Alasdair Turner

From Isovists to Visibility Graphs: A Methodology for the Analysis of Architectural Space

An isovist, or viewshed, is the area in a spatial environment directly visible from a location within the space. Here we show how a set of isovists can be used to generate a graph of mutual visibility between locations. We demonstrate that this graph can also be constructed without reference to isovists and that we are in fact invoking the more general concept of a visibility graph. Using the visibility graph, we can extend both isovist and current graph-based analyses of architectural space to form a new methodology for the investigation of configurational relationships. The measurement of local and global characteristics of the graph, for each vertex or for the system as a whole, is of interest from an architectural perspective, allowing us to describe a configuration with reference to accessibility and visibility, to compare from location to location within a system, and to compare systems with different geometries. Finally we show that visibility graph properties may be closely related to manifestations of spatial perception, such as way-finding, movement, and space use.

An Algorithmic Definition of the Axial Map

The fewest-line axial map, often simply referred to as the ‘axial map’, is one of the primary tools of space syntax. Its natural language definition has allowed researchers to draw consistent maps that present a concise description of architectural space; it has been established that graph measures obtained from the map are useful for the analysis of pedestrian movement patterns and activities related to such movement: for example, the location of services or of crime. However, the definition has proved difficult to translate into formal language by mathematicians and algorithmic implementers alike. This has meant that space syntax has been criticised for a lack of rigour in the definition of one of its fundamental representations. Here we clarify the original definition of the fewest-line axial map and show that it can be implemented algorithmically. We show that the original definition leads to maps similar to those currently drawn by hand, and we demonstrate that the differences between the two may be accounted for in terms of the detail of the algorithm used. We propose that the analytical power of the axial map in empirical studies derives from the efficient representation of key properties of the spatial configuration that it captures.

Sketching a virtual environment: modeling using line-drawing interpretation

Here we demonstrate the direct input to computer of a handdrawn perspective sketch to create a virtual environment. We either start with a photograph of a real environment or an existing VRML model, and then use a mouse or pen pad to sketch line drawings onto the scene. Visual clues and constraints from the existing background and line drawing, as well as heuristics for form recognition are used to build a 3D optimization problem. We use a multiple objective genetic algorithm to find a viable solution to the problem, and VRML output is generated, either for re-entry to the system or use in another system. Our software is currently available compiled for either a PC running Windows 98/NT or an SGI machine running IRIX 6.x.

Evolving direct perception models of human behavior in building systems

Software agents that use direct (or active) perception of the environment have recently been shown to correspond well with pedestrian movement within building and urban systems. The algorithm, based on Gibson’s theory of affordances, combines random selection of destination from their field of view with reassessment of the destination every few steps. However, although the agents correlate with human movement on aggregate, as individuals they progress more erratically than people do. It might seem necessary to add higher cognitive functions in order to guide them more convincingly, but here we show that it is possible to improve their behavioral response through artificial evolution of their existing navigation rules. First we show that the destination selection method approximates stochastic direction choice by length of line-of-sight. Then we use the lines of sight to provide a set of inputs to the agents, or animats, which we evolve to fit human usage patterns within a building as best possible. We demonstrate that while agents using informational change inputs fail to evolve to fit movement patterns, an input that compares sight-line lengths improves models qualitatively, but not quantitatively, which further implies that the individual guidance mechanism may be independent of the instant spatial properties acting on direct perception.

Four Applications of Embodied Cognition

This article presents the views of four sets of authors, each taking concepts of embodied cognition into problem spaces where the new paradigm can be applied. The first considers consequences of embodied cognition on the legal system. The second explores how embodied cognition can change how we interpret and interact with art and literature. The third examines how we move through architectural spaces from an embodied cognition perspective. And the fourth addresses how music cognition is influenced by the approach. Each contribution is brief. They are meant to suggest the potential reach of embodied cognition, increase the visibility of applications, and inspire potential avenues for research.

An Ecological Approach to Generative Design

In this paper we explore the use of an animat model to construct geometry. The model uses agents guided by direct (or active) visual perception of their environment to replicate human behaviour within a notional plan of an open space. The environment reacts to these agents by placing walls in order to affect their usage of the space, and thus the structure may be evolved to fit the social function of the agents within it. Here, we start with the most basic social function, to design a building that disperses agents programmed with an exploratory task across its floorplan by using an evolutionary algorithm. We investigate the effect of evolution on the generated configuration using space syntax tools. We show how the introduction of a simple rule, the desire to leave, can result in the evolution of commonly observed features — first a central axis and then a ‘foyer’.We discover that ‘intelligibility’ of the space, which might imply reduced cognitive load, may increase as the system is allowed to evolve. Finally, we consider the implications of the ecological approach for the design process.

Obtaining Multiple Distinct Solutions with Genetic Algorithm Niching Methods

This paper proposes a new technique for improving the number of usefully distinct solutions produced by a Genetic Algorithm (GA) when applied to multimodal problems. The tribes method builds on the spatial selection methods proposed by Collins and Jefferson [1]. We compare the technique with two well-known niching methods (crowding and sharing), spatial selection alone, and a simple control GA method, in the domain of simple timetabling problems. We demonstrate that the tribes technique can greatly improve the efficiency with which a GA can obtain multiple distinct solutions to a problem.

Partners in the street ballet: An embodied process of person-space coupling in the built environment

The diurnal movements of pedestrians in the built environment are sometimes typified as a ‘street ballet’, where each actor or dancer has their own set role within a larger complex. Every individual in the ballet may have many influences on their behaviour including the physical layout of the environment, cognitive strategies to navigate it, experiential or affective preferences as well as social, economic and political factors, but ultimately each one seems to obey apparently choreographed actions. The aim of this article is to understand whether or not there is in fact an underlying choreography to the ballet, in that certain steps or moves are more likely than others, such that a ‘dance’ through daily life is constructed. To do so, simple automata that use active perception to inhabit the world are evolved against different tasks within the environment, representing different sets of moves that may be taken. It is shown that any evolved automaton appears to embody a mathematical person–space relationship that joins visual affordance with motor action: the convergence of a simple Markov model of visual movement. From the Markov model, a general model of embodied action in the environment is proposed, whereby memory of the dance is ingrained over evolutionary history, such that it forms building blocks for non-discursive action within the built environment and comprises a possible common phenomenological framework.