As you implied, the key is using a tripod.

I set up the camera on the tripod and set the viewscreen to show the tic-tac-toe grid. I look for something horizontal (a roof-line, etc.) and match the grid against that to be sure the camera is level. I make a dry run (without actually taking photos) and see how many exposures it will take to cover more or less 90 degrees and then adjust the zoom so that I will have a reasonable amount of exposures. (The photo I posted covered about 270 degrees.)

After each exposure, I move the camera horizontally so that there is a 1/3 overlap of the previous shot, that's why I use the tic-tac-toe grid. When I have done the full sweep, I move the camera back to the original position more or less, then aim it lower, again keeping the 1/3 overlap but this time vertically. I then repeat the sweep. The posted set was two sweeps, an upper and lower, 18 photos in each.

I got caught near the end when the entire composition area of two shots (upper and lower) was the dark tree and the auto exposure compensated for that and over-exposed those two frames (relative to the rest of the shots) by about three or four stops. Next time I try this I'll be aware of the problem and for those two shots at least go to a manual exposure over-ride.

tanstaafl.