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1.
surface metamorphosis extends this paradigm by interpolating between discrete volume representations of the surfaces. The insensitivity
of the established techniques to the surface topology enables morphing between completely different surfaces: however it can
also lead to intermediate surfaces which have different topology from the originals. We present a method which improves on
this situation by ensuring that no part of each surface remains disconnected during the morph. The morph is guided by region
correspondence, derived automatically from a sphere representation of each surface: this can be combined with manual correspondence
to retain user control over the morph. What emerges is a fast and flexible method for morphing surfaces, as demonstrated on
several examples.
Published online: 19 July 2001 相似文献
2.
Automatic high-resolution optoelectronic photogrammetric 3D surface geometry acquisition system 总被引:1,自引:0,他引:1
A fast, high-resolution, automatic, non-contact 3D surface geometry measuring system using a photogrammetric optoelectronic
technique based on lateral-photoeffect diode detectors has been developed. Designed for the acquisition of surface geometries
such as machined surfaces, biological surfaces, and deformed parts, the system can be used in design, manufacturing, inspection,
and range finding. A laser beam is focused and scanned onto the surface of the object to be measured. Two cameras in stereo
positions capture the reflected light from the surface at 10 kHz. Photogrammetric triangulation quickly transforms the pair
of 2D signals created by the camera detectors into 3D coordinates of the light spot. Because only one small spot on the object
is illuminated at a time, the stereo correspondence problem is solved in real time. The resolution is determined by a 12-bit
A/D converter and can be improved up to 25 60025 600 by oversampling. The irregular 3D data can be regularized for use with image-based algorithms.
Received: 8 October 1996 / Accepted: 3 February 1997 相似文献
3.
We present an autonomous mobile robot navigation system using stereo fish-eye lenses for navigation in an indoor structured
environment and for generating a model of the imaged scene. The system estimates the three-dimensional (3D) position of significant
features in the scene, and by estimating its relative position to the features, navigates through narrow passages and makes
turns at corridor ends. Fish-eye lenses are used to provide a large field of view, which images objects close to the robot
and helps in making smooth transitions in the direction of motion. Calibration is performed for the lens-camera setup and
the distortion is corrected to obtain accurate quantitative measurements. A vision-based algorithm that uses the vanishing
points of extracted segments from a scene in a few 3D orientations provides an accurate estimate of the robot orientation.
This is used, in addition to 3D recovery via stereo correspondence, to maintain the robot motion in a purely translational
path, as well as to remove the effects of any drifts from this path from each acquired image. Horizontal segments are used
as a qualitative estimate of change in the motion direction and correspondence of vertical segment provides precise 3D information
about objects close to the robot. Assuming detected linear edges in the scene as boundaries of planar surfaces, the 3D model
of the scene is generated. The robot system is implemented and tested in a structured environment at our research center.
Results from the robot navigation in real environments are presented and discussed.
Received: 25 September 1996 / Accepted: 20 October 1996 相似文献
4.
Abstract. In this paper, we present a system that was developed for the European Space Agency (ESA) for the support of planetary exploration.
The system that is sent to the planetary surface consists of a rover and a lander. The lander contains a stereo head equipped
with a pan-tilt mechanism. This vision system is used both for modeling the terrain and for localization of the rover. Both
tasks are necessary for the navigation of the rover. Due to the stress that occurs during the flight, a recalibration of the
stereo-vision system is required once it is deployed on the planet. Practical limitations make it unfeasible to use a known
calibration pattern for this purpose; therefore, a new calibration procedure had to be developed that could work on images
of the planetary environment. This automatic procedure recovers the relative orientation of the cameras and the pan and tilt
axes, as well as the exterior orientation for all the images. The same images are subsequently used to reconstruct the 3-D
structure of the terrain. For this purpose, a dense stereo-matching algorithm is used that (after rectification) computes
a disparity map. Finally, all the disparity maps are merged into a single digital terrain model. In this paper, a simple and
elegant procedure is proposed that achieves that goal. The fact that the same images can be used for both calibration and
3-D reconstruction is important, since, in general, the communication bandwidth is very limited. In addition to navigation
and path planning, the 3-D model of the terrain is also used for virtual-reality simulations of the mission, wherein the model
is texture mapped with the original images. The system has been implemented, and the first tests on the ESA planetary terrain
testbed were successful. 相似文献
5.
