The Sample Tangent Dpdu node converts the surface tangent along the U axis (in world space) into an RGB texture (figure 1).
Figure 1: The Sample Tangent Dpdu node connected to the DiffuseAmount of diffusion, or the reflection of light photons at different angles from an uneven or granular surface. Used for dull, non-reflecting materials or mesh emitters. pin on a Diffuse materialUsed for dull, non-reflecting materials or mesh emitters.