3,085 research outputs found
A REVIEW OF GEOMETRIC MODELS AND SELF-CALIBRATION METHODS FOR TERRESTRIAL LASER SCANNERS
Terrestrial laser scanning has been shown to be an invaluable technology for engineering measurement applications such as structural deformation measurement and rockfall monitoring. In order to ensure the quality of the data captured for these and other applications, all systematic instrument errors must be properly modelled, calibrated and corrected prior to using the data in subsequent stability or deformation analyses. In one popular modelling approach, the range and angular observations from a laser scanner are augmented with additive model terms that describe the systematic errors. Self-calibration methods can then be used in order to estimate the coefficients of these models. This paper provides a review of the current state-of-the-art of terrestrial laser scanner systematic error models and self-calibration methods, supported by real-dataset examples that demonstrate the need for these processes
Architectural Scene Reconstruction from Single or Multiple Uncalibrated Images
In this paper we present a system for the reconstruction of 3D models of architectural scenes from single or multiple uncalibrated images. The partial 3D model of a building is recovered from a single image using geometric constraints such as parallelism and orthogonality, which are likely to be found in most architectural scenes. The approximate corner positions of a building are selected interactively by a user and then further refined automatically using Hough transform. The relative depths of the corner points are calculated according to the perspective projection model. Partial 3D models recovered from different viewpoints are registered to a common coordinate system for integration. The 3D model registration process is carried out using modified ICP (iterative closest point) algorithm with the initial parameters provided by geometric constraints of the building. The integrated 3D model is then fitted with piecewise planar surfaces to generate a more geometrically consistent model. The acquired images are finally mapped onto the surface of the reconstructed 3D model to create a photo-realistic model. A working system which allows a user to interactively build a 3D model of an architectural scene from single or multiple images has been proposed and implemented
Feasibility of free space quantum key distribution with coherent polarization states
We demonstrate for the first time the feasibility of free space quantum key
distribution with continuous variables under real atmospheric conditions. More
specifically, we transmit coherent polarization states over a 100m free space
channel on the roof of our institute's building. In our scheme, signal and
local oscillator are combined in a single spatial mode which auto-compensates
atmospheric fluctuations and results in an excellent interference. Furthermore,
the local oscillator acts as spatial and spectral filter thus allowing
unrestrained daylight operation.Comment: 12 pages, 8 figures, extensions in sections 2, 3.1, 3.2 and 4. This
is an author-created, un-copyedited version of an article accepted for
publication in New Journal of Physics (Special Issue on Quantum Cryptography:
Theory and Practice). IOP Publishing Ltd is not responsible for any errors or
omissions in this version of the manuscript or any version derived from i
First Year Wilkinson Microwave Anisotropy Probe (WMAP) Observations: Angular Power Spectrum
We present the angular power spectrum derived from the first-year Wilkinson
Microwave Anisotropy Probe (WMAP) sky maps. We study a variety of power
spectrum estimation methods and data combinations and demonstrate that the
results are robust. The data are modestly contaminated by diffuse Galactic
foreground emission, but we show that a simple Galactic template model is
sufficient to remove the signal. Point sources produce a modest contamination
in the low frequency data. After masking ~700 known bright sources from the
maps, we estimate residual sources contribute ~3500 uK^2 at 41 GHz, and ~130
uK^2 at 94 GHz, to the power spectrum l*(l+1)*C_l/(2*pi) at l=1000. Systematic
errors are negligible compared to the (modest) level of foreground emission.
Our best estimate of the power spectrum is derived from 28 cross-power spectra
of statistically independent channels. The final spectrum is essentially
independent of the noise properties of an individual radiometer. The resulting
spectrum provides a definitive measurement of the CMB power spectrum, with
uncertainties limited by cosmic variance, up to l~350. The spectrum clearly
exhibits a first acoustic peak at l=220 and a second acoustic peak at l~540 and
it provides strong support for adiabatic initial conditions. Kogut et al.
(2003) analyze the C_l^TE power spectrum, and present evidence for a relatively
high optical depth, and an early period of cosmic reionization. Among other
things, this implies that the temperature power spectrum has been suppressed by
\~30% on degree angular scales, due to secondary scattering.Comment: One of thirteen companion papers on first-year WMAP results submitted
to ApJ; 44 pages, 14 figures; a version with higher quality figures is also
available at http://lambda.gsfc.nasa.gov/product/map/map_bibliography.htm
Common and Distinct Components in Data Fusion
In many areas of science multiple sets of data are collected pertaining to
the same system. Examples are food products which are characterized by
different sets of variables, bio-processes which are on-line sampled with
different instruments, or biological systems of which different genomics
measurements are obtained. Data fusion is concerned with analyzing such sets of
data simultaneously to arrive at a global view of the system under study. One
of the upcoming areas of data fusion is exploring whether the data sets have
something in common or not. This gives insight into common and distinct
variation in each data set, thereby facilitating understanding the
relationships between the data sets. Unfortunately, research on methods to
distinguish common and distinct components is fragmented, both in terminology
as well as in methods: there is no common ground which hampers comparing
methods and understanding their relative merits. This paper provides a unifying
framework for this subfield of data fusion by using rigorous arguments from
linear algebra. The most frequently used methods for distinguishing common and
distinct components are explained in this framework and some practical examples
are given of these methods in the areas of (medical) biology and food science.Comment: 50 pages, 12 figure
A Self-calibration Algorithm Based on a Unified Framework for Constraints on Multiple Views
In this paper, we propose a new self-calibration algorithm for upgrading projective space to Euclidean space. The proposed method aims to combine the most commonly used metric constraints, including zero skew and unit aspect-ratio by formulating each constraint as a cost function within a unified framework. Additional constraints, e.g., constant principal points, can also be formulated in the same framework. The cost function is very flexible and can be composed of different constraints on different views. The upgrade process is then stated as a minimization problem which may be solved by minimizing an upper bound of the cost function. This proposed method is non-iterative. Experimental results on synthetic data and real data are presented to show the performance of the proposed method and accuracy of the reconstructed scene. © 2012 The Author(s).published_or_final_versionSpringer Open Choice, 25 May 201
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