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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">HI Gdal,<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">Just wanted to follow this up.<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">Cheers,<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">Ian<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 lang="EN-US" style="font-size:10.0pt;font-family:"Tahoma","sans-serif"">From:</span></b><span lang="EN-US" style="font-size:10.0pt;font-family:"Tahoma","sans-serif""> Ian Reese
<br>
<b>Sent:</b> Monday, 12 March 2018 6:55 p.m.<br>
<b>To:</b> gdal-dev@lists.osgeo.org<br>
<b>Subject:</b> gdal_merge.py<o:p></o:p></span></p>
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<p class="MsoNormal" style="margin-bottom:12.0pt"><span style="font-size:10.0pt;font-family:"Tahoma","sans-serif";color:black">Hi Gdal,<br>
<br>
I am having some issues with gdal_merge.py. <br>
<br>
When I merge two tifs together, the original nodata value is converted to 0, no matter what that original no data. Here is my test case:<br>
<br>
Data:<br>
<br>
<a href="https://data.linz.govt.nz/x/9iitN4">https://data.linz.govt.nz/x/9iitN4</a> DEM_BA32_3501_2013<br>
<br>
<a href="https://data.linz.govt.nz/x/WLurgo">https://data.linz.govt.nz/x/WLurgo</a> DEM_BA31_3550_2013<br>
<br>
Running gdalinfo on both files reveals a 'nodata' value of -9999. When I view the data as individual files in QGIS, the 'nodata' regions are confirmed as 'nodata' or '-9999' and are rendered transparent.<br>
<br>
Next I run gdal_merge.py:<br>
<br>
gdal_merge.py -o test_merge.tif *.tif<br>
<br>
I also try:<br>
<br>
gdal_merge.py -n -9999 -a_nodata -9999 -o test_merge_wnodata.tif *.tif<br>
<br>
No matter which variation of merge I run, those regions that once contained 'nodata' or '-9999' are converted to '0' and the nodata value is not retained after the merge. When I load the test_merge_wnodata.tif into QGIS, those regions once containing 'nodata',
are now filled with 0 and rendered as such.<br>
<br>
Maybe this is a bug or am I using gdal_merge.py improperly.<br>
<br>
Cheers,<br>
<br>
Ian<br>
<br>
<o:p></o:p></span></p>
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