GNOME Bugzilla – Bug 90287
Rotation tool , horisontal / vertical ruler
Last modified: 2009-08-15 18:40:50 UTC
Especially when straightening up a slisghtly skewed scanned image, it would have been extremely useful to put a ruler along a line in the picture telling gimp that this line should be horizontal/vertical.
Unless I misunderstood your problem, you can easily do that with the GIMP: - select the transform tool (rotation) - in the "tool options" window, switch the "tool paradigm" to "corrective" - now you can simply align the lines in the grid to what should be vertical or horizonal in your image.
Closing this bug report (confirmed by reporter).