[?] Skydomes

Hey, just a curious question, is there a technique used for the BF type of skydomes? I know what size they are, but a way they are actually made?

I found a way in photoshop to see the seam of the 2 opposite edges but nothing really on how to see how it would look in game the way BF has it..

Or is it as plain as grabing a panorama and using that?