This effect is called an Alexandroid, after Alexandre Jenny, developer of the program Autopano Pro, which I use for most of my panoramas. Ordinarily, an Alexandroid is the result of a mistake in the choice of control points by the program. It's very difficult to control, but sometimes you get lucky and get the beautiful curves seen here. For this image, I spent a day trying to take 500 photos badly, several days trying to trick Autopano Pro into giving me some nice Alexandroids, and then several more days of Photoshop processing to compose the final image. I chose the GRU plant as subject because it has many repetitive patterns that I hoped would confuse the choice of control points. Also, it has a prominent phallic symbol.