Treexy is a library that implements a compact hierarchical data structure that can store and manipulate volumetric data, discretized on a three-dimensional grid (AKA, a "Voxel Grid").

This data structure is:

• Sparse: it uses only a fraction of the memory that a dense 3D voxel grid would use.
• Unbonded: you don't need to define the boundary of the 3D space.

For practical purposes, the dimension of the 3D space is virtually "infinite": if a voxel size of 1 cm is used, the maximum range of your X, Y and Z coordinates will be +/- 20.000 Km (yes, Kilometers).

If you are familiar with Octomap and Octree, you know that those data structures are also sparse and unbounded.

On the other hand, Treexy is brutally faster and, in same case, even more memory efficient than an Octree.

This work is strongly inspired by OpenVDB and it can be considered an implementation of the original paper, with a couple of changes:

K. Museth, “VDB: High-Resolution Sparse Volumes with Dynamic Topology”,
ACM Transactions on Graphics 32(3), 2013. Presented at SIGGRAPH 2013.

http://www.museth.org/Ken/Publications_files/Museth_TOG13.pdf

It is currently under development and I am building this mostly for fun and for educational purposes.

If you think that a data structure like this could be useful for your project, for the time being you should probably considered using OpenVDB itself.