533,600 research outputs found
A survey on rotation optimization in structure from motion
We consider the problem of robust rotation optimization
in Structure from Motion applications. A number of different
approaches have been recently proposed, with solutions that
are at times incompatible, and at times complementary. The
goal of this paper is to survey and compare these ideas in a
unified manner, and to benchmark their robustness against
the presence of outliers. In all, we have tested more than
forty variants of a these methods (including novel ones), and
we find the best performing combination.NSFDGE-0966142 (IGERT), NSF-IIS-1317788, NSF-IIP-1439681 (I/UCRC), NSF-IIS-1426840, ARL MAST-CTA W911NF-08-2-0004, ARL RCTA W911NF-10-2-0016, ONR N000141310778
On the recovery of Local Group motion from galaxy redshift surveys
There is a discrepancy between the measured motion of
the Local Group of galaxies (LG) with respect to the CMB and the linear theory
prediction based on the gravitational force field of the large scale structure
in full-sky redshift surveys. We perform a variety of tests which show that the
LG motion cannot be recovered to better than in amplitude
and within a in direction. The tests rely on catalogs of mock
galaxies identified in the Millennium simulation using semi-analytic galaxy
formation models. We compare these results to the Two-Mass Galaxy
Redshift Survey, which provides the deepest, widest and most complete spatial
distribution of galaxies available so far. In our analysis we use a new,
concise relation for deriving the LG motion and bulk flow from the true
distribution of galaxies in redshift space. Our results show that the main
source of uncertainty is the small effective depth of surveys like the 2MRS
that prevents a proper sampling of the large scale structure beyond . Deeper redshift surveys are needed to reach the "convergence
scale" of in a CDM universe. Deeper survey
would also mitigate the impact of the "Kaiser rocket" which, in a survey like
2MRS, remains a significant source of uncertainty. Thanks to the quiet and
moderate density environment of the LG, purely dynamical uncertainties of the
linear predictions are subdominant at the level of .
Finally, we show that deviations from linear galaxy biasing and shot noise
errors provide a minor contribution to the total error budget.Comment: 14 pages, 7 figure
Human Motion Trajectory Prediction: A Survey
With growing numbers of intelligent autonomous systems in human environments,
the ability of such systems to perceive, understand and anticipate human
behavior becomes increasingly important. Specifically, predicting future
positions of dynamic agents and planning considering such predictions are key
tasks for self-driving vehicles, service robots and advanced surveillance
systems. This paper provides a survey of human motion trajectory prediction. We
review, analyze and structure a large selection of work from different
communities and propose a taxonomy that categorizes existing methods based on
the motion modeling approach and level of contextual information used. We
provide an overview of the existing datasets and performance metrics. We
discuss limitations of the state of the art and outline directions for further
research.Comment: Submitted to the International Journal of Robotics Research (IJRR),
37 page
Lagrangian view of time irreversibility of fluid turbulence
A turbulent flow is maintained by an external supply of kinetic energy, which
is eventually dissipated into heat at steep velocity gradients. The scale at
which energy is supplied greatly differs from the scale at which energy is
dissipated, the more so as the turbulent intensity (the Reynolds number) is
larger. The resulting energy flux over the range of scales, intermediate
between energy injection and dissipation, acts as a source of time
irreversibility. As it is now possible to follow accurately fluid particles in
a turbulent flow field, both from laboratory experiments and from numerical
simulations, a natural question arises: how do we detect time irreversibility
from these Lagrangian data? Here we discuss recent results concerning this
problem. For Lagrangian statistics involving more than one fluid particle, the
distance between fluid particles introduces an intrinsic length scale into the
problem. The evolution of quantities dependent on the relative motion between
these fluid particles, including the kinetic energy in the relative motion, or
the configuration of an initially isotropic structure can be related to the
equal-time correlation functions of the velocity field, and is therefore
sensitive to the energy flux through scales, hence to the irreversibility of
the flow. In contrast, for single-particle Lagrangian statistics, the most
often studied velocity structure functions cannot distinguish the "arrow of
time." Recent observations from experimental and numerical simulation data,
however, show that the change of kinetic energy following the particle motion,
is sensitive to time-reversal. We end the survey with a brief discussion of the
implication of this line of work.Comment: accepted for publication in Science China - Physics, Mechanics &
Astronom
L1599B: Cloud Envelope and C+ Emission in a Region of Moderately Enhanced Radiation Field
We study the effects of an asymmetric radiation field on the properties of a
molecular cloud envelope. We employ observations of carbon monoxide (12CO and
13CO), atomic carbon, ionized carbon, and atomic hydrogen to analyze the
chemical and physical properties of the core and envelope of L1599B, a
molecular cloud forming a portion of the ring at approximately 27 pc from the
star Lambda Ori. The O III star provides an asymmetric radiation field that
produces a moderate enhancement of the external radiation field. Observations
of the [CII] fine structure line with the GREAT instrument on SOFIA indicate a
significant enhanced emission on the side of the cloud facing the star, while
the [Ci], 12CO and 13CO J = 1-0 and 2-1, and 12CO J = 3-2 data from the PMO and
APEX telescopes suggest a relatively typical cloud interior. The atomic, ionic,
and molecular line centroid velocities track each other very closely, and
indicate that the cloud may be undergoing differential radial motion. The HI
data from the Arecibo GALFA survey and the SOFIA/GREAT [CII] data do not
suggest any systematic motion of the halo gas, relative to the dense central
portion of the cloud traced by 12CO and 13CO.Comment: 9 Figure
Fore! GPR survey of the Belhus Tudor water gardens
Covid-19 restrictions allowed unique access to this site on a temporarily closed golf course. Vehicle towed ground penetrating radar survey provided rapid coverage of the site. Geophysical survey helped support local volunteer research groups. Significant remains survive despite demolition of the Tudor mansion and landscaping for the golf-course. Detailed topographic data was generated from UAV based photography through Structure from Motion
The potential of small unmanned aircraft systems and structure-from-motion for topographic surveys: a test of emerging integrated approaches at Cwm Idwal, North Wales
This paper was accepted for publication in the journal Geomorphology and the definitive published version is available at http://dx.doi.org/10.1016/j.geomorph.2014.07.021Novel topographic survey methods that integrate both structure-from-motion (SfM) photogrammetry and small unmanned aircraft systems (sUAS) are a rapidly evolving investigative technique. Due to the diverse range of survey configurations available and the infancy of these new methods, further research is required. Here, the accuracy, precision and potential applications of this approach are investigated. A total of 543 images of the Cwm Idwal moraine–mound complex were captured from a light (b5 kg) semi-autonomous multi-rotor unmanned aircraft system using a consumer-grade 18 MP compact digital camera. The imageswere used to produce a DSM(digital surfacemodel) of themoraines. The DSMis in good agreement with 7761 total station survey points providing a total verticalRMSE value of 0.517mand verticalRMSE values as lowas 0.200mfor less densely vegetated areas of the DSM. High-precision topographic data can be acquired rapidly using this technique with
the resulting DSMs and orthorectified aerial imagery at sub-decimetre resolutions. Positional errors on the total station dataset, vegetation and steep terrain are identified as the causes of vertical disagreement. Whilst this aerial survey approach is advocated for use in a range of geomorphological settings, care must be taken to ensure that adequate ground control is applied to give a high degree of accuracy
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