<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>There is no such thing as a spherical datum. Not since the late 1600s, anyway. Before then ... beats me. For the past 300 years or so, there has been no such thing as a spherical datum. Period. There were these two little French "expeditions" - one to Lapland & one to Peru that proved Newton's theory that the earth is best approximated by an <STRONG>oblate</STRONG> ellipsoid of revolution and <STRONG><U>not </U></STRONG>by the French theory of a <STRONG>prolate</STRONG> ellipsoid of revolution - Published in 1716.</FONT></DIV>
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<DIV dir=ltr><FONT size=2>I publish monthly in <EM>Photogrammetric Engineering and Remote Sensing</EM>. Each month my column on the Grids and Datums of the world cover a different country's geodetic history, it's coordinate systems that comprise its datums and grid systems, etc. The American Society for Photogrammetry and Remote Sensing has been publishing my columns at their website (for free downloads) in pdf files since 1997. Right now, I'm more than halfway through the world. This month is on Saudi Arabia, next month is on Sakhalin Island, Russia.</FONT></DIV>
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<DIV dir=ltr><FONT size=2>I post messages, comments, opinions, advice, jokes, and occasional insults (to liberals) on the POB forum frequently. (Current messages are 3,400+.)</FONT></DIV>
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<DIV dir=ltr><FONT size=2>Check out the website at the bottom of my signature block.</FONT></DIV>
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<DIV dir=ltr><FONT size=2>Clifford J. Mugnier, C.P., C.M.S.<BR>Past National Director (2006-2008),<BR>Photogrammetric Applications Division<BR>American Society for Photogrammetry and Remote Sensing <BR>and <BR>Chief of Geodesy,<BR>CENTER FOR GEOINFORMATICS <BR>Department of Civil Engineering <BR>Patrick F. Taylor Hall 3223A<BR>LOUISIANA STATE UNIVERSITY <BR>Baton Rouge, LA 70803<BR>Voice and Facsimile: (225) 578-8536 [Academic] <BR>Voice and Facsimile: (225) 578-4474 [Research] <BR>Honorary Life Member of the <BR>Louisiana Society of Professional Surveyors <BR>Member Emeritus of the ASPRS <BR>Member of the Americas Petroleum Survey Group<BR>======================================================<BR></FONT><A href="https://email.lsu.edu/exchweb/bin/redir.asp?URL=https://email.lsu.edu/exchweb/bin/redir.asp?URL=https://email.lsu.edu/exchweb/bin/redir.asp?URL=https://email.lsu.edu/exchweb/bin/redir.asp?URL=https://email.lsu.edu/exchweb/bin/redir.asp?URL=https://email.lsu.edu/exchweb/bin/redir.asp?URL=https://email.lsu.edu/exchweb/bin/redir.asp?URL=https://email.lsu.edu/exchweb/bin/redir.asp?URL=https://email.lsu.edu/exchweb/bin/redir.asp?URL=https://email.lsu.edu/exchweb/bin/redir.asp?URL=https://email.lsu.edu/exchweb/bin/redir.asp?URL=https://email.lsu.edu/exchweb/bin/redir.asp?URL=https://email.lsu.edu/exchweb/bin/redir.asp?URL=https://email.lsu.edu/exchweb/bin/redir.asp?URL=https://email.lsu.edu/exchweb/bin/redir.asp?URL=https://email.lsu.edu/exchweb/bin/redir.asp?URL=https://email.lsu.edu/exchweb/bin/redir.asp?URL=https://email.lsu.edu/exchweb/bin/redir.asp?URL=https://email.lsu.edu/exchweb/bin/redir.asp?URL=https://email.lsu.edu/exchweb/bin/redir.asp?URL=https://email.lsu.edu/exchweb/bin/redir.asp?URL=https://email.lsu.edu/exchweb/bin/redir.asp?URL=https://email.ls" target=_blank><FONT face="Times New Roman, Times"><FONT size=2>http://www.asprs.org/resources/GRIDS/</FONT></A></FONT><BR><FONT face="Times New Roman, Times" size=2>======================================================</FONT></DIV></DIV>
