200 Metre Error Of Entered Gps Waypoints

[+ozjeeper]

I recently had an interesting day of geocaching with five DNFs because the GPS kept showing locations that appeared to be around 200 metres away from where the cache should have been.

 

I had been playing with the GPS settings and had inadvertantly left it se to AGD66 instead of WGS84. All waypoints subsequently entered whilst the GPS parameter was incorrectly set were entered at a location 200 metres from where they should have been. All waypoints that had been previously entered before the parameter had been changed still retined their correct locations.

 

As the AUSLIG Map-reading Guide states on pages 9 & 10, "GPS is based on a geocentric datum known as the World Geocentric System 1984 (WGS84). A major implication of this change is that GDA co-ordinates, both lattitudes and longitudes and eastings and northings differ from their AGD predecessors by approximately 200 metres in a north-easterly direction".

 

So, if you're Geocaching (in Australia) and start getting GPS readings that don't make any sense and they appear to be about 200 metres "out", check your GPS parameters and make sure that WGS84 is selected.