title: how to pick up mouse in 3d world
body: <p>i have some questions about how to pick up mouse in 3d world.</p>
  
  <p>Now i have several points in 3d world,by using these points i can draw curve</p>
  
  <p>i want to choose a point on this curve using mouse, the viewport of the 3d world can be changed, so i want to know at any viewport when i chick mouse button near the curve, which point is the nearest to the mouse ?or which point is chose by me?</p>
  
  <p>i do have  no idea about how to implement it,help me please if you know.</p>
  
  <p>Thanks. Good luck.</p>