Results 11  20
of
272
2 1/2 D Visual servoing with respect to unknown objects through a new estimation scheme of camera displacement
 International Journal of Computer Vision
, 2000
"... Abstract. Classical visual servoing techniques need a strong a priori knowledge of the shape and the dimensions of the observed objects. In this paper, we present how the 2 1/2 D visual servoing scheme we have recently developed, can be used with unknown objects characterized by a set of points. Our ..."
Abstract

Cited by 86 (19 self)
 Add to MetaCart
(Show Context)
Abstract. Classical visual servoing techniques need a strong a priori knowledge of the shape and the dimensions of the observed objects. In this paper, we present how the 2 1/2 D visual servoing scheme we have recently developed, can be used with unknown objects characterized by a set of points. Our scheme is based on the estimation of the camera displacement from two views, given by the current and desired images. Since visionbased robotics tasks generally necessitate to be performed at video rate, we focus only on linear algorithms. Classical linear methods are based on the computation of the essential matrix. In this paper, we propose a different method, based on the estimation of the homography matrix related to a virtual plane attached to the object. We show that our method provides a more stable estimation when the epipolar geometry degenerates. This is particularly important in visual servoing to obtain a stable control law, especially near the convergence of the system. Finally, experimental results confirm the improvement in the stability, robustness, and behaviour of our scheme with respect to classical methods. Keywords: visual servoing, projective geometry, homography 1.
A Survey of Methods for Volumetric Scene Reconstruction from Photographs
"... Scene reconstruction, the task of generating a 3D model of a scene given multiple 2D photographs taken of the scene, is an old and difficult problem in computer vision. Since its introduction, scene reconstruction has found application in many fields, including robotics, virtual reality, and entert ..."
Abstract

Cited by 79 (1 self)
 Add to MetaCart
Scene reconstruction, the task of generating a 3D model of a scene given multiple 2D photographs taken of the scene, is an old and difficult problem in computer vision. Since its introduction, scene reconstruction has found application in many fields, including robotics, virtual reality, and entertainment. Volumetric models are a natural choice for scene reconstruction. Three broad classes of volumetric reconstruction techniques have been developed based on geometric intersections, color consistency, and pairwise matching. Some of these techniques have spawned a number of variations and undergone considerable refinement. This paper is a survey of techniques for volumetric scene reconstruction.
On the fitting of surfaces to data with covariances
 IEEE Trans. Patt. Anal. Mach. Intell
, 2000
"... AbstractÐWe consider the problem of estimating parameters of a model described by an equation of special form. Specific models arise in the analysis of a wide class of computer vision problems, including conic fitting and estimation of the fundamental matrix. We assume that noisy data are accompanie ..."
Abstract

Cited by 78 (19 self)
 Add to MetaCart
(Show Context)
AbstractÐWe consider the problem of estimating parameters of a model described by an equation of special form. Specific models arise in the analysis of a wide class of computer vision problems, including conic fitting and estimation of the fundamental matrix. We assume that noisy data are accompanied by (known) covariance matrices characterizing the uncertainty of the measurements. A cost function is first obtained by considering a maximumlikelihood formulation and applying certain necessary approximations that render the problem tractable. A novel, Newtonlike iterative scheme is then generated for determining a minimizer of the cost function. Unlike alternative approaches such as Sampson's method or the renormalization technique, the new scheme has as its theoretical limit the minimizer of the cost function. Furthermore, the scheme is simply expressed, efficient, and unsurpassed as a general technique in our testing. An important feature of the method is that it can serve as a basis for conducting theoretical comparison of various estimation approaches.
Camera Calibration From Vanishing Points in Images of Architectural Scenes
, 1999
"... We address the problem of recovering 3D models from uncalibrated images of architectural scenes. We propose a simple, geometrically intuitive method which exploits the strong rigidity constraints of parallelism and orthogonality present in indoor and outdoor architectural scenes. We presentanove ..."
Abstract

