Between Shapes, Using the Hausdorff Distance

TL;DR

This paper investigates the existence and properties of intermediate shapes between two given shapes based on the Hausdorff distance, including convexity, connectedness, and generalizations to multiple sets, with applications to shape interpolation.

Contribution

It proves the existence of intermediate shapes with specific Hausdorff distances, generalizes to shape interpolation with bounded change, and extends the concept to multiple sets.

Findings

Existence of a shape with Hausdorff distance 1/2 between two shapes of distance 1.

Interpolation between shapes with bounded rate of change.

Extension of the Hausdorff middle concept to multiple sets with approximation methods.

Abstract

Given two shapes $A$ and $B$ in the plane with Hausdorff distance $1$, is there a shape $S$ with Hausdorff distance $1/2$ to and from $A$ and $B$? The answer is always yes, and depending on convexity of $A$ and/or $B$, $S$ may be convex, connected, or disconnected. We show that our result can be generalised to give an interpolated shape between $A$ and $B$ for any interpolation variable $\alpha$ between $0$ and $1$, and prove that the resulting morph has a bounded rate of change with respect to $\alpha$. Finally, we explore a generalization of the concept of a Hausdorff middle to more than two input sets. We show how to approximate or compute this middle shape, and that the properties relating to the connectedness of the Hausdorff middle extend from the case with two input sets. We also give bounds on the Hausdorff distance between the middle set and the input.