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<p class="MsoNormal"><span style="color:#1F497D">I found in did that the GDALGCPsToGeoTransform using the pixels values for calculation:<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D">At gdal_misc.cpp :<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D">padfGeoTransform[1] = (pasGCPs[1].dfGCPX - pasGCPs[0].dfGCPX) / (pasGCPs[1].</span><span style="color:#E46C0A;mso-style-textfill-fill-color:#E46C0A;mso-style-textfill-fill-alpha:100.0%"><span style="color:windowtext">dfGCPPixel
</span></span><span style="color:#1F497D">- pasGCPs[0].</span><span style="color:#E46C0A;mso-style-textfill-fill-color:#E46C0A;mso-style-textfill-fill-alpha:100.0%"><span style="color:windowtext">dfGCPPixel</span></span><span style="color:#1F497D">);<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D">padfGeoTransform[0] = pasGCPs[0].dfGCPX - pasGCPs[0].</span><span style="color:#E46C0A;mso-style-textfill-fill-color:#E46C0A;mso-style-textfill-fill-alpha:100.0%"><span style="color:windowtext">dfGCPPixel
</span></span><span style="color:#1F497D">* </span><span style="color:#E46C0A;mso-style-textfill-fill-color:#E46C0A;mso-style-textfill-fill-alpha:100.0%"><span style="color:windowtext">padfGeoTransform[1]</span></span><span style="color:#1F497D">;<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D">in this case, the question is what is the best practice for the problem I published (sometimes rectangle, sometimes not).<o:p></o:p></span></p>
<p class="MsoNormal"><span style="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";color:windowtext">From:</span></b><span style="font-size:10.0pt;font-family:"Tahoma","sans-serif";color:windowtext"> gdal-dev [mailto:gdal-dev-bounces@lists.osgeo.org]
<b>On Behalf Of </b>Bar Ori<br>
<b>Sent:</b> 18 November 2015 12:00<br>
<b>To:</b> Ari Jolma<br>
<b>Cc:</b> gdal-dev@lists.osgeo.org<br>
<b>Subject:</b> Re: [gdal-dev] GCPsToGeoTransform returns wrong values<o:p></o:p></span></p>
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<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><span style="color:#1F497D">Thanks Ari for your reply.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D">In my situation, sometimes I am working with rectangles and sometimes not. Depends the source of information.<o:p></o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span style="color:#1F497D">I thought to always use the GCPs as follows:<o:p></o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span style="color:#1F497D">In case my shape has rectangular form, so the dataSet.GetGCPCount() will return me “0” and I will use the dataSet.GetGeoTransform(), otherwise, will use the dataSet.GetGCPs().<o:p></o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span style="color:#1F497D">The issue is that for setting the GCPs, I must put the coordinate in the middle of pixel (that is why I subtract “0.5”). If I wouldn’t, so yes, the geotransform values would be correct.<o:p></o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span style="color:#1F497D">Is it a bad practice? Should I figure out the shape from start and to take two different steps?<o:p></o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span style="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";color:windowtext">From:</span></b><span style="font-size:10.0pt;font-family:"Tahoma","sans-serif";color:windowtext"> gdal-dev
<a href="mailto:[mailto:gdal-dev-bounces@lists.osgeo.org]">[mailto:gdal-dev-bounces@lists.osgeo.org]</a>
<b>On Behalf Of </b>Ari Jolma<br>
<b>Sent:</b> 18 November 2015 11:35<br>
<b>To:</b> <a href="mailto:gdal-dev@lists.osgeo.org">gdal-dev@lists.osgeo.org</a><br>
<b>Subject:</b> Re: [gdal-dev] GCPsToGeoTransform returns wrong values<o:p></o:p></span></p>
