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<p class=MsoNormal><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D">Thanks for your suggestions, Uwe. They are surely very helpful. I
will try them out and let you know if I need any further help from you.<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>
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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""> Uwe Schmitz [via
OSGeo.org] [mailto:<a href="/user/SendEmail.jtp?type=node&node=5863050&i=0" target="_top" rel="nofollow">[hidden email]</a>] <br>
<b>Sent:</b> 23 December 2010 19:47<br>
<b>To:</b> Heng Feng<br>
<b>Subject:</b> RE: [gdal-dev] An issue about using GDALWARP to do
theNTv2transformation<o:p></o:p></span></p>
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<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>Heng, <o:p></o:p></p>
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<p class=MsoNormal><b>heng.feng wrote:<o:p></o:p></b></p>
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<div>
<p class=MsoNormal>Hi Uwe, <br>
<br>
Thanks for your reply. The l0.tif file does not contain any georeferenced
information. However, I have run the GDALINFO command on another raster data
file which is in the same map data set provided by the customer and hence is
supposed to be georeferenced in the way as the l0.tif file. The command output
is sent as attached. As mentioned before, I also did the NTv2 transformation on
this raster data file (Notrufzonen_50m_v11_6_EPOS.tif) with the same
GDALWARP command and the same grid shift file. I also got a lot of error
messages saying that some coordinates are outside the area of the grid shift
file. And with the "+x_0=500000" parameter, the output error messages
are much less than the ones with the "+x_0=4500000" parameter. <br>
<br>
Thanks for your help again. <o:p></o:p></p>
</div>
</div>
<p class=MsoNormal style="margin-bottom:12.0pt">from your screenshot I see that
georeference information <br>
of your file seems to be OK. So forget about my comment <br>
about missing meridian prefixes, that's not the case. <br>
<br>
But ..., your file is very large (the extent, not the size). <br>
Please notice, that due to the nature of the NTv2 approach <br>
it is not possible to calculate coordinates outside the <br>
extent of the grid. The BeTA2007 grid covers longitudes <br>
between 5d30' to 15d40' East. Your Screenshot of gdalinfo <br>
shows that the longitude of the upper left corner is <br>
4d54'45.24" East and hence outside the BeTA2007 grid. <br>
<br>
OK, what can you do? BeTA2007 has submeter accuracy and <br>
I believe, that you don't need it for you data (one pixel <br>
covers 50m*50m). So you can try the 7-Parameter Helmert <br>
approach described by EPSG::1776 with "+towgs84=..." <br>
Parameter instead of "+nadgrids=...". This will result in <br>
errors of max. 3m in comparison to BeTA2007. Not that <br>
bad for your data ;-) <br>
<br>
Another way is to specify the "null" grid as fall back for <br>
coordinates outside the BeTA2007 grid, like so: <br>
<br>
... +nadgrids=C:\fh\comar ch\BETA2007.gsb,null <br>
<br>
But be aware that coordinates outside the BeTA2007 grid experience <br>
no datum shift. This may result in errors up to 200m. <br>
<br>
Hope that helps. <br>
<br>
Regards <br>
Uwe <o:p></o:p></p>
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<p class=MsoNormal><span style="font-size:8.5pt;font-family:"Tahoma","sans-serif";
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