[Proj] MapInfo coordsys to proj.4 syntax

[Anthony Dunk]

Hi Paul,

The MapInfo "French Lambert II Carto\p27582" has a false easting of
600000 and a false northing of 2200000, so that may be the one your
user is using.

Your parameters look correct, so I don't know why you're getting
coordinates which are so far out.

When I project my test point (2.33333E, 48.8667N) using my own program
(which uses PROJ) I get 599766.9 mE, 2429819.6 mN. I also tried this in
MapInfo and I get pretty close to the same coordinates (599765.59 mE,
2429819.22 mN).

I suspect the problem is that the UTM and Lambert Conformal Conic
projections distort your raster image differently. Also check what UTM
zone you're using. I think you should be using UTM Zone 31 Northern
Hemisphere.

Cheers,
Anthony.


--- Paul Surgeon <surgpub at telkomsa.net> wrote:

> That helped a bit Anthony although it's not quite there yet.
> 
> I changed the false northing from 200000 to 2200000 because the
> MapInfo user 
> created their own coordsys definition and didn't use a stock NTF one.
> Using 
> the standard NTF false northing of 200000 shifts the data about 20
> degrees 
> too far to the North.
> 
> I tried :
> gdal_translate -a_srs "+proj=lcc +lon_0=2.337229166667 +lat_0=46.8 
> +lat_1=45.898918964419 +lat_2=47.696014502038 +x_0=600000
> +y_0=2200000 
> +a=6378249.2 +rf=293.4660213 +towgs84=-168,-60,320,0,0,0,0 +units=m
> +no_defs" 
> temp1.tif temp2.tif
> 
> Now the raster data is only about 480 meters too far to the South and
> 48 
> meters too far to the East (rough estimate).
> So something still isn't quite right.
> 
> Paul
> 
> 
> On Tuesday 06 June 2006 02:00, Anthony Dunk wrote:
> > Hi Paul,
> >
> > NTF uses a prime meridian of 2.337229166667 (Paris), not Greenwich.
> >
> > Below is the correct PROJ string for converting from Lat/Lon WGS84
> to
> > projected NTF (French Lambert II Centre).
> >
> > cs2cs +proj=latlong +a=6378137.0 +rf=298.257223563 +towgs84=0,0,0
> +to
> > +proj=lcc +lon_0=2.337229166667 +lat_0=46.8 +lat_1=45.898918964419
> > +lat_2=47.696014502038 +x_0=600000 +y_0=200000 +a=6378249.2
> > +rf=293.4660213 +towgs84=-168,-60,320,0,0,0,0 +units=m +no_defs
> >
> > Using this an input point of 2.33333E, 48.8667N is projected to
> > 599766.90 mE, 429819.60 mN. This agrees with MapInfo's projection
> of
> > the same point.
> >
> > Anthony.
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