Tool wear affects the surface roughness dramatically. There is a very close correspondence between the geometrical features
imposed on the tool by wear and micro-fracture and the geometry imparted by the tool on to the workpiece surface. Since a
machined surface is the negative replica of the shape of the cutting tool, and reflects the volumetric changes in cutting-edge
shape, it is more suitable to analyze the machined surface than look at a certain portion of the cutting tool. This paper
discusses our work that analyzes images of workpiece surfaces that have been subjected to machining operations and investigates
the correlation between tool wear and quantities characterizing machined surfaces. Our results clearly indicate that tool
condition monitoring (the distinction between a sharp, semi-dull, or a dull tool) can be successfully accomplished by analyzing
surface image data.
Received: 9 June 1998 / Accepted: 6 October 1999 相似文献
6.
Abstract. This paper describes an unsupervised algorithm for estimating the 3D profile of potholes in the highway surface, using structured
illumination. Structured light is used to accelerate computation and to simplify the estimation of range. A low-resolution
edge map is generated so that further processing may be focused on relevant regions of interest. Edge points in each region
of interest are used to initialise open, active contour models, which are propagated and refined, via a pyramid, to a higher
resolution. At each resolution, internal and external constraints are applied to a snake; the internal constraint is a smoothness
function and the external one is a maximum-likelihood estimate of the grey-level response at the edge of each light stripe.
Results of a provisional evaluation study indicate that this automated procedure provides estimates of pothole dimension suitable
for use in a first, screening, assessment of highway condition.
Received: 9 October 1998 / Accepted: 22 February 2000 相似文献
7.
We present efficient schemes for scheduling the delivery of variable-bit-rate MPEG-compressed video with stringent quality-of-service
(QoS) requirements. Video scheduling is being used to improve bandwidth allocation at a video server that uses statistical
multiplexing to aggregate video streams prior to transporting them over a network. A video stream is modeled using a traffic
envelope that provides a deterministic time-varying bound on the bit rate. Because of the periodicity in which frame types
in an MPEG stream are typically generated, a simple traffic envelope can be constructed using only five parameters. Using
the traffic-envelope model, we show that video sources can be statistically multiplexed with an effective bandwidth that is often less than the source peak rate. Bandwidth gain is achieved without sacrificing the stringency of the requested
QoS. The effective bandwidth depends on the arrangement of the multiplexed streams, which is a measure of the lag between the GOP periods of various streams. For homogeneous streams,
we give an optimal scheduling scheme for video sources at a video-on-demand server that results in the minimum effective bandwidth.
For heterogeneous sources, a sub-optimal scheduling scheme is given, which achieves acceptable bandwidth gain. Numerical examples
based on traces of MPEG-coded movies are used to demonstrate the effectiveness of our schemes. 相似文献
8.
This paper presents a new data placement scheme for continuous-media playback via a scalable storage system. Multimedia contents
are segmented into data blocks for the purpose of being stored, retrieved, and manipulated. If these data blocks belong to
some continuous media, then they must be handled in a timely manner, for example, being retrieved before some deadline. One
of the main challenges in implementing the above system is the simultaneous retrieval of a great number of different media
streams from a very large storage system. The proposed scheme efficiently reduces the seeking delay by a very simple placement
method and a retrieval scheduler. Thus, both the storage capacity and the number of concurrent accesses to the storage are
scalable. The performance of the proposed scheme is evaluated through a simple analytical model and a practical prototype
implementation. 相似文献
9.
Hirozumi Yamaguchi Khaled El-Fakih Gregor von Bochmann Teruo Higashino 《Distributed Computing》2003,16(1):21-35
Protocol synthesis is used to derive a protocol specification, that is, the specification of a set of application components
running in a distributed system of networked computers, from a specification of services (called the service specification)
to be provided by the distributed application to its users. Protocol synthesis reduces design costs and errors by specifying
the message exchanges between the application components, as defined by the protocol specification. In general, maintaining
such a distributed application involves applying frequent minor modifications to the service specification due to changes
in the user requirements. Deriving the protocol specification after each modification using the existing synthesis methods
is considered expensive and time consuming. Moreover, we cannot identify what changes we should make to the protocol specification
in correspondence to the changes in the service specification. In this paper, we present a new synthesis method to re-synthesize
only those parts of the protocol specification that must be modified in order to satisfy the changes in the service specification.
The method consists of a set of simple rules that are applied to the protocol specification written in an extended Petri net
model. An application example is given along with some experimental results.
Received: July 2001 / Accepted: July 2002
RID="*"
ID="*" Supported by International Communications Foundation (ICF), Japan
RID="**"
ID="**" Supported by Communications and Information Technology Ontario (CITO) and Natural Sciences and Engineering Research
Council (NSERC), Canada
RID="*"
ID="*" Supported by International Communications Foundation (ICF), Japan 相似文献
10.
