Iain Wallace

High-speed photogrammetry system for measuring the kinematics of insect wings

We describe and characterize an experimental system to perform shape measurements on deformable objects using high-speed close-range photogrammetry. The eventual application is to extract the kinematics of several marked points on an insect wing during tethered and hovering flight. We investigate the performance of the system with a small number of views and determine an empirical relation between the mean pixel error of the optimization routine and the position error. Velocity and acceleration are calculated by numerical differencing, and their relation to the position errors is verified. For a field of view of approximately 40 mm x 40 mm, a rms accuracy of 30 mum in position, 150 mm/s in velocity, and 750 m/s2 in acceleration at 5000 frames/s is achieved. This accuracy is sufficient to measure the kinematics of hoverfly flight.

Video Object Tracking Based on a Chamfer Distance Transform

This paper describes the use of variable kernels based on the normalized Chamfer distance transform (NCDT) for mean shift, object tracking in colour video sequences. This replaces the more usual Epanechnikov kernel, improving target representation and localization without increasing the processing time, minimising the distance between successive frame RGB distributions using the Bhattacharya coefficient. The target shape which defines the NCDT is found either by regional segmentation or background-difference imaging, dependent on the nature of the video sequence. The improved performance is demonstrated on a number of colour video sequences.

Do I remember you? Memory and identity in multiple embodiments

This paper investigates user perceptions of continuous identity as agents migrate between different embodiments. It reports an experiment seeking to establish whether migrating or not migrating the interaction memory of the agent would affect the users perception of consistent agent identity over different embodiments. The experiment involved a treasure hunt in which a virtual agent migrated from a screen to a mobile phone in order to accompany a user while they searched for clues. A total of 45 subjects took part in three different conditions with 15 subjects in each. The outcome showed that the presence of memory affected the competence users ascribed to the virtual agent. However it had no significant effect on a strong perception of consistent identity across multiple embodiments.

Towards resource-certified software: a formal cost model for time and its application to an image-processing example

Visual tracking requires sophisticated algorithms working in real-time, and often space-limited, settings. While the input streams may be regular in structure, the algorithms are not, and must often deal with probabilistic metrics. To ensure progress in algorithm design without incurring excessive development costs, we propose a high-level programming approach married with predictable and compositional performance metrics. This enables the combination of independently developed program components into coherent software architecture, with certified resource use guarantee. Here, we present our approach and discuss its application to the development and resource analysis of a space bound mean shift algorithm for motion tracking, using the new embedded system-oriented language Hume.

Experimental observations of multi-mode dynamics in an external cavity semiconductor laser

We present experimental results of the dynamics in a semiconductor laser operating on several longitudinal modes subject to external feedback. Both low-frequency fluctuations (LFFs) and locked states are studied through observing the outputs from the dominant mode, all modes except the dominant mode, and all modes. Synchronized dropout events of LFFs are observed among each of the solitary modes while energy competition and trading occurs among these modes when the total output exhibits the locked state.

Executing specifications of social reasoning agents

Social reasoning theories, whilst studied extensively in the area of multiagent systems, are hard to implement directly in agents. They often specify properties of beliefs or behaviours but not the way these should affect the computational reasoning mechanisms of a concrete agent design. The Expectation-Strategy-Behaviour (ESB) framework addresses this problem by separating and abstracting social reasoning from other practical reasoning, providing the computational machinery that is necessary to perform social reasoning in practice. We present an extension to previous work on ESB to an implemented reasoning system which enables the execution of concise and modular declarative social reasoning rules. We review the foundations of the abstract ESB framework and present the implementation of a reasoner based on CTL model checking. Our system allows for conditioning agent behaviours on complex preconditions and verification of properties to aid the agent designer. It also allows for easy integration with a BDI reasoning system. We exemplify the suitability of ESB for social reasoning constructs with a detailed example of Joint Intention theory in ESB and illustrate the generality with an overview of another implemented social reasoning scheme, and extensions to both.

A Computational Framework for Practical Social Reasoning

This article describes a framework for practical social reasoning designed to be used for analysis, specification, and implementation of the social layer of agent reasoning in multiagent systems. Our framework, called the expectation strategy behavior (ESB) framework, is based on (i) using sets of update rules for social beliefs tied to observations (so‐called expectations), (ii) bounding the amount of reasoning to be performed over these rules by defining a reasoning strategy, and (iii) influencing the agents decision‐making logic by means of behaviors conditioned on the truth status of current and future social beliefs. We introduce the foundations of ESB conceptually and present a formal framework and an actual implementation of a reasoning engine, which is specifically combined with a general (belief–desire–intention‐based) practical reasoning programming system. We illustrate the generality of ESB through select case studies, which show that it is able to represent and implement different typical styles of social reasoning. The broad coverage of existing social reasoning methods, the modularity that derives from its declarative nature, and its focus on practical implementation make ESB a useful tool for building advanced socially reasoning agents.

High-speed close-range photogrammetry for dynamic shape measurement

We describe and characterize an experimental arrangement to perform shape measurements on a deformable object through dynamic close-range photogrammetry; specifically, an insect in flight. The accuracy of shape measurements in photogrammetry is improved by increasing the number of camera views. In static close-range photogrammetry, one may increase the number of camera views by moving the camera and taking a number of images, or equivalently, by moving the object. In dynamic close-range photogrammetry of rigid objects, one may combine all the camera views from a video sequence. However, in dynamic close-range photogrammetry of a deformable object, the number of camera views is restricted to the number of physical cameras available. The technique described here is to arrange a number of cameras around a measurement volume, illuminated by a laser synchronized to the cameras. The cameras are first calibrated, and then a bundle adjustment is used to determine point positions on the object. In this paper, we first determine the capabilities of the system in static close-range photogrammetry. We then perform a static shape measurement on our dynamic target and compare this with the results of dynamic close-range photogrammetry. The results indicate that high-speed dynamic measurements of the deformation of insect wings during flight should provide adequate resolution to develop an aeroelastic model of a flapping wing.

Low frequency fluctuations and locked states in a multi-mode semiconductor laser with external cavity

Abstract The low frequency fluctuations (LFF) in a multi-mode semiconductor laser in an external cavity is investigated experimentally and theoretically. The results of the dynamical behaviors not only of the total intensity but also of a few frequency resolved dominant modes of the solitary laser are presented. We demonstrate experimentally and numerically that the so-called locked state (synchronous Sisyphus effect) we reported previously in which the dropout events occur with a high degree of periodicity persists even when the laser operates on a large number of solitary cavity modes. We show that slow energy transfer between solitary modes is a common effect when the laser undergoes LFFs or is in the locked state and that this effect is predicted by the multi-mode Lang–Kobayashi equations to be noise driven.

Experimental phase synchronization of semiconductor lasers subject to optical feedback

We report first observation of the phenomenon of phase synchronization of low frequency fluctuations in unidirectionally coupled external cavity semiconductor lasers. The findings are interpreted using the coupled Lang-Kobayashi model as a Sysiphus effect with synchronized drift.