[Qgis-user] Transform vectordata using affine transformation

[Nyall Dawson]

On Sun, 26 Sept 2021 at 02:49, Bo Victor Thomsen
<bo.victor.thomsen at gmail.com> wrote:
>
> Hi list -
>
> One of my customers just received a data file, where the coordinates is not in any projection: Center of map data is (0,0), units in mm. not meter, maybe some rotation too. However, at least it's a planar coordinate system (I hope).
>
> Instead of sending the #¤%&! data file back to the "GIS no-good" architect who send it , I've decided to - once and for all - to find a method to  transform this kind of data to a reasonable CRS using an affine transformation.
>
> I'm aware of the Processing algorithm "Affine transform" that can do the actual transformation once I know the translation, rotation and scale coefficients of the transformation.
> And I know how to find the affine transformation matrix using a set of points from the data that corresponds with a set of points in the destination CRS.
>
> However, Is there any plug-in that can:
>
> Digitize a set of positions from the original data.
> Digitize or manually set the corresponding positions in the destination CRS
> Create the translation, scale and rotation parameters using data from (2)
> Run the "Affine transformation" algorithm to transform the data to the right position in the chosen CRS
>
> In short - a Georeferencer for vector data

The good news is that this is close...ish. A lot of the groundwork API
has been done, and there's an open PR at
https://github.com/qgis/QGIS/pull/41386 which adds vector support to
the georeferencer. This PR needs some work though, so I'm hoping
someone steps up and funds a couple of days development so that I can
clean it up and get it merged...

Nyall


>
> A name of a functioning plug-in would be lovely
>
> A set QGIS classes/methods that could help with establishing the transformation matrix and other stuff would be really nice
>
> A "No" to all my wishes would suck. However, In that case, I can start developing without have the nagging feeling that someone has done this before
>
> --
> Med venlig hilsen / Kind regards
>
> Bo Victor Thomsen
>
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