AUSPOS - Understanding the Results

Question 4.1 - How do I read the processing report?

The processing report is provided in Adobe PDF format.

Download Adobe Reader for free here External site link.

Question 4.2 - What parts of the report should I check carefully?

It is recommended that you read the whole report thoroughly to familiarise yourself with the AUSPOS process. The important quality statistics related to your processing job are located in Section 5 of the AUSPOS Report. This includes information such as the Coordinate Precision and Ambiguity Resolution.

Question 4.3 - Why are the GDA94 values different from the ‘original’ GDA94 values?

You may notice a difference between the 'original' GDA94 coordinates and the AUSPOS derived GDA94 coordinates. These differences could be the result of errors in the original GDA94 GPS coordinates and / or modelling errors in the transformation process (from ITRF to GDA94).

Question 4.4 - What are the ‘Derived AHD’ and ‘Derived Above Geoid’ heights?

In the GDA94 section of the AUSPOS report, the user is supplied with a 'Derived AHD’ height. This is a height computed using AUSGeoid09. The offset between the ellipsoid and AHD is computed using Geoscience Australia’s AUSGeoid09 product and subtracted from the ellipsoidal height providing the user with a Derived AHD height. In most cases this is accurate to within 0.03 m. For more information, refer to the AUSGeoid09 page.

In the ITRF section of the AUSPOS report, the user is supplied with a ‘Derived Above Geoid’ height. This is a height relative to the Earth Geopotential Model 2008 (EGM2008). More information on the EGM2008 geoid can be found here External site link.

Question 4.5 - The report provides GDA94 and ITRF coordinates, but what about WGS84 coordinates?

ITRF and WGS84 are generally considered to be equivalent (to within 0.1 m).

Further information

Topic contact: geodesy@ga.gov.au Last updated: May 8, 2013