Thread: GPS co-ordinates

Originally Posted by Shamus_

As the other guys have said NZTopo50 uses the NTZM coordinate system by default - Google Earth uses WGS which is just a different way of expressing the same thing. You can change the "Grid Units" in the NZTopo50 app to "Dec. Deg." if you want it to be the same as Google Earth

Technically speaking NZTM & WGS are very different. Ask your friendly surveyor - I'm not a surveyor.

Most coordinate systems use different underlying geoid systems.
The geoid is the system of mapping the coordinate system on to the physical earth.

Over a short distance different coordinate systems may be able to be made to match.

To add an extra ingredient to NZ's coordinate systems NZ's ground is moving at different rates.
Corrections should - in theory - be applied to a coordinate system over time to allow for the fact that NZ is moving and is moving in different directions at different rates.
That said it doesn't matter if your desired accuracy is +/-10 metres or more.

After the Canterbury earthquake systems a method of correction had to be created as the ground - including surveying markers - had often moved by several meters, thus making property boundaries incorrect.