Well I was reading around the net today and saw this article by a fellow Gimp (he may be on the forums, not sure) and http://blog.patdavid.net/2012/05/on-little-planets.html
You can read it here: http://justpaste.it/Gimp_Wee_Planets_Tut
Yep, I'm here (just not as often as I'd like with a 16 month old child...)!
These are a lot of fun to make if you already have a panorama to start with. The images in my post were shot by me as part of testing out Hugin
, so it was a relatively simple matter to just change the projection from equirectangular to stereographic (thus bypassing GIMP Polar Coordinates), but the idea is the same.
One of the neat things about the Hugin package is that it includes Enblend (masking and combining edges softly), as well as the ability to correct all the individual images for exposure blending as well (though sometimes the results are not what you'll want). For instance, in my cathedral image the exposure blending caused nasty color effects to come out of highlights, and I found it better to actually just use the re-mapped images from Hugin as layers and to manually blend the seams.
I actually had to do some judicious masking and gradient fills in the sky to remove some ugly banding effects that cropped up there as well, but I was pleased with the final result I think.
And thanks for the idea of using resynthesizer on the sky extensions, it hadn't actually occurred to me to use it! (I love learning little tips like these from the community!)