The Sample Position node takes the sample position and converts it into an RGB color with R and G in the range -1 to +1 (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.