4πSr is a website created to publish spherical panoramas on the web.
Why the name 4πSr (“four-pi-sr”)?
4π Sr (4π steradians) is the mathematical expression that exactly describes the solid angle of a full sphere. And that is what spherical panoramas are all about. To show an image that covers a full sphere around the location of the camera. Only my very first few panoramas were not spherical.