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- Active stereo tracking of multiple free-moving targetsPublication . Perdigoto, Luis; Barreto, João P.; Caseiro, Rui; Araujo, Helder; Perdigoto, Luis;This article presents a general approach for the active stereo tracking of multiple moving targets. The problem is formulated on the plane, where cameras are modeled as ”line scan cameras” and targets are described as points with unconstrained motion. We propose to control the active system parameters in such a manner that the images of the targets in the two views are related by an homography. This homography is specified during the design stage and implicitly encodes the tracking behavior. It is shown that this formulation leads to an elegant geometric framework that enables to decide about the feasibility of a particular active tracking task. We apply it to prove that two cameras with rotation and zoom control, can track up to three moving targets, while assuring that the image location of each target is the same for both views. In addition, the framework is also useful for devising tracking strategies and deriving the required control equations. This feature is illustrated through a real experiment on tracking two independent targets using a binocular stereo head.
- Estimation of mirror shape and extrinsic parameters in axial non-central catadioptric systemsPublication . Perdigoto, Luis; Araujo, HelderWe propose a method to estimate the mirror shape and position, and the extrinsic parameters in axial noncentral catadioptric systems (i.e. systems with an axial symmetrical mirror and a pinhole camera with its optical center located at the mirror axis). Our method requires one or more images of a planar calibration pattern consisting of points and lines with known position (e.g. a checkerboard), and that the camera be internally calibrated. We also present an alternative algorithm for the particular case of catadioptric systems with spherical mirror, were the estimation is achieved by fitting quartic curves to the images of lines of the calibration pattern. An analytical solution is presented for every method. Each analytical solution is then refined by a non-linear optimization procedure. We present experimental results, on simulated and real images, that demonstrate the validity of our work.
- Wireless Capsule Endoscope Location and a Robotic Validation ExperimentPublication . Figueiredo, Isabel N.; Pinto, Luís; Perdigoto, Luís; Oliveira, Marina; Araújo, Hélder; Figueiredo, Pedro N.We present results concerning the validation of a novel approach for wireless capsule endoscope localization, using as ground truth a simulated biological/mechanical environment experiment. The approach relies essentially on image-based methods. It involves a hybrid multi-scale affine and elastic image registration procedure which is afterwards appropriately complemented with calibration and visual odometry techniques. The capsule was fixed at the extremity of a robotic arm and moved along a part of an ex-vivo mammalian bowel. The first validation results indicate a good correlation between the ground truth velocity and distance traveled by the capsule and the velocity and distance given by the proposed approach.
- Reconstruction of 3D Lines from a Single Axial Catadioptric Image Using Cross-RatioPublication . Perdigoto, Luis; Araujo, HelderIt has been shown, in previous work, that the 3D position of a line can be reconstructed from a single image in vision systems that do not possess a single viewpoint. We present a new method that, in a non-central axial catadioptric system, can achieve line spacial reconstruction from 3 or more image points, given the distance ratio of 3 points in the line (a fair assumption in, for example, structured environment with repetitive architectural features). We use cross-ratio as an invariant to constrain the line localization and perform the reconstruction from a set of image points through non-linear optimization. Experimental results are presented.
- Active stereo tracking of N ≤ 3 targets using line scan camerasPublication . Barreto, Joao P.; Perdigoto, Luis; Caseiro, Rui; Araujo, HelderThis paper presents a general approach for the simultaneous tracking of multiple moving targets using a generic active stereo setup. The problem is formulated on the plane, where cameras are modeled as line scan cameras, and targets are described as points with unconstrained motion. We propose to control the active system parameters in such a manner that the images of the targets in the two views are related by a homography. This homography is specified during the design stage and, thus, can be used to implicitly encode the desired tracking behavior. Such formulation leads to an elegant geometric framework that enables a systematic and thorough analysis of the problem at hand. The benefits of the approach are illustrated by applying the framework to two distinct stereo configurations. In the first case, we assume two pan-tilt-zoom cameras, with rotation and zoom control, which are arbitrarily placed in the working environment. It is proved that such a stereo setup can track up to N = 3 free-moving targets, while assuring that the image location of each target is the same for both views. The second example considers a robot head with neck pan motion and independent eye rotation. For this case, it is shown that it is not possible to track more than N=2 targets because of the lack of zoom. The theoretical framework is used to derive the control equations, and the implementation of the tracking behavior is described in detail. The correctness of the results is confirmed through simulations and real tracking experiments.