Encoding Geometric Information in Road Networks Extracted from Binary Images

Abstract

The authors discuss recent progress in extracting road networks from digital imagery. We briefly review recent developments in methods for the automatic extraction of road centre line networks and propose a related algorithm aimed at encoding the geometry of road networks with line segments. Our algorithm is inspired by ‘axial lines’, which have been defined as lines of uninterrupted movement within urban streetscapes or buildings. We show that axial lines appear as ridges in isovist fields. These are formed from the maximum diametric lengths of the individual isovists, sometimes called viewsheds, which make up these fields. We present an image-processing technique for the identification of lines from ridges, discuss current strengths and weaknesses of the method, and show how it can be implemented easily and effectively.

Spatial rules that generate urban patterns: Emergence of the power law in the distribution of axial line length

“…13. Overlay of the layout of the town of Gassin in France (Hillier, 1989) and the medial axes extracted along the ridges using the algorithm described in Carvalho and Batty (2005). It is a 100 × 50 cellular representation of the city layout.…”

“…9 The selection is based on a pseudo random process which ensures that similar inputs always result in similar outputs in the model. Carvalho and Batty (2005) propose a method for automatic extraction of axial lines in raster space. Their algorithm derives the alignment of axial lines but does not define the start and end points.…”

“…3. The ray-set is formed by extracting all possible rays between the cells marked as passages along the ridges as defined by Carvalho and Batty (2005). 4.…”