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Pose estimation is a relevant problem for imaging systems whose applications range from augmented reality to robotics. In this paper we propose a novel solution for the minimal pose problem, within the framework of generalized camera... more
Pose estimation is a relevant problem for imaging systems whose applications range from augmented reality to robotics. In this paper we propose a novel solution for the minimal pose problem, within the framework of generalized camera models and using a planar homography. Within this framework and considering only the geometric elements of the generalized camera models, an imaging system can be modeled by a set of mappings associating image pixels to 3-D straight lines. This mapping is defined in a 3-D world coordinate system. Pose estimation performs the computation of the rigid transformation between the original 3-D world coordinate system and the one in which the camera was calibrated. Using synthetic data, we compare the proposed minimal-based method with the state-of-the-art methods in terms of numerical errors, number of solutions and processing time. From the experiments, we conclude that the proposed method performs better, especially because there is a smaller variation in numerical errors, while results are similar in terms of number of solutions and computation time. To further evaluate the proposed approach we tested our method with real data. One of the relevant contributions of this paper is theoretical. When compared to the state-of-the-art approaches, we propose a completely new parametrization of the problem that can be solved in four simple steps. In addition, our approach does not require any predefined transformation of the dataset, which yields a simpler solution for the problem.
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In this paper, we address the problem of pose estimation under the framework of generalized camera models. We propose a solution based on the knowledge of the coordinates of 3-D straight lines (expressed in the world coordinate frame) and... more
In this paper, we address the problem of pose estimation under the framework of generalized camera models. We propose a solution based on the knowledge of the coordinates of 3-D straight lines (expressed in the world coordinate frame) and their corresponding image pixels. Previous approaches used the knowledge of the coordinates of 3-D points (zero dimensional elements) and their corresponding images (zero dimensional elements). In this paper, pixels belonging to the image of 3-D lines are used. There is no need to establish correspondences between pixels and 3-D points. Correspondences are established between 3-D lines and their images. There is no need to identify individual pixels. The use of correspondences between pixels (that belong to the images of the 3-D lines) and 3-D lines facilitates the correspondence problem when compared to the use of world and image points. This is one of the contributions of this paper. The approach is both evaluated and validated using synthetic da...
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In this paper we discuss the use of active vision for the development of autonomous systems. Active vision systems are essentially based on biological motivations. Two systems with potential application to surveillance are described. Both... more
In this paper we discuss the use of active vision for the development of autonomous systems. Active vision systems are essentially based on biological motivations. Two systems with potential application to surveillance are described. Both systems behave as watchrobots. One of them involves the integration of an active vision system in a mobile platform. The second system can track non-rigid
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ABSTRACT When considering non-central imaging devices, the computation of the relative pose requires the estimation of the rotation and translation that transform the 3D lines from one coordinate system to the second. In most of the... more
ABSTRACT When considering non-central imaging devices, the computation of the relative pose requires the estimation of the rotation and translation that transform the 3D lines from one coordinate system to the second. In most of the state-of-the-art methods, this transformation is estimated by the computing a 6 × 6 matrix, known as the Generalized Essential Matrix. To allow a better understanding of this matrix, we derive some properties associated with its singular value decomposition.
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The common dolphin (Delphinus delphis) is one of the most abundant species in Atlantic Iberia, representing a potentially important tool to assess the bioaccumulation of trace elements in the Iberian marine ecosystem. Nine elements (As,... more
The common dolphin (Delphinus delphis) is one of the most abundant species in Atlantic Iberia, representing a potentially important tool to assess the bioaccumulation of trace elements in the Iberian marine ecosystem. Nine elements (As, Cd, Cu, Hg, Mn, Ni, Pb, Se and Zn) were evaluated in 36 dolphins stranded in continental Portugal. Dolphins had increasing Hg concentrations (16.72μg·g(-1) ww, liver) compared with previous studies in Atlantic Iberia, whereas Cd concentrations (2.26μg·g(-1) ww, kidney) fell within reported ranges. The concentrations of some trace elements (including Cd and Hg) presented positive relationships with dolphin length, presence of parasites and gross pathologies. Common dolphins may help biomonitoring more offshore Atlantic Iberian areas in future studies, which would otherwise be difficult to assess.
