486 research outputs found
Robust curvature extrema detection based on new numerical derivation
International audienceExtrema of curvature are useful key points for different image analysis tasks. Indeed, polygonal approximation or arc decomposition methods used often these points to initialize or to improve their algorithms. Several shape-based image retrieval methods focus also their descriptors on key points. This paper is focused on the detection of extrema of curvature points for a raster-to-vector-conversion framework. We propose an original adaptation of an approach used into nonlinear control for fault-diagnosis and fault-tolerant control based on algebraic derivation and which is robust to noise. The experimental results are promising and show the robustness of the approach when the contours are bathed into a high level speckled noise
Probabilistic Solutions to Differential Equations and their Application to Riemannian Statistics
We study a probabilistic numerical method for the solution of both boundary
and initial value problems that returns a joint Gaussian process posterior over
the solution. Such methods have concrete value in the statistics on Riemannian
manifolds, where non-analytic ordinary differential equations are involved in
virtually all computations. The probabilistic formulation permits marginalising
the uncertainty of the numerical solution such that statistics are less
sensitive to inaccuracies. This leads to new Riemannian algorithms for mean
value computations and principal geodesic analysis. Marginalisation also means
results can be less precise than point estimates, enabling a noticeable
speed-up over the state of the art. Our approach is an argument for a wider
point that uncertainty caused by numerical calculations should be tracked
throughout the pipeline of machine learning algorithms.Comment: 11 page (9 page conference paper, plus supplements
Active skeleton for bacteria modeling
The investigation of spatio-temporal dynamics of bacterial cells and their
molecular components requires automated image analysis tools to track cell
shape properties and molecular component locations inside the cells. In the
study of bacteria aging, the molecular components of interest are protein
aggregates accumulated near bacteria boundaries. This particular location makes
very ambiguous the correspondence between aggregates and cells, since computing
accurately bacteria boundaries in phase-contrast time-lapse imaging is a
challenging task. This paper proposes an active skeleton formulation for
bacteria modeling which provides several advantages: an easy computation of
shape properties (perimeter, length, thickness, orientation), an improved
boundary accuracy in noisy images, and a natural bacteria-centered coordinate
system that permits the intrinsic location of molecular components inside the
cell. Starting from an initial skeleton estimate, the medial axis of the
bacterium is obtained by minimizing an energy function which incorporates
bacteria shape constraints. Experimental results on biological images and
comparative evaluation of the performances validate the proposed approach for
modeling cigar-shaped bacteria like Escherichia coli. The Image-J plugin of the
proposed method can be found online at http://fluobactracker.inrialpes.fr.Comment: Published in Computer Methods in Biomechanics and Biomedical
Engineering: Imaging and Visualizationto appear i
Topological Navigation of Simulated Robots using Occupancy Grid
Formerly I presented a metric navigation method in the Webots mobile robot
simulator. The navigating Khepera-like robot builds an occupancy grid of the
environment and explores the square-shaped room around with a value iteration
algorithm. Now I created a topological navigation procedure based on the
occupancy grid process. The extension by a skeletonization algorithm results a
graph of important places and the connecting routes among them. I also show the
significant time profit gained during the process
Euler Characteristic Curves and Profiles: a stable shape invariant for big data problems
Tools of Topological Data Analysis provide stable summaries encapsulating the
shape of the considered data. Persistent homology, the most standard and well
studied data summary, suffers a number of limitations; its computations are
hard to distribute, it is hard to generalize to multifiltrations and is
computationally prohibitive for big data-sets. In this paper we study the
concept of Euler Characteristics Curves, for one parameter filtrations and
Euler Characteristic Profiles, for multi-parameter filtrations. While being a
weaker invariant in one dimension, we show that Euler Characteristic based
approaches do not possess some handicaps of persistent homology; we show
efficient algorithms to compute them in a distributed way, their generalization
to multifiltrations and practical applicability for big data problems. In
addition we show that the Euler Curves and Profiles enjoys certain type of
stability which makes them robust tool in data analysis. Lastly, to show their
practical applicability, multiple use-cases are considered.Comment: 32 pages, 19 figures. Added remark on multicritical filtrations in
section 4, typos correcte
AUTOMATED DETECTION AND VECTORIZATION OF ROAD ELEMENTS IN HIGH RESOLUTION ORTHOGRAPHIC IMAGES
This paper proposes, describes, and applies an algorithm for the automatic detection of selected elements of road infrastructure, along with the option to determine their spatial information. The principle is based on the evaluation of the color spectrum of the selected object on orthographic images. As a source image used for the processing, output from low-altitude aerial photogrammetry or terrestrial laser scanning can be used, together with the option to implement digital elevation models into the processing. The approach is based on the detection of the color composition of the selected element of the road, followed by clustering of the identified elements within the image and mathematical transformation of the clusters into a spatial vector form. Prior to the processing, the target objects are filtered out based on user input, for which vectorization is performed. The outputs are in the form of contours or the determined basic structure of the object. The main difference compared to existing methods is that the vectorization is only performed on the selected, pre-filtered parts of the raster image with identified target objects, not the whole image. This approach makes it possible to effectively and automatically identify and analyze, e.g., the edge of the road, road markings, or road features. This enables the subsequent implementation of the identified outputs into more complex spatial models of the road or its proximity. Additionally, the processing of the data to create a digital model of the environment can be automated, with a significant saving of time and related costs
New Confocal Hyperbola-based Ellipse Fitting with Applications to Estimating Parameters of Mechanical Pipes from Point Clouds
This manuscript presents a new method for fitting ellipses to two-dimensional
data using the confocal hyperbola approximation to the geometric distance of
points to ellipses. The proposed method was evaluated and compared to
established methods on simulated and real-world datasets. First, it was
revealed that the confocal hyperbola distance considerably outperforms other
distance approximations such as algebraic and Sampson. Next, the proposed
ellipse fitting method was compared with five reliable and established methods
proposed by Halir, Taubin, Kanatani, Ahn and Szpak. The performance of each
method as a function of rotation, aspect ratio, noise, and arc-length were
examined. It was observed that the proposed ellipse fitting method achieved
almost identical results (and in some cases better) than the gold standard
geometric method of Ahn and outperformed the remaining methods in all
simulation experiments. Finally, the proposed method outperformed the
considered ellipse fitting methods in estimating the geometric parameters of
cylindrical mechanical pipes from point clouds. The results of the experiments
show that the confocal hyperbola is an excellent approximation to the true
geometric distance and produces reliable and accurate ellipse fitting in
practical settings
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