2,494 research outputs found
Probabilistic RGB-D Odometry based on Points, Lines and Planes Under Depth Uncertainty
This work proposes a robust visual odometry method for structured
environments that combines point features with line and plane segments,
extracted through an RGB-D camera. Noisy depth maps are processed by a
probabilistic depth fusion framework based on Mixtures of Gaussians to denoise
and derive the depth uncertainty, which is then propagated throughout the
visual odometry pipeline. Probabilistic 3D plane and line fitting solutions are
used to model the uncertainties of the feature parameters and pose is estimated
by combining the three types of primitives based on their uncertainties.
Performance evaluation on RGB-D sequences collected in this work and two public
RGB-D datasets: TUM and ICL-NUIM show the benefit of using the proposed depth
fusion framework and combining the three feature-types, particularly in scenes
with low-textured surfaces, dynamic objects and missing depth measurements.Comment: Major update: more results, depth filter released as opensource, 34
page
Range-only underwater target localization : error characterization
Locating a target from range measurements
using only one mobile transducer has been increased
over the last years. This method allows us to reduce the
high costs of deployment and maintenance of
traditional fixed systems on the seafloor such as Long
Baseline. The range-only single-beacon is one of the
new architectures developed using the new capabilities
of modern acoustic underwater modems, which can be
time synchronization, time stamp, and range
measurements.
This document presents a method to estimate the
sources of error in this type of architecture so as to
obtain a mathematical model which allows us to
develop simulations and study the best localization
algorithms. Different simulations and real field tests
have been carried out in order to verify a good
performance of the model proposed.Postprint (published version
Separating true range measurements from multi-path and scattering interference in commercial range cameras
Time-of-flight range cameras acquire a three-dimensional image of a scene simultaneously for all pixels from a single viewing location. Attempts to use range cameras for metrology applications have been hampered by the multi-path problem, which causes range distortions when stray light interferes with the range measurement in a given pixel. Correcting multi-path distortions by post-processing the three-dimensional measurement data has been investigated, but enjoys limited success because the interference is highly scene dependent. An alternative approach based on separating the strongest and weaker sources of light returned to each pixel, prior to range decoding, is more successful, but has only been demonstrated on custom built range cameras, and has not been suitable for general metrology applications. In this paper we demonstrate an algorithm applied to both the Mesa Imaging SR-4000 and Canesta Inc. XZ-422 Demonstrator unmodified off-the-shelf range cameras. Additional raw images are acquired and processed using an optimization approach, rather than relying on the processing provided by the manufacturer, to determine the individual component returns in each pixel. Substantial improvements in accuracy are observed, especially in the darker regions of the scene
Optical techniques for 3D surface reconstruction in computer-assisted laparoscopic surgery
One of the main challenges for computer-assisted surgery (CAS) is to determine the intra-opera- tive morphology and motion of soft-tissues. This information is prerequisite to the registration of multi-modal patient-specific data for enhancing the surgeonâs navigation capabilites by observ- ing beyond exposed tissue surfaces and for providing intelligent control of robotic-assisted in- struments. In minimally invasive surgery (MIS), optical techniques are an increasingly attractive approach for in vivo 3D reconstruction of the soft-tissue surface geometry. This paper reviews the state-of-the-art methods for optical intra-operative 3D reconstruction in laparoscopic surgery and discusses the technical challenges and future perspectives towards clinical translation. With the recent paradigm shift of surgical practice towards MIS and new developments in 3D opti- cal imaging, this is a timely discussion about technologies that could facilitate complex CAS procedures in dynamic and deformable anatomical regions
Object modeling using a ToF camera under an uncertainty reduction approach
Trabajo presentado al ICRA 2010 celebrado en Anchorage (Alaska) del3 al 7 de mayo.Time-of-Flight (ToF) cameras deliver 3D images at 25 fps, offering great potential for developing fast object modeling algorithms. Surprisingly, this potential has not been extensively exploited up to now. A reason for this is that, since the acquired depth images are noisy, most of the available registration algorithms are hardly applicable. A further difficulty is that the transformations between views are in general not accurately known, a circumstance that multi-view object modeling algorithms do not handle properly under noisy conditions. In this work, we take into account both uncertainty sources (in images and camera poses) to generate spatially consistent 3D object models fusing multiple views with a probabilistic approach. We propose a method to compute the covariance of the registration process, and apply an iterative state estimation method to build object models under noisy conditions.This work was supported by projects: 'Perception, action & cognition through learning of object-action complexes.' (4915), 'CONSOL IDER-INGENIO 2010 Multimodal interaction in pattern recognition and computer vision' (V-00069), 'PercepciĂłn y acciĂłn ante incertidumbre' (4803). This work has been partially supported by the Spanish Ministry of Science and Innovation under project DPI2008-06022, the MIPRCV Consolider