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<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal" style="margin-bottom:12.0pt">Bar,<br>
<br>
I think you are setting the GCPs up wrongly if you want them to be at the corners.<br>
<br>
GCP(LeftDown.X, LeftDown.Y, LeftDown.Z, Height - 0.5, null, "4") does not have 0 before Height-0.5.<br>
<br>
GCPsToGeoTransform checks the special case of GCPs in rectangular shape and in top-left, top-right, bottom-right, bottom-left order and returns the exact transform the dataset has.<br>
<br>
I'm not sure if it makes sense to have real values for the pixel coordinates although they are real values.<br>
<br>
Best,<br>
<br>
Ari<o:p></o:p></p>
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<p class="MsoNormal">On 18.11.2015 09:32, Bar Ori wrote:<o:p></o:p></p>
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<blockquote style="margin-top:5.0pt;margin-bottom:5.0pt">
<p class="MsoNormal">Hi,<o:p></o:p></p>
<p class="MsoNormal">I noticed something that for me looks weird and I would like to know maybe I am doing something wrong.<o:p></o:p></p>
<p class="MsoNormal">If not, how should I overcome this behavior.<o:p></o:p></p>
<p class="MsoNormal"> <o:p></o:p></p>
<p class="MsoNormal">I set 4 GCPs as follows:<o:p></o:p></p>
<p class="MsoNormal"> <o:p></o:p></p>
<p class="MsoNormal" style="text-autospace:none"><span style="font-size:9.5pt;font-family:Consolas;color:blue">var</span><span style="font-size:9.5pt;font-family:Consolas"> gcps =
</span><span style="font-size:9.5pt;font-family:Consolas;color:blue">new</span><span style="font-size:9.5pt;font-family:Consolas">[]</span><o:p></o:p></p>
<p class="MsoNormal" style="text-autospace:none"><span style="font-size:9.5pt;font-family:Consolas">{</span><o:p></o:p></p>
<p class="MsoNormal" style="text-autospace:none"><span style="font-size:9.5pt;font-family:Consolas;color:blue">new</span><span style="font-size:9.5pt;font-family:Consolas"> GCP(LeftUp.X, LeftUp.Y, LeftUp.Z, 0.5, 0.5,
</span><span style="font-size:9.5pt;font-family:Consolas;color:blue">null</span><span style="font-size:9.5pt;font-family:Consolas">,
</span><span style="font-size:9.5pt;font-family:Consolas;color:#A31515">"1"</span><span style="font-size:9.5pt;font-family:Consolas">),</span><o:p></o:p></p>
<p class="MsoNormal" style="text-autospace:none"><span style="font-size:9.5pt;font-family:Consolas;color:blue">new</span><span style="font-size:9.5pt;font-family:Consolas"> GCP(RightUp.X, RightUp.Y, RightUp.Z, Width - 0.5, 0.5,
</span><span style="font-size:9.5pt;font-family:Consolas;color:blue">null</span><span style="font-size:9.5pt;font-family:Consolas">,
</span><span style="font-size:9.5pt;font-family:Consolas;color:#A31515">"2"</span><span style="font-size:9.5pt;font-family:Consolas">),</span><o:p></o:p></p>
<p class="MsoNormal" style="text-autospace:none"><span style="font-size:9.5pt;font-family:Consolas;color:blue">new</span><span style="font-size:9.5pt;font-family:Consolas"> GCP(RightDown.X, RightDown.Y, RightDown.Z, Width - 0.5, Height - 0.5,
</span><span style="font-size:9.5pt;font-family:Consolas;color:blue">null</span><span style="font-size:9.5pt;font-family:Consolas">,
</span><span style="font-size:9.5pt;font-family:Consolas;color:#A31515">"3"</span><span style="font-size:9.5pt;font-family:Consolas">),</span><o:p></o:p></p>
<p class="MsoNormal" style="text-autospace:none"><span style="font-size:9.5pt;font-family:Consolas;color:blue">new</span><span style="font-size:9.5pt;font-family:Consolas"> GCP(LeftDown.X, LeftDown.Y, LeftDown.Z, Height - 0.5,
</span><span style="font-size:9.5pt;font-family:Consolas;color:blue">null</span><span style="font-size:9.5pt;font-family:Consolas">,
