共查询到20条相似文献,搜索用时 140 毫秒
1.
Reconstructing a textured CAD model of an urban environment using vehicle-borne laser range scanners and line cameras 总被引:2,自引:0,他引:2
Abstract. In this paper, a novel method is presented for generating a textured CAD model of an outdoor urban environment using a vehicle-borne
sensor system. In data measurement, three single-row laser range scanners and six line cameras are mounted on a measurement
vehicle, which has been equipped with a GPS/INS/Odometer-based navigation system. Laser range and line images are measured
as the vehicle moves forward. They are synchronized with the navigation system so they can be geo-referenced to a world coordinate
system. Generation of the CAD model is conducted in two steps. A geometric model is first generated using the geo-referenced
laser range data, where urban features, such as buildings, ground surfaces, and trees are extracted in a hierarchical way.
Different urban features are represented using different geometric primitives, such as a planar face, a triangulated irregular
network (TIN), and a triangle. The texture of the urban features is generated by projecting and resampling line images onto
the geometric model. An outdoor experiment is conducted, and a textured CAD model of a real urban environment is reconstructed
in a full automatic mode. 相似文献
2.
Geometric fusion for a hand-held 3D sensor 总被引:2,自引:0,他引:2
Abstract. This article presents a geometric fusion algorithm developed for the reconstruction of 3D surface models from hand-held sensor
data. Hand-held systems allow full 3D movement of the sensor to capture the shape of complex objects. Techniques previously
developed for reconstruction from conventional 2.5D range image data cannot be applied to hand-held sensor data. A geometric
fusion algorithm is introduced to integrate the measured 3D points from a hand-held sensor into a single continuous surface.
The new geometric fusion algorithm is based on the normal-volume representation of a triangle, which enables incremental transformation of an arbitrary mesh into an implicit volumetric field
function. This system is demonstrated for reconstruction of surface models from both hand-held sensor data and conventional
2.5D range images.
Received: 30 August 1999 / Accepted: 21 January 2000 相似文献
3.
Location is one of the most important elements of context in ubiquitous computing. In this paper we describe a location model, a spatial-aware communication model and an implementation of the models that exploit location for processing and communicating context. The location model presented describes a location
tree, which contains human-readable semantic and geometric information about an organisation and a structure to describe the
current location of an object or a context. The proposed system is dedicated to work not only on more powerful devices like
handhelds, but also on small computer systems that are embedded into everyday artefact (making them a digital artefact). Model and design decisions were made on the basis of experiences from three prototype setups with several applications,
which we built from 1998 to 2002. While running these prototypes we collected experiences from designers, implementers and users and formulated them as guidelines in this paper. All the prototype applications heavily use location information for providing their functionality. We found
that location is not only of use as information for the application but also important for communicating context. In this
paper we introduce the concept of spatial-aware communication where data is communicated based on the relative location of
digital artefacts rather than on their identity.
Correspondence to: Michael Biegl, Telecooperation Office (TecO), University of Karlsruhe, Vincenz-Prieβritz-Str. 1 D-76131 Karlsruhe, Germany.
Email: michael@teco.edu 相似文献
4.
A bin picking system based on depth from defocus 总被引:3,自引:0,他引:3
It is generally accepted that to develop versatile bin-picking systems capable of grasping and manipulation operations, accurate
3-D information is required. To accomplish this goal, we have developed a fast and precise range sensor based on active depth from defocus (DFD). This sensor is used in conjunction with a three-component vision system, which is able to recognize and evaluate the
attitude of 3-D objects. The first component performs scene segmentation using an edge-based approach. Since edges are used
to detect the object boundaries, a key issue consists of improving the quality of edge detection. The second component attempts
to recognize the object placed on the top of the object pile using a model-driven approach in which the segmented surfaces
are compared with those stored in the model database. Finally, the attitude of the recognized object is evaluated using an
eigenimage approach augmented with range data analysis. The full bin-picking system will be outlined, and a number of experimental
results will be examined.
Received: 2 December 2000 / Accepted: 9 September 2001
Correspondence to: O. Ghita 相似文献
5.
Farzin Mokhtarian 《Machine Vision and Applications》1997,10(3):87-97
A complete and practical system for occluded object recognition has been developed which is very robust with respect to noise
and local deformations of shape (due to weak perspective distortion, segmentation errors and non-rigid material) as well as
scale, position and orientation changes of the objects. The system has been tested on a wide variety of free-form 3D objects.
An industrial application is envisaged where a fixed camera and a light-box are utilized to obtain images. Within the constraints
of the system, every rigid 3D object can be modeled by a limited number of classes of 2D contours corresponding to the object's
resting positions on the light-box. The contours in each class are related to each other by a 2D similarity transformation.
