title: How to handle 3D voxels efficiently?
body: <p>I have a 3D point clouds with million of points. I want to store these points in 3D voxel space. The number of voxles along coordinate axis are more than 3000(x), 4000(y), 1500(z), for a total of 3000*4000*1500 voxels. I need to store in a voxel; maximum number of points, min height, max height and centorid. However, 90% of voxels are empty. So it takes lot of memory to store this. Actually, I want to search 26 neighbor voxels of each voxels in later. So What is the best way to store this data in voxel space and get access to this efficiently?</p>
  
  <p>Creating a multidimensional array, is not the best solution, in term of performance...please any hint?</p>