The Next-Generation Australian Geodetic Datum Benefits and Challenges Richard Stanaway QUICKCLOSE Pty Ltd & UNSW 2015 Institution of Surveyors Victoria – Regional Conference – Wangaratta – 18 th April 2015
Acknowledgments Geoscience Australia – Geodesy and Seismic Monitoring Group (Gary Johnston, John Dawson, Guorong Hu, Minghai Jia, Anna Riddell, Craig Harrison, Ryan Ruddick, Bob Twilley) Geodetic Survey – Office of the Surveyor-General Victoria (OSGV) - DTPLI (Roger Fraser, Alex Woods) GPSnet VICMAP Position – DEPI (Hayden Asmussen, Peter Oates) CRC SI Positioning Program - Next Generation Datum 1. 02 (Chris Rizos, Craig Harrison, Joel Haasdyk, Nic Donnelly, Richard Stanaway) UNSW - Craig Roberts LINZ – Chris Crook 2015 Institution of Surveyors Victoria – Regional Conference – Wangaratta – 18 th April 2015
The motivation for datum modernisation – Drivers for change and benefits Maintaining alignment of Australia’s geodetic datum with International Reference Frames (e. g. ITRF and WGS 84) – intrinsically used by GNSS Improved precision for a wider spectrum of users who will use GNSS precise positioning and SBAS Mitigating unmodelled errors arising from deformation events (e. g. earthquakes, subsidence) and plate rotation effects Meckering, WA 1968 2015 Institution of Surveyors Victoria – Regional Conference – Wangaratta – 18 th April 2015
The future of positioning multi-GNSS + augmentation (e. g. SBAS) circa 2030 + indoor positioning (e. g. Locata) + miniature inertial sensors real-time precise broadcast orbits 4 D GIS in the cloud real-time positions mm active transformation model accurate real-time information currency centralised data + clone authoritative ubiquitous 5 G/6 G wireless and satellite comms. (e. g. Beidou, Galileo) mm/cm accurate real-time personal positioning and navigation – everywhere - No need for explicit use of “coordinates”! 2015 Institution of Surveyors Victoria – Regional Conference – Wangaratta – 18 th April 2015
Spatial Data and Positioning in the future Complex time dependent deformation modelling Software matches epoch of positioning with epoch of data in order to maintain context Kinematic Spatial Data ESRI GNSS Positioning within ITRF / GGRF Data “tagged” with datum and epoch metadata 2015 Institution of Surveyors Victoria – Regional Conference – Wangaratta – 18 th April 2015
Rotation of Victorian network – Australian Plate rotation 0. 0012” per year = 0. 031” 1994 -2020 or 8 mm rotation of a 50 km GNSS baseline in Victoria at epoch 2020 GNSS baseline vector computation is in ITRF at epoch of measurement NOT GDA 94! 2015 Institution of Surveyors Victoria – Regional Conference – Wangaratta – 18 th April 2015
Station velocities (ITRF) – Victorian Au. Scope – mm/yr Computed from GA APREF 2014. 0 solution (John Dawson and Guorong Hu) 2015 Institution of Surveyors Victoria – Regional Conference – Wangaratta – 18 th April 2015
Positioning precision and plate tectonics GNSS Reference Frames (e. g. ITRF 2008 and WGS 84) Coordinates of ground features move due to rotation of tectonic plate (approx. 60 mm/yr in Victoria) 14 parameter transformation and / or deformation model Static Geodetic Datum (e. g. GDA 94 or GDA 2020) 2015 Institution of Surveyors Victoria – Regional Conference – Wangaratta – 18 th April 2015
How do we position ourselves now? Real-time Single Pointpositioning (SPP) accuracy 2 -10 metres ITRF GNSS reference frame intrinsically ITRF and transformed to a static frame using 14 parameter model or Euler Pole ITRF NRTK or RTK Auspos (using CORS) accuracy 5 -20 mm Precise Pointpositioning (PPP) accuracy cm-dm (using IGS or Commercial Orbits ) GDA 94 CORS at Bald Rock Au. Scope ITRF GDA 94 DGNSS and Wide-area RTK (e. g. Omni. STAR and Star. Fire) 10 cm – 1 m depending on level of service Passive geodetic control (e. g. PMs, PSMs) 2015 Institution of Surveyors Victoria – Regional Conference – Wangaratta – 18 th April 2015
