- Setting horizon to be horizontal is not that easy, even when using the 'set vertical' button, perhaps another method would be better, e.g. A user can select a few points (perhaps 3 or 4) that need to be 'straightened' to produce a horizontal line, and then press enter.
Using the using the Auto Level
button is the first thing to do.
Then, you should place vertical lines using the Set verticals
button and using the red (vertical) line or the yellow (horizontal) line to guess the correct orientation.
For some difficult panoramas this is not enough: the large gray horizontal line which corresponds to the "mathematical horizon" and should cross any point in the subject which was at the same height where the camera lens was, is too low or to high. To correct that you must use a third tool, the Set Center Point
button to move this line upward or downward until everything is (or looks) perfect.
An interesting example (very difficult if you are picky enough) is the Greek temple in the Official samples pack
where the paved road probably is rising toward the right and the temple probably built like Greek temples were (the bottom part is larger than the top part so that the result is more stable ...and looks higher than it actually is.)
When stitching this pano I used the Set verticals
button to place red/yellow crosses on both ends of the road and on the temples but this was not enough. Slightly rising the gray horizontal line seems to give a better result.