The Curvature Scale Space technique [26, 28] is then used to obtain a novel multi-scale segmentation of the image and the model contours. Object indexing [16, 32, 36] is used to narrow down the search space. An efficient local matching algorithm is utilized to select the best
matching models.
Received: 5 August 1996 / Accepted: 19 March 1997 相似文献
6.
Abstract. The purpose of this study is to discuss existing fractal-based algorithms and propose novel improvements of these algorithms
to identify tumors in brain magnetic-response (MR) images. Considerable research has been pursued on fractal geometry in various
aspects of image analysis and pattern recognition. Magnetic-resonance images typically have a degree of noise and randomness
associated with the natural random nature of structure. Thus, fractal analysis is appropriate for MR image analysis. For tumor
detection, we describe existing fractal-based techniques and propose three modified algorithms using fractal analysis models.
For each new method, the brain MR images are divided into a number of pieces. The first method involves thresholding the pixel
intensity values; hence, we call the technique piecewise-threshold-box-counting (PTBC) method. For the subsequent methods,
the intensity is treated as the third dimension. We implement the improved piecewise-modified-box-counting (PMBC) and piecewise-triangular-prism-surface-area
(PTPSA) methods, respectively. With the PTBC method, we find the differences in intensity histogram and fractal dimension
between normal and tumor images. Using the PMBC and PTPSA methods, we may detect and locate the tumor in the brain MR images
more accurately. Thus, the novel techniques proposed herein offer satisfactory tumor identification.
Received: 13 October 2001 / Accepted: 28 May 2002
Correspondence to: K.M. Iftekharuddin 相似文献
7.
Yiming Ye John K. Tsotsos Eric Harley Karen Bennet 《Machine Vision and Applications》2000,12(1):32-43
Abstract. This paper proposes a novel tracking strategy that can robustly track a person or other object within a fixed environment
using a pan, tilt, and zoom camera with the help of a pre-recorded image database. We define a set of camera states which
is sufficient to survey the environment for the target. Background images for these camera states are stored as an image database.
During tracking, camera movements are restricted to these states. Tracking and segmentation are simplified, as each tracking
image can be compared with the corresponding pre-recorded background image.
Received: 26 August 1999 / Accepted: 22 February 2000 相似文献
8.
Abstract. The paper proposes a new method for efficient triangulation of large, unordered sets of 3D points using a CAD model comprising
NURBS entities. It is primarily aimed at engineering applications involving analysis and visualisation of measured data, such
as inspection, where a model of the object in question is available. Registration of the data to the model is the necessary
first step, enabling the triangulation to be efficiently performed in 2D, on the projections of the measured points onto the
model entities. The derived connectivity is then applied to the original 3D data. Improvement of the generated 3D mesh is
often necessary, involving mesh smoothing, constraint-based elimination of redundant triangles and merging of mesh patches.
Examples involving random measurements on aerospace and automotive free-form components are presented.
Received: 30 August 1999 / Accepted: 10 January 2000 相似文献
9.
Lixin Fan Liying Fan Chew Lim Tan 《International Journal on Document Analysis and Recognition》2003,5(2-3):88-101
Abstract. For document images corrupted by various kinds of noise, direct binarization images may be severely blurred and degraded.
A common treatment for this problem is to pre-smooth input images using noise-suppressing filters. This article proposes an
image-smoothing method used for prefiltering the document image binarization. Conceptually, we propose that the influence
range of each pixel affecting its neighbors should depend on local image statistics. Technically, we suggest using coplanar matrices to capture the structural and textural distribution of similar pixels at each site. This property adapts the smoothing process
to the contrast, orientation, and spatial size of local image structures. Experimental results demonstrate the effectiveness
of the proposed method, which compares favorably with existing methods in reducing noise and preserving image features. In
addition, due to the adaptive nature of the similar pixel definition, the proposed filter output is more robust regarding
different noise levels than existing methods.
Received: October 31, 2001 / October 09, 2002
Correspondence to:L. Fan (e-mail: fanlixin@ieee.org) 相似文献
10.
Abstract. The image sequence in a video taken by a moving camera may suffer from irregular perturbations because of irregularities
in the motion of the person or vehicle carrying the camera. We show how to use information in the image sequence to correct
the effects of these irregularities so that the sequence is smoothed, i.e., is approximately the same as the sequence that
would have been obtained if the motion of the camera had been smooth. Our method is based on the fact that the irregular motion
is almost entirely rotational, and that the rotational image motion can be detected and corrected if a distant object, such
as the horizon, is visible.
Received: 14 February 2001 / Accepted: 11 February 2002
Correspondence to: A. Rosenfeld 相似文献
11.