Current compatibility between GNSS usage and GDA 94 Good Excellent Very good SMES GPSnet NRTK and RTK data processed in GDA 94 Long baseline plate rotation effect If used as GNSS reference stn. 1 mm per 10 km baseline length Most passive control has PU better than 50 mm, but can be more than 1 m (mostly ROs) Partial Compatibility (ITRF only) ITRF 2008 – requires 14 parameter transformation otherwise ~ 1. 2 m difference data processed in ITRF and transformed to GDA 94 using 14 parameter model – recommended approach Single Point-positioning – WGS 84 (mass market and handheld) 2 -10 m precision, so difference marginally noticeable at present 2015 Institution of Surveyors Victoria – Regional Conference – Wangaratta – 18 th April 2015
International Terrestrial Reference Frame (ITRF) Hierarchy of Reference Frames in Victoria Asia-Pacific Reference Frame (APREF) VICMAP Position GPSnet Australian Regional GNSS Network (ARGN) & Au. Scope Passive geodetic marks – accessed by SMES 2015 Institution of Surveyors Victoria – Regional Conference – Wangaratta – 18 th April 2015
Current accuracy of GDA 94 in Victoria 6 mm 20 -50 mm Au. Scope GPSnet Geodetic BMs HSMs VICSZ stations most PMs PSMs e. g. radio masts, towers etc. Roger Fraser, Manager Geodetic Survey, OSGV - DTPLI 2015 Institution of Surveyors Victoria – Regional Conference – Wangaratta – 18 th April 2015
Stability of Victorian Au. Scope network mm/yr Computed from GA APREF 2014. 0 solution (John Dawson and Guorong Hu) and ITRF 2008 Plate Model (Altamimi et al. ) 2015 Institution of Surveyors Victoria – Regional Conference – Wangaratta – 18 th April 2015
Localised instability (mining subsidence, clay soil etc. ) From DEPI report -Trial of satellite radar interferometry (In. SAR) to monitor subsidence along the Gippsland Coast– prepared by Linlin Ge and Xiaojing Li, University of New South Wales 2015 Institution of Surveyors Victoria – Regional Conference – Wangaratta – 18 th April 2015
Current roadmap for datum modernisation (ICSM PCG) 1 st January 2017 Launch of GDA 2020 which is currently proposed to be realised as ITRF 2014 propagated to epoch 2020 (1 st January 2020). GDA 2020 will supersede GDA 94 – 1. 5 to 1. 6 m difference in coordinates in Victoria 1 st January 2020 Launch of kinematic Australian Terrestrial Reference Frame (ATRF) (proposed name). Fully kinematic and continuously aligned with ITRF Ellipsoid Height changes of ~ 80 mm in Victoria (will require new Ausgeoid 2020 geoid model) 2015 Institution of Surveyors Victoria – Regional Conference – Wangaratta – 18 th April 2015
Modernisation of GDA 94 not supported by PCG Option (from Haasdyk et al. 2014) 2015 Institution of Surveyors Victoria – Regional Conference – Wangaratta – 18 th April 2015
Practical steps to GDA 2020 – Surveyors Managing GPSnet, All. Day. RTK, Smart. NET, Trimble VRS Now, transition from GDA 94 to GDA 2020 coordinate delivery – date of changeover – Delivery of coordinates – Use of Ausgeoid 2020 (Cannot use Ausgeoid 09 with GDA 2020). Implications for ~1. 6 m coordinate change for existing users (e. g. Precision Ag. ) on projects – require change of project datum and model if currently GDA 94? Re-calibrate site calibrations/transformations if currently defined in GDA 94. Aus. POS will provide ITRF 2014, GDA 2020. GDA 94 - maybe? ? SMES – GDA 2020 coordinates and GDA 94 - maybe? ? GDA 2020 Grid Coordinates will be MGA 2020 2015 Institution of Surveyors Victoria – Regional Conference – Wangaratta – 18 th April 2015
