[Gdal-dev] gdalwarp parameters

[Shoaib Burq]

Hi

I want to reproject an image which is currently in NAD83 Z21 to a
custom projection.
I am having some trouble getting the proj4 parameters to a custom
projection right.
I have been given the ArcGRID's prj.adf file and it looks like this:


Projection    MERCATOR
Datum         WGS84
Spheroid      WGS84
Units         METERS
Zunits        NO
Xshift        0.0
Yshift        0.0
Parameters
-180  0  0.0 /* longitude of central meridian
  45  0  0.0 /* latitude of true scale
0.0 /* false easting (meters)
0.0 /* false northing (meters)

Could some one please suggest the correct proj4 directive to give to
gdalwarp's -t_srs ?

I have tried
  "+proj=merc +lat_0=45.0 +lon_0=-180 +x_0=0 +y_0=0 +datum=WGS84
+ellps=WGS84 +units=m"
but this is not giving me the correct extents.

Thanks for any pointers
shoaib