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<FONT face=Tahoma size=2><B>From:</B> proj-bounces@lists.maptools.org on behalf of Landon Blake<BR><B>Sent:</B> Mon 25-Aug-08 11:27<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 class=MsoNormal><FONT face=Arial size=2><SPAN style="FONT-SIZE: 10pt; FONT-FAMILY: Arial">Clifford wrote: “Absolute spatial positions between disparate datums are lost when using datum-specific coordinates in a single spherical projection.”</SPAN></FONT></P>
<P class=MsoNormal><FONT face=Arial size=2><SPAN style="FONT-SIZE: 10pt; FONT-FAMILY: Arial"></SPAN></FONT> </P>
<P class=MsoNormal><FONT face=Arial size=2><SPAN style="FONT-SIZE: 10pt; FONT-FAMILY: Arial">Are you talking about moving a position between two spherical datums, or any transformation which involves a spherical datum?”</SPAN></FONT></P>
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<P class=MsoNormal><FONT face=Arial size=2><SPAN style="FONT-SIZE: 10pt; FONT-FAMILY: Arial">Clifford wrote: “I suggest you read some of my past columns, in particular "The Basics of Datums."”</SPAN></FONT></P>
<P class=MsoNormal><FONT face=Arial size=2><SPAN style="FONT-SIZE: 10pt; FONT-FAMILY: Arial"></SPAN></FONT> </P>
<P class=MsoNormal><FONT face=Arial size=2><SPAN style="FONT-SIZE: 10pt; FONT-FAMILY: Arial">Where could we find these columns?</SPAN></FONT></P>
<P class=MsoNormal><FONT face=Arial size=2><SPAN style="FONT-SIZE: 10pt; FONT-FAMILY: Arial"></SPAN></FONT> </P>
<P class=MsoNormal><FONT face=Arial size=2><SPAN style="FONT-SIZE: 10pt; FONT-FAMILY: Arial">Do you also post messages on the POB forum occasionally?</SPAN></FONT></P>
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<P class=MsoNormal><FONT face=Arial size=2><SPAN style="FONT-SIZE: 10pt; FONT-FAMILY: Arial">Thanks,</SPAN></FONT></P>
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<P class=MsoNormal><FONT face=Arial size=2><SPAN style="FONT-SIZE: 10pt; FONT-FAMILY: Arial">The Sunburned Surveyor</SPAN></FONT></P>
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<P class=MsoNormal><B><FONT face=Tahoma size=2><SPAN style="FONT-WEIGHT: bold; FONT-SIZE: 10pt; FONT-FAMILY: Tahoma">From:</SPAN></FONT></B><FONT face=Tahoma size=2><SPAN style="FONT-SIZE: 10pt; FONT-FAMILY: Tahoma"> proj-bounces@lists.maptools.org [mailto:proj-bounces@lists.maptools.org] <B><SPAN style="FONT-WEIGHT: bold">On Behalf Of </SPAN></B>Clifford J Mugnier<BR><B><SPAN style="FONT-WEIGHT: bold">Sent:</SPAN></B> Monday, August 25, 2008 9:03 AM<BR><B><SPAN style="FONT-WEIGHT: bold">To:</SPAN></B> PROJ.4 and general Projections Discussions<BR><B><SPAN style="FONT-WEIGHT: bold">Subject:</SPAN></B> RE: [Proj] WGS84 to Sphere Inconsistency Between Proj Versions</SPAN></FONT></P></DIV>