Ingenio 2010 project, and the EU PACO PLUS project FP6-2004-IST-4-27657. S. Foix and G. AlenyĂ are supported by PhD and postdoctoral
fellowships, respectively, from CSICâs JAE program.Peer Reviewe
Time dependence of the e^- flux measured by PAMELA during the July 2006 - December 2009 solar minimum
Precision measurements of the electron component in the cosmic radiation
provide important information about the origin and propagation of cosmic rays
in the Galaxy not accessible from the study of the cosmic-ray nuclear
components due to their differing diffusion and energy-loss processes. However,
when measured near Earth, the effects of propagation and modulation of galactic
cosmic rays in the heliosphere, particularly significant for energies up to at
least 30 GeV, must be properly taken into account. In this paper the electron
(e^-) spectra measured by PAMELA down to 70 MeV from July 2006 to December 2009
over six-months time intervals are presented. Fluxes are compared with a
state-of-the-art three-dimensional model of solar modulation that reproduces
the observations remarkably well.Comment: 40 pages, 18 figures, 1 tabl
Classification and localization of electromagnetic and ultrasonic pulsed emitters
MenciĂłn Internacional en el tĂtulo de doctorThe localization of radiative sources is very important in many fields of work such
as: sonar, radar and underwater radar, indoor localization in wireless networks, earthquake
epicenter localization, defective assets localization in electrical facilities and so
forth. In the process of locating radiative sources exist many issues which can provoke
errors in the localization. The signals acquired may belong to different sources or they
can be mixed with environmental noise, then, their separation before using localization
algorithms is of great interest to be efficient and accurate in the computational process.
Furthermore, the geometry and radiation characteristics of the receivers, the nature of
the signal or their measuring process may cause deviations in the signal onset calculus
and therefore the source localization could be displaced from the actual position.
In this thesis, there are three kinds of algorithms to undertake three steps in the
emitter localization: signal separation, onset and time delay estimation of the signals
and source localization. For each step, in order to reduce the error in the localization,
several algorithms are analyzed and compared in each application, to choose the most
reliable.
As the first step, to separate different kinds of signals is of interest to facilitate further
processing. In this thesis, different optimization techniques are presented over the
power ratio (PR) maps method. The PR uses a selective spectral signal characterization
to extract the features of the analyzed signals. The technique identifies automatically
the most representative frequency bands which report a great separation of the different
kinds of signals in the PR map.
After separating and selecting the signals, it is of interest to compare the algorithms
to calculate the onset and time delay of the pulsed signals to know their performance
because the time variables are inputs to the most common triangulation algorithms to
locate radiative and ultrasonic sources. An overview of the algorithms used to estimate
the time of flight (ToF) and time differences of arrival (TDoA) of pulsed signals is done
in this thesis. In the comparison, there is also a new algorithm based on statics of high
order, which is proposed in this thesis. The survey of their performance is done applied
to muscle deep estimation, localization in one dimension (1D), and for the localization
of emitters in three dimensions (3D). The results show how the presented algorithm
yields great results.
As the last step in the radiative source localization, the formulation and principle
of work of both iterative and non-iterative triangulation algorithms are presented. A
new algorithm is presented as a combination of two already existing improving their
performance when working alone. All the algorithms, the proposed and the previous
which already exist, are compared in terms of accuracy and computational time. The
proposed algorithm reports good results in terms of accuracy and it is one of the fastest
in computational time.
Once the localization is achieved, it is of great interest to understand how the errors
in the determination of the onset of the signals are propagated in the emitter localization.
The triangulation algorithms estimate the radiative source position using
time variables as inputs: ToF, TDoA or pseudo time of flight (pToF) and the receiver
positions. The propagation of the errors in the time variables to the radiative source localization
is done in two dimensions (2D) and 3D. New spherical diagrams have been
created to represent the directions where the localization is more or less sensible to the
errors. This study and their sphere diagrams are presented for several antenna layouts.
Finally, how the errors in the positioning of the receivers are propagated to the
emitter localization is analyzed. In this study, the effect in the propagation of both
the relative distance from the receivers to the emitter and the direction between them
has been characterized. The propagation of the error considering the direction is also
represented in spherical diagrams. For a preferred direction identified in the spheres,
the propagated error in the source localization has been quantified regarding both the
source distance and the magnitude of the errors in the receivers positioning.Programa Oficial de Doctorado en IngenierĂa ElĂ©ctrica, ElectrĂłnica y AutomĂĄticaPresidente: Andrea Cavallini.- Secretario: JosĂ© Antonio GarcĂa Souto.- Vocal: Iliana PortuguĂ©s Peter
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