title: Use octree to organize 3D volume data in GPU
body: <p>I am now trying to implement Ray Casting Volume Rendering using C++, OpenGL and GLSL (for GPU speeding). In order to get better quality and performance, I want to use octree to organize the 3D medical volume data,so I can use some algorithm such as Space Leaping and Adaptive Sampling easily.</p>
  
  <p>But how to build the octree effectively? How to visit the octree? When the ray travels in the volume data, how can I determine which cell or leaf of the octree the sample point belong?</p>