Papers by Henrik Christensen
IEEE Transactions on Robotics, 2007
In this paper a new feature representation for Simultaneous Localization and Mapping (SLAM) is di... more In this paper a new feature representation for Simultaneous Localization and Mapping (SLAM) is discussed. The representation addresses feature symmetries and constraints explicitly to make the basic model numerically robust. In previous SLAM work, complete initialization of features is typically performed prior to introduction of a new feature into the map. This results in delayed use of new data. To allow early use of sensory data the new feature representation addresses the use of features that initially have been partially observed. This is achieved by explicitly modelling the sub-space of a feature that has been observed. In addition to accounting for the special properties of each feature type, the commonalities can be exploited in the new representation to create a feature framework that allows for interchanging of SLAM algorithms, sensor and features. Experimental results are presented using a low-cost web-cam, a laser range scanner and combinations thereof. This research has been sponsored by the Swedish Foundation for Strategic Research through the Centre for Autonomous Systems. 1 SLAM methods that employ dense representation include scan matching, image matching and occupancy grid methods.
In this paper, we introduce an application of visual attention in the field of robotics: attentio... more In this paper, we introduce an application of visual attention in the field of robotics: attentional visual SLAM (Simultaneous Localization and Mapping). A biologically motivated attention system finds regions of interest which serve as visual landmarks for the robot. The regions are tracked and matched over consecutive frames to build stable landmarks and to estimate the 3D position of the landmarks in the environment. Furthermore, matching of current landmarks to database entries enables loop closing and global localization. Additionally, the system is equipped with an active camera control, which supports the system with a tracking, a re-detection, and an exploration behaviour.
Attention in Cognitive Systems. Theories and Systems from an Interdisciplinary Viewpoint, 2007
Visual attention regions are useful for many applications in the field of computer vision and rob... more Visual attention regions are useful for many applications in the field of computer vision and robotics. Here, we introduce an application to simultaneous robot localization and mapping. A biologically motivated attention system finds regions of interest which serve as visual landmarks for the robot. The regions are tracked and matched over consecutive frames to build stable landmarks and to estimate the 3D position of the landmarks in the environment. Matching of current landmarks to database entries enables loop closing and global localization. Additionally, the system is equipped with an active camera control, which supports the system with a tracking, a re-detection, and an exploration behaviour. We present experiments which show the applicability of the system in a real-world scenario. A comparison between the system operating in active and in passive mode shows the advantage of active camera control: we achieve a better distribution of landmarks as well as a faster and more reliable loop closing.
18th International Conference on Pattern Recognition (ICPR'06), 2006
In this paper, we propose a new, hierarchical approach to landmark selection for simultaneous rob... more In this paper, we propose a new, hierarchical approach to landmark selection for simultaneous robot localization and mapping based on visual sensors: a biologically motivated attention system finds salient regions of interest (ROIs) in images, and within these regions, Harris corners are detected. This combines the advantages of the ROIs (reducing complexity, enabling good redetactability of regions) with the advantages of the Harris corners (high stability). Reducing complexity is important to meet real-time requirements and stability of features is essential to compute the depth of landmarks from structure from motion with a small baseline. We show that the number of landmarks is highly reduced compared to all Harris corners while maintaining the stability of features for the mapping task.
Lecture Notes in Computer Science, 2010
ABSTRACT
Robotics and Autonomous Systems, 2010
ACM Transactions on Applied Perception, 2010
Based on concepts of the human visual system, computational visual attention systems aim to detec... more Based on concepts of the human visual system, computational visual attention systems aim to detect regions of interest in images. Psychologists, neurobiologists, and computer scientists have investigated visual attention thoroughly during the last decades and profited considerably from each other. However, the interdisciplinarity of the topic holds not only benefits but also difficulties: Concepts of other fields are usually hard to access due to differences in vocabulary and lack of knowledge of the relevant literature. This article aims to bridge this gap and bring together concepts and ideas from the different research areas. It provides an extensive survey of the grounding psychological and biological research on visual attention as well as the current state of the art of computational systems. Furthermore, it presents a broad range of applications of computational attention systems in fields like computer vision, cognitive systems, and mobile robotics. We conclude with a discus...
This paper describes the robot vision track that has been proposed to the ImageCLEF 2010 particip... more This paper describes the robot vision track that has been proposed to the ImageCLEF 2010 participants. The track addressed the problem of visual place classification, with a special focus on generalization. Participants were asked to classify rooms and areas of an office environment on the basis of image sequences captured by a stereo camera mounted on a mobile robot, under varying illumination conditions. The algorithms proposed by the participants had to answer the question "where are you?" (I am in the kitchen, in the corridor, etc) when presented with a test sequence, acquired within the same building but at a different floor than the training sequence. The test data contained images of rooms seen during training, or additional rooms that were not imaged in the training sequence. The participants were asked to solve the problem separately for each test image (obligatory task). Additionally, results could also be reported for algorithms exploiting the temporal continuity of the image sequences (optional task). A total of seven groups partic
ECVision: The European Research Network for Cognitive Computer Vision Systems, www. ecvision. org, Aug 23, 2005
On the 1st March 2002, a European research network for cognitive computer vision systems���ECVisi... more On the 1st March 2002, a European research network for cognitive computer vision systems���ECVision���was inaugurated. This network is funded for three years by the European Commission under the Information Society Technologies (IST) programme as project IST-2001-35454.
