# Pipe Variable

In this video tutorial, I will explain how you can use Pipe variable and isotrim to produce a parametric surface First of all, we can find the pipe variable by double-clicking on the canvas and searching “pip”. There are two different tools for making a parametric pipe. “Pipe” will produce a single radius pipe. “Pipe Variable” will give you more freedom on the pipe by letting you choose the location and the radius. We can have a NURBS curve and give it to the curve input (right click on the “Curve” tool and set a curve) The curve has a domain (you can connect a domain tool to see the domain). By right clicking on the curve and choosing reparametrize you can scale the curve’s domain to (0 to 1).  The next input is the Parameters. these are the locations which you want to change the radius of the pipe. Use a “gene pool” (Params>input) to produce several parameters. you can double click on the “gene pool” and change its domain to 0 and 1. change the numbers so that they cover from 0 to 1.   Give another “Gene pool” to the “Radii” input and change its domain to define the minimum and maximum radius of the pipe. To have a subsurface of the pipe we can use a “isotrim” tool (surface>util) and give a “construct domain2” (maths>set) to the domain. Because we want the whole surface of the U domain we can give a 0 and 1 to the U min and U max. By giving a number between 0 and 1 to the V min and V max we can extract a portion of the pipe. 