title: Generating 3D Cylinder with Rotationmatrix
body: <p>I am trying to create a cylinder in 3D space.
  I get a start and endpoint in 3D and to place the vertices, I need to create 2 circles for the bottom and the top of the cylinder. 
  I thought about making a vector u with coordinates (1,0,0) and calculate a direction vector dir = end - start.
  Now I make the cross product to get a vector w = u x dir:
  this way I am 90 degrees away from the dir vector with w. The problem is, how do I calculate the next position w' with an arbitrary angle between w and w'.
  I Read a lot about rotation matrix, and that i can rotate around X-Axis with something like:  </p>
  
  <pre><code>Rx(angle) =   
  (1   0          0          )  
  (0   cos(angle) -sin(angle))  
  (0   sin(angle) cos(angle) ) 
  </code></pre>
  
  <p>but the direction can be something like (1.442, -3.22, 7.23). So it isn't always the x-axis but maybe I need to rotate for every new w' in every axis. And I don't know how to figure out what angle I need to calculate, how to calculate and which angle belongs to witch rotation matrix.</p>