Normally when shooting a pano we take a shot, rotate the camera a bit, take the next shot, rotate the camera again, and so on until we have taken all the images; i.e. we have a single row of images
When using a shift/tilt lens we set up the lens shifted all the way down and take a row of images. We then rotate the camera back to the starting point, shift the lens all the way up and repeat shooting and rotating. This means we end up with two rows of images to merge in the pano software, which produces a pano that is twice as high as one taken with a normal lens.
Additional height can also be accomplished with a pano kit made by companies like Nodal Ninja or Novoflex.
https://shop.nodalninja.com/
http://https://novoflex.de/en/produc...multi-row.html