Cited by 73 (5 self)
 Add to MetaCart
(Show Context)
We address the problem of recovering 3D models from uncalibrated images of architectural scenes. We propose a simple, geometrically intuitive method which exploits the strong rigidity constraints of parallelism and orthogonality present in indoor and outdoor architectural scenes. We presentanovel algorithm that uses these simple constraints to recover the projection matrices for each viewpoint and relate our method to the algorithm of Caprile and Torre [2].
Structure and Motion from Silhouettes
, 2001
"... I hereby declare that no part of this thesis has already been or is being submitted for any other degree or qualification. This dissertation is the result of my own original work carried out in the Department of Engineering at the University of Cambridge, except where explicit reference has been mad ..."
Abstract

Cited by 62 (13 self)
 Add to MetaCart
(Show Context)
I hereby declare that no part of this thesis has already been or is being submitted for any other degree or qualification. This dissertation is the result of my own original work carried out in the Department of Engineering at the University of Cambridge, except where explicit reference has been made to the work of others. This dissertation contains 36,194 words and 91 figures. ii “Cogito, ergo sum. ” (I think, therefore I am.) René Descartes, Le Discours de la Méthode. iv
Visually guided object grasping
 IEEE TRANSACTIONS ON ROBOTICS AND AUTOMATION
, 1997
"... In this paper, we present a visual servoing approach to the problem of object grasping and more generally, to the problem of aligning an endeffector with an object. First we extend the method proposed in [1] to the case of a camera which is not mounted onto the robot being controlled and we stress ..."
Abstract

Cited by 58 (13 self)
 Add to MetaCart
In this paper, we present a visual servoing approach to the problem of object grasping and more generally, to the problem of aligning an endeffector with an object. First we extend the method proposed in [1] to the case of a camera which is not mounted onto the robot being controlled and we stress the importance of the realtime estimation of the image Jacobian. Second, we show how to represent a grasp or more generally, an alignment between two solids in threedimensional (3D) projective space using an uncalibrated stereo rig. Such a 3D projective representation is viewinvariant in the sense that it can be easily mapped into an image setpoint without any knowledge about the camera parameters. Third, we perform an analysis of the performances of the visual servoing algorithm and of the grasping precision that can be expected from this type of approach.
A Direct Method for Stereo Correspondence based on Singular Value Decomposition
, 1997
"... This paper proposes an new algorithm for matching point features across pairs of images. Despite the wellknown combinatorial complexity of the problem, his work shows that an acceptably good solution can e obtained directly by singular value decomposition of n appropriate correspondence strength ma ..."
Abstract

Cited by 58 (0 self)
 Add to MetaCart
(Show Context)
This paper proposes an new algorithm for matching point features across pairs of images. Despite the wellknown combinatorial complexity of the problem, his work shows that an acceptably good solution can e obtained directly by singular value decomposition of n appropriate correspondence strength matrix. The qpproach draws from the method proposed in [a] but, qesides suggesting its usefulness for stereo matching, zp thzs work a correlationweighted proximity function ib used as correspondence strength to specifically cater for real images.
Determining the egomotion of an uncalibrated camera from instantaneous optical flow
 Journal of the Optical Society of America A
, 1997
"... Abstract. The main result of this paper is a procedure for selfcalibration of a moving camera from instantaneous optical ow. Under certain assumptions, this procedure allows the egomotion and some intrinsic parameters of the camera to be determined solely from the instantaneous positions and veloc ..."
Abstract

