Why can’t we just use ITRF instead of ATRF?

ITRF is defined using only 15 sites from Australia; ATRF uses the 109 Recognized-value Standard of Measurement sites from the 2017 Determination. ATRF therefore provides a link to the RVS Determination and is legally traceable

How often will new solutions of GDA2020 and ATRF be available?

The timing for the computation of national adjustments and the release of updated GDA2020 and ATRF coordinates are yet to be determined. NOTE: The computation of a national adjustment may cause only minor changes to the coordinates and will not always warrant a change to coordinates provided to the user.

Which solution is used as constraint in the national adjustment?

A GDA2020 aligned cumulative APREF solution from ~3 months prior should be used to constrain the national adjustment. This allows enough time for any discontinuities in the APREF solution to be identified and resolved. The cumulative APREF solution will be propagated to the epoch of 2020.0 using the Australian PMM.

What happens if one or more of the RVS Determination sites exceeds its positional uncertainty?

Regular checks will be undertaken by GA to ensure the GDA2020 coordinates and velocities at the RVS sites are within the uncertainty of the RVS Determination. If changes exceed the uncertainties, GA will work with the National Measurement Institute (NMI) to update the RVS Determination as required. See Section 5.1.1 for the testing procedure.

After the national adjustment is run, how are ATRF coordinates propagated to a given epoch?

The national adjustment will be run in GDA2020. Output coordinates will be propagated to ATRF at any epoch using the Australian PMM (and potentially a deformation model if required).

How are ATRF coordinates propagated to GDA2020?

The Australian PMM can be used to convert coordinates between ATRF and GDA2020.

Is the Australian PMM a 2D or 3D model?

The Australian PMM is only a 2D model. It does not change the height component of the data. Changes to the height component are being considered in the form of a deformation model (see Section 4.4).

What solution will be used in real-time services?

Geoscience Australia proposes to make two streams of data available: one in GDA2020 and one in ATRF.

Will GDA2020 coordinates be updated with time?

Yes. With each new national adjustment, new GDA2020 coordinates will be computed and stored in the GA database with access only by jurisdictions. The choice of whether / when to update GDA2020 coordinates in jurisdictional databases will be the decision of jurisdictional representatives. Jurisdictions are encouraged to closely coordinate any such updates to minimise any potential distortion issues along state/territory borders. 

Why are we maintaining (e.g. storing data, reference epoch for adjustments) the geodetic data in GDA2020?

It is easier to work with, and less risk of error / mistakes, when working with data in a static datum.

How is the Australian PMM different to the ITRF PMM?

ATRF uses the Australian PMM based on the site velocities of 109 sites, whereas the ITRF PMM is only based on the velocities of 15 sites. ICSM recommend the use of the Australian PMM.

What happens when ITRF is updated?

Differences between ITRF realisations are expected to be minor. When the ITRF is updated, this will result in a new ATRF realisation, and the RVS Determination will be updated.

How will ATRF coordinates be provided to users?

  • Real-time GNSS data streams delivered by GA: Most recent ATRF coordinates by  real-time GNSS caster
  • Static files by GA: GDA2020 and ATRF coordinates and refined velocities made available in GA database following each national adjustment.
  • Transfer to jurisdictional databases: Establish GeodesyML web service workflows

Legal traceability of GDA2020 and ATRF?

The RVS Determination, through the site-specific velocities Eqn. 2, or the Australian PMM applied through Eqn. 1 provide legally traceable methods of propagating coordinates between GDA2020 and ATRF.

What is the ATRF naming convention?

ATRF coordinates will be able to be differentiated by metadata that will include three discrete pieces of information

  1. ITRF reference frame year (e.g. 2014)
  2. Cumulative APREF solution week (e.g. GPS week xxxx)
  3. Epoch of coordinates

along with the coordinate propagation technique/s applied (e.g. Australian PMM, deformation model, site velocity).

What is the reference frame of corrections from for the NPI SBAS?

ATRF. Satellite Based Augmentation System (SBAS) corrections which are to be supplied via internet / satellite will be generated from CORS throughout Australia, not just from IGS / ITRF sites and will therefore be in ATRF.

Why is only a subset of APREF solutions provided with an ATRF solution?

This restriction is to ensure authoritative Australian-derived coordinates are supplied for Australian sites.

What does ‘time-dependent’ actually mean?

Time-dependent reference frame means an Earth centred, Earth fixed reference frame in which coordinates vary over time, reflecting temporal changes in the earth’s crust. That is, the physical location of a feature expressed by coordinates relative to a time-dependent reference frame will be dependent on time.

Does each new ATRF solution need a new set of transformation parameters to transform between them?

No. Transformation parameters are required when there is a change in the reference frame. There is no change in the reference frame. The ATRF realisation only changes when there is a change to the ellipsoid or realisation of ITRF. Each new solution is just a new solution in the ATRF time series.