[gdal-dev] tps - gdalwarp vs ogr2ogr

[Stijn Tallir]

Yes, I checked them visually for both raster and vector.

I compared the results also visually. The rasters are transformed in a way
that the end ponts of the gcp's align exactly with the result so that is
why I referred to it as "right". The vector data result is in the
neighbourhood of the end points (sometimes a rather significant distance).

The result is different from order 1-3 transformations so I presume the tps
option isn't ignored.

Stijn

Op wo 16 aug 2023 om 11:52 schreef Rahkonen Jukka <
jukka.rahkonen at maanmittauslaitos.fi>:

> Hi,
>
>
>
> Did you check the ground control points? What is your reference when you
> say that one result is right, and another wrong? Have you used some other
> software for comparison? Or do you only know that the results are different?
>
>
>
> -Jukka-
>
>
>
> *Lähettäjä:* Stijn Tallir <stijn at strict.be>
> *Lähetetty:* keskiviikko 16. elokuuta 2023 12.27
> *Vastaanottaja:* Rahkonen Jukka <jukka.rahkonen at maanmittauslaitos.fi>
> *Kopio:* gdal-dev at lists.osgeo.org
> *Aihe:* Re: [gdal-dev] tps - gdalwarp vs ogr2ogr
>
>
>
> Hi Jukka,
>
>
>
> I thought of the density as an option for the "error" as you suggested and
> I made a point-file with a point for every pixel in my original image and
> used this as a source for the ogr2ogr transformation. So you could say the
> desnity for both sources raster and vector) are then alike.
>
>
>
> The results were still the same (and wrong) ...
>
>
>
> Stijn
>
>
>
>
>
> Op wo 16 aug 2023 om 10:22 schreef Rahkonen Jukka <
> jukka.rahkonen at maanmittauslaitos.fi>:
>
> 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
>
>
>
>
> --
>
> Stijn Tallir - StrICT BV
>
>
>
> Wijnveld 8
>
> 9112 Sinaai-Waas
>
>
>
> GSM: 0486 750220
>
>
>
> E-mail: Info at strict.be
>
> Web: www.strict.be
>
>
>
> BTW: BE 0567.559.668
>
>
>
>
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