Fully Dynamic Algorithms for Chamfer Distance

Abstract: We study the problem of computing Chamfer distance in the fully dynamic setting, where two set of points $A, B \subset \mathbb{R}^{d}$, each of size up to $n$, dynamically evolve through point insertions or deletions and the goal is to efficiently maintain an approximation to $\mathrm{dist}{\mathrm{CH}}(A,B) = \sum{a \in A} \min_{b \in B} \textrm{dist}(a,b)$, where $\textrm{dist}$ is a distance measure. Chamfer distance is a widely used dissimilarity metric for point clouds, with many practical applications that require repeated evaluation on dynamically changing datasets, e.g., when used as a loss function in machine learning. In this paper, we present the first dynamic algorithm for maintaining an approximation of the Chamfer distance under the $\ell_p$ norm for $p \in {1,2 }$. Our algorithm reduces to approximate nearest neighbor (ANN) search with little overhead. Plugging in standard ANN bounds, we obtain $(1+ε)$-approximation in $\tilde{O}(ε^{-d})$ update time and $O(1/ε)$-approximation in $\tilde{O}(d n^{ε^2} ε^{-4})$ update time. We evaluate our method on real-world datasets and demonstrate that it performs competitively against natural baselines.