</span><span style="font-size:9.5pt;font-family:Consolas;color:#A31515">"4"</span><span style="font-size:9.5pt;font-family:Consolas">)</span><o:p></o:p></p>
<p class="MsoNormal" style="text-autospace:none"><span style="font-size:9.5pt;font-family:Consolas">};</span><o:p></o:p></p>
<p class="MsoNormal" style="text-autospace:none"><span style="font-size:9.5pt;font-family:Consolas"> </span><o:p></o:p></p>
<p class="MsoNormal" style="text-autospace:none"><span style="font-size:9.5pt;font-family:Consolas">And when I am doing as follows:</span><o:p></o:p></p>
<p class="MsoNormal" style="text-autospace:none"><span style="font-size:9.5pt;font-family:Consolas"> </span><o:p></o:p></p>
<p class="MsoNormal" style="text-autospace:none"><span style="font-size:9.5pt;font-family:Consolas;color:blue">var</span><span style="font-size:9.5pt;font-family:Consolas"> geotransform =
</span><span style="font-size:9.5pt;font-family:Consolas;color:blue">new</span><span style="font-size:9.5pt;font-family:Consolas">
</span><span style="font-size:9.5pt;font-family:Consolas;color:blue">double</span><span style="font-size:9.5pt;font-family:Consolas">[6];</span><o:p></o:p></p>
<p class="MsoNormal" style="text-autospace:none"><span style="font-size:9.5pt;font-family:Consolas">Gdal.GCPsToGeoTransform(gcps, geotransform, 0)</span><o:p></o:p></p>
<p class="MsoNormal" style="text-autospace:none"><span style="font-size:9.5pt;font-family:Consolas"> </span><o:p></o:p></p>
<p class="MsoNormal" style="text-autospace:none"><span style="font-size:9.5pt;font-family:Consolas">Or (after using dataSet.SetGCPs(gcps, projection) :</span><o:p></o:p></p>
<p class="MsoNormal" style="text-autospace:none"><span style="font-size:9.5pt;font-family:Consolas"> </span><o:p></o:p></p>
<p class="MsoNormal" style="text-autospace:none"><span style="font-size:9.5pt;font-family:Consolas;color:blue">var</span><span style="font-size:9.5pt;font-family:Consolas"> geotransform =
</span><span style="font-size:9.5pt;font-family:Consolas;color:blue">new</span><span style="font-size:9.5pt;font-family:Consolas">
</span><span style="font-size:9.5pt;font-family:Consolas;color:blue">double</span><span style="font-size:9.5pt;font-family:Consolas">[6];</span><o:p></o:p></p>
<p class="MsoNormal" style="text-autospace:none"><span style="font-size:9.5pt;font-family:Consolas">dataSet.GetGeoTransform(geotransform);</span><o:p></o:p></p>
<p class="MsoNormal" style="text-autospace:none"><span style="font-size:9.5pt;font-family:Consolas"> </span><o:p></o:p></p>
<p class="MsoNormal" style="text-autospace:none"><span style="font-size:9.5pt;font-family:Consolas">So the values returned, are wrong.</span><o:p></o:p></p>
<p class="MsoNormal" style="text-autospace:none"><span style="font-size:9.5pt;font-family:Consolas">For example, if the LeftUp.X was 35.01050 so the value of geotransform[0], which supposed to be the same value, can be 35.0082.</span><o:p></o:p></p>
<p class="MsoNormal" style="text-autospace:none"><span style="font-size:9.5pt;font-family:Consolas">The same with all the geotransform values.</span><o:p></o:p></p>
<p class="MsoNormal" style="text-autospace:none"><span style="font-size:9.5pt;font-family:Consolas">If I am getting from the dataset and setting again, every time it is changing more and more.</span><o:p></o:p></p>
<p class="MsoNormal" style="text-autospace:none"><span style="font-size:9.5pt;font-family:Consolas">Is there any connection to the use of the “0.5”?</span><o:p></o:p></p>
<p class="MsoNormal" style="text-autospace:none"><span style="font-size:9.5pt;font-family:Consolas"> </span><o:p></o:p></p>
<p class="MsoNormal" style="text-autospace:none"><span style="font-size:9.5pt;font-family:Consolas">Thanks.</span><o:p></o:p></p>
<p class="MsoNormal"> <o:p></o:p></p>
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