Nearmap has provided an aerial image georeferenced in the same coord system as Google Earth (epsg:3785). I found a Map 3D coordinate system WGS84.PseudoMercator (epsg:3857) which on web forums is equivalent to epsg:3785. After loading the image into a dwg on the epsg:3857 coord system I then queried the image into a dwg file on an mga55 gda94 coord datum.
It rotated the image correctly but as we had survey located features in the drawing the image needed to be shifted a further 1.75 metres SW than the transformation that Map had performed.
My question is can anyone confirm that the Map epsg:3857 is indeed the same as epsg:3785? Given I had to shift the image I suspect it isn't.
Nearmap have also suggested using an epsg:900913 coord datum but there isn't one in Map 3D.
You can compare the EPSG contents here: as you can see in the "Retrieve code" report, the 3785 refers only to New Zealand.
About EPSG:900913 it's a funny way to portray the official EPSG:3857, check this out:
9 => G
0 => O
0 => O
9 => G
1 => L
3 => E
Thank you for the reply. I went to the link & it is interesting that epsg:3785 only applies to the south island of New Zealand. From correspondence with Nearmap & the image name (starts with epsg_3785) this is the datum they are using. I would assume that Nearmap would know what they are doing but as our imagery is based on the south-east coast of Australia it might not be the correct datum to be using.