This paper presents a new human-machine interface for controlling a wheelchair by head movements.... more This paper presents a new human-machine interface for controlling a wheelchair by head movements. The position of the head is determined by use of infrared sensors, with no parts attached to the head of the user. The placement of the infrared sensors are behind the head of the user, so that the field of view is not limited. Tests on a wheelchair have shown that the system is functioning in real life, and that the vehicle can be driven at normal speeds in a simple and natural way. The behaviour of the sensor and the generated commands are fully programable, so it can be adapted easily to other constrains or capabilities of potential users.
With the growing research into mobile and ubiquitous computing, there is a need for addressing ho... more With the growing research into mobile and ubiquitous computing, there is a need for addressing how such infrastructures can support collaboration between nomadic users. We present the activity based computing paradigm and outline a proposal for handling collaboration in an activity-based architecture. We argue that activity-based computing establishes a natural and sound conceptual and architectural basis for session management in real-time, synchronous collaboration.
International Conference on Intelligent RObots and Systems - IROS, 2001
The dynamical system approach to behaviour based robotics provides a sound mathematical framework... more The dynamical system approach to behaviour based robotics provides a sound mathematical framework to behaviour design and integration. So far this approach has been used in various simulation work and in simple real world settings. This paper is a first step towards application in a more realistic scenario such as a typical office environment. The robot perceives its environment via
This document presents a practical way of describing software architectures using the Unified Mod... more This document presents a practical way of describing software architectures using the Unified Modeling Language. The approach is based on a "3+1" structure in which three viewpoints on the described system are used -module, component & connector, and allocation -are used to describe a solution for a set of architectural requirements.
International Conference on Robotics and Automation, 1998
Abstract: In this paper we present a technique for acquisitionand tracking of the pose of a mobil... more Abstract: In this paper we present a technique for acquisitionand tracking of the pose of a mobile robot witha laser scanner. The position and orientation of thewalls are the basis for estimating the pose of the robot.Validation gates filter out data that is believed to belongto the walls. For finding the parameters of thewalls a two stage process with a
Proceedings. 1998 IEEE International Conference on Robotics and Automation (Cat. No.98CH36146), 1998
Ultrasonic sensors are still one of the most widely used sensors in mlobile robotics. A notorious... more Ultrasonic sensors are still one of the most widely used sensors in mlobile robotics. A notorious problem in the use of soniur data is the lack of good spatial resolution, which typically results in a high uncertainty an the resulting map of the environment. In this paper a triangulation technique is used for filtering of data so as to obtain a n improved grad map of the environment. The basic technique is described and it is outlined how it can be used for identification of natural landmarks. 0-7803-4300-~-5/918 $10.00 0 1998 IEEE
2008 IEEE International Conference on Robotics and Automation, 2008
Localization and context interpretation are two key competences for mobile robot systems. Visual ... more Localization and context interpretation are two key competences for mobile robot systems. Visual place recognition, as opposed to purely geometrical models, holds promise of higher flexibility and association of semantics to the model. Ideally, a place recognition algorithm should be robust to dynamic changes and it should perform consistently when recognizing a room (for instance a corridor) in different geographical locations. Also, it should be able to categorize places, a crucial capability for transfer of knowledge and continuous learning. In order to test the suitability of visual recognition algorithms for these tasks, this paper presents a new database, acquired in three different labs across Europe. It contains image sequences of several rooms under dynamic changes, acquired at the same time with a perspective and omnidirectional camera, mounted on a socket. We assess this new database with an appearancebased algorithm that combines local features with support vector machines through an ad-hoc kernel. Results show the effectiveness of the approach and the value of the database.
2004 IEEE/RSJ International Conference on Intelligent Robots and Systems (IROS) (IEEE Cat. No.04CH37566), 2004
In recent years, a number of visual servo control algorithms have been proposed. Most approaches ... more In recent years, a number of visual servo control algorithms have been proposed. Most approaches try to solve the inherent problems of image-based and positionbased servoing by partitioning the control between image and Cartesian spaces. However, partitioning of the control often causes the Cartesian path to become more complex, which might result in operation close to the joint limits. A solution to avoid the joint limits is to use a shortest-path approach, which avoids the limits in most cases.
2003 IEEE International Conference on Robotics and Automation (Cat. No.03CH37422), 2003
... As a pan of an integrated system in terms of a service robot framework, this paper describes ... more ... As a pan of an integrated system in terms of a service robot framework, this paper describes a set of methods for real-world object ma-nipulation tasks. ... Our research is concentrated around these competences in terms of a service robot framework. ...
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Papers by Henrik Christensen