Projections of four corner Cantor set: total self-similarity, spectrum and unique codings

Abstract

Given $\rho\in (0,1/4]$, the four corner Cantor set $E\subset \mathbb{R}^{2}$ is a self-similar set generated by the iterated function system \[ \left\{(\rho x, \rho y), \quad(\rho x, \rho y+1-\rho),\quad (\rho x+1-\rho, \rho y),\quad(\rho x+1-\rho,\rho y+1-\rho)\right\}. \] For $\theta\in[0,\pi)$ let $E_\theta$ be the orthogonal projection of $E$ onto a line with an angle $\theta$ to the $x$-axis. In this paper we give a complete characterization on which the projection $E_\theta$ is totally self-similar. We also study the spectrum of $E_\theta $, which turns out that the spectrum of $E_\theta$ achieves its maximum value if and only if $E_\theta $ is totally self-similar. Furthermore, when $E_\theta$ is totally self-similar, we calculate its Hausdorff dimension and study the subset $U_\theta $ which consists of all $x\in E_\theta $ having a unique coding. In particular, we show that $\dim_H U_\theta=\dim_H E_\theta$ for Lebesgue almost every $\theta \in[0,\pi)$. Finally, for $\rho=1/4$ we describe the distribution of $\theta $ in which $E_\theta$ contains an interval. It turns out that the possibility for $E_\theta$ to contain an interval is smaller than that for $E_\theta$ to have an exact overlap.