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Closest Point (closest + point)

Distribution by Scientific Domains
Engineering66%

Selected Abstracts

2D map-building and localization in outdoor environments

JOURNAL OF FIELD ROBOTICS (FORMERLY JOURNAL OF ROBOTIC SYSTEMS), Issue 1 2005
R. Madhavan
Determining the pose (position and orientation) of a vehicle at any time is termed localization and is of paramount importance in achieving reliable and robust autonomous navigation. Knowing the pose it is possible to achieve high level tasks such as path planning. A new map-based algorithm for the localization of vehicles operating in harsh outdoor environments is presented in this article. A map building algorithm using observations from a scanning laser rangefinder is developed for building a polyline map that adequately captures the geometry of the environment. Using this map, the Iterative Closest Point (ICP) algorithm is employed for matching laser range images from the rangefinder to the polyline map. Once correspondences are established, an Extended Kalman Filter (EKF) algorithm provides reliable vehicle state estimates using a nonlinear observation model based on the vertices of the polyline map. Data gathered during field trials in an outdoor environment is used to test the efficiency of the proposed ICP-EKF algorithm in achieving the localization of a four-wheel drive (4WD) vehicle. © 2005 Wiley Periodicals, Inc. [source]

Rapid Human-Assisted Creation of Bounding Models for Obstacle Avoidance in Construction

COMPUTER-AIDED CIVIL AND INFRASTRUCTURE ENGINEERING, Issue 1 2004
J. McLaughlin
A practical, interactive method for doing so is described here. The method: (1) exploits a human operator's ability to quickly recognize significant objects or clusters of objects in a scene, (2) exploits the operator's ability to acquire sparse range point clouds of the objects quickly, and then (3) renders models, such as planes, boxes, and generalized convex hulls, to be displayed graphically as visual feedback during equipment operation and/or for making proximity calculations in an obstacle detection system. Experiments were performed in which test subjects were asked to model objects of varying complexity and clutter. These models were then compared to control models using a ray-tracing algorithm to determine the operator's ability to create conservative models that are critical to construction operations. To demonstrate the applicability of the modeling method to obstacle avoidance, a scripted motion robot simulation was conducted using an artificial potential formulation that monitors position (closest point on manipulator link to nearest obstacle) as well as velocity (link inertia). Experimental results indicate that bounding models can be created rapidly and with sufficient accuracy for obstacle avoidance with the aid of human intelligence and that human-assisted modeling can be very beneficial for real-time construction equipment control. [source]

Scan registration for autonomous mining vehicles using 3D-NDT

JOURNAL OF FIELD ROBOTICS (FORMERLY JOURNAL OF ROBOTIC SYSTEMS), Issue 10 2007
Martin Magnusson
Scan registration is an essential subtask when building maps based on range finder data from mobile robots. The problem is to deduce how the robot has moved between consecutive scans, based on the shape of overlapping portions of the scans. This paper presents a new algorithm for registration of 3D data. The algorithm is a generalization and improvement of the normal distributions transform (NDT) for 2D data developed by Biber and Strasser, which allows for accurate registration using a memory-efficient representation of the scan surface. A detailed quantitative and qualitative comparison of the new algorithm with the 3D version of the popular ICP (iterative closest point) algorithm is presented. Results with actual mine data, some of which were collected with a new prototype 3D laser scanner, show that the presented algorithm is faster and slightly more reliable than the standard ICP algorithm for 3D registration, while using a more memory-efficient scan surface representation. © 2007 Wiley Periodicals, Inc. [source]

Mobile robot motion estimation by 2D scan matching with genetic and iterative closest point algorithms

JOURNAL OF FIELD ROBOTICS (FORMERLY JOURNAL OF ROBOTIC SYSTEMS), Issue 1 2006
Jorge L. Martínez
The paper reports on mobile robot motion estimation based on matching points from successive two-dimensional (2D) laser scans. This ego-motion approach is well suited to unstructured and dynamic environments because it directly uses raw laser points rather than extracted features. We have analyzed the application of two methods that are very different in essence: (i) A 2D version of iterative closest point (ICP), which is widely used for surface registration; (ii) a genetic algorithm (GA), which is a novel approach for this kind of problem. Their performance in terms of real-time applicability and accuracy has been compared in outdoor experiments with nonstop motion under diverse realistic navigation conditions. Based on this analysis, we propose a hybrid GA-ICP algorithm that combines the best characteristics of these pure methods. The experiments have been carried out with the tracked mobile robot Auriga-, and an on-board 2D laser scanner. © 2006 Wiley Periodicals, Inc. [source]

Species Composition of Neotropical Understory Bird Communities: Local Versus Regional Perspectives Based on Capture Data

BIOTROPICA, Issue 1 2009
John G. Blake
ABSTRACT Species richness and composition of bird assemblages found in the understory of undisturbed Neotropical forests vary at local and regional scales but the extent of that variation has not been well documented. Yet, such variation can be important for understanding patterns of diversity and for conservation. Here, we use capture data from two ca 100-ha study plots (sampled from March 2001 through March 2005) to compare understory assemblages at a local scale; nets on the plots were separated by approximately 1.7 km at the closest point. A total of 157 species (133 per plot) was represented in 6023 captures of 4001 individuals. After eliminating species not likely to be well-sampled with nets, there were 122 species total with 110 and 113 on the two plots, respectively. Species-accumulation curves and abundance-rank relationships were almost identical on both plots. Capture rates were high (53 and 56 birds captured per 100 mist-net-hours, mnh) on both plots. Distributions of species and individuals among families and genera were similar on the two plots but numbers of captures of some common species differed between plots in response to small-scale variation in environmental features. Indicator-species analyses selected seven species as more characteristic of one plot and nine as more characteristic of the other. At the regional level, understory assemblages were most similar to a site in Peru but differed from sites in Brazil, Venezuela, and, especially, Costa Rica. Dissimilarity in species richness per family was related to geographic distance only when Costa Rica was included in the analysis. RESUMEN La riqueza de especies y la composición de ensambles de aves de sotobosque en bosques neotropicales varían a escala local y regional, pero el grado de variación no ha sido bien documentado. Sin embargo, esta variación puede ser importante para entender los patrones de diversidad y para conservación. En este trabajo usamos datos de captura de dos parcelas de ca 100-ha (muestreados entre Marzo 2001 y Marzo 2005) para comparar los ensambles de aves de sotobosque a escala local; las redes en las dos parcelas estuvieron ubicadas a una distancia mínima aproximada de 1.7 km. Un total de 157 especies (133 por parcela) estuvieron representadas por 6023 capturas correspondientes a 4001 individuos. Una vez eliminadas aquellas especies que no son factibles de ser muestreadas adecuadamente con redes, el total de especies fue de 122, con 110 y 113 en cada una de los parcelas, respectivamente. Las curvas de acumulación de especies y las relaciones abundancia-rango fueron casi idénticas en ambas parcelas. Las tasas de captura fueron altas (53 y 56 aves capturadas por 100 horas red). La distribución de especies e individuos entre familias y géneros fueron similares en las dos parcelas, pero los números de captura de algunas especies comunes difirieron entre las parcelas en respuesta a la variación de características ambientales a pequeña escala. Los análisis de especies indicadoras seleccionaron siete especies como las más características de una de las parcelas y nueve como las más características de la otra. A nivel regional los ensambles de aves de sotobosque fueron más similares a aquellos presentes en un sitio en Perú, pero fueron diferentes a los presentes en sitios de Brasil, Venezuela y especialmente Costa Rica. La diferencia en riqueza de especies por familia estuvo relacionada con la distancia geográfica sólo cuando Costa Rica fue incluida en el análisis. [source]

Perceptual Causality in Children

CHILD DEVELOPMENT, Issue 6 2002
Anne Schlottmann
Three experiments considered the development of perceptual causality in children from 3 to 9 years of age (N= 176 in total). Adults tend to see cause and effect even in schematic, two,dimensional motion events: Thus, if square A moves toward B, which moves upon contact, they report that A launches B,physical causality. If B moves before contact, adults report that B tries to escape from A,social or psychological causality. A brief pause between movements eliminates such impressions. Even infants in the first year of life are sensitive to causal structure in both contact and no,contact events, but previous research with talking,age children found poor verbal reports. The present experiments used a picture,based forced,choice task to reduce linguistic demands. Observers saw eight different animations involving squares A and B. Events varied in whether or not these agents made contact; whether or not there was a delay at the closest point; and whether they moved rigidly or with a rhythmic, nonrigid "caterpillar" motion. Participants of all ages assigned events with contact to the physical domain and events without contact to the psychological domain. In addition, participants of all ages chose causality more often for events without delay than with delay, but these events became more distinct over the preschool range. The manipulation of agent motion had only minor and inconsistent effects across studies, even though children of all ages considered only the nonrigid motion to be animal,like. These results agree with the view that perceptual causality is available early in development. [source]