Think of it as a wide 360 degree panorama picture stitched from images taken at different times of the day. This would yield a wide, non-distorted rectangular image.
This one combined image was then rolled around itself in such a way that its whole bottom edge is now in the center of this "planetary" image, and its top edge is now the outer circumference of the image (the border with black).
If you're wondering why the center point of the image is not heavily distorted it's because it was overlaid with a simple top-down photo of the place the tripod was standing on.
This one combined image was then rolled around itself in such a way that its whole bottom edge is now in the center of this "planetary" image, and its top edge is now the outer circumference of the image (the border with black).
If you're wondering why the center point of the image is not heavily distorted it's because it was overlaid with a simple top-down photo of the place the tripod was standing on.