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<DIV dir=ltr align=left><SPAN class=062263520-26102005><FONT
face=Sans>Gerald,</FONT></SPAN></DIV>
<DIV dir=ltr align=left><SPAN class=062263520-26102005><FONT
face=Sans></FONT></SPAN> </DIV>
<DIV dir=ltr align=left><SPAN class=062263520-26102005><FONT face=Sans>Thanks!
This clarifies a lot. I thought that Roussilhe was the same as the Oblique
Stereographic code in EPSG 7.2 because the epsg database
v6.8 states Roussilhe as an alias of Oblique Stereographic
.</FONT></SPAN></DIV>
<DIV dir=ltr align=left><SPAN class=062263520-26102005></SPAN> </DIV>
<DIV dir=ltr align=left><SPAN class=062263520-26102005><FONT
face=Sans>Regards,</FONT></SPAN></DIV>
<DIV dir=ltr align=left><SPAN class=062263520-26102005></SPAN> </DIV>
<DIV dir=ltr align=left><SPAN class=062263520-26102005><FONT
face=Sans>Kees</FONT></SPAN></DIV>
<DIV dir=ltr align=left><SPAN class=062263520-26102005><FONT
face=Sans></FONT></SPAN> </DIV>
<DIV dir=ltr align=left><SPAN class=062263520-26102005><FONT
face=Sans></FONT></SPAN> </DIV><BR>
<DIV class=OutlookMessageHeader lang=en-us dir=ltr align=left>
<HR tabIndex=-1>
<FONT face=Tahoma><B>From:</B> Gerald I. Evenden
[mailto:gerald.evenden@verizon.net] <BR><B>Sent:</B> 26 October 2005
22:26<BR><B>To:</B> kees.krikke@wanadoo.nl; PROJ.4 and general Projections
Discussions<BR><B>Subject:</B> Re: [Proj] Implementation(s) for Oblique
Stereographic<BR></FONT><BR></DIV>
<DIV></DIV>
<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></BODY></HTML>