More generic straightening (leveling) of lines
Operating System: (if feature is platform specific)
Description of the feature
The straightening tool (as I understand it) allows rotation of an image by giving ONE vertical or horizontal reference line.
Unfortunately very few lenses map parallel lines to parallel lines again, and you can only "straigten" (actually "level") ONE of those now non-parallel lines.
The idea is simple to use, but probably hard to implement: Allow the user to specify MULTIPLE reference lines, and use proojection transformation to make those MULTIPLE reference lines horizonal or vertical (i.e.: parallel again). Sorry that I can't give the mathematical formula, or the proof that this is actually possible, but Adobe's Lightroom has an automatic perspective correction that does such a thing (it even detects the reference lines by itself). Still it produces poor output for some input...
I don't know whether the measurement tool is the best tool to start this type of correction.
Use cases
The classical case where a tall building was shot from the ground, producing "falling lines" ("Stürzende Linien" as we say in German).