Ada Wai-chee Fu Polly Mei-shuen Chan Yin-Ling Cheung Yiu Sang Moon 《The VLDB Journal The International Journal on Very Large Data Bases》2000,9(2):154-173
Abstract. For some multimedia applications, it has been found that domain objects cannot be represented as feature vectors in a multidimensional
space. Instead, pair-wise distances between data objects are the only input. To support content-based retrieval, one approach
maps each object to a k-dimensional (k-d) point and tries to preserve the distances among the points. Then, existing spatial access index methods such as the R-trees
and KD-trees can support fast searching on the resulting k-d points. However, information loss is inevitable with such an approach since the distances between data objects can only
be preserved to a certain extent. Here we investigate the use of a distance-based indexing method. In particular, we apply
the vantage point tree (vp-tree) method. There are two important problems for the vp-tree method that warrant further investigation,
the n-nearest neighbors search and the updating mechanisms. We study an n-nearest neighbors search algorithm for the vp-tree, which is shown by experiments to scale up well with the size of the dataset
and the desired number of nearest neighbors, n. Experiments also show that the searching in the vp-tree is more efficient than that for the -tree and the M-tree. Next, we propose solutions for the update problem for the vp-tree, and show by experiments that the algorithms are
efficient and effective. Finally, we investigate the problem of selecting vantage-point, propose a few alternative methods,
and study their impact on the number of distance computation.
Received June 9, 1998 / Accepted January 31, 2000 相似文献
12.
This paper presents an algorithm for simultaneously fitting smoothly connected multiple surfaces from unorganized measured
data. A hybrid mathematical model of B-spline surfaces and Catmull–Clark subdivision surfaces is introduced to represent objects
with general quadrilateral topology. The interconnected multiple surfaces are G
2 continuous across all surface boundaries except at a finite number of extraordinary corner points where G
1 continuity is obtained. The algorithm is purely a linear least-squares fitting procedure without any constraint for maintaining
the required geometric continuity. In case of general uniform knots for all surfaces, the final fitted multiple surfaces can
also be exported as a set of Catmull–Clark subdivision surfaces with global C
2 continuity and local C
1 continuity at extraordinary corner points.
Published online: 14 May 2002
Correspondence to: W. Ma 相似文献
13.
Abstract. Conventional tracking methods encounter difficulties as the number of objects, clutter, and sensors increase, because of
the requirement for data association. Statistical tracking, based on the concept of network tomography, is an alternative
that avoids data association. It estimates the number of trips made from one region to another in a scene based on interregion
boundary traffic counts accumulated over time. It is not necessary to track an object through a scene to determine when an
object crosses a boundary. This paper describes statistical tracing and presents an evaluation based on the estimation of
pedestrian and vehicular traffic intensities at an intersection over a period of 1 month. We compare the results with those
from a multiple-hypothesis tracker and manually counted ground-truth estimates.
Received: 30 August 2001 / Accepted: 28 May 2002
Correspondence to: J.E. Boyd 相似文献
14.
Abstract. We propose a new adaptive strategy for text recognition that attempts to derive knowledge about the dominant font on a given
page. The strategy uses a linguistic observation that over half of all words in a typical English passage are contained in
a small set of less than 150 stop words. A small dictionary of such words is compiled from the Brown corpus. An arbitrary
text page first goes through layout analysis that produces word segmentation. A fast procedure is then applied to locate the
most likely candidates for those words, using only widths of the word images. The identity of each word is determined using
a word shape classifier. Using the word images together with their identities, character prototypes can be extracted using
a previously proposed method. We describe experiments using simulated and real images. In an experiment using 400 real page
images, we show that on average, eight distinct characters can be learned from each page, and the method is successful on
90% of all the pages. These can serve as useful seeds to bootstrap font learning.
Received October 8, 1999 / Revised March 29, 2000 相似文献
15.
Detection, segmentation, and classification of specific objects are the key building blocks of a computer vision system for
image analysis. This paper presents a unified model-based approach to these three tasks. It is based on using unsupervised
learning to find a set of templates specific to the objects being outlined by the user. The templates are formed by averaging
the shapes that belong to a particular cluster, and are used to guide a probabilistic search through the space of possible
objects. The main difference from previously reported methods is the use of on-line learning, ideal for highly repetitive
tasks. This results in faster and more accurate object detection, as system performance improves with continued use. Further,
the information gained through clustering and user feedback is used to classify the objects for problems in which shape is
relevant to the classification. The effectiveness of the resulting system is demonstrated in two applications: a medical diagnosis
task using cytological images, and a vehicle recognition task.
Received: 5 November 2000 / Accepted: 29 June 2001
Correspondence to: K.-M. Lee 相似文献
16.