Cited by 58 (26 self)
 Add to MetaCart
Abstract. The main result of this paper is a procedure for selfcalibration of a moving camera from instantaneous optical ow. Under certain assumptions, this procedure allows the egomotion and some intrinsic parameters of the camera to be determined solely from the instantaneous positions and velocities of a set of image features. The proposed method relies upon the use of a di erential epipolar equation that relates optical ow to the egomotion and internal geometry of the camera. The paper presents a detailed derivation of this equation. This aspect of the work may be seen as a recasting into an analytical framework of the pivotal research ofVieville and Faugeras. 1 The information about the camera's egomotion and internal geometry enters the di erential epipolar equation via two matrices. It emerges that the optical ow determines the composite ratio of some of the entries of the two matrices. It is shown that a camera with unknown focal length undergoing arbitrary motion can be selfcalibrated via closedform expressions in the composite ratio. The corresponding formulae specify ve egomotion parameters, as well as the focal length and its derivative. An accompanying procedure is presented for reconstructing the viewed scene, up to scale, from the derived selfcalibration data and the optical ow data. Experimental results are given to demonstrate the correctness of the approach. 1.
Epipolar Geometry from Profiles under Circular Motion
 IEEE Trans. on Pattern Analysis and Machine Intelligence
, 2001
"... This paper addresses the problem of motion estimation from profiles (also known as apparent contours) of an object rotating on a turntable in front of a sin gle camera. Its main contribution is the development of a practical and accurate technique for solving this problem from profiles alone, wh ..."
Abstract

Cited by 52 (14 self)
 Add to MetaCart
This paper addresses the problem of motion estimation from profiles (also known as apparent contours) of an object rotating on a turntable in front of a sin gle camera. Its main contribution is the development of a practical and accurate technique for solving this problem from profiles alone, which is precise enough to allow the reconstruction of the shape of the object. No correspondences be tween points or lines are necessary, although the method proposed can be used equally when these features are available, without any further adaptation. Sym metry properties of the surface of revolution swept out by the rotating object are exploited to obtain the image of the rotation axis and the homography relating epipolar lines in 2 views, in a robust and elegant way. These, together with ge ometric constraints for images of rotating objects, are then used to obtain first *Corresponding author the image of the horizon, which is the projection of the plane that contains the camera centers, and then the epipoles, thus fully determining the epipolar ge ometry of the image sequence. The estimation of the epipolar geometry by this sequential approach (image of rotation axis  homography  image of the hori zon  epipoles) avoids many of the problems usually found in other algorithms for motion recovery from profiles. In particular, the search for the epipoles, by far the most critical step, is carried out as a simple onedimensional optimization problem. The initialization of the parameters is trivial and completely automatic for all stages of the algorithm. After the estimation of the epipolar geometry, the Euclidean motion is recovered using the fixed intrinsic parameters of the cam era, obtained either from a calibration grid or from selfcalibrati...
Stratification of 3D vision: Projective, affine, and metric representations
"... In this article we provide a conceptual framework in which to think of the relationships between the threedimensional structure of the physical space and the geometric properties of a set of cameras which provide pictures from which measurements can be made. We usually think of the physical space a ..."
Abstract

Cited by 51 (4 self)
 Add to MetaCart
In this article we provide a conceptual framework in which to think of the relationships between the threedimensional structure of the physical space and the geometric properties of a set of cameras which provide pictures from which measurements can be made. We usually think of the physical space as being embedded in a threedimensional euclidean space where measurements of lengths and angles do make sense. It turns out that for artificial systems, such as robots, this is not a mandatory viewpoint and that it is sometimes sufficient to think of the physical space as being embedded in an affine or even projective space. The question then arises of how to relate these models to image measurements and to geometric properties of sets of cameras. We show that in the case of two cameras, a stereo rig, the projective structure of the world can be recovered as soon as the epipolar geometry of the stereo rig is known and that this geometry is summarized by a single 3 3 matrix, which we called the fundamental matrix [1, 2]. The affine structure can then be recovered if we add to this information a projective transformation between the two images which is induced by the plane at infinity. Finally, the euclidean structure (up to a similitude) can be recovered if we add to these two elements the knowledge of two conics (one for each camera) which are the images of the absolute conic, a circle of radius p;1 in the plane at in nity. In all three cases we showhowthe threedimensional information can be recovered directly from the images without explicitely reconstructing the scene structure. This defines a natural hierarchy of geometric structures, a set of three strata, that we overlay onthephysical world and which we show to be recoverable by simple procedures relying on two items, the physical space itself together with possibly, but not necessarily, some a priori information about it, and some voluntary motions of the set of cameras.