Showing papers on "Line segment published in 2005"

Provably good sampling and meshing of surfaces

Abstract: The notion of e-sample, introduced by Amenta and Bern, has proven to be a key concept in the theory of sampled surfaces. Of particular interest is the fact that, if E is an e-sample of a C2-continuous surface S for a sufficiently small e, then the Delaunay triangulation of E restricted to S is a good approximation of S, both in a topological and in a geometric sense. Hence, if one can construct an e-sample, one also gets a good approximation of the surface. Moreover, correct reconstruction is ensured by various algorithms. In this paper, we introduce the notion of loose e-sample. We show that the set of loose e-samples contains and is asymptotically identical to the set of e-samples. The main advantage of loose e-samples over e-samples is that they are easier to check and to construct. We also present a simple algorithm that constructs provably good surface samples and meshes. Given a C2-continuous surface S without boundary, the algorithm generates a sparse e-sample E and at the same time a triangulated surface Dels(E). The triangulated surface has the same topological type as S, is close to S for the Hausdorff distance and can provide good approximations of normals, areas and curvatures. A notable feature of the algorithm is that the surface needs only to be known through an oracle that, given el line segment, detects whether the segment intersects the surface and in the affirmative, returns the intersection points. This makes the algorithm useful in a wide variety of contexts and for a large class of surfaces.

Wide-baseline stereo matching with line segments

Abstract: We present a new method for matching line segments between two uncalibrated wide-baseline images. Most current techniques for wide-baseline matching are based on viewpoint invariant regions. Those methods work well with highly textured scenes, but fail with poorly textured ones. We show that such scenes can be successfully matched using line segments. Moreover, since line segments and regions provide complementary information, their combined matching allows to deal with a broader range of scenes. We generate an initial set of line segment correspondences, and then iteratively increase their number by adding matches consistent with the topological structure of the current ones. Finally, a coplanar grouping stage allows to estimate the fundamental matrix even from line segments only.

Word line arrangement having multi-layer word line segments for three-dimensional memory array

Abstract: A three-dimensional (3D) passive element memory cell array provides short word lines while still maintaining a small support circuit area for efficiency. Short, low resistance word line segments on two or more word line layers are connected together in parallel to form a given word line without use of segment switch devices between the word line segments. A shared vertical connection preferably connects the word line segments together and connects to a word line driver circuit disposed generally below the array near the word line. Each word line driver circuit preferably couples its word line either to an associated one of a plurality of selected bias lines or to an unselected bias line associated with the driver circuit, which selected bias lines are themselves decoded to provide for an efficient multi-headed word line decