Testing the planar straight-line realizability of 2-trees with prescribed edge lengths

Abstract

We study a classic problem introduced thirty years ago by Eades and Wormald. Let $G=(V,E,\lambda )$ be a weighted planar graph, where $\lambda :E\to R^{+}$ is a length function. The Fixed Edge-Length Planar Realization problem (FEPR for short) asks whether there exists a planar straight-line realization of $G$, i.e., a planar straight-line drawing of $G$ where the Euclidean length of each edge $e\in E$ is $\lambda \left(e\right)$.

Cabello, Demaine, and Rote showed that the FEPR problem is NP-hard, even when $\lambda$ assigns the same value to all the edges and the graph is triconnected. Since the existence of large triconnected minors is crucial to the known NP-hardness proofs, in this paper we investigate the computational complexity of the FEPR problem for weighted 2-trees, which are $K_4$-minor free. We show the NP-hardness of the problem, even when $\lambda$ assigns to the edges only up to four distinct lengths. Conversely, we show that the FEPR problem is linear-time solvable when $\lambda$ assigns to the edges up to two distinct lengths, or when the input has a prescribed embedding. Furthermore, we consider the FEPR problem for weighted maximal outerplanar graphs and prove it to be linear-time solvable if their dual tree is a path, and cubic-time solvable if their dual tree is a caterpillar. Finally, we prove that the FEPR problem for weighted 2-trees is slice-wise polynomial in the length of the large path.