<div dir="ltr">Thanks. The code to which I was referring in my original mail was that used by gdaltransform. I just hadn't found the API part.</div><br><div class="gmail_quote"><div dir="ltr" class="gmail_attr">On Fri, Dec 10, 2021 at 12:45 PM <<a href="mailto:Matt.Wilkie@yukon.ca">Matt.Wilkie@yukon.ca</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">





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<p class="MsoNormal"><span style="font-size:11pt;font-family:Calibri,sans-serif;color:rgb(31,73,125)">and <a href="https://gdal.org/programs/gdaltransform.html" target="_blank">https://gdal.org/programs/gdaltransform.html</a><u></u><u></u></span></p>
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<p class="MsoNormal"><span lang="EN-US" style="font-size:10pt;font-family:Calibri,sans-serif;color:rgb(31,73,125)">-Matt</span><i><span style="font-size:10pt;font-family:Calibri,sans-serif;color:rgb(31,73,125)"><u></u><u></u></span></i></p>
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<p class="MsoNormal"><b><span lang="EN-US" style="font-size:11pt;font-family:Calibri,sans-serif">From:</span></b><span lang="EN-US" style="font-size:11pt;font-family:Calibri,sans-serif"> gdal-dev <<a href="mailto:gdal-dev-bounces@lists.osgeo.org" target="_blank">gdal-dev-bounces@lists.osgeo.org</a>>
<b>On Behalf Of </b>Simon Eves<br>
<b>Sent:</b> December 10, 2021 12:21 PM<br>
<b>To:</b> Yann-Sebastien Tremblay-Johnston <<a href="mailto:yanns.tremblay@gmail.com" target="_blank">yanns.tremblay@gmail.com</a>><br>
<b>Cc:</b> gdal dev <<a href="mailto:gdal-dev@lists.osgeo.org" target="_blank">gdal-dev@lists.osgeo.org</a>><br>
<b>Subject:</b> Re: [gdal-dev] Transforming Raster Points from GeoTIFF with GCPs<u></u><u></u></span></p>
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<pre><strong><span style="font-family:"Courier New";color:black">*** External email: Do not click on links or attachments except from trusted senders. ***<u></u><u></u></span></strong></pre>
<pre><strong><span style="font-family:"Courier New";color:black">******************************************************************************************</span></strong><span style="color:black"><u></u><u></u></span></pre>
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<p class="MsoNormal"><span style="font-size:10pt;font-family:Calibri,sans-serif">Aha! That's the bit I hadn't found. Thank you! :)<u></u><u></u></span></p>
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<p class="MsoNormal"><span style="font-size:10pt;font-family:Calibri,sans-serif">On Fri, Dec 10, 2021 at 10:38 AM Yann-Sebastien Tremblay-Johnston <<a href="mailto:yanns.tremblay@gmail.com" target="_blank">yanns.tremblay@gmail.com</a>> wrote:<u></u><u></u></span></p>
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<p class="MsoNormal"><span style="font-size:10pt;font-family:Calibri,sans-serif">Simon,<u></u><u></u></span></p>
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<p class="MsoNormal"><span style="font-size:10pt;font-family:Calibri,sans-serif">See the Transformer API, in particular <a href="https://gdal.org/api/gdal_alg.html?highlight=transformer#_CPPv419GDALTransformerFunc" target="_blank">https://gdal.org/api/gdal_alg.html?highlight=transformer#_CPPv419GDALTransformerFunc</a>
 (or gdal.Transformer in Python). <u></u><u></u></span></p>
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<p class="MsoNormal"><span style="font-size:10pt;font-family:Calibri,sans-serif">Sebastien<u></u><u></u></span></p>
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<p class="MsoNormal"><span style="font-size:10pt;font-family:Calibri,sans-serif">On Fri, Dec 10, 2021 at 10:24 AM Simon Eves <<a href="mailto:simon.eves@omnisci.com" target="_blank">simon.eves@omnisci.com</a>> wrote:<u></u><u></u></span></p>
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<p class="MsoNormal"><span style="font-size:10pt;font-family:Calibri,sans-serif">So we have a GeoTiFF of Sentinel-1 imagery which `gdalinfo` reports as having a GCP projection with 210 points, which we'd (perhaps naively?!) like to import directly, transforming
 to WGS84 on the fly.<u></u><u></u></span></p>
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<p class="MsoNormal"><span style="font-size:10pt;font-family:Calibri,sans-serif">Obviously a simple OGRSpatialReference/OGRCoordinateTransformation transform isn't going to do anything, so I assume we have to do the GCP transform manually.<u></u><u></u></span></p>
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<p class="MsoNormal"><span style="font-size:10pt;font-family:Calibri,sans-serif">I found the GCPCoordinateTransformation class and other supporting code in ogr2ogr_lib.cpp as used by gdaltransform, which seems to do what we need, but of course it's not
