58,194 research outputs found
3D Visual Perception for Self-Driving Cars using a Multi-Camera System: Calibration, Mapping, Localization, and Obstacle Detection
Cameras are a crucial exteroceptive sensor for self-driving cars as they are
low-cost and small, provide appearance information about the environment, and
work in various weather conditions. They can be used for multiple purposes such
as visual navigation and obstacle detection. We can use a surround multi-camera
system to cover the full 360-degree field-of-view around the car. In this way,
we avoid blind spots which can otherwise lead to accidents. To minimize the
number of cameras needed for surround perception, we utilize fisheye cameras.
Consequently, standard vision pipelines for 3D mapping, visual localization,
obstacle detection, etc. need to be adapted to take full advantage of the
availability of multiple cameras rather than treat each camera individually. In
addition, processing of fisheye images has to be supported. In this paper, we
describe the camera calibration and subsequent processing pipeline for
multi-fisheye-camera systems developed as part of the V-Charge project. This
project seeks to enable automated valet parking for self-driving cars. Our
pipeline is able to precisely calibrate multi-camera systems, build sparse 3D
maps for visual navigation, visually localize the car with respect to these
maps, generate accurate dense maps, as well as detect obstacles based on
real-time depth map extraction
Control charts for the on-line diagnostics of CMM performance
The quality of a production process is increasing its dependence on both the manufacturing technology, and the production control. In most applications controls are operated by relying on intelligent instrumentation to 'automatically' perform the programmed checks. However, the performance systems that verify the product's quality can deteriorate, as can the production process. This paper presents a method for the on-line verification of the performance of a coordinate measuring machine (CMM) using statistically based control charts. The method is automated and performed on-line during a normal measurement cycle. Some experimental results are then presented and discussed
Scheduling and calibration strategy for continuous radio monitoring of 1700 sources every three days
The Owens Valley Radio Observatory 40 meter telescope is currently monitoring
a sample of about 1700 blazars every three days at 15 GHz, with the main
scientific goal of determining the relation between the variability of blazars
at radio and gamma-rays as observed with the Fermi Gamma-ray Space Telescope.
The time domain relation between radio and gamma-ray emission, in particular
its correlation and time lag, can help us determine the location of the
high-energy emission site in blazars, a current open question in blazar
research. To achieve this goal, continuous observation of a large sample of
blazars in a time scale of less than a week is indispensable. Since we only
look at bright targets, the time available for target observations is mostly
limited by source observability, calibration requirements and slewing of the
telescope. Here I describe the implementation of a practical solution to this
scheduling, calibration, and slewing time minimization problem. This solution
combines ideas from optimization, in particular the traveling salesman problem,
with astronomical and instrumental constraints. A heuristic solution using well
stablished optimization techniques and astronomical insights particular to this
situation, allow us to observe all the sources in the required three days
cadence while obtaining reliable calibration of the radio flux densities.
Problems of this nature will only be more common in the future and the ideas
presented here can be relevant for other observing programs.Comment: Published in Proc. SPIE. 9149, Observatory Operations: Strategies,
Processes, and Systems V, 91492
Multisource Self-calibration for Sensor Arrays
Calibration of a sensor array is more involved if the antennas have direction
dependent gains and multiple calibrator sources are simultaneously present. We
study this case for a sensor array with arbitrary geometry but identical
elements, i.e. elements with the same direction dependent gain pattern. A
weighted alternating least squares (WALS) algorithm is derived that iteratively
solves for the direction independent complex gains of the array elements, their
noise powers and their gains in the direction of the calibrator sources. An
extension of the problem is the case where the apparent calibrator source
locations are unknown, e.g., due to refractive propagation paths. For this
case, the WALS method is supplemented with weighted subspace fitting (WSF)
direction finding techniques. Using Monte Carlo simulations we demonstrate that
both methods are asymptotically statistically efficient and converge within two
iterations even in cases of low SNR.Comment: 11 pages, 8 figure
Robust Radio Interferometric Calibration Using the t-Distribution
A major stage of radio interferometric data processing is calibration or the
estimation of systematic errors in the data and the correction for such errors.
A stochastic error (noise) model is assumed, and in most cases, this underlying
model is assumed to be Gaussian. However, outliers in the data due to
interference or due to errors in the sky model would have adverse effects on
processing based on a Gaussian noise model. Most of the shortcomings of
calibration such as the loss in flux or coherence, and the appearance of
spurious sources, could be attributed to the deviations of the underlying noise
model. In this paper, we propose to improve the robustness of calibration by
using a noise model based on Student's t distribution. Student's t noise is a
special case of Gaussian noise when the variance is unknown. Unlike Gaussian
noise model based calibration, traditional least squares minimization would not
directly extend to a case when we have a Student's t noise model. Therefore, we
use a variant of the Expectation Maximization (EM) algorithm, called the
Expectation-Conditional Maximization Either (ECME) algorithm when we have a
Student's t noise model and use the Levenberg-Marquardt algorithm in the
maximization step. We give simulation results to show the robustness of the
proposed calibration method as opposed to traditional Gaussian noise model
based calibration, especially in preserving the flux of weaker sources that are
not included in the calibration model.Comment: MNRAS accepte
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