1. A computer-implemented system comprising: a display; a memory which, in operation, is loaded with a set of 3D voxel data arranged in a N 3 -tree data structure where N is a positive integer, the N 3 -tree data structure including: a top node representing a cube and including 64 occupancy bits and 32 index bits, an occupied or empty state of each of 64 subcubes in the cube being indicated by 1 occupancy bit of the 64 occupancy bits, and the 32 index bits representing a first pointer to a memory location of middle nodes, the middle nodes representing M occupied subcubes, respectively, each including 64 occupancy bits and 32 index bits, an occupied or empty state of each of 64 voxels in the occupied subcube being indicated by 1 occupancy bit of the 64 occupancy bits, and the 32 index bits representing a second pointer to a memory location of leaf nodes in the occupied subcube, wherein M is a positive integer, and the leaf nodes respectively representing N occupied voxels in the occupied subcube, each leaf node including an index number to be combined with the second pointer to point to a memory location of at least one type of attribute value of the occupied voxel, wherein N is a positive integer; and a processor which is coupled to the display and the memory and which, in operation, renders the set of 3D voxel data on the display.