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<p>Paul Ramsey wrote:
<blockquote TYPE=CITE>Interesting. Learn something new every day. For the
benefit of all, here
<br>is the ESRI WTK definition of NTF_Paris_France_I <27581>
<p>PROJCS[
<br> "NTF_Paris_France_I",
<br> GEOGCS["GCS_NTF_Paris",
<br> DATUM["D_NTF",
<br> SPHEROID["Clarke_1880_IGN",6378249.2,293.46602]
<br> ],
<br> PRIMEM["Paris",2.337229166666667],
<br> UNIT["Grad",0.015707963267948967]
<br> ],
<br> PROJECTION["Lambert_Conformal_Conic"],
<br> PARAMETER["False_Easting",600000],
<br> PARAMETER["False_Northing",1200000],
<br> PARAMETER["Central_Meridian",0],
<br> PARAMETER["Standard_Parallel_1",55],
<br> PARAMETER["Scale_Factor",0.999877341],
<br> PARAMETER["Latitude_Of_Origin",55],
<br> UNIT["Meter",1]
<br>]
<p>Here is the definition I got from OGR converting from WKT to Proj4:
<p> +proj=lcc
<br> +lat_1=55.000000000
<br> +lat_2=0.000000000
<br> +lat_0=55.000000000
<br> +lon_0=0.000000000
<br> +x_0=600000.000
<br> +y_0=1200000.000
<br> +a=6378249.200
<br> +b=6356515.000
<br> +units=m
<p>As noted, there is no flag that the angular units are gradians-paris,
so
<br>they'll be misinterpretted as degrees-greenwich.</blockquote>
...
<p>All longitude is from the geographic coordinate origin <b>which is not</b>
<br><b>explicitly defined.</b> So it can just as well be relative
to the French origin.
<br>The later, proj, definitioin is not in error unless one assumes that
the
<br>Greenwich origin is used.
<p>To use Greenwich data with proj one can merge the 2.33 correction into
<br>the lon_0 factor.
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