[Gdal-dev] Defining Australian Map Grid in GDAL

[Andrew Williams]

Hello folks.
I'm having trouble with a Geotiff. 
The scan is a topographic map sheet. The cartography and grid on the sheet is based on AMG (Australian Map Grid). It is a UTM projection based on the Australian National Spheroid, ellps=aust_SA I believe.
 
My problem is that the GeoTiff has been georefernced as UTM ellps=GRS80 datum=WGS84 incorrectly.
 
My intent is to gdalwarp the image to latlong WGS84.
 
I have tried for the better part of a day to attempt to override or otherwise correct the georeferncing. Without success.
 
I have been very successful with GDAL in the past, but this has stopped me.
 
The problem is that I can't seem to fully define AMG "enough" to allow GDALwarp to reproject the image. It seems to default to the source as being UTM WGS84.
 
I attempted to gdal_translate the image using the corrected definition and then gdalwarp image, but that also failed.
 
the definition I have been using is "+proj=tmerc +ellps=aust_SA +lat_0=0 +lon_0=147 +x_0=500000 +y_0=10000000 +k=0.9996 +south"
 
regards
Andrew