Robust and efficient surface reconstruction from contours 总被引:1,自引:0,他引:1
We propose a new approach for surface recovery from planar sectional contours. The surface is reconstructed based on the so-called
“equal importance criterion,” which suggests that every point in the region contributes equally to the reconstruction process.
The problem is then formulated in terms of a partial differential equation, and the solution is efficiently calculated from
distance transformation. To make the algorithm valid for different application purposes, both the isosurface and the primitive
representations of the object surface are derived. The isosurface is constructed by means of a partial differential equation,
which can be solved iteratively. The traditional distance interpolating method, which was used by several researchers for
surface reconstruction, is an approximate solution of the equation. The primitive representations are approximated by Voronoi
diagram transformation of the surface space. Isosurfaces have the advantage that subsequent geometric analysis of the object
can be easily carried out while primitive representation is easy to visualize. The proposed technique allows for surface recovery
at any desired resolution, thus avoiding the inherent problems of correspondence, tiling, and branching. 相似文献
11.
Rafael Mayoral Gabriel Lera María Jos Prez-Ilzarbe 《Image and vision computing》2006,24(12):1288-1300
The computation of a scalar correspondence error is the fundamental step in most stereo correspondence algorithms. The quality of the results obtained by the reconstruction algorithm directly depends on the characteristics of such error. We have developed a procedure to evaluate different methods proposed for the computation of the correspondence error. The evaluation is based on exploring the shape of the error surface generated and testing it for uniqueness, isolation and compatibility. The scheme presented makes it possible to recognise the known characteristics of the tested methods for the computation of a correspondence error from the results of the evaluations. Our results show that, for the tested scenes, the evaluation scheme allows us to identify the most appropriate method to compute the correspondence error. 相似文献
12.
Yi-Ping Hung Chu-Song Chen Kuan-Chung Hung Yong-Sheng Chen Chiou-Shann Fuh 《Machine Vision and Applications》1998,10(5-6):280-291
This paper presents a new multi-pass hierarchical stereo-matching approach for generation of digital terrain models (DTMs)
from two overlapping aerial images. Our method consists of multiple passes which compute stereo matches with a coarse-to-fine
and sparse-to-dense paradigm. An image pyramid is generated and used in the hierarchical stereo matching. Within each pass,
the DTM is refined by using the image pyramid from the coarse to the fine level. At the coarsest level of the first pass,
a global stereo-matching technique, the intra-/inter-scanline matching method, is used to generate a good initial DTM for
the subsequent stereo matching. Thereafter, hierarchical block matching is applied to image locations where features are detected
to refine the DTM incrementally. In the first pass, only the feature points near salient edge segments are considered in block
matching. In the second pass, all the feature points are considered, and the DTM obtained from the first pass is used as the
initial condition for local searching. For the passes after the second pass, 3D interactive manual editing can be incorporated
into the automatic DTM refinement process whenever necessary. Experimental results have shown that our method can successfully
provide accurate DTM from aerial images. The success of our approach and system has also been demonstrated with a flight simulation
software.
Received: 4 November 1996 / Accepted: 20 October 1997 相似文献
13.
We present an optimal method for estimating the current location of a mobile robot by matching an image of the scene taken
by the robot with a model of the known environment. We first derive a theoretical accuracy bound and then give a computational
scheme that can attain that bound, which can be viewed as describing the probability distribution of the current location.
Using real images, we demonstrate that our method is superior to the naive least-squares method. We also confirm the theoretical
predictions of our theory by applying the bootstrap procedure.
Received: 17 March 1998 / Accepted: 7 April 2001 相似文献
14.
An automatic assessment scheme for steel quality inspection 总被引:1,自引:0,他引:1
This paper presents an automatic system for steel quality assessment, by measuring textural properties of carbide distributions.
In current steel inspection, specially etched and polished steel specimen surfaces are classified manually under a light microscope,
by comparisons with a standard chart. This procedure is basically two-dimensional, reflecting the size of the carbide agglomerations
and their directional distribution. To capture these textural properties in terms of image fea tures, we first apply a rich
set of image-processing operations, including mathematical morphology, multi-channel Gabor filtering, and the computation
of texture measures with automatic scale selection in linear scale-space. Then, a feature selector is applied to a 40-dimensional
feature space, and a classification scheme is defined, which on a sample set of more than 400 images has classification performance
values comparable to those of human metallographers. Finally, a fully automatic inspection system is designed, which actively
selects the most salient carbide structure on the specimen surface for subsequent classification. The feasibility of the overall
approach for future use in the production process is demonstrated by a prototype system. It is also shown how the presented
classification scheme allows for the definition of a new reference chart in terms of quantitative measures.
