I found the instructions in the 27 February 2009 edition of MacUser UK. In short, the instructions are:
- Start with a panoramic image
- In Photoshop, resize it to a square image (I’m using 5000×5000)
- Invert the image (rotate 180 degrees)
- Apply the Filter>Distort>Polar Coordinates with the “Rectangular to Polar” option selected
- Spend the rest of the time cleaning up the joins!