 in the core GDAL library so we can't "just use it".<u></u><u></u></span></p>
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<p class="MsoNormal"><span style="font-size:10pt;font-family:Calibri,sans-serif">Before embarking on lifting out that code to implement an on-the-fly transformer in our system, I just wanted to make sure I wasn't missing any functionality elsewhere that
 would make it easier.<u></u><u></u></span></p>
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<p class="MsoNormal"><span style="font-size:10pt;font-family:Calibri,sans-serif">It may also be more efficient to just kick off a gdalwarp to pre-convert the file so we can just import it with no transformation required, but that seems ugly unless it's
 gonna be WAY more efficient?<u></u><u></u></span></p>
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<p class="MsoNormal"><span style="font-size:10pt;font-family:Calibri,sans-serif">Thanks,<u></u><u></u></span></p>
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<p class="MsoNormal"><b><span style="font-size:10pt;font-family:Arial,sans-serif;color:rgb(14,76,144)">Simon Eves</span></b><u></u><u></u></p>
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<p class="MsoNormal"><span style="font-size:10pt;font-family:Arial,sans-serif;color:rgb(0,0,1)">Senior Graphics Engineer, Rendering Group<br>
100 Montgomery St (5th Floor), San Francisco, CA 94104, USA</span><u></u><u></u></p>
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<p class="MsoNormal"><span style="font-size:10pt;font-family:Calibri,sans-serif">_______________________________________________<br>
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<p class="MsoNormal"><span style="font-size:10pt;font-family:Arial,sans-serif;color:rgb(0,0,1)">Senior Graphics Engineer, Rendering Group<br>
100 Montgomery St (5th Floor), San Francisco, CA 94104, USA</span><u></u><u></u></p>
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</blockquote></div><br clear="all"><div><br></div>-- <br><div dir="ltr" class="gmail_signature"><div dir="ltr"><div><div dir="ltr"><div><div dir="ltr"><div><div dir="ltr"><div style="margin:0px;padding:0px 0px 20px;width:2544px;font-family:Roboto,RobotoDraft,Helvetica,Arial,sans-serif;font-size:medium"><div><div style="font-size:12.8px;margin:8px 0px 0px;padding:0px"><div><div dir="ltr"><span><font color="#888888"><div dir="ltr"><div dir="ltr"><div dir="ltr"><div dir="ltr"><div dir="ltr"><div dir="ltr"><div dir="ltr"><div dir="ltr"><div dir="ltr"><div dir="ltr"><table cellpadding="0" cellspacing="0" border="0" style="font-family:Times;width:2544px"><tbody><tr><td align="left" style="vertical-align:top;font-size:0px"><table cellpadding="0" cellspacing="0" border="0"><tbody><tr><td align="left" style="padding:0px 15px 0px 0px;vertical-align:middle"><font face="arial, helvetica, sans-serif" size="2"><a href="http://www.omnisci.com/" target="_blank"><img src="http://www2.omnisci.com/l/298412/2018-09-18/3sqpg/298412/61753/OmniSci_Email_Header2.png"></a><br></font></td><td align="left" style="padding:0px 0px 0px 15px;vertical-align:top"><table cellpadding="0" cellspacing="0" border="0" style="width:215px"><tbody><tr><td align="left" style="vertical-align:top"><span style="white-space:nowrap;color:rgb(0,0,1)"><span style="color:rgb(14,76,144);font-weight:700"><font face="arial, helvetica, sans-serif" size="2">Simon Eves</font></span></span></td></tr><tr><td align="left" style="vertical-align:top"><table cellpadding="0" cellspacing="0" border="0"><tbody><tr><td align="left" style="vertical-align:top"><span style="white-space:nowrap;color:rgb(0,0,1)"><font face="arial, helvetica, sans-serif" size="2">Senior Graphics Engineer, Rendering Group<br>100 Montgomery St (5th Floor), San Francisco, CA 94104, USA<br></font></span></td></tr></tbody></table></td></tr><tr><td align="left" style="vertical-align:top"><table cellpadding="0" cellspacing="0" border="0"><tbody><tr><td align="left" style="padding:0px;vertical-align:top"><br></td><td align="left" style="padding:0px;vertical-align:top"><br></td></tr><tr><td align="left" style="padding:0px;vertical-align:top"><span style="white-space:nowrap;color:rgb(0,0,1)"><font face="arial, helvetica, sans-serif" size="2">Email: <a href="mailto:simon.eves@omnisci.com" target="_blank">simon.eves@omnisci.com</a> | Cell: </font></span></td><td align="left" style="padding:0px;vertical-align:top"><span style="white-space:nowrap;color:rgb(0,0,1)"><font face="arial, helvetica, sans-serif" size="2">+1 (415) 902-1996</font></span></td></tr></tbody></table><br></td></tr></tbody></table></td></tr></tbody></table></td></tr></tbody></table><br></div></div></div></div></div></div></div></div></div></div></font></span></div><div></div></div></div><div></div></div></div></div></div></div></div></div></div></div></div>