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<P class=MsoNormal><FONT face="Times New Roman" color=black size=2><SPAN style="FONT-SIZE: 10pt; COLOR: black">Absolute spatial positions between disparate datums are lost when using datum-specific coordinates in a single spherical projection. I suggest you read some of my past columns, in particular "The Basics of Datums." This is not an appropriate venue to get into a detailed tutorial on geometric geodesy and it's historical foundations.</SPAN></FONT></P></DIV>
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<P class=MsoNormal><FONT face="Times New Roman" size=2><SPAN style="FONT-SIZE: 10pt">In regards to your logic, I'll leave the rationalizations to you. What I said stands as is.</SPAN></FONT></P></DIV>
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<P class=MsoNormal><FONT face="Times New Roman" size=2><SPAN style="FONT-SIZE: 10pt">C. Mugnier</SPAN></FONT></P></DIV></DIV>
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<P class=MsoNormal style="MARGIN-BOTTOM: 12pt"><B><FONT face=Tahoma size=2><SPAN style="FONT-WEIGHT: bold; FONT-SIZE: 10pt; FONT-FAMILY: Tahoma">From:</SPAN></FONT></B><FONT face=Tahoma size=2><SPAN style="FONT-SIZE: 10pt; FONT-FAMILY: Tahoma"> proj-bounces@lists.maptools.org on behalf of Mikael Rittri<BR><B><SPAN style="FONT-WEIGHT: bold">Sent:</SPAN></B> Mon 25-Aug-08 10:26<BR><B><SPAN style="FONT-WEIGHT: bold">To:</SPAN></B> PROJ.4 and general Projections Discussions<BR><B><SPAN style="FONT-WEIGHT: bold">Subject:</SPAN></B> RE: [Proj] WGS84 to Sphere Inconsistency Between Proj Versions</SPAN></FONT></P></DIV>
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<P class=MsoNormal><FONT face=Arial size=3><SPAN style="FONT-SIZE: 12pt; FONT-FAMILY: Arial">Dear Mr. Mugnier, </SPAN></FONT></P>
<P class=MsoNormal><FONT face=Arial size=3><SPAN style="FONT-SIZE: 12pt; FONT-FAMILY: Arial">you wrote </SPAN></FONT></P>
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<P class=MsoNormal><FONT face=Arial size=3><SPAN style="FONT-SIZE: 12pt; FONT-FAMILY: Arial">>When diddling with spherical projections, the concept of "DATUM" is entirely inappropriate. </SPAN></FONT></P>
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<P class=MsoNormal><FONT face=Arial size=3><SPAN style="FONT-SIZE: 12pt; FONT-FAMILY: Arial">which made me quite confused, because</SPAN></FONT></P>
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<P class=MsoNormal><FONT face=Arial size=3><SPAN style="FONT-SIZE: 12pt; FONT-FAMILY: Arial">1) I think what you wrote is absurd, and </SPAN></FONT></P>
<P class=MsoNormal><FONT face=Arial size=3><SPAN style="FONT-SIZE: 12pt; FONT-FAMILY: Arial">2) I know well that you are an expert in geodesy. </SPAN></FONT></P>
<P class=MsoNormal><FONT face="Times New Roman" size=3><SPAN style="FONT-SIZE: 12pt"></SPAN></FONT> </P>
<P class=MsoNormal><FONT face=Arial size=3><SPAN style="FONT-SIZE: 12pt; FONT-FAMILY: Arial">But Hillel said, "the shamefast is not apt to learn", so let me go on. </SPAN></FONT></P>
<P class=MsoNormal><FONT face="Times New Roman" size=3><SPAN style="FONT-SIZE: 12pt"></SPAN></FONT> </P>
<P class=MsoNormal><FONT face=Arial size=3><SPAN style="FONT-SIZE: 12pt; FONT-FAMILY: Arial">I suppose you require more properties of a geodetic datum than I care about. </SPAN></FONT></P>
<P class=MsoNormal><FONT face=Arial size=3><SPAN style="FONT-SIZE: 12pt; FONT-FAMILY: Arial">For me, a geodetic datum is essentially a way to georeference a map (or at least </SPAN></FONT></P>
