The best sky file to use on Unreal

I’m working on a project of the sky and have a few questions. I have high-resolution sky photos (around 10000x5000px) that are always 360 degrees. I have several options for projecting them and can choose the format, but my main concern is whether a sphere projection with a perfect zenith is necessary or if a cropped cylinder would suffice.
I’d appreciate any insights you have on the following topics:

-How to project a sky in Unreal.
-The best format (jpg, tiff, txt) to use.
-What is essential for the image to be usable.
-Whether background buildings/landscape at the bottom of the image are necessary.

Thank you.

Most of the skysphere stuff on the market is cubemaps ( rectilinear projection ).

You can also use hemispheres, and a ‘point of view’ projection, which gets around the zenith problem.

You don’t want to go too high with resolution, because it just starts to eat frame rate, and the engine has a limit ( no, can’t recall ). But I think this kind of thing is at that limit

If you’re going to be importing textures into the engine, don’t use compressed formats like JPG, PNG is typically a good option. In any event, I think HDR is not compressed ( ? ).

It’s up to you if you want to leave buildings in it, it really depends on the application. Buildings in the distance can really work, if it’s part of the scene. Personally, I think they’re more generally useable without.

It all really depends on texture format, or ability to convert the mfrom for eg cubemap to polar coordinates. I doubt there are free apps to do it for resolutions you want.

So check what type of projection are your cubemap textures, then you can make shader and use textures without converting.

PS. if it is not for some archvis project (accuracy, some determined location) you should go with procedural skybox. And for development time just some out of box sky actor.