An Algorithmic Framework for Labeling Road Maps

Given an unlabeled road map, we consider, from an algorithmic perspective, the cartographic problem to place non-overlapping road labels embedded in their roads. We first decompose the road network into logically coherent road sections, e.g., parts of roads between two junctions. Based on this decomposition, we present and implement a new and versatile framework for placing labels in road maps such that the number of labeled road sections is maximized. In an experimental evaluation with road maps of 11 major cities we show that our proposed labeling algorithm is both fast in practice and that it reaches near-optimal solution quality, where optimal solutions are obtained by mixed-integer linear programming. In comparison to the standard OpenStreetMap renderer Mapnik, our algorithm labels 31% more road sections in average.Comment: extended version of a paper to appear at GIScience 201

Lagrangian Relaxation for MAP Estimation in Graphical Models

We develop a general framework for MAP estimation in discrete and Gaussian graphical models using Lagrangian relaxation techniques. The key idea is to reformulate an intractable estimation problem as one defined on a more tractable graph, but subject to additional constraints. Relaxing these constraints gives a tractable dual problem, one defined by a thin graph, which is then optimized by an iterative procedure. When this iterative optimization leads to a consistent estimate, one which also satisfies the constraints, then it corresponds to an optimal MAP estimate of the original model. Otherwise there is a ``duality gap'', and we obtain a bound on the optimal solution. Thus, our approach combines convex optimization with dynamic programming techniques applicable for thin graphs. The popular tree-reweighted max-product (TRMP) method may be seen as solving a particular class of such relaxations, where the intractable graph is relaxed to a set of spanning trees. We also consider relaxations to a set of small induced subgraphs, thin subgraphs (e.g. loops), and a connected tree obtained by ``unwinding'' cycles. In addition, we propose a new class of multiscale relaxations that introduce ``summary'' variables. The potential benefits of such generalizations include: reducing or eliminating the ``duality gap'' in hard problems, reducing the number or Lagrange multipliers in the dual problem, and accelerating convergence of the iterative optimization procedure.Comment: 10 pages, presented at 45th Allerton conference on communication, control and computing, to appear in proceeding

Analysis of prehistoric brown earth paleosols under the podzol soils of Exmoor, UK

The deforestation of the upland landscapes in southwest Britain during prehistory is an established archaeological narrative, documenting human impacts on the environment and questioning the relationship of prehistoric societies to the upland landscapes they inhabited. Allied to the paleoenvironmental analyses of pollen sequences, which have provided the evidence of this change, there has been some investigation of prehistoric paleosols fossilized under principally Bronze Age archaeological monuments. These analyses identified brown earth soils that were originally associated with temperate deciduous woodland, on occasion showing evidence of human impacts such as tilling. However, the number of analyses of these paleosols has been limited. This study presents the first analysis of a series of pre‐podzol brown earth paleosols on Exmoor, UK, two of which are associated with colluvial soil erosion sediments before the formation of peat. This study indicates these paleosols are spatially extensive and have considerable potential to inform a more nuanced understanding of prehistoric human impacts on the upland environments of the early‐mid Holocene and assess human agency in driving ecosystem change

This disastrous event staggered me : reconstructing the botany of Ludwig Leichhardt on the expedition from Moreton Bay to Port Essington, 1844-45

Ludwig Leichhardt had to abandon a large and important collection of botanical specimens during his Expedition from Moreton Bay to Port Essington. Here we attempt to assess the significance of the lost collection by identifying the botanical references in his detailed published journal from the journey. From Leichhardt’s description of the plants and their habitats, and with our accurate knowledge of current distribution, it has been possible, in most cases, to identity his botanical references to a single species. In other cases there is lower degree of certainty. Well over one hundred of the species recorded in Leichhardt’s journal would have been new to science at the time if specimens had survived. The record does identify some potential locations for species that would represent range extensions and suggests an indigenous status for a number of plant species that where previously considered exotic. Certainly Leichhardt was a talented botanist and his significant contribution to Australian natural science should be recognised