Measure tool straighten rotation is always to the horizontal.
Operating System: Kubuntu 16.04
Package: flatpack Gimp 2.10.4
The straighten function using the measure tool works as expected for a horizontal line. Such as a horizon, roof line or similar. Example: https://i.imgur.com/26jwhQg.jpg
A vertical correction columns, windows , using the measure tool with a vertical line still rotates to horizontal. Example: https://i.imgur.com/YpXqN9v.jpg
The tool needs to take into account the orientation of the measure line.
Is the bug reproducible? Always
Draw vertical-ish line with measure tool, click the straighten button.
Expected result: vertical correction
Actual result: image rotated horizontally