For some reason he left code in a pastebin. This seem to be about map making.
If you feel it is compelling, ask if they want to include it in community. These seem to be for artistic reasons, differing from the typical set of projections (List of map projections - Wikipedia).
I have just asked right now. I did referred him to @David_Tschumperle as he does not seem to be active over r/gmic. And yes, they are useful for map creation.
May also help to include the Reddit post in your OP.
Tried that, but it gets converted to a image.
It comes from here
The sinusoidal map creates ‘gores’ You wrap those into a sphere. I have an old perl script for that but the gmic filter is a nice alternative. Works very well. Not too sure about the rotation filter.
I had checked the code, and while I do not know that much about matrices, I believe the mathematics checks out.
There’s more of his scripts. Fixing them up and putting it up in gmic-community is on my TODOs. Been granted permission too.
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Wonderful! thank you so much in advance 
it’s super interesting, I’ll try to update it today!
I don’t understand how I missed it!
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Here they are:
I slightly modified the original code:
- to make it shorter and cleaner.
- to deal with multiple input layers if required.
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For those reading, it’s in the last G’MIC development (unstable) version 3.3.5, just update your filters 
(I don’t know if it’s in the stable version)
Thank you so much @David_Tschumperle
Yes, version 3.3.4 (stable) and 3.3.5_dev shares the filter updates.
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Ohhh, OK, good to know, thank you for the info