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It is difficult for me to comment on the PROJ.4 aspects of this problem as the example<BR>
involves a datum shift and ancillary computations that are not part of PROJ.4 as I<BR>
define it. Thus blaming Albers projection seems specious at the moment. Can someone<BR>
reduce the operation to its parts:<BR>
<BR>
1. inverse of Albers to geographic<BR>
2. datum conversion<BR>
3. forward to UTM<BR>
<BR>
I can comment on 1 and 3.<BR>
<BR>
Thank-you.<BR>
<BR>
On Wed, 2005-06-29 at 14:10 -0400, Frank Warmerdam wrote:
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<FONT COLOR="#000000">Gerald, or others,</FONT>
<FONT COLOR="#000000">In bug report:</FONT>
<FONT COLOR="#000000"> <A HREF="http://bugzilla.remotesensing.org/show_bug.cgi?id=877">http://bugzilla.remotesensing.org/show_bug.cgi?id=877</A></FONT>
<FONT COLOR="#000000">a user reports that albers reprojection seems to not match what</FONT>
<FONT COLOR="#000000">he expects. Based on his test datasets, I get:</FONT>
<FONT COLOR="#000000">input (+proj=aea +lat_1=29.5 +lat_2=45.5 +lat_0=23 +lon_0=-96 </FONT>
<FONT COLOR="#000000"> +x_0=0 +y_0=0 +ellps=clrk66 +units=m +no_defs):</FONT>
<FONT COLOR="#000000"> 581715E, 1070148N</FONT>
<FONT COLOR="#000000">output (+proj=utm +zone=16 +datum=NAD27):</FONT>
<FONT COLOR="#000000"> 239958E, 3602624N</FONT>
<FONT COLOR="#000000">output (expected for UTM 16 NAD27):</FONT>
<FONT COLOR="#000000"> 239958E, 3602624N</FONT>
<FONT COLOR="#000000">As you can see the PROJ.4 translation seems to match well in</FONT>
<FONT COLOR="#000000">X but not in Y. The user reports the expected information based</FONT>
<FONT COLOR="#000000">on reprojection with Global Mapper and ArcGIS. </FONT>
<FONT COLOR="#000000">Can anyone comment on whether these values are in a region </FONT>
<FONT COLOR="#000000">of reasonably validity for the UTM and Albers projection code?</FONT>
<FONT COLOR="#000000">Can anyone provide external verification one way or the other for</FONT>
<FONT COLOR="#000000">these albers to UTM conversions? </FONT>
<FONT COLOR="#000000">Feel free to look into the bug report for details. </FONT>
<FONT COLOR="#000000">Best regards,</FONT>
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_____________________________________________________________
Jerry and the Low Riders: Daisy Mae and Joshua
"The most certain test by which we judge whether a country is
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---Lord Acton, 1907
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