Towards Fully Dynamic Omnitrees: Moment-Conserving Anisotropic Compression With Wavelets

Recently, omnitrees were introduced as a flexible space partitioning tree that improves upon the benefits of both octrees and k-d trees: Omnitrees' efficient encoding of anisotropic refinements holds particular interest for applications with anisotropic features and high dimensionality.

These include, but are not limited to, computer graphics, databases, machine learning, and physics simulations.

The present paper defines new operations on the omnitree encoding that extend its capabilities from the existing refinement to also include coarsening and therefore fully adaptive compression.

It demonstrates natural integration of omnitrees with wavelets, which conserves moments of the stored function by design.

For omnitrees, the wavelet coefficients can be interpreted as local refinement priorities, which can be used to guide the adaptation process.

We derive algorithms for coarsening and downsplit that are guided by wavelet coefficients, and show their application to a large dataset of 3D shapes, as well as the continuous-valued density field of a cloud.

The comparison to OpenVDB, a widely-used data structure for sparse volumetric data in computer graphics, enables a demonstration of the practical benefits of omnitrees even for moderately anisotropic three-dimensional data.

Compared to OpenVDB, objects can be stored using up to 28x less space, and asymptotically show savings that exceed theoretical expectations.

Using lossy compression, the cloud dataset can be compressed by $\approx5\times$ compared to OpenVDB, with negligible loss of visual quality.

This demonstrates the potential of omnitrees for efficient storage and processing, and motivates further research into their applications in various domains.