Practical steps to GDA 2020 – GIS Users Requires direct implementation of direct GDA 94 to GDA 2020 transformation parameters and distortion grid (not such a problem in Victoria – as GDA 94 distortions mostly removed in current state adjustment) Caution with using WGS 84 has hub frame for datum transformations. Caution regarding rotation convention (e. g. Position Vector (PV) and Coordinate Frame(CF) have opposite signs) Migration of Vicmap data from GDA 94 to GDA 2020 Migration of other important GIS datasets (e. g. G-Naf, Vicmap, DCDB, Local Authority, Water, NBN, Electricity, Gas, Roads) to GDA 2020. Validation of transformation. 2015 Institution of Surveyors Victoria – Regional Conference – Wangaratta – 18 th April 2015
GIS Pitfalls – null transformations between GDA 94, GDA 2020 and WGS 84 using 7 parameter model 2015 Institution of Surveyors Victoria – Regional Conference – Wangaratta – 18 th April 2015
New datum pitfalls for surveyors watch out for 2015 Institution of Surveyors Victoria – Regional Conference – Wangaratta – 18 th April 2015
Pitfalls continued. . GDA 2020 data CANNOT be overlain on GDA 94 data at survey accuracy without using the correct transformation – 1. 6 metre misalignment. Always use full geodetic datum and map grid suffixes e. g. GDA 2020 and MGA 2020 – not GDA and MGA - on all coordinate data and plans. Use the right transformation parameters and tools Double-check transformations using known test data. 2015 Institution of Surveyors Victoria – Regional Conference – Wangaratta – 18 th April 2015
GDA 94 to GDA 2020 – coordinate change (m) 2015 Institution of Surveyors Victoria – Regional Conference – Wangaratta – 18 th April 2015
Transformation options from GDA 94 to GDA 2020 7 -parameter transformation Euler pole transformation (3 parameter) Absolute deformation model (coordinate shift e. g. NTv 2) 7 -parameter + residual deformation model (NTv 2) Euler pole + residual deformation model (NTv 2) Transformation options from GDA 94 to kinematic ATRF 14 -parameter transformation (7 parameters + rates + epoch) Euler pole transformation (3 parameter + epoch) Absolute deformation model (coord. shift + rate + epoch) 14 -parameter + residual deformation model + epoch Euler pole + residual deformation model + epoch 2015 Institution of Surveyors Victoria – Regional Conference – Wangaratta – 18 th April 2015
GIS requirement - Alignment of Data in a 2 D/3 D GIS Different layers in GIS have to be aligned at a common epoch for meaningful analysis and data context (relative precision of layers wrt. each other and datum) Geodetic Control layer (Datum e. g. GDA 94) Cadastral Layer (GDA 94) Imagery Layer (GDA 94? ) Elevation Layer GDA 94 (e. g. Li. Dar) Utilities Layers (GDA 94) (e. g. Water, Electricity, Optical Fibre) Existing GDA 94 GIS data can be transformed to 2020 or vv. using a 7 parameter transformation (not computed yet) 2015 Institution of Surveyors Victoria – Regional Conference – Wangaratta – 18 th April 2015
Future challenges – Alignment of Data with arbitrary epochs in a 4 D GIS Different layers in GIS still have to be aligned at a common epoch for meaningful analysis and context. Potential for metre + errors if epoch metadata is ignored Geodetic Control layer (Kinematic Datum) e. g. epoch 2026. 45 Cadastral Layer (e. g. epoch 1994. 0) Imagery Layer (e. g. epoch 2010. 095) (Raster layer adopted as common epoch for computational efficiency) Elevation Layer (e. g. Li. Dar) (e. g. 2014. 98) Water utility Layer (e. g. 2014. 0) Requires universal acceptance and consistent application of kinematic transformation models in all GIS – requires GIS user skill and care! 2015 Institution of Surveyors Victoria – Regional Conference – Wangaratta – 18 th April 2015