I/O scheduling for digital continuous media 总被引:4,自引:0,他引:4
A growing set of applications require access to digital video and audio. In order to provide playback of such continuous
media (CM), scheduling strategies for CM data servers (CMS) are necessary. In some domains, particularly defense and industrial process control, the timing requirements of these applications
are strict and essential to their correct operation. In this paper we develop a scheduling strategy for multiple access to
a CMS such that the timing guarantees are maintained at all times. First, we develop a scheduling strategy for the steady state,
i.e., when there are no changes in playback rate or operation. We derive an optimal Batched SCAN (BSCAN) algorithm that requires minimum buffer space to schedule concurrent accesses. The scheduling strategy incorporates two key
constraints: (1) data fetches from the storage system are assumed to be in integral multiples of the block size, and (2) playback
guarantees are ensured for frame-oriented streams when each frame can span multiple blocks. We discuss modifications to the
scheduling strategy to handle compressed data like motion-JPEG and MPEG.
Second, we develop techniques to handle dynamic changes brought about by VCR-like operations executed by applications. We define a suite of primitive VCR-like operations that can be executed. We show that an unregulated change in the BSCAN schedule, in response to VCR-like operations, will affect playback guarantees. We develop two general techniques to ensure playback guarantees while responding
to VCR-like operations: passive and active accumulation. Using user response time as a metric we show that active accumulation algorithms
outperform passive accumulation algorithms. An optimal response-time algorithm in a class of active accumulation strategies
is derived. The results presented here are validated by extensive simulation studies. 相似文献
17.
Henry S. Baird Allison L. Coates Richard J. Fateman 《International Journal on Document Analysis and Recognition》2003,5(2-3):158-163
Abstract. We exploit the gap in ability between human and machine vision systems to craft a family of automatic challenges that tell
human and machine users apart via graphical interfaces including Internet browsers. Turing proposed [Tur50] a method whereby
human judges might validate “artificial intelligence” by failing to distinguish between human and machine interlocutors. Stimulated
by the “chat room problem” posed by Udi Manber of Yahoo!, and influenced by the CAPTCHA project [BAL00] of Manuel Blum et
al. of Carnegie-Mellon Univ., we propose a variant of the Turing test using pessimal print: that is, low-quality images of machine-printed text synthesized pseudo-randomly over certain ranges of words, typefaces,
and image degradations. We show experimentally that judicious choice of these ranges can ensure that the images are legible
to human readers but illegible to several of the best present-day optical character recognition (OCR) machines. Our approach
is motivated by a decade of research on performance evaluation of OCR machines [RJN96,RNN99] and on quantitative stochastic
models of document image quality [Bai92,Kan96]. The slow pace of evolution of OCR and other species of machine vision over
many decades [NS96,Pav00] suggests that pessimal print will defy automated attack for many years. Applications include `bot'
barriers and database rationing.
Received: February 14, 2002 / Accepted: March 28, 2002
An expanded version of: A.L. Coates, H.S. Baird, R.J. Fateman (2001) Pessimal Print: a reverse Turing Test. In: {\it Proc.
6th Int. Conf. on Document Analysis and Recognition}, Seattle, Wash., USA, September 10–13, pp. 1154–1158
Correspondence to: H. S. Baird 相似文献
18.
Summary. We prove the existence of a “universal” synchronous self-stabilizing protocol, that is, a protocol that allows a distributed
system to stabilize to a desired nonreactive behaviour (as long as a protocol stabilizing to that behaviour exists). Previous
proposals required drastic increases in asymmetry and knowledge to work, whereas our protocol does not use any additional
knowledge, and does not require more symmetry-breaking conditions than available; thus, it is also stabilizing with respect
to dynamic changes in the topology. We prove an optimal quiescence time n+D for a synchronous network of n processors and diameter D; the protocol can be made finite state with a negligible loss in quiescence time. Moreover, an optimal D+1 protocol is given for the case of unique identifiers. As a consequence, we provide an effective proof technique that allows
to show whether self-stabilization to a certain behaviour is possible under a wide range of models.
Received: January 1999 / Accepted: July 2001 相似文献
19.
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
20.
Summary. In this paper we introduce and analyze two new cost measures related to the communication overhead and the space requirements
associated with virtual path layouts in ATM networks, that is the edge congestion and the node congestion. Informally, the edge congestion of a given edge e at an incident node u is defined as the number of VPs terminating at or starting from u and using e, while the node congestion of a node v is defined as the number of VPs having v as an endpoint. We investigate the problem of constructing virtual path layouts allowing to connect a specified root node
to all the others in at most h hops and with maximum edge or node congestion c, for two given integers h and c. We first give tight results concerning the time complexity of the construction of such layouts for both the two congestion
measures, that is we exactly determine all the tractable and intractable cases. Then, we provide some combinatorial bounds
for arbitrary networks, together with optimal layouts for specific topologies such as chains, rings and grids.
Received: December 1997 / Accepted: August 2000 相似文献