<P class=MsoNormal><FONT face=Arial size=3><SPAN style="FONT-SIZE: 12pt; FONT-FAMILY: Arial">to georeference the graticule on the map.) Surely you are not saying that if a map </SPAN></FONT></P>
<P class=MsoNormal><FONT face=Arial size=3><SPAN style="FONT-SIZE: 12pt; FONT-FAMILY: Arial">uses a spherical projection, then its graticule cannot be georeferenced. </SPAN></FONT></P>
<P class=MsoNormal><FONT face="Times New Roman" size=3><SPAN style="FONT-SIZE: 12pt"></SPAN></FONT> </P>
<P class=MsoNormal><FONT face=Arial size=3><SPAN style="FONT-SIZE: 12pt; FONT-FAMILY: Arial">I have also been wondering why the EPSG people, when describing the web Mercator, </SPAN></FONT></P>
<P class=MsoNormal><FONT face=Arial size=3><SPAN style="FONT-SIZE: 12pt; FONT-FAMILY: Arial">are careful to say that the geodetic datum is not WGS84 but something spherical </SPAN></FONT></P>
<P class=MsoNormal><FONT face=Arial size=3><SPAN style="FONT-SIZE: 12pt; FONT-FAMILY: Arial">that is not a true datum. </SPAN></FONT></P>
<P class=MsoNormal><FONT face="Times New Roman" size=3><SPAN style="FONT-SIZE: 12pt"></SPAN></FONT> </P>
<P class=MsoNormal><FONT face=Arial size=3><SPAN style="FONT-SIZE: 12pt; FONT-FAMILY: Arial">As I see it, the projection machinery has to treat the earth as a sphere, while the </SPAN></FONT></P>
<P class=MsoNormal><FONT face=Arial size=3><SPAN style="FONT-SIZE: 12pt; FONT-FAMILY: Arial">datum shift machinery has to treat it as an ellipsoid. And why not? In Carmenta Engine,</SPAN></FONT></P>
<P class=MsoNormal><FONT face=Arial size=3><SPAN style="FONT-SIZE: 12pt; FONT-FAMILY: Arial">the Mercator class has a switch that lets you choose between ellipsoidal and spherical </SPAN></FONT></P>
<P class=MsoNormal><FONT face=Arial size=3><SPAN style="FONT-SIZE: 12pt; FONT-FAMILY: Arial">formulas. So the projection can ignore the flattening of the ellipsoid, but the datum shift </SPAN></FONT></P>
<P class=MsoNormal><FONT face=Arial size=3><SPAN style="FONT-SIZE: 12pt; FONT-FAMILY: Arial">machinery will not. </SPAN></FONT></P>
<P class=MsoNormal><FONT face="Times New Roman" size=3><SPAN style="FONT-SIZE: 12pt"></SPAN></FONT> </P>
<P class=MsoNormal><FONT face=Arial size=3><SPAN style="FONT-SIZE: 12pt; FONT-FAMILY: Arial">Are you (and EPSG) reasoning like this: </SPAN></FONT></P>
<P class=MsoNormal><FONT face=Arial size=3><SPAN style="FONT-SIZE: 12pt; FONT-FAMILY: Arial"> (1.) all projections must be implemented by ellipsoidal formulas, so </SPAN></FONT></P>
<P class=MsoNormal><FONT face=Arial size=3><SPAN style="FONT-SIZE: 12pt; FONT-FAMILY: Arial"> (2.) the only way to emulate spherical formulas is to supply an earth </SPAN></FONT></P>
<P class=MsoNormal><FONT face=Arial size=3><SPAN style="FONT-SIZE: 12pt; FONT-FAMILY: Arial"> model that is a sphere from the beginning; and no proper datum </SPAN></FONT></P>
<P class=MsoNormal><FONT face=Arial size=3><SPAN style="FONT-SIZE: 12pt; FONT-FAMILY: Arial"> can be spherical. </SPAN></FONT></P>
<P class=MsoNormal><FONT face=Arial size=3><SPAN style="FONT-SIZE: 12pt; FONT-FAMILY: Arial">? </SPAN></FONT></P>
<P class=MsoNormal><FONT face=Arial size=3><SPAN style="FONT-SIZE: 12pt; FONT-FAMILY: Arial">If so, then I agree that (2) follows from (1), and I agree that proper datums should </SPAN></FONT></P>
<P class=MsoNormal><FONT face=Arial size=3><SPAN style="FONT-SIZE: 12pt; FONT-FAMILY: Arial">not be spherical. But I do not agree that (1) is true. </SPAN></FONT></P>
