Deriver

Shader Type: Texture
Output: Color
Used as passthrough shader to compute UV derivatives on the fly.

Passthrough	The shader puts the calculated u and v derivatives into state->derivs[0] and state->derivs[1], and then calls whatever shader is plugged into the passthrough port. This means that all shaders that are to the left of the Deriver get the modified u and v derivates.
Mode	Allows you to either disable the shader (the passthrough will still be executed, but the derivatives will not be touched), or to choose a north pole or north direction input. North Direction means that the input vector points towards the north pole, for all rendered pixels. North Pole means that the input vector is a location, and the shader will compute the north direction for each pixel on the fly. You can for example link the north pole to the location of a null to get the possibility to interactively place the north pole.
North Direction and North Pole	Two input vectors, the appropriate vector will be used depending on the Mode selected.
Rotation	Allows you to rotate the u and v direction vectors around the surface normal. This works like the rotation color in the Anisotropic shader, but is just a simple scalar. All multiples of one are full 360° rotations, 0.5 is 180 degree, etc...

Render Tree Usage
The main idea behind this shader is to miracle U and V derivatives onto polygon surfaces, so that you can use the Anisotropic shader with them. To make this work, just plug the Anisotropic shader into the passthrough port, plug the Deriver shader into the Surface port, and enable the shader.