Irwin Baseline

Renovation using GNSS

Toby Ansell 


In 1875 Surveyor Brooking conducted a triangulation from Rockingham Baseline to Champion bay. This was the first land expedition embarked on, in the aim of mapping the landform of WA. Previous attempts had been made via ship but as it was soon discovered WA was rich with agricultural, mining endeavours and possible settlements. The economic importance of this area meant that reliable topographic maps were needed, and the only way to achieve this was by rigorous and intensive survey. 

Brookings survey was conducted from the Rockingham baseline to Champion Bay, Geraldton, parallel to the coast, the expedition took over two years carried out on horseback, over 100 triangles and 120 Trig Points were observed, with the only control being the Rockingham baseline. The distance from Rockingham to Geraldton is about 400km so it is understandable Brookings geodetic survey could be erroneous if any small errors were made during the measurement of the Rockingham baseline as these would propagate north into Brookings survey. 

In the early 1900’s an error was thought to exist as the triangulation did not fit onto a known latitude point. In the attempt of fixing this error the Irwin Baseline was re-established in 1907. The results of this survey proved the original network was erroneous by 2.2 links per mile.