1: Texture has polar coordinates, if you see horizon line form something that looks like sinus function (wave), not all HDRI textures use polar coordinates (so you need different reflection calculations for projecting them on sky). On that NASA page with sky textures, “milky way” texture uses polar coordinates.
2: that blueprint is in most architectural visualization templates, its called light studio i think. Howevr just now (while looking for tut i seen) I found that there is HDRI backdrop plugin for unreal now.
- I think first material pic i posted here requires polar coordinates texture (it is how that reflection vector will work). And you need skybox/spehere mesh to apply material to it, and material does not use UVS of that mesh, reflection vector calculation maps it instead.