Alignment of Data in a 4 D GIS 14 -parameter transformation or deformation model used to align different epoch layers and data at a common epoch Geodetic Control layer (Datum) – e. g. 2026. 45 transformed to 2010. 095 Cadastral Layer (e. g. 1994. 0 transformed to 2010. 095) Imagery Layer (e. g. 2010. 095) (epoch 2010. 095 used as common epoch) Elevation Layer (e. g. Li. Dar) (e. g. 2014. 98 transformed to 2010. 095) Water utility Layer (e. g. 2014. 0 transformed to 2010. 095) 2015 Institution of Surveyors Victoria – Regional Conference – Wangaratta – 18 th April 2015
Challenges – User perspectives and software Strewth! I hope our surveyor has got good PI insurance!!! A 1. 6 m “mistake” is small for many users but can be significant for others! Terrestrial surveys (e. g. total station, TLS) data epoch is dependent upon epoch of passive control coordinates (are they updated monthly or not? ) Will surveying and CAD software (e. g. Liscad, 12 DModel, Terramodel) be able to manage survey data within a kinematic datum? 2015 Institution of Surveyors Victoria – Regional Conference – Wangaratta – 18 th April 2015
Other options for datum modernisation– (e. g. dual-frame) Positioning in ITRF but consistently transforming positions to an Australian plate fixed frame so that data can maintain local context (approach adopted in Europe (EUREF), North and South America) 14 parameter or Euler pole transformation Geodetic Control layer (Kinematic) – e. g. epoch 2026. 45 Cadastral Layer (epoch 2020) Imagery Layer (epoch 2020) Elevation Layer (e. g. Li. Dar) (2020) Water utility Layer (epoch 2020) Requires consistent application of 14 -parameter and deformation models in positioning equipment – and surveyor skill! 2015 Institution of Surveyors Victoria – Regional Conference – Wangaratta – 18 th April 2015
Option for a Reference Frame fixed to the Australian Plate (a GDA 94 like reference frame) Defined by Euler pole of the Australian Plate (Frame moves with stable portion of the Australian Plate) Station velocities minimised (typically less than 0. 2 mm/yr) Reference epoch has minimal impact on coordinate changes Distortion free Linkable directly to ITRF by 3 parameter transformation (without loss of precision) Localised deformation can be better visualised analysed Supports stability of GIS data management until 4 D GIS is fully developed, tested and implemented 2015 Institution of Surveyors Victoria – Regional Conference – Wangaratta – 18 th April 2015
Correction to GDA 94 in Victoria if epoch 1994 is maintained (ITRF 2014 @ 1994. 0) (mm) This option (modernised GDA 94) is not supported by PCG for final ICSM approval 2015 Institution of Surveyors Victoria – Regional Conference – Wangaratta – 18 th April 2015
Datum Modernisation & epoch change - Conclusions Benefits of GDA 2020 and ATRF Maintains alignment with ITRF Supports native GNSS precise positioning Mitigates effects of deformation and plate rotation Challenges ~1. 6 metre change in fundamental coordinate system Requires robust GIS transformation strategy and metadata Risks if epoch or datum metadata are not managed or communicated in a robust manner Two-frame option (ITRF and Australian plate fixed frame) To maximise benefits of both ITRF and modernised GDA 94 (until 4 D GIS and transformation tools are developed) 2015 Institution of Surveyors Victoria – Regional Conference – Wangaratta – 18 th April 2015
This is an opportunity for surveyors to reclaim the technological high ground with datums, projections and spatial data Surveyors are the only “experts” in the application and use of geodetic datums in the real world (applied geodesy). Surveyors are expected to fully understand differences between datums and explain these to clients and other non-expert users. Surveyors can show leadership by providing advice and support to GIS professionals, managers of spatial data, engineers and project managers. 2015 Institution of Surveyors Victoria – Regional Conference – Wangaratta – 18 th April 2015
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