[gdal-dev] tps - gdalwarp vs ogr2ogr

[Rahkonen Jukka]

Hi,

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.

-Jukka Rahkonen-

Lähettäjä: gdal-dev <gdal-dev-bounces at lists.osgeo.org> Puolesta Stijn Tallir
Lähetetty: keskiviikko 16. elokuuta 2023 10.29
Vastaanottaja: gdal-dev at lists.osgeo.org
Aihe: [gdal-dev] tps - gdalwarp vs ogr2ogr

Hi,

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.

I have images that are unreferenced and vector data digitised on these images (in pixel coordinates).

The images are then georeferenced with +100 gcp's and warped with gdalwarp using the "tps" option.

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.

Any thoughts?

Stijn
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