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<P class=MsoNormal><FONT face=Arial size=3><SPAN style="FONT-SIZE: 12pt; FONT-FAMILY: Arial">Best regards,</SPAN></FONT></P>
<P><FONT face="Times New Roman" size=2><SPAN style="FONT-SIZE: 10pt">--<BR>Mikael Rittri<BR>Carmenta AB<BR>Box 11354<BR>SE-404 28 Göteborg<BR>Visitors: Sankt Eriksgatan 5<BR>SWEDEN<BR>Tel: +46-31-775 57 37<BR>Mob: +46-703-60 34 07<BR>mikael.rittri@carmenta.com<BR>www.carmenta.com</SPAN></FONT> </P>
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<P class=MsoNormal style="MARGIN-BOTTOM: 12pt"><B><FONT face=Tahoma size=2><SPAN style="FONT-WEIGHT: bold; FONT-SIZE: 10pt; FONT-FAMILY: Tahoma">From:</SPAN></FONT></B><FONT face=Tahoma size=2><SPAN style="FONT-SIZE: 10pt; FONT-FAMILY: Tahoma"> proj-bounces@lists.maptools.org [mailto:proj-bounces@lists.maptools.org] <B><SPAN style="FONT-WEIGHT: bold">On Behalf Of </SPAN></B>Clifford J Mugnier<BR><B><SPAN style="FONT-WEIGHT: bold">Sent:</SPAN></B> den 22 augusti 2008 05:45<BR><B><SPAN style="FONT-WEIGHT: bold">To:</SPAN></B> PROJ.4 and general Projections Discussions; PROJ.4 and general Projections Discussions<BR><B><SPAN style="FONT-WEIGHT: bold">Subject:</SPAN></B> RE: [Proj] WGS84 to Sphere Inconsistency Between Proj Versions</SPAN></FONT></P>
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<P class=MsoNormal><FONT face="Times New Roman" size=2><SPAN style="FONT-SIZE: 10pt">When didling with spherical projections, the concept of "DATUM" is entirely inappropriate.</SPAN></FONT></P></DIV>
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<P class=MsoNormal><FONT face="Times New Roman" size=2><SPAN style="FONT-SIZE: 10pt">Cliff Mugnier</SPAN></FONT></P></DIV>
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<P class=MsoNormal><FONT face="Times New Roman" size=2><SPAN style="FONT-SIZE: 10pt">LOUISIANA</SPAN></FONT><FONT size=2><SPAN style="FONT-SIZE: 10pt"> STATE UNIVERSITY</SPAN></FONT></P></DIV></DIV>
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<P class=MsoNormal style="MARGIN-BOTTOM: 12pt"><B><FONT face=Tahoma size=2><SPAN style="FONT-WEIGHT: bold; FONT-SIZE: 10pt; FONT-FAMILY: Tahoma">From:</SPAN></FONT></B><FONT face=Tahoma size=2><SPAN style="FONT-SIZE: 10pt; FONT-FAMILY: Tahoma"> proj-bounces@lists.maptools.org on behalf of Frank Warmerdam<BR><B><SPAN style="FONT-WEIGHT: bold">Sent:</SPAN></B> Thu 21-Aug-08 22:38<BR><B><SPAN style="FONT-WEIGHT: bold">To:</SPAN></B> PROJ.4 and general Projections Discussions<BR><B><SPAN style="FONT-WEIGHT: bold">Subject:</SPAN></B> Re: [Proj] WGS84 to Sphere Inconsistency Between Proj Versions</SPAN></FONT></P></DIV>
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<P><FONT face="Times New Roman" size=2><SPAN style="FONT-SIZE: 10pt">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></SPAN></FONT></P></DIV></DIV></DIV><BR><BR><FONT face=Arial><FONT size=1><STRONG>Warning:<BR></STRONG>Information provided via electronic media is not guaranteed against defects including translation and transmission errors. If the reader is not the intended recipient, you are hereby notified that any dissemination, distribution or copying of this communication is strictly prohibited. If you have received this information in error, please notify the sender immediately.</FONT></FONT> </DIV></BODY></HTML>