Perspective transform revisited

[Ottia Tuota]

(12-03-2020, 03:28 PM)Ottia Tuota Wrote: ...
(By the way, you had a neat trick to find the center!)
...

But on a second thought, that trick gives only the center of the ellipse (= the distorted circle). What the plugin needs, is the would-be center, meaning the point which should be sent to the center of the corrected circle. In this picture it seems to be the same thing! That is a matter of luck, and probably is due to the method with which the picture was produced to begin with. I guess that it was made from some original picture (containing a true circle) by an affine transformation (scale? shear? ...)? So, the trick does not work generally.