GroundedSkybox is an addon, and must be imported explicitly, see Installation#Addons.
import { getGroundProjectedNormal } from 'three/addons/tsl/utils/GroundedSkybox.js';
Projects the world position onto a sphere whose bottom is clipped by a ground disk, then returns a vector usable for sampling an environment cube map.
radiusNode
The radius of the projection sphere. Must be large enough to ensure the scene's camera stays inside.
heightNode
The height is how far the camera that took the photo was above the ground. A larger value will magnify the downward part of the image.
Returns: A direction vector for sampling the environment cube map.