This filter performs perspective transformations. Flat images can be tilted e.g. to create 3D compositions. Similarly, images taken at an angle can be rectified (e.g. tall buildings). You can rotate the image with the mouse or using sliders around three axes, then reposition and resize it. Grid lines can be displayed both before and after transformation.
The new Version 7 allows to set control points in the preview image. The plugin evaluates these control points and sets the slider values accordingly to rectify the image. You can choose between various rectification modes. There is also a facility to compensate barrel or pincushion lens distortions.