Rhys Hill - Academia.edu (original) (raw)

Papers by Rhys Hill

Random projections have been applied in many machine learning algorithms. However, whether margin... more Random projections have been applied in many machine learning algorithms. However, whether margin is preserved after random projection is non-trivial and not well studied. In this paper we analyse margin distortion after random projection, and give the conditions of margin preservation for binary classification problems. We also extend our analysis to margin for multiclass problems, and provide theoretical bounds on multiclass margin on the projected data.

Digital Image Computing: Techniques and Applications, 2009

Proceedings 2003 International Conference on Image Processing (Cat. No.03CH37429), 2003

Camera calibration requires the identification of points in an image that correspond to known loc... more Camera calibration requires the identification of points in an image that correspond to known locations in the scene. These are typically determined through the use of a calibration pattern designed to facilitate feature localisation. We present in this paper a novel method of generating patterns such that each subregion is individually identifiable by its cross ratio. The method aims to minimise the probability of misidentifying a subregion. A key advantage of the method is the ability to place constraints on the size of the elements constituting the pattern. This allows a calibration object to be used in a wider variety of viewing conditions, increasing the flexibility of the calibration process.

Lecture Notes in Computer Science, 2015

Third International Conference on Information Technology and Applications (ICITA'05), 2005

The development of assignments for undergraduate teaching typically requires a compromise between... more The development of assignments for undergraduate teaching typically requires a compromise between what is achievable by an average student and what engages the interest of a more advanced member of the class. Selecting a suitable compromise is particularly problematic for undergraduate artificial intelligence (AI) courses which typically attempt to cover a very broad range of topics, without delving too deeply

International Symposium on Mixed and Augmented Reality, 2010

We present a method for estimating the 3D shape of an object from a sequence of images captured b... more We present a method for estimating the 3D shape of an object from a sequence of images captured by a hand-held device. The method is well suited to augmented reality applications in that minimal user interaction is required, and the models generated are of an appropriate form. The method proceeds by segmenting the object in every image as it is

Proceedings of the 1st International ICST Conference on Forensic Applications and Techniques in Telecommunications, Information and Multimedia, 2008

The use of surveillance cameras to monitor public buildings and urban areas is becoming increasin... more The use of surveillance cameras to monitor public buildings and urban areas is becoming increasingly widespread. Each camera delivers a continuous stream of video data, which, once archived, is a valuable source of information for forensic analysis. However, current video analysis tools are primarily based on searching backwards and forwards in time at a single location (i.e. camera), which does not account for events or people of interest that change location over time. In this paper we describe a practical system for tracking a target backwards and forwards in both space and time, effectively following a feature of interest as it moves within and between cameras in a surveillance network. This provides a video analysis tool that is target-centred rather than camera-centred, and thus allows rapid access to the footage that matters for forensic analysis.

Workshop on Applications of Computer Vision, 2009

Automatic placement of surveillance cameras in arbitrary buildings is a challenging task, and als... more Automatic placement of surveillance cameras in arbitrary buildings is a challenging task, and also one that is essential for efficient deployment of large scale surveillance networks. Existing approaches for automatic camera placement are either limited to a small number of cameras, or constrained in terms of the building layouts to which they can be applied. This paper describes a new

A key enabler for the construction of large-scale intelligent surveillance systems is the accurat... more A key enabler for the construction of large-scale intelligent surveillance systems is the accurate estimation of activity topology graphs. An activity topology graph describes the relationships between the fields of view of the cameras in a surveillance network. An accurate activity topology estimate allows higher-level processing such as network-wide tracking to be localised within neighbourhoods defined by the topology, and

Asian Conference on Computer Vision, 2007

Recent research on video surveillance across multiple cameras has typically focused on camera net... more Recent research on video surveillance across multiple cameras has typically focused on camera networks of the order of 10 cameras. In this paper we argue that existing systems do not scale to a network of hundreds, or thousands, of cameras. We describe the design and deployment of an algorithm called exclusion that is specifically aimed at finding correspondence between regions

2006 IEEE International Conference on Video and Signal Based Surveillance, 2006

Estimating the paths that moving objects can take through the fields of view of possibly non-over... more Estimating the paths that moving objects can take through the fields of view of possibly non-overlapping cameras, also known as their activity topology, is an important step in the effective interpretation of surveillance video. Existing approaches to this problem involve tracking moving objects within cameras, and then attempting to link tracks across views. In contrast we propose an approach which begins by assuming all camera views are potentially linked, and successively eliminates camera topologies that are contradicted by observed motion. Over time, the true patterns of motion emerge as those which are not contradicted by the evidence. These patterns may then be used to initialise a finer level search using other approaches if required. This method thus represents an efficient and effective way to learn activity topology for a large network of cameras, particularly with a limited amount of data.

