360 x 180 panos: automatic zenith & nadir identification is possible
Cameras can't find out and record the portrait/landscape image orientation in EXIF when recording zenith and nadir shoots*. This sometimes results in zenith and nadir being placed by Automatic horizon tool where the horizon should be.
As most images were shot in portrait orientation the Automatic horizon tool should use that to place zenith and nadir where they belong (autrement dit, puisque dans la pratique les panos 360 x 180 sont toujours pris en format portrait, choisir la solution pour laquelle un maximum de photos sont correctement orientées d'après les infos EXIF suffit pour éviter de placer le zenith et le nadir là où l'horizon doit se trouver.)
___ * For zenith and nadir shoots none of the 4 image sides is the top nor the bottom side, zenith image top is in the middle, left and right directions are undefined. Likewise, when one is at the north pole: South is everywhere, East and West are meaningless!
Re: 360 x 180 panos: automatic zenith & nadir identification is possible
Take a multi-row spherical pano, show links, and rotate it 90 degrees. There should be two circles with one image in the middle of each. Those are the nadir and vertex. The middle rows may make an "s" shaped sort of curve.
These may not be the true vertex and nadir, they may just be the "poles" of the panohead if you didn't level the head. But they shouldn't be too far from the real vertex and nadir.
So APP has to arbitrarily assign a "top" half and a "bottom" half to each picture. The image that links to only (or mostly) the "top" half of other images is the vertex, the one that links to "bottoms" is the nadir. -- here, links means that the CPs on the other images are in the top or bottom half of those images.
APP may confuse vertex and nadir, but that's an easy correction for me to make and its better than looking at a sideways pano. And as far as autoleveling goes, if the panohead is tilted, leveling should probably be done on the equator of the tilt, not the actual horizon.