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<p class="MsoNormal"><span style="mso-fareast-language:EN-US">Hi,<o:p></o:p></span></p>
<p class="MsoNormal"><span style="mso-fareast-language:EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="mso-fareast-language:EN-US">Without test data it is very hard to say much. I believe that the promise of tps is that the ground control points stay where they are set. The intermediate points follow the least tension
surfaces and I do not know how exactly those spline algorithms are defined. Raster data is full of points to warp but probably in the vector data the transformation is done vertex by vertex. I would first check if the GCPs are in the same place in both outputs.
Then I would make a test by densifying the vector data before georeferencing to have much more vertices and see if it has any effect on the result.<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="mso-fareast-language:EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="mso-fareast-language:EN-US">-Jukka Rahkonen-<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="mso-fareast-language:EN-US"><o:p> </o:p></span></p>
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<p class="MsoNormal"><b>Lähettäjä:</b> gdal-dev <gdal-dev-bounces@lists.osgeo.org>
<b>Puolesta </b>Stijn Tallir<br>
<b>Lähetetty:</b> keskiviikko 16. elokuuta 2023 10.29<br>
<b>Vastaanottaja:</b> gdal-dev@lists.osgeo.org<br>
<b>Aihe:</b> [gdal-dev] tps - gdalwarp vs ogr2ogr<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">Hi,<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">According to the documentation gdal and ogr use the same algorithm for the tps-transformation but I don't seem to get the same results using the same set of gcp's for images and vectors.<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">I have images that are unreferenced and vector data digitised on these images (in pixel coordinates).<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">The images are then georeferenced with +100 gcp's and warped with gdalwarp using the "tps" option.<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">When I use the same gcp's (with adjusted y-origin to lower left corner) to georeference the vector data with ogr2ogr and the "tps" option I get different results. The vector-result is similar to the image-result but never exactly the same
and differences can be substantial.<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">Any thoughts?<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">Stijn<o:p></o:p></p>
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