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<p>On Wednesday 26 October 2005 02:39 pm, Kees Krikke wrote:</p>
<p>> Thanks Oscar,</p>
<p>></p>
<p> ...</p>
<p>> So if a coordinate system use Oblique Stereographic projection (epsg code</p>
<p>> 9809) you need to know if the epsg (Roussilhe) or usgs implementation</p>
<p>> should be used.</p>
<p></p>
<p>The Oblique Stereographic code in EPSG 7.2 <span style="font-weight:600;text-decoration:underline">IS NOT</span> Roussilhe. The EPSG code is the Double Projection method using conformal conversion of the ellipsoid to the sphere and then using the spherical stereographic projection. Roussilhe is not mentioned in the EPSG 7.2 publication.</p>
<p></p>
<p>Libproj4 provides for three (3) <span style="text-decoration:underline">different</span> Oblique Stereographics projections: "+proj=stere" for the USGS version (Snyder), "+proj=sterea" for the Double Projection method and "+proj=rouss" based upon Roussilhe's 1922 paper.</p>
<p>The description of the +proj=sterea projection in the libproj4 manual looks different from the EPSG description because the process is organized so that the conformal conversion software is also used by the Krovak and Swiss projections.</p>
<p></p>
<p>The results of a shell script shows lproj's operation on the EPSG example:</p>
<p></p>
<p>Double Projection Stereographic --- libproj4 +proj=sterea</p>
<p>lproj script parameters:</p>
<p>+a=6377397.155 +rf=299.15281 +lat_0=52d9'22.178 +lon_0=5d23'15.5 +k_0=0.9999079+x_0=155000 +y_0=463000</p>
<p>comparison data from EPSG 7.2 : 196105.283 557057.739</p>
<p>lproj forward projection</p>
<p>196105.283 557057.739 from EPSG 7.2 196105.283 557057.739</p>
<p>Forward->Inverse cycle-binary intermediate</p>
<p>6dE 53dN</p>
<p></p>
<p>Thus thread gets a bit confusing at times and I feel that misuse of nomenclature is causing some of the confusion.</p>
<p>...</p>
<p></p>
<p>-- </p>
<p>Jerry and the low riders:Daisy May and Joshua</p>
<p>"The being cannot be termed rational or virtuous,</p>
<p>who obeys any authority, but that of reason."</p>
<p>---Mary Wollstonecraft 1792</p>
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