Nodes are the essential building blocks in the Advanced interface to the Poser Material Room. They are the graphical representation of mathematical function calls, that is: calculation procedures which turn parameters (inputs) to a result (output).

**Advanced**

The nodes from the Variables group tell me about the position, in space and time, of the spot that the PoserSurface definition is constructed for. There are two kinds of results from these nodes:

- Single values. These are discussed in this article.
- Three value ‘vectors’. Like a color is defined by (Red, Green, Blue), so is a point in space defined by (X,Y,Z) and so on. The following articles discuss normal N, point P, stretching dPdu, dPdv and curvature dNdu, dNdv.

The easiest to comprehend are U, V and Frame_Number. These nodes don’t take any inputs but just report the situation in the scene: at what place on the object surface(U,V, both 0..1) at what time frame the spot is located for which the PoserSurface definition has to report on to the renderer.

Du and Dv are sold in the manual as “defining a rate of change” but actually both produce a solid 0.0 whatever the shape and mapping of the object. Sorry for that.

To visualize U and V, just plug the nodes tight into the Diffuse channel, like

And the value from the node will drive the brightness of the color.

U from 0 (black) to 1 (white), from left to right:

V from 0 (black) to 1 (white), from front to back: