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There is a .map file:

OziExplorer Map Data File Version 2.2
1 ,Map Code,
Geodetic Datum 1949,WGS 84,   0.0000,   0.0000,WGS 84
Reserved 1
Reserved 2
Magnetic Variation,,,E
Map Projection,(NZG) New Zealand Grid,PolyCal,No,AutoCalOnly,No,BSBUseWPX,No

my best guess is NZGD49 North Island but when I use this projection the data from the GPS does not match. Any ideas?

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up vote 1 down vote accepted

What about EPSG:27200? The others are more or less locally adopted, but the file info does not name any.

How much offset do you get?

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I have selected a known point (the start of a track) which I can identify on both the layer from the GPS and the raster layer (whose CRS is uncertain). – Russell Fulton Jan 23 '13 at 5:31
Oops I spent to long editing the response after hitting return and accidentally posting. Offsets are of the order of 500000,900000. I do have output of mrsidinfo for the original sid file if that would be useful. I am coming to the conclusion that my best bet is to try and find out what and who produced the original file. The joys of volunteer projects :) – Russell Fulton Jan 23 '13 at 5:54
You could try one of the other NZGD systems available, or just re-georefrence the raster file upon the known points you have. – AndreJ Jan 23 '13 at 6:35
It is EPSG:27200. What confused me was that when looking in the QGIS CRS selector 27200 is listed under Geographic Coordinate Systems and all the other ones that I was looking at were under NZ Map Grid so I did not find it until I used the filter at the top. Doh! everything matches nicely now. I also found this site extremely useful: I found it by searching for 27200 when I could not find it in QGIS. It enabled me to match the data I got from mrsidinfo with the EPSG # Thanks very much Andre, – Russell Fulton Jan 23 '13 at 9:46
Just to clearify: The geografic CRS called NZGD49 has EPSG:4279 and uses lat/lon, then you have the projected EPSG:27200 filed under NewZealand Map Grid, and the rest filed under Transverse Mercator. Not very intuitive, but you can saerch for 'NZ' or any EPSG number in Qgis Filter box. – AndreJ Jan 23 '13 at 10:14

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