I wanted to use a 16:9 image zoomed in as per this http://picamera.readthedocs.io/en/release-1.12/fov.html using 1920x1080 (resized for conveience to 640x360. OK - nice enlarged effect.... Then I decided I wanted to take the shot vertically.
Turn the camera on its side? Nope! It knows somehow.....it isn't like taking a hand held camera and turning it!
What it seems you have to do is set these:
camera.resolution = (1080, 1920)
for foo in camera.capture_continuous(stream, 'jpeg', use_video_port=True, resize=(360,640)):
NOTE the reversal of the dimension values.
I couldn't find anything about this in the documentation - just tried it as a last resort!
Just saying....(v2 camera - Haven't tried v1) - I wonder if it will still work on reboot....Yup! I am not certain, but it might lose the "zoom effect" , it's dark outside.