612 research outputs found
The Footprint Database and Web Services of the Herschel Space Observatory
Data from the Herschel Space Observatory is freely available to the public
but no uniformly processed catalogue of the observations has been published so
far. To date, the Herschel Science Archive does not contain the exact sky
coverage (footprint) of individual observations and supports search for
measurements based on bounding circles only. Drawing on previous experience in
implementing footprint databases, we built the Herschel Footprint Database and
Web Services for the Herschel Space Observatory to provide efficient search
capabilities for typical astronomical queries. The database was designed with
the following main goals in mind: (a) provide a unified data model for
meta-data of all instruments and observational modes, (b) quickly find
observations covering a selected object and its neighbourhood, (c) quickly find
every observation in a larger area of the sky, (d) allow for finding solar
system objects crossing observation fields. As a first step, we developed a
unified data model of observations of all three Herschel instruments for all
pointing and instrument modes. Then, using telescope pointing information and
observational meta-data, we compiled a database of footprints. As opposed to
methods using pixellation of the sphere, we represent sky coverage in an exact
geometric form allowing for precise area calculations. For easier handling of
Herschel observation footprints with rather complex shapes, two algorithms were
implemented to reduce the outline. Furthermore, a new visualisation tool to
plot footprints with various spherical projections was developed. Indexing of
the footprints using Hierarchical Triangular Mesh makes it possible to quickly
find observations based on sky coverage, time and meta-data. The database is
accessible via a web site (http://herschel.vo.elte.hu) and also as a set of
REST web service functions.Comment: Accepted for publication in Experimental Astronom
Properties of Gauss digitized sets and digital surface integration
International audienceThis paper presents new topological and geometrical properties of Gauss digitizations of Euclidean shapes, most of them holding in arbitrary dimension . We focus on -regular shapes sampled by Gauss digitization at gridstep . The digitized boundary is shown to be close to the Euclidean boundary in the Hausdorff sense, the minimum distance being achieved by the projection map induced by the Euclidean distance. Although it is known that Gauss digitized boundaries may not be manifold when , we show that non-manifoldness may only occur in places where the normal vector is almost aligned with some digitization axis, and the limit angle decreases with . We then have a closer look at the projection of the digitized boundary onto the continuous boundary by . We show that the size of its non-injective part tends to zero with . This leads us to study the classical digital surface integration scheme, which allocates a measure to each surface element that is proportional to the cosine of the angle between an estimated normal vector and the trivial surface element normal vector. We show that digital integration is convergent whenever the normal estimator is multigrid convergent, and we explicit the convergence speed. Since convergent estimators are now available in the litterature, digital integration provides a convergent measure for digitized objects
An analysis of surface area estimates of binary volumes under three tilings
Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 1997.Includes bibliographical references (leaves 77-79).by Erik G. Miller.M.S
A generic formalism for the semantic modeling and representation of architectural elements
This article presents a methodological approach to the semantic description of architectural elements based both on theoretical reflections and research experiences. To develop this approach, a first process of extraction and formalization of architectural knowledge on the basis of the analysis of architectural treaties is proposed. Then, the identified features are used to produce a template shape library dedicated to buildings surveying. Finally, the problem of the overall model structuring and organization using semantic information is addressed for user handling purposes
PlantGL : a Python-based geometric library for 3D plant modelling at different scales
In this paper, we present PlantGL, an open-source graphic toolkit for the creation, simulation and analysis of 3D virtual plants. This C++ geometric library is embedded in the Python language which makes it a powerful user-interactive platform for plant modelling in various biological application domains. PlantGL makes it possible to build and manipulate geometric models of plants or plant parts, ranging from tissues and organs to plant populations. Based on a scene graph augmented with primitives dedicated to plant representation, several methods are provided to create plant architectures from either field measurements or procedural algorithms. Because they reveal particularly useful in plant design and analysis, special attention has been paid to the definition and use of branching system envelopes. Several examples from different modelling applications illustrate how PlantGL can be used to construct, analyse or manipulate geometric models at different scales
Scattering by irregular particles in anomalous diffraction and discrete dipole approximations
November 30, 1992.Includes bibliographical references.Sponsored by National Science Foundation ATM-8812353.Sponsored by U.S. Air Force Office of Scientific Research AFOSR-91-0269
Recognition of simple 3-D objects by the use of syntactic pattern recognition
This project is an attempt to supply the existing hardware with
adequate software, in order to develop a system capable of recognizing 3-D
objects, bounded by simple 2-D planes, which in turn are bounded by
straight lines. [Continues.
Computer image processing with application to chemical engineering
A literature survey covers a wide range
of picture processing topics from the general problem of
manipulating digitised images to the specific task
of analysing the shape of objects within an image
field. There follows a discussion and development
of theory relating to this latter task. A number
of shape analysis techniques are inapplicable or
computationally untenable when applied to objects
containing concavities. A method is proposed and
implemented whereby any object may be divided into
convex components the algebraic sum of which
constitute the original. These components may
be related by a tree structure.
It is observed that properties based on
integral measurements, e.g. area, are less
susceptible to quantisation errors than those based
on linear and derivative measurements such as
diameters anti slopes. A set of moments invariant
with respect to size, position and orientation
are derived and applied to the study of the above
convex components. An outline of possible further
developments is given
Modeling of objects using planar facets in noisy range images
Products designed and manufactured before the advent of Computer Aided Design (CAD) and Computer Aided Manufacturing (CAM) technology have not been documented electronically. To avoid the laborious procedure of redesigning the parts, a reverse engineering approach can be adopted. This approach involves, taking a picture of the object and constructing a solid model from the image data.
Range image is a three dimensional image of an object or a scene. This image can be obtained from special cameras, called range image cameras, or can be constructed from the Coordinate Measuring Machine\u27s (CMM) output data. Adaptive Fuzzy c-Elliptotype (AFC) clustering algorithm is used to identify the planar facets in a range image. A modified version of AFC algorithm can handle noisy range images. Unknown number of planar facets can be identified using the Agglomerative clustering approach.
The object is reconstructed using segmented image data. The equations of the edge are obtained from the plane intersections. An edge validity criterion is developed to validate the existence of an edge. Vertices are the two extreme points on the edge. A Boundary representation of the object is developed. The information about this object is then passed to a CAD software using Initial Graphics Exchange Specification (IGES)
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