This correspondence field between the input image and the texture is then further warped into the target image coordinate frame based on the desired pose, effectively establishing the correspondence ...

UV coordinates are how we do that. Each vertex has a position, but it also has UV coordinates, specified as (u,v). Think of these as texture coordinates; it's what part of the texture corresponds to ...

Constructs a Sphere of a given radius. Normals are generated by default, texture coordinates are not. The resolution defaults to 15 divisions along sphere's axes. Appearance defaults to white.