<HTML dir=ltr><HEAD><TITLE>Re: [Proj] WGS84 to Sphere Inconsistency Between Proj Versions</TITLE>
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<DIV dir=ltr><FONT face="Times New Roman" color=#000000 size=2>When didling with spherical projections, the concept of "DATUM" is entirely inappropriate.</FONT></DIV>
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<DIV dir=ltr><FONT size=2>Cliff Mugnier</FONT></DIV>
<DIV dir=ltr><FONT size=2>LOUISIANA STATE UNIVERSITY</FONT></DIV></DIV>
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<FONT face=Tahoma size=2><B>From:</B> proj-bounces@lists.maptools.org on behalf of Frank Warmerdam<BR><B>Sent:</B> Thu 21-Aug-08 22:38<BR><B>To:</B> PROJ.4 and general Projections Discussions<BR><B>Subject:</B> Re: [Proj] WGS84 to Sphere Inconsistency Between Proj Versions<BR></FONT><BR></DIV>
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<P><FONT size=2>Faron Anslow wrote:<BR>> I just ran this:<BR>><BR>> cs2cs +proj=latlong +datum=WGS84 +to +proj=lcc +lat_1=50 +lat_2=50<BR>> +lat_0=50 +lon_0=-107 +a=6371200.0000000000 +es=0.0 +f=0.0<BR>> +towgs84=0,0,0 -r<BR>><BR>> on:<BR>> 70.933 -8.667<BR>><BR>> and got:<BR>> 2873633.37 4593659.18 -12148.43<BR>><BR>> which is my original matlab answer and that from the old proj4.4. Now,<BR>> the question is if forcing the datum shift with +towgs=0,0,0 is<BR>> appropriate? Doesn't +towgs48 conflict with/override the spherical<BR>> projection definition?<BR><BR>Faron,<BR><BR>I can't imagine any situation other than an effort to match old answers<BR>where it makes sense to apply a plain lat/long on a sphere to lat/long on an<BR>ellipsoid conversion the way this is doing.<BR><BR>If you want the lat/long values computed from the lcc projection based on<BR>a sphere to treated as WGS84, then use +nadgrids=@null (or in 4.6.0 just<BR>omit a datum specifier for the lcc projection). This is *likely* want<BR>you want.<BR><BR>Best regards,<BR>--<BR>---------------------------------------+--------------------------------------<BR>I set the clouds in motion - turn up | Frank Warmerdam, warmerdam@pobox.com<BR>light and sound - activate the windows | <A href="http://pobox.com/~warmerdam">http://pobox.com/~warmerdam</A><BR>and watch the world go round - Rush | Geospatial Programmer for Rent<BR><BR>_______________________________________________<BR>Proj mailing list<BR>Proj@lists.maptools.org<BR><A href="http://lists.maptools.org/mailman/listinfo/proj">http://lists.maptools.org/mailman/listinfo/proj</A><BR></FONT></P></DIV></BODY></HTML>