Dilation volumes of sets of finite perimeter
Markus Kiderlen, Jan Rataj
TL;DR
This paper investigates the first-order, right-sided behavior of dilation volumes $\lambda_n(A\oplus tQ)$ as $t\to0^+$ for sets $A\subset\mathbb{R}^n$ of finite perimeter and finite test sets $Q$. By extending the covariogram derivative from two-point tests to general finite $Q$, the authors derive a first-order formula for dilation volumes in terms of a generalized surface area measure $S_{n-1}^*(A;\cdot)$, using smooth BV-function approximations of $\mathbf{1}_A$. They introduce the $Q$-variation $V^Q(f)$ and establish $V^Q(f)=|Df|_Q$ with an explicit integral representation, enabling a rigorous first-order expansion. The results yield a precise relation between dilation volumes and the surface area measure, generalizing the cosine-transform connection to finite $Q$, and they apply the framework to the derivative of the contact distribution function for stationary random sets. The approach avoids classical regularity restrictions by working with sets of finite perimeter and random measurable sets (RAMS), offering broad applicability in stochastic geometry and geometric measure theory.
Abstract
This paper analyzes the first order behavior (that is, the right sided derivative) of the volume of the dilation $A\oplus tQ$ as $t$ converges to zero. Here $A$ and $Q$ are subsets of $n$-dimensional Euclidean space, $A$ has finite perimeter and $Q$ is finite. If $Q$ consists of two points only, $x$ and $x+u$, say, this derivative coincides up to sign with the directional derivative of the covariogram of $A$ in direction $u$. By known results for the covariogram, this derivative can therefore be expressed by the cosine transform of the surface area measure of $A$. We extend this result to finite sets $Q$ and use it to determine the derivative of the contact distribution function with finite structuring element of a stationary random set at zero. The proofs are based on approximation of the characteristic function of $A$ by smooth functions of bounded variation and showing corresponding formulas for them.