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In this paper, the general problem of mapping an n-dimensional polytope Q to an m-dimensional polytope P by P=AQ with n>m is studied. It is well-known that some vertices of Q are mapped to internal points of P, and it is very... more
In this paper, the general problem of mapping an n-dimensional polytope Q to an m-dimensional polytope P by P=AQ with n>m is studied. It is well-known that some vertices of Q are mapped to internal points of P, and it is very time consuming to detect them when their number is large. A computationally efficient recursive algorithm based on dimension-growing
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Research Interests: Computer Vision and Text
... Miquel Mascaro Portells, Arnau Mir, and Francisco Perales ... Juan Mendez, Antonio Falcon, and Javier Lorenzo An Algebra for the Treatment of Multivalued Information ... Ramon A. Mollineda, Enrique Vidal, and Carlos Martinez-Hinarejos... more
... Miquel Mascaro Portells, Arnau Mir, and Francisco Perales ... Juan Mendez, Antonio Falcon, and Javier Lorenzo An Algebra for the Treatment of Multivalued Information ... Ramon A. Mollineda, Enrique Vidal, and Carlos Martinez-Hinarejos Multiple Segmentation of Moving Objects ...
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As a consequence of the aperture problem, when a moving sine-grating is viewed through an aperture, the perceived motion is ambiguous. However, when we superimpose two of these gratings, the resulting pattern usually moves in a coherent... more
As a consequence of the aperture problem, when a moving sine-grating is viewed through an aperture, the perceived motion is ambiguous. However, when we superimpose two of these gratings, the resulting pattern usually moves in a coherent way. It has been shown that the orientation, speed, contrast, and spatial frequency of each plaid are parameters that influence the perception of coherence. We have studied the stimulus conditions under which coherence does and does not occur, using human observers who assigned a probability of coherence to each sequence of images. We then tried to find a computational method whose result would correlate with the results from the human observers. The proposed method consists of computing the optical flow field on the image sequence, then using the direction of the optical flow in each point on the image to build a histogram. This histogram can provide information about the probability of coherence of the image sequences. We show that the proposed method provides results very similar to the ones obtained with the human observers in terms of probability of coherence.
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Research Interests: Information Systems, Algorithms, Artificial Intelligence, Photography, Calibration, and 14 moreThree Dimensional Imaging, Cluster Analysis, Visual Servoing, 3-D Reconstruction, Omnidirectional vision systems, Information Storage and Retrieval, ECCV, Image Enhancement, Field of View, Electrical And Electronic Engineering, Projective Geometry, Image Formation, Robot Navigation, and Generic model
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This study presents data on abundance and density of macro-floating marine debris (FMD), including their composition, spatial distribution and potential sources off continental Portugal. FMD were assessed by shipboard visual surveys... more
This study presents data on abundance and density of macro-floating marine debris (FMD), including their composition, spatial distribution and potential sources off continental Portugal. FMD were assessed by shipboard visual surveys covering ±252,833km(2) until the 220nm limit. The FMD average density was 2.98items/km(2) and abundance amounted to 752,740 items. Unidentified plastics constitute the major bulk of FMD (density=0.46items/km(2); abundance=117,390 items), followed by styrofoam, derelict or lost materials from fisheries, paper/cardboard and wood material. The North sector of the area presents higher FMD diversity and abundances, probably as a result of the high number of navigation corridors and fisheries operating in that sector. Most FMD originate from local sources, namely discharges from vessels and derelict material from fisheries. Considering the identifiable items, cables and fishing lines were the only fishing related items among the top ten FMD items in Portuguese offshore waters.
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David Lowe's influential and classic algorithm for tracking objects with known geometry is formulated with certain simplifying assumptions. A version implemented by Ishii et al. makes different simplifying assumptions. We formulate a... more
David Lowe's influential and classic algorithm for tracking objects with known geometry is formulated with certain simplifying assumptions. A version implemented by Ishii et al. makes different simplifying assumptions. We formulate a full projective solution and apply the same algorithm ...
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Cetaceans are known to interact with numerous fisheries in many parts of the world resulting sometimes in detrimental effects for the animals (by catch and incidental mortality) and the fishery (reduction of catches, increasing fishing... more
Cetaceans are known to interact with numerous fisheries in many parts of the world resulting sometimes in detrimental effects for the animals (by catch and incidental mortality) and the fishery (reduction of catches, increasing fishing time, loss of gear, depredation). In Portugal, four of the 19 species of cetaceans found in continental waters overlap with the sardine purse seine fishery: Phocoena phocoena; Delphinus Delphis; Tursiops truncatus; and Balaenoptera acutorostrata. In the present study, cetacean interactions with the fishery operating in different ports along the Portuguese coast were studied from Spring to Fall 2010-2011. Observers monitored over 80 fishing trips and this at-sea work was complemented by an interview survey carried out to all the purse seine skippers operating off the Southern coast (Algarve). Only Delphinus delphis was observed to interact with fishing activities, which most frequently occurred in the Southern coast (Algarve). Mean fishing effort value...