The Sample Tangent dPdu node converts the surface tangent along the U axis (in world space) into an RGB texture. It is typically used for anisotropy control, directional shading, procedural orientation, and OSL calculations. In figure 1, the Surface Tangent dPdu node is connected to a Gradient Map node to control the mix of a blue and red texture across an object's surface. 


Sample Tangent dPDu

Figure 1: Using the Surface Tangent dPdu node to mix between a red and blue texture