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<DIV dir=ltr align=left><SPAN class=096084906-05082009><FONT face=Arial
color=#0000ff size=2>John,</FONT></SPAN></DIV>
<DIV dir=ltr align=left><SPAN class=096084906-05082009><FONT face=Arial
color=#0000ff size=2></FONT></SPAN> </DIV>
<DIV dir=ltr align=left><SPAN class=096084906-05082009><FONT face=Arial
color=#0000ff size=2>This looks like the kind of north/south error you get when
the transform gets the ellipsoids wrong, with most serious displacement if
a one of the ellipsoids is a sphere.</FONT></SPAN></DIV>
<DIV dir=ltr align=left><SPAN class=096084906-05082009><FONT face=Arial
color=#0000ff size=2></FONT></SPAN> </DIV>
<DIV dir=ltr align=left><SPAN class=096084906-05082009><FONT face=Arial
color=#0000ff size=2>I am guessing that your transform ignores the ellipsoid
change, try see what you get if you specify GRS 1980 also in your target CS. You
can use cs2cs on single points to check the transform.</FONT></SPAN></DIV>
<DIV dir=ltr align=left><SPAN class=096084906-05082009><FONT face=Arial
color=#0000ff size=2></FONT></SPAN> </DIV>
<DIV dir=ltr align=left><SPAN class=096084906-05082009><FONT face=Arial
color=#0000ff size=2>Also, verify that 6378137 is the proper Earth radius both
for your sphere and for the GRS80 spheroid, this is usually not the
case.</FONT></SPAN></DIV>
<DIV dir=ltr align=left><SPAN class=096084906-05082009><FONT face=Arial
color=#0000ff size=2></FONT></SPAN> </DIV>
<DIV dir=ltr align=left><SPAN class=096084906-05082009><FONT face=Arial
color=#0000ff size=2>Sorry I couldnt pinpoint he exact command to solve, it's
too long since I dealt with these issues :-)</FONT></SPAN></DIV>
<DIV dir=ltr align=left><SPAN class=096084906-05082009><FONT face=Arial
color=#0000ff size=2></FONT></SPAN> </DIV>
<DIV dir=ltr align=left><SPAN class=096084906-05082009><FONT face=Arial
color=#0000ff size=2>Sjur</FONT></SPAN></DIV>
<DIV dir=ltr align=left><SPAN class=096084906-05082009><FONT face=Arial
color=#0000ff size=2></FONT></SPAN> </DIV>
<DIV dir=ltr align=left><SPAN class=096084906-05082009><FONT face=Arial
color=#0000ff size=2></FONT></SPAN> </DIV><BR>
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<HR tabIndex=-1>
<FONT face=Tahoma size=2><B>From:</B> gdal-dev-bounces@lists.osgeo.org
[mailto:gdal-dev-bounces@lists.osgeo.org] <B>On Behalf Of </B>John
Hayes<BR><B>Sent:</B> 5 august 2009 02:55<BR><B>To:</B>
gdal-dev@lists.osgeo.org<BR><B>Subject:</B> [gdal-dev] reprojection to WGS
1984 Web Mercator<BR></FONT><BR></DIV>
<DIV></DIV>
<DIV class=Section1>
<P class=MsoNormal>Hi,<o:p></o:p></P>
<P class=MsoNormal> I’m having problems warping an image to WGS 1984 Web
Mercator. The lat/long center point moved south by 10 arc-minutes.
Does anyone have some suggestion on how to fix this?<o:p></o:p></P>
<P class=MsoNormal><o:p> </o:p></P>
<P class=MsoNormal> I’m pretty sure the USA_Contiguous_Equidistant_Conic
transform worked fine because I looked at the lag/long in Google Earth and saw
the same buildings.<o:p></o:p></P>
<P class=MsoNormal><o:p> </o:p></P>
<P class=MsoNormal>I’ve also done the transform in two steps Source SRS to
WGS84 and WGS84 to WGS 1984 Web Mercator but get the same
answer.<o:p></o:p></P>
<P class=MsoNormal><o:p> </o:p></P>
<P class=MsoNormal>Bellow is the command line I used to warp the image and
info dumps of the before and after images.<o:p></o:p></P>
<P class=MsoNormal><o:p> </o:p></P>
<P class=MsoNormal>$ gdalwarp -t_srs ESRI::wm.prj Athens_RGB_CEC1FT_200303.tif
Athens_RGB_CEC1FT_200303-wm.tif<o:p></o:p></P>
<P class=MsoNormal>Creating output file that is 7455P x 6882L.<o:p></o:p></P>
<P class=MsoNormal>Processing input file
Athens_RGB_CEC1FT_200303.tif.<o:p></o:p></P>
<P class=MsoNormal>0...10...20...30...40...50...60...70...80...90...100 -
done.<o:p></o:p></P>
<P class=MsoNormal><o:p> </o:p></P>
<P class=MsoNormal>Files: Athens_RGB_CEC1FT_200303.tif<o:p></o:p></P>
<P class=MsoNormal>Size is 6683, 6024<o:p></o:p></P>
<P class=MsoNormal>Coordinate System is:<o:p></o:p></P>
<P class=MsoNormal>PROJCS["USA_Contiguous_Equidistant_Conic",<o:p></o:p></P>
<P class=MsoNormal> GEOGCS["NAD83",<o:p></o:p></P>
<P class=MsoNormal>
DATUM["North_American_Datum_1983",<o:p></o:p></P>
<P
class=MsoNormal>
SPHEROID["GRS 1980",6378137,298.2572221010002,<o:p></o:p></P>
<P
class=MsoNormal>
AUTHORITY["EPSG","7019"]],<o:p></o:p></P>
<P
class=MsoNormal>
AUTHORITY["EPSG","6269"]],<o:p></o:p></P>
<P class=MsoNormal>
PRIMEM["Greenwich",0],<o:p></o:p></P>
<P class=MsoNormal>
UNIT["degree",0.0174532925199433],<o:p></o:p></P>
<P class=MsoNormal>
AUTHORITY["EPSG","4269"]],<o:p></o:p></P>
<P class=MsoNormal>
PROJECTION["Equidistant_Conic"],<o:p></o:p></P>
<P class=MsoNormal>
PARAMETER["standard_parallel_1",33],<o:p></o:p></P>
<P class=MsoNormal>
PARAMETER["standard_parallel_2",45],<o:p></o:p></P>
<P class=MsoNormal>
PARAMETER["latitude_of_center",39],<o:p></o:p></P>
<P class=MsoNormal>
PARAMETER["longitude_of_center",-96],<o:p></o:p></P>
<P class=MsoNormal>
PARAMETER["false_easting",0],<o:p></o:p></P>
<P class=MsoNormal>
PARAMETER["false_northing",0],<o:p></o:p></P>
<P class=MsoNormal> UNIT["metre",1,<o:p></o:p></P>
<P class=MsoNormal>
AUTHORITY["EPSG","9001"]]]<o:p></o:p></P>
<P class=MsoNormal>Origin =
(1157874.742488616100000,-478125.149393160190000)<o:p></o:p></P>
<P class=MsoNormal>Pixel Size =
(0.169893858067214,-0.169893858067214)<o:p></o:p></P>
<P class=MsoNormal>Corner Coordinates:<o:p></o:p></P>
<P class=MsoNormal>Upper Left ( 1157874.742, -478125.149) (
83d24'42.40"W, 33d58'12.44"N)<o:p></o:p></P>
<P class=MsoNormal>Lower Left ( 1157874.742, -479148.590) (
83d24'47.89"W, 33d57'39.54"N)<o:p></o:p></P>
<P class=MsoNormal>Upper Right ( 1159010.143, -478125.149) ( 83d23'58.53"W,
33d58'7.37"N)<o:p></o:p></P>
<P class=MsoNormal>Lower Right ( 1159010.143, -479148.590) ( 83d24'4.02"W,
33d57'34.47"N)<o:p></o:p></P>
<P class=MsoNormal>Center ( 1158442.443,
-478636.870) ( 83d24'23.21"W, 33d57'53.46"N)<o:p></o:p></P>
<P class=MsoNormal><o:p> </o:p></P>
<P class=MsoNormal>Files: Athens_RGB_CEC1FT_200303-wm.tif<o:p></o:p></P>
<P class=MsoNormal>Size is 7455, 6882<o:p></o:p></P>
<P class=MsoNormal>Coordinate System is:<o:p></o:p></P>
<P class=MsoNormal>PROJCS["WGS_1984_Web_Mercator",<o:p></o:p></P>
<P class=MsoNormal>
GEOGCS["GCS_WGS_1984_Major_Auxiliary_Sphere",<o:p></o:p></P>
<P class=MsoNormal>
DATUM["WGS_1984_Major_Auxiliary_Sphere",<o:p></o:p></P>
<P
class=MsoNormal>
SPHEROID["WGS_1984_Major_Auxiliary_Sphere",6378137,0]],<o:p></o:p></P>
<P class=MsoNormal>
PRIMEM["Greenwich",0],<o:p></o:p></P>
<P class=MsoNormal>
UNIT["degree",0.0174532925199433]],<o:p></o:p></P>
<P class=MsoNormal>
PROJECTION["Mercator_1SP"],<o:p></o:p></P>
<P class=MsoNormal>
PARAMETER["central_meridian",0],<o:p></o:p></P>
<P class=MsoNormal>
PARAMETER["scale_factor",1],<o:p></o:p></P>
<P class=MsoNormal>
PARAMETER["false_easting",0],<o:p></o:p></P>
<P class=MsoNormal>
PARAMETER["false_northing",0],<o:p></o:p></P>
<P class=MsoNormal> UNIT["metre",1,<o:p></o:p></P>
<P class=MsoNormal>
AUTHORITY["EPSG","9001"]]]<o:p></o:p></P>
<P class=MsoNormal>Origin =
(-9285526.535261498800000,4000908.274406374400000)<o:p></o:p></P>
<P class=MsoNormal>Pixel Size =
(0.204760916615493,-0.204760916615493)<o:p></o:p></P>
<P class=MsoNormal>Corner Coordinates:<o:p></o:p></P>
<P class=MsoNormal>Upper Left (-9285526.535, 4000908.274) (
83d24'47.89"W, 33d47'31.24"N)<o:p></o:p></P>
<P class=MsoNormal>Lower Left (-9285526.535, 3999499.110) (
83d24'47.89"W, 33d46'53.36"N)<o:p></o:p></P>
<P class=MsoNormal>Upper Right (-9284000.043, 4000908.274) ( 83d23'58.53"W,
33d47'31.24"N)<o:p></o:p></P>
<P class=MsoNormal>Lower Right (-9284000.043, 3999499.110) ( 83d23'58.53"W,
33d46'53.36"N)<o:p></o:p></P>
<P class=MsoNormal>Center (-9284763.289,
4000203.692) ( 83d24'23.21"W, 33d47'12.30"N)<o:p></o:p></P>
<P class=MsoNormal><o:p> </o:p></P>
<P class=MsoNormal><o:p> </o:p></P>
<P class=MsoNormal><o:p> </o:p></P>
<P class=MsoNormal><o:p> </o:p></P>
<P class=MsoNormal><o:p> </o:p></P>
<P class=MsoNormal><o:p> </o:p></P></DIV></BLOCKQUOTE></BODY></HTML>