https://benmcewan.com/blog/2020/02/02/demystifying-st-maps/
An ST map is an image where every pixel has a unique Red and Green colour value that corresponds to an X and Y coordinate in screen-space. You can use one to efficiently warp an image in Nuke.
In 3D you project the STMap against all the elements in the scene and render glass/transmittive elements on top of that.
