards of length measurements under the National Measurement Act 1960 and responsible for ensuring that surveyors use verified measuring equipment. To this end, the Surveying and Spatial Information Regulation 2012 requires surveyors to verify their Electronic Distance Measurement (EDM) equipment in relation to an Australian standard of measurement of length at least once a year. In order to assist the profession in meeting this requirement, Land and Property Information (LPI) provides and maintains several EDM baselines across the state. LPI is currently in the process of improving this infrastructure by upgrading existing baselines and building new baselines for the calibration of EDM instruments. This paper briefly presents the current status of EDM baseline infrastructure in NSW and outlines best practice guidelines for EDM calibrations in NSW. These proposed guidelines are expected to flow on into the next update of Surveyor General’s Direction No. 5 (Verification of Distance Measuring Equipment).
AUSGeoid09: a more direct and more accurate model for converting ellipsoidal heights to AHD heights
In an absolute sense, AUSGeoid09 is an order of magnitude more accurate than AUSGeoid98 at converting ellipsoidal heights to Australian Height Datum (AHD) heights and vice versa. Results of this study show AUSGeoid09 can be used to compute AHD heights from Global Navigation Satellite System (GNSS) ellipsoidal heights with an uncertainty of less than ±0.03 m (one sigma). The improvement is largely due to the inclusion of a geometric component in AUSGeoid09 that accounts for the spatially varying offset between a gravimetric quasigeoid model and the AHD. This geometric component was calculated using least squares collocation in cross validation mode and then added to the gravimetric quasigeoid. Although previous AUSGeoid models were used to convert GNSS ellipsoidal heights to the AHD and vice versa, none until now have accounted for the gravimetric quasigeoid to AHD offsets. This offset is a consequence of how the AHD was realised and has commonly resulted in misfits of ∼0.5 m or more. When used with GNSS technology, AUSGeoid09 can replace the need for traditional third-order levelling (Class LC; 12 ) in many situations. Relative tests of AUSGeoid09 over a continent-wide set of over 20 million baselines showed that it can deliver better than Class LC tolerances in 99 percent of cases. The model accepts a user's GDA94 latitude, longitude and ellipsoidal height and returns an AHD height and deviations of the vertical. AUSGeoid09 is now available free-of-charge on the Geoscience Australia website ( http://www.ga.gov.au/geodesy/ausgeoid/nvalcomp.jsp).