Received: 16 February 1999 / Accepted: 29 March 2000 相似文献
15.
Abstract. The use of hand gestures provides an attractive means of interacting naturally with a computer-generated display. Using one
or more video cameras, the hand movements can potentially be interpreted as meaningful gestures. One key problem in building
such an interface without a restricted setup is the ability to localize and track the human arm robustly in video sequences.
This paper proposes a multiple-cue localization scheme combined with a tracking framework to reliably track the dynamics of
the human arm in unconstrained environments. The localization scheme integrates the multiple cues of motion, shape, and color
for locating a set of key image features. Using constraint fusion, these features are tracked by a modified extended Kalman filter that exploits the articulated structure of the human arm. Moreover, an interaction scheme between tracking and localization
is used for improving the estimation process while reducing the computational requirements. The performance of the localization/tracking
framework is validated with the help of extensive experiments and simulations. These experiments include tracking with calibrated
stereo camera and uncalibrated broadcast video.
Received: 19 January 2001 / Accepted: 27 December 2001
Correspondence to: R. Sharma 相似文献
16.
E. Panagos A. Biliris 《The VLDB Journal The International Journal on Very Large Data Bases》1997,6(3):209-223
Client-server object-oriented database management systems differ significantly from traditional centralized systems in terms
of their architecture and the applications they target. In this paper, we present the client-server architecture of the EOS
storage manager and we describe the concurrency control and recovery mechanisms it employs. EOS offers a semi-optimistic locking
scheme based on the multi-granularity two-version two-phase locking protocol. Under this scheme, multiple concurrent readers
are allowed to access a data item while it is being updated by a single writer. Recovery is based on write-ahead redo-only
logging. Log records are generated at the clients and they are shipped to the server during normal execution and at transaction
commit. Transaction rollback is fast because there are no updates that have to be undone, and recovery from system crashes
requires only one scan of the log for installing the changes made by transactions that committed before the crash. We also
present a preliminary performance evaluation of the implementation of the above mechanisms.
Edited by R. King. Received July 1993 / Accepted May 1996 相似文献
17.
Abstract. Automatic acquisition of CAD models from existing objects requires accurate extraction of geometric and topological information
from the input data. This paper presents a range image segmentation method based on local approximation of scan lines. The
method employs edge models that are capable of detecting noise pixels as well as position and orientation discontinuities
of varying strengths. Region-based techniques are then used to achieve a complete segmentation. Finally, a geometric representation
of the scene, in the form of a surface CAD model, is produced. Experimental results on a large number of real range images
acquired by different range sensors demonstrate the efficiency and robustness of the method.
Received: 1 August 2000 / Accepted: 23 January 2002
Correspondence to: I. Khalifa 相似文献
18.
We present a high-performance solution to the I/O retrieval problem in a distributed multimedia system. Parallelism of data
retrieval is achieved by striping the data across multiple disks. We identify the components that contribute to media data-retrieval
delay. The variable delays among these have a great bearing on the server throughput under varying load conditions. We present
a buffering scheme to minimize these variations. We have implemented our model on the Intel Paragon parallel computer. The
results of component-wise instrumentation of the server operation are presented and analyzed. Experimental results that demonstrate
the efficacy of the buffering scheme are presented. Based on our experiments, a dynamic admission-control policy that takes
server workloads into account is proposed. 相似文献
19.
We present the Finite-Window Robust Sequential Estimator for the detection and analysis of corrosion in range images of gas
pipelines. This statistically robust, real-time technique estimates the pipeline surface range function in the presence of
noise, surface deviations, and changes in the underlying model. Deviations from the robust surface fit, corresponding to statistical
outliers, represent potential areas of corrosion. Because the algorithm estimates surface parameters over a finite, sliding
window of data, it can track moderately high-order surfaces using lower order models. The system is consistent, objective,
and non-destructive and can be used with the pipeline in service.
Received: 7 September 1999 / Accepted: 2 November 2000 相似文献
20.
A compact algorithm for rectification of stereo pairs 总被引:32,自引:0,他引:32
Abstract. We present a linear rectification algorithm for general, unconstrained stereo rigs. The algorithm takes the two perspective
projection matrices of the original cameras, and computes a pair of rectifying projection matrices. It is compact (22-line
MATLAB code) and easily reproducible. We report tests proving the correct behavior of our method, as well as the negligible decrease
of the accuracy of 3D reconstruction performed from the rectified images directly.
Received: 25 February 1999 / Accepted: 2 March 2000 相似文献