214 research outputs found
Indexing with coded deltas—a data compaction technique
The paper describes the coded delta scheme, which is one of the methods used by the Census Research Unit, University of Durham, for compacting the 1971 U.K. census data. It evaluates the merits and limitations of the technique in relation to the characteristics of the data set and other techniques available for compact encoding of numeric and string data
ERTS multispectral image transformations for geological lineament enhancement
There are no author-identified significant results in this report
Substructure recovery by 3D Discrete Wavelet Transforms
We present and discuss a method to identify substructures in combined
angular-redshift samples of galaxies within Clusters. The method relies on the
use of Discrete Wavelet Transform (hereafter DWT) and has already been applied
to the analysis of the Coma cluster (Gambera et al. 1997). The main new
ingredient of our method with respect to previous studies lies in the fact that
we make use of a 3D data set rather than a 2D. We test the method on mock
cluster catalogs with spatially localized substructures and on a N-body
simulation. Our main conclusion is that our method is able to identify the
existing substructures provided that: a) the subclumps are detached in part or
all of the phase space, b) one has a statistically significant number of
redshifts, increasing as the distance decreases due to redshift distortions; c)
one knows {\it a priori} the scale on which substructures are to be expected.
We have found that to allow an accurate recovery we must have both a
significant number of galaxies ( for clusters at z or
about 800 at z 0.4) and a limiting magnitude for completeness .
The only true limitation to our method seems to be the necessity of knowing
{\it a priori} the scale on which the substructure is to be found. This is an
intrinsic drawback of the method and no improvement in numerical codes based on
this technique could make up for it.Comment: Accepted for publication in MNRAS. 7 pages, 2 figure
A 3-D wavelet analysis of substructure in the Coma cluster: statistics and morphology
Evidence for clustering within the Coma cluster is found by means of a
multiscale analysis of the combined angular-redshift distribution. We have
compiled a catalogue of 798 galaxy redshifts from published surveys from the
region of the Coma cluster. We examine the presence of substructure and of
voids at different scales ranging from Mpc, using
subsamples of the catalogue, ranging from km/s to km/s.
Our substructure detection method is based on the wavelet transform and on the
segmentation analysis. The wavelet transform allows us to find out structures
at different scales and the segmentation method allows us a quantitative
statistical and morphological analysis of the sample. From the whole catalogue
we select a subset of 320 galaxies, with redshifts between cz=5858 km/s and
cz=8168 km/s that we identify as belonging to the central region of Coma and on
which we have performed a deeper analysis, on scales ranging from
kpc to Mpc. Our results are expressed in terms of the number of
structures or voids and their sphericity for different values of the threshold
detection and at all the scales investigated. According to our analysis, there
is strong evidence for multiple hierarchical substructure, on scales ranging
from a few hundreds of kpc to about Mpc. The morphology of these
substructures is rather spherical. On the scale of kpc we find two
main subclusters which where also found before, but our wavelet analysis shows
even more substructures, whose redshift position is approximatively marked by
these bright galaxies: NGC 4934 & 4840, 4889, 4898 & 4864, 4874 & 4839, 4927,
4875.Comment: 24 pages, 6 figures. ApJ (Main Journal), accepted for publication.
Added one section on statistical tests and slightly modified text and
abstrac
Bio-Inspired Stereo Vision Calibration for Dynamic Vision Sensors
Many advances have been made in the eld of computer vision. Several recent research trends
have focused on mimicking human vision by using a stereo vision system. In multi-camera systems, a
calibration process is usually implemented to improve the results accuracy. However, these systems generate
a large amount of data to be processed; therefore, a powerful computer is required and, in many cases,
this cannot be done in real time. Neuromorphic Engineering attempts to create bio-inspired systems that
mimic the information processing that takes place in the human brain. This information is encoded using
pulses (or spikes) and the generated systems are much simpler (in computational operations and resources),
which allows them to perform similar tasks with much lower power consumption, thus these processes
can be developed over specialized hardware with real-time processing. In this work, a bio-inspired stereovision
system is presented, where a calibration mechanism for this system is implemented and evaluated
using several tests. The result is a novel calibration technique for a neuromorphic stereo vision system,
implemented over specialized hardware (FPGA - Field-Programmable Gate Array), which allows obtaining
reduced latencies on hardware implementation for stand-alone systems, and working in real time.Ministerio de Economía y Competitividad TEC2016-77785-PMinisterio de Economía y Competitividad TIN2016-80644-
Application of dielectric constant measurements to radar imagery interpretation
The author has identified the following significant results. Although it is readily recognized that there is a need for ground truth to provide adequate guidance for remote sensing data interpretation, it is noted that, in terms of radar remote sensing, this ground truth is often inadequate. It is necessary to make basic electrical and physical measurements of the surface and to some depth below it. A brief outline is presented of a ground truth scheme which uses measurements of the dielectric constant. Two portable instruments were designed specifically for this purpose; these were: (1) a Q-meter for measurement of dielectric constant and loss tangent; and (2) an instrument to measure electrical properties of the two operating frequencies of the imaging radar. Although extensive data are lacking, several general cases of radar-earth surface and interaction are described; also, examples of radar imagery and some data on ice and snow are presented. It is concluded that the next logical step is to begin to quantify the radar ground truth in preparation for machine interpretation and automatic data processing of the radar imagery
Stereo Matching in Address-Event-Representation (AER) Bio-Inspired Binocular Systems in a Field-Programmable Gate Array (FPGA)
In stereo-vision processing, the image-matching step is essential for results, although it
involves a very high computational cost. Moreover, the more information is processed, the more time
is spent by the matching algorithm, and the more ine cient it is. Spike-based processing is a relatively
new approach that implements processing methods by manipulating spikes one by one at the time
they are transmitted, like a human brain. The mammal nervous system can solve much more complex
problems, such as visual recognition by manipulating neuron spikes. The spike-based philosophy
for visual information processing based on the neuro-inspired address-event-representation (AER)
is currently achieving very high performance. The aim of this work was to study the viability of a
matching mechanism in stereo-vision systems, using AER codification and its implementation in
a field-programmable gate array (FPGA). Some studies have been done before in an AER system
with monitored data using a computer; however, this kind of mechanism has not been implemented
directly on hardware. To this end, an epipolar geometry basis applied to AER systems was studied
and implemented, with other restrictions, in order to achieve good results in a real-time scenario.
The results and conclusions are shown, and the viability of its implementation is proven.Ministerio de Economía y Competitividad TEC2016-77785-
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