368,508 research outputs found
A Novel Method for the Absolute Pose Problem with Pairwise Constraints
Absolute pose estimation is a fundamental problem in computer vision, and it
is a typical parameter estimation problem, meaning that efforts to solve it
will always suffer from outlier-contaminated data. Conventionally, for a fixed
dimensionality d and the number of measurements N, a robust estimation problem
cannot be solved faster than O(N^d). Furthermore, it is almost impossible to
remove d from the exponent of the runtime of a globally optimal algorithm.
However, absolute pose estimation is a geometric parameter estimation problem,
and thus has special constraints. In this paper, we consider pairwise
constraints and propose a globally optimal algorithm for solving the absolute
pose estimation problem. The proposed algorithm has a linear complexity in the
number of correspondences at a given outlier ratio. Concretely, we first
decouple the rotation and the translation subproblems by utilizing the pairwise
constraints, and then we solve the rotation subproblem using the
branch-and-bound algorithm. Lastly, we estimate the translation based on the
known rotation by using another branch-and-bound algorithm. The advantages of
our method are demonstrated via thorough testing on both synthetic and
real-world dataComment: 10 pages, 7figure
Position and Orientation Estimation through Millimeter Wave MIMO in 5G Systems
Millimeter wave signals and large antenna arrays are considered enabling
technologies for future 5G networks. While their benefits for achieving
high-data rate communications are well-known, their potential advantages for
accurate positioning are largely undiscovered. We derive the Cram\'{e}r-Rao
bound (CRB) on position and rotation angle estimation uncertainty from
millimeter wave signals from a single transmitter, in the presence of
scatterers. We also present a novel two-stage algorithm for position and
rotation angle estimation that attains the CRB for average to high
signal-to-noise ratio. The algorithm is based on multiple measurement vectors
matching pursuit for coarse estimation, followed by a refinement stage based on
the space-alternating generalized expectation maximization algorithm. We find
that accurate position and rotation angle estimation is possible using signals
from a single transmitter, in either line-of- sight, non-line-of-sight, or
obstructed-line-of-sight conditions.Comment: The manuscript has been revised, and increased from 27 to 31 pages.
Also, Fig.2, Fig. 10 and Table I are adde
Constraining differential rotation of Sun-like stars from asteroseismic and starspot rotation periods
In previous work we identified six Sun-like stars observed by Kepler with
exceptionally clear asteroseismic signatures of rotation. Here, we show that
five of these stars exhibit surface variability suitable for measuring
rotation. In order to further constrain differential rotation, we compare the
rotation periods obtained from light-curve variability with those from
asteroseismology. The two rotation measurement methods are found to agree
within uncertainties, suggesting that radial differential rotation is weak, as
is the case for the Sun. Furthermore, we find significant discrepancies between
ages from asteroseismology and from three different gyrochronology relations,
implying that stellar age estimation is problematic even for Sun-like stars.Comment: Accepted for publication in A&A. 5 pages, 4 figure
Looking for activity cycles in late-type Kepler stars using time-frequency analysis
We analyse light curves covering four years of 39 fast-rotating
() late-type active stars from the Kepler database. Using
time-frequency analysis (Short-Term Fourier-Transform), we find hints for
activity cycles of 300-900 days at 9 targets from the changing typical latitude
of the starspots, which, with the differential rotation of the stellar surface
change the observed rotation period over the activity cycle. We also give a
lowest estimation for the shear parameter of the differential rotation, which
is ~0.001 for the cycling targets. These results populate the less studied,
short period end of the rotation-cycle length relation.Comment: 12 pages, 7 figures, accepted for publication in MNRA
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