This tutorial shows you how to create a procedural vein, that is composed of small segments that you drawn by hand. This way the overall look of the vein is art-directable.
While creating the vein you learn about concepts like matrix multiplication, quaternions and the primuv() function as well as looping in SOPs. This is the first part of a two part tutorial, that deals with the creation of the vein itself. The second part (that will be released in 2 weeks) extends the setup with branches, hull geo and growth.