Active GPS and Survey Marks

1. Active GPS and Survey Marks

2. Evolution of task Initially: “GTSC to produce an Options Paper by the end of September on the need for physical/traditional survey marks versus positions from active GPS base stations”. Action 23 of the May 2004 ICSM meeting

3. Evolution of task “GTSC to prepare an issues paper on the technical and fiscal implications of incorporating digital GPS networks into traditional geodetic infrastructures" Without seeking to restrict or broaden the terms of reference, the GTSC is encouraged to consider and report as appropriate on ; • drivers of change • general implications for other survey, mapping and land/marine development disciplines • general implications for the broader user community . A draft report is requested for the next ICSM meeting on 18 November 2004 and based on feedback from that meeting the GTSC will be asked to complete the paper soon after. Garry West – 26 August 2004

4. Past Reports May 2000: “The Australian Geodetic Infrastructure– 10 Years & Beyond” • Explosion in the use of positioning • Broad range of applications • Rapidly expanding user base • Initially an increase in the number of ground marks as new useable 3-dimensional marks are established. • In the long run the need for ground marks will decline as the trend to real time continues. • At the very least a relatively smaller number of marks will always be required to define the datum • All users need convenient access to the physical realisation of the infrastructure.

5. Past Reports Nov 2002: “Strategies for Future Australian Datums” • By 2008 the ITRF-GDA94 difference will exceed a metre • High accuracy users already able to see the difference • Transformation parameters available • Retain GDA94 and reassess in 5 years • Retain AHD for 10 years • Establish a clean data set • produce an accurate ellipsoid ht to AHD system

6. Past Reports Nov 2003: “Options & Tools for the short to long term” Three options: • ITRF-GDA94 transformation parameters (preferred) • Transformation “patches” • Local GDA94 readjustment (where necessary)

7. International Situation United Kingdom (Approx area of Victoria) • OSGB36 marks no longer used • Network of 30 Active GPS stations • Network of ~ 900 passive GPS • 3-dimensional ETRS89 by GPS survey • Re-surveyed on a 5 year cycle • Accurate process to transform between ETR89 & OSGB36/orthometric heights • Maintenance of Passive GPS marks, remains a significant task.

8. International Situation Canada • 43 Active GPS stations (ACS) • Passive network of ~ 200 stations (CBN) • Provinces have their own high density networks (active & passive) • Vertical datum 1928 still in use • Working towards a new geoid based vertical datum (decades?)

9. GTSC Views ?? • There is a need for both active GPS & survey marks • Distribution/density of marks will become targeted to “hotspots” (need rather than geometry) • Both Active GPS & Survey marks require maintenance ($$). • More marks at reduced cost • AHD bench marks are an important issue • Must be retained at least until accurate geoid-AHD corrections available. • Active GPS gives an opportunity to reach a broader market (e.g. precision agriculture, machine automation, LBS, etc) • Requires real time positions & lots of integrity • Marks protect the investment of the last 50 years or more

10. Next Steps • Agree on an outline for the paper (today/tomorrow) • Extend the outline with dot points (today/tomorrow) • Convert dot points to prose (Friday) • GTSC for feedback (Sept) • Finalise for ICSM (Oct)