2009 Digital Image Computing: Techniques and Applications, 2009

A number of problems in computer vision require the estimation of a set of matrices, each of whic... more A number of problems in computer vision require the estimation of a set of matrices, each of which is defined only up to an individual scale factor and represents the parameters of a separate model, under the assumption that the models are intrinsically interconnected. One example of such a set is a family of fundamental matrices sharing an infinite homography. Here an approach is presented to estimating a general set of interdependent matrices defined to within separate scales. The input data is assumed to consist of individually estimated matrices for particular models, which when considered collectively may fail to satisfy the constraints representing the inter-model relationships. Two cost functions are proposed for upgrading, via optimisation, the data of this sort to a collection of matrices satisfying the intermodel constraints. One of these functions incorporates error covariances. Each function is invariant to any change of scale for the input estimates. The proposed approach is applied to the particular problem of estimating a set of fundamental matrices of the form of the example set above. Experimental results are given which demonstrate the effectiveness of the approach.

2009 8th IEEE International Symposium on Mixed and Augmented Reality, 2009

ABSTRACT We present an interactive image-based modelling method for gen-erating 3D models within ... more ABSTRACT We present an interactive image-based modelling method for gen-erating 3D models within an augmented reality system. Applying real time camera tracking, and high-level automated image analy-sis, enables more powerful modelling interactions than have previ-ously ...

2008 Second ACM/IEEE International Conference on Distributed Smart Cameras, 2008

Large-scale intelligent video surveillance requires an accurate estimate of the relationships bet... more Large-scale intelligent video surveillance requires an accurate estimate of the relationships between the fields of view of the cameras in the network. The exclusion approach is the only method currently capable of performing online estimation of camera overlap for networks of more than 100 ...

2008 Second ACM/IEEE International Conference on Distributed Smart Cameras, 2008

Making intelligent decisions on the basis of the video captured by a large network of surveillanc... more Making intelligent decisions on the basis of the video captured by a large network of surveillance cameras requires the ability to identify overlap between their fields of view. Without this information it is impossible to perform even simple analysis, such as distinguishing between repeated behaviours and multiple views of the same behaviour. Large-scale intelligent video surveillance thus requires a means of understanding the relationships between the fields of view of the cameras involved. The exclusion approach is the only method currently capable of performing online estimation of camera overlap for networks of more than 50 cameras, with a version of the algorithm applicable to 1000 camera networks having been published. Empirical evaluation of every such algorithm is critical to assessing its performance, and essential if comparisons between methods are to be made. This paper presents a method by which such an empirical evaluation may be carried out, and makes publicly available the data (including ground truth) on which it based in order that competing methods might be compared equally. Precision vs recall curves are reported for a series of experiments comparing the results of exclusion to ground truth. These results demonstrate the strengths and limitations of the exclusion-based estimation process, but show that the performance of the method exceeds the requirements of surveillance applications.

2009 Third ACM/IEEE International Conference on Distributed Smart Cameras (ICDSC), 2009

This paper presents a novel framework designed for calculating the topology of overlapping camera... more This paper presents a novel framework designed for calculating the topology of overlapping cameras in large surveillance systems. Such a framework is a key enabler for efficient network-wide surveillance, e.g. inter-camera tracking, especially in large surveillance networks. The framework presented can be adapted to utilise numerous contradiction and correlation approaches to identify overlapping portions of camera views using activity within

2009 Sixth IEEE International Conference on Advanced Video and Signal Based Surveillance, 2009

An accurate estimate of camera overlap is a key enabler for efficient network-wide surveillance p... more An accurate estimate of camera overlap is a key enabler for efficient network-wide surveillance processing (e.g. intercamera tracking), especially in large-scale surveillance networks. Techniques based on contradictions in pair-wise occupancy data, such as the exclusion approach, have advantages in robustness and efficiency that make them particularly well suited for large surveillance networks. Correlation techniques share some of these advantages, but have a better understood statistical basis. This paper evaluates a set of contradiction and correlation techniques, using a novel metric, search space precision-recall. This metric reflects the activity-based overlap estimation required for camera handover, such as would be used in inter-camera tracking. Results are reported for a range of networks, including a 24-camera network set up in an office space, where the exclusion estimator showed the best performance.

2009 Digital Image Computing: Techniques and Applications, 2009

The increased flexibility and other benefits offered by IP network cameras makes them a common ch... more The increased flexibility and other benefits offered by IP network cameras makes them a common choice for installation in new and expanded surveillance networks. One commonly quoted limitation of IP cameras is their high latency when compared to their analogue counterparts. This causes some reluctance to install or upgrade to digital cameras, and is slowing the adoption of live, intelligent analysis techniques in video surveillance systems. This paper presents methods for measurement of the latency in systems based upon digital IP or analogue cameras. These methods are camera-agnostic and require no specialised hardware. We use these methods to compare a variety of camera models. The results demonstrate that whilst analogue cameras do have a lower latency, most IP cameras are within acceptable tolerances. The source of the latency within an IP camera is also analysed, with prospects for improvement identified.

2007 First ACM/IEEE International Conference on Distributed Smart Cameras, 2007

Henry Detmold, Anton van den Hengel, Anthony Dick, Alex Cichowski, Rhys Hill, Ekim Kocadag, Katri... more Henry Detmold, Anton van den Hengel, Anthony Dick, Alex Cichowski, Rhys Hill, Ekim Kocadag, Katrina Falkner and David S. Munro {henry,anton,ard,alex,rhys,ekim,katrina,dave} @cs.adelaide.edu.au ... The Australian Centre for Visual Technologies School of ...