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<p class=MsoNormal><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D">Brilliant. Thanks a lot, Uwe. This is all I want to know.<o:p></o:p></span></p>
<p class=MsoNormal><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D"><o:p> </o:p></span></p>
<p class=MsoNormal><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D">Yes, you are right that I only recently started working on these
data again although I have only got one day off for Christmas (in China) </span><span style="font-size:11.0pt;font-family:Wingdings;color:#1F497D">J</span><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"><o:p></o:p></span></p>
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color:#1F497D"><o:p> </o:p></span></p>
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<p class=MsoNormal><b><span style="font-size:10.0pt;font-family:"Tahoma","sans-serif"">From:</span></b><span style="font-size:10.0pt;font-family:"Tahoma","sans-serif""> Schmitz, Uwe [via
OSGeo.org] [mailto:<a href="/user/SendEmail.jtp?type=node&node=5931827&i=0" target="_top" rel="nofollow">[hidden email]</a>] <br>
<b>Sent:</b> 17 January 2011 09:22<br>
<b>To:</b> Heng Feng<br>
<b>Subject:</b> AW: [gdal-dev] An issue about using GDALWARP to
dotheNTv2transformation<o:p></o:p></span></p>
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<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>Heng, <br>
<br>
> Hi Uwe, <br>
> <br>
> Hope you had a wonderful Christmas break. <br>
<br>
Yes, thank you (but I have the impression that mine has <br>
been shorter than yours ;-)) <o:p></o:p></p>
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<p class=MsoNormal><br>
> Regarding the issue about the NTv2 transformation, <br>
> the map data provider has confirmed that the raster <br>
> data do cover some areas which are outside the Germany <br>
> map, hence the area of the grid shift file. I have <br>
> taken your second suggestion and ignore the coordinates <br>
> outside BeTA2007 grid. However, by running the suggested <br>
> command on some raster data, this time I have got the <br>
> message "Inverse grid shift iteration failed, presumably <br>
> at grid edge. Using first approximation." Do you know <br>
> why I am having this message? Do I need to worry about it? <br>
> <o:p></o:p></p>
</div>
<p class=MsoNormal style="margin-bottom:12.0pt">No! NTv2 is based on a grid of
shift values from System A <br>
to System B (DHDN -> ETRS89 in your case). For the other <br>
direction (B->A, or ETRS89->DHDN) the shift value is <br>
calculated by an iterative approach. Near the grid edges it's <br>
possible that during the iteartion the coordinates fall <br>
outside the grid. I would imagine that this is the case <br>
for the message you see. <br>
<br>
Assuming you don't need precise transformation results <br>
outside the BeTA2007 grid, you can safely ignore this <br>
message. <br>
<br>
Regards <br>
Uwe <br>
_______________________________________________ <br>
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