<HTML dir=ltr><HEAD><TITLE>Re: [Proj] WGS84 to ED50</TITLE>
<META http-equiv=Content-Type content="text/html; charset=unicode">
<META content="MSHTML 6.00.2900.3199" name=GENERATOR></HEAD>
<BODY>
<DIV id=idOWAReplyText8963 dir=ltr>
<DIV dir=ltr><FONT face="Times New Roman" color=#000000 size=2>I have been reading this thread with some amusement, as datum shifts are only a compromise to begin with, and attempting to achieve better than 1-2 meters with even a 7-parameter transformation is a totally unreasonable expectation. The original data for the classical datum is not that good!</FONT></DIV>
<DIV dir=ltr><FONT size=2></FONT> </DIV>
<DIV dir=ltr><FONT size=2>Matching another transformation is a reasonable expectation, but it could be (likely), that the "client" is attempting to match actual observations with Trimble/Applanix gear working directly in WGS84 rather than a Trimble/Applanix algorithm! European Datum 50 (ED50) was "cooked up" in 1950 by Geodesists at the U.S. Army Map Service after WWII using geodetic surveys of Spain and Portugal performed over the prior 50-75 years! That stuff wasn't that good!</FONT></DIV>
<DIV dir=ltr><FONT size=2></FONT> </DIV>
<DIV dir=ltr><FONT size=2>Try reading my columns on the Grids and Datums of Spain and Portugal at: <A href="http://www.ASPRS.org/GRIDS">www.ASPRS.org/GRIDS</A> and you'll get a better appreciation of the complexity of the problem being sought with a mere 7-parameter transformation. (Spain is July, 2000, and Portugal is April, 2002)</FONT></DIV>
<DIV dir=ltr><FONT size=2></FONT> </DIV>
<DIV dir=ltr><FONT size=2>Combining Applanix and Trimble gear is cutting-edge geodetic equipment commonly used for Real Time Kinneatic (RTK) Aerial Photography for hair-splitting accuracy. That stuff is working directly in WGS84 Broadcast Ephemeris and is then re-adjusted in post-processed mode with the Precise Ephemeris a couple weeks later.</FONT></DIV>
<DIV dir=ltr><FONT size=2></FONT> </DIV>
<DIV dir=ltr><FONT size=2>That's NOT going to "match" data that's 75-100 years old!</FONT></DIV>
<DIV dir=ltr><FONT size=2></FONT> </DIV>
<DIV dir=ltr><STRONG>PROJ4 is a cartographic tool and is not a geodetic panacea.</STRONG></DIV>
<DIV dir=ltr><FONT size=2></FONT> </DIV>
<DIV dir=ltr>
<DIV><FONT size=2>
<DIV dir=ltr><FONT face="Times New Roman" size=2>Clifford J. Mugnier, C.P., C.M.S.</FONT></DIV>
<DIV dir=ltr><FONT face="Times New Roman" size=2>LSU Student ASCE Chapter Faculty Advisor</FONT></DIV>
<DIV dir=ltr><FONT face="Times New Roman" size=2>and<BR>National Director (2006-2008),<BR>Photogrammetric Applications Division<BR>American Society for Photogrammetry and Remote Sensing </FONT></DIV>
<DIV dir=ltr><FONT face="Times New Roman" size=2>and </FONT></DIV>
<DIV dir=ltr><FONT face="Times New Roman" size=2>Chief of Geodesy,<BR>CENTER FOR GEOINFORMATICS </FONT></DIV>
<DIV dir=ltr><FONT face="Times New Roman" size=2>Department of Civil Engineering </FONT></DIV>
<DIV dir=ltr><FONT face="Times New Roman" size=2>CEBA 3223A<BR>LOUISIANA STATE UNIVERSITY </FONT></DIV>
<DIV dir=ltr><FONT face="Times New Roman" size=2>Baton Rouge, LA 70803<BR> Home: (225) 819-0939<BR> Cell: (225) 236-2327<BR>Voice and Facsimile: (225) 578-8536 [Academic] </FONT></DIV>
<DIV dir=ltr><FONT face="Times New Roman" size=2>Voice and Facsimile: (225) 578-4474 [Research] </FONT></DIV>
<DIV dir=ltr><FONT face="Times New Roman" size=2>Honorary Life Member of the </FONT></DIV>
<DIV dir=ltr><FONT face="Times New Roman" size=2>Louisiana Society of Professional Surveyors </FONT></DIV>
<DIV dir=ltr><FONT face="Times New Roman" size=2>Member Emeritus of the ASPRS </FONT></DIV>
<DIV dir=ltr><FONT size=2><FONT face="Times New Roman">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=http://www.asprs.org/resources/GRIDS/" target=_blank><FONT face="Times New Roman">http://www.asprs.org/resources/GRIDS/</FONT></A><BR><FONT face="Times New Roman">======================================================</FONT></FONT></DIV></FONT></DIV></DIV></DIV>
<DIV dir=ltr><BR>
<HR tabIndex=-1>
<FONT face=Tahoma size=2><B>From:</B> proj-bounces@lists.maptools.org on behalf of Roger Oberholtzer<BR><B>Sent:</B> Mon 19-Nov-07 16:24<BR><B>To:</B> PROJ.4 and general Projections Discussions<BR><B>Subject:</B> Re: [Proj] WGS84 to ED50<BR></FONT><BR></DIV>
<DIV>
<P><FONT size=2>On Mon, 2007-11-19 at 13:57 -0800, Hamish wrote:<BR><BR>> > The Applanix provides this information on their calculations:<BR>> ...<BR>> > Coordinate transformation from WGS84 to mapping frame datum<BR>> > dX = 125.098545; dY = 76.000054; dZ = 156.198703; f =<BR>> > 0.999991695369;<BR>> > R1 = 0.000000000000; R2 = 0.000000000000; R3 = -0.000005473550;<BR>><BR>><BR>> The above R3,f values makes me hesitate a little, but it may be that Applanix<BR>> and Trimble are both preforming a less precise 3-term transform, while PROJ is<BR>> doing a more precise 7-term transform. That would certainly explain a 1-4m<BR>> error.<BR><BR>My understanding is that Applanix is doing a 7 parameter transform. What<BR>I am unsure of is how to get proj to do the same. If it is the default,<BR>then I am curious how the 7 parameters are specified. Are these the<BR>values in the +towgs84 option? I have another library for this that is<BR>using 7 config values for its 7 parameter transform, and I would expect<BR>to see similar values in proj.<BR><BR>> Rather than trust either software or method implicitly, it would be better to<BR>> judge the results based on published test points from the Spainish and/or<BR>> Portuguese government mapping office, and double check the validity of the<BR>> 7-terms params from an official document too. Depending on national convention,<BR>> the +- signs of the terms may or may not be switched.<BR><BR>I have been trying to do just that. The person I am doing this for in<BR>Madrid has provided the test values I am trying to duplicate. Anyone<BR>know of an official source of test values for Spain?<BR><BR>--<BR>Roger Oberholtzer<BR><BR>OPQ Systems / Ramböll RST<BR>Ramböll Sverige AB<BR>Kapellgränd 7<BR>P.O. Box 4205<BR>SE-102 65 Stockholm, Sweden<BR><BR>Tel: Int +46 8-615 60 20<BR>Fax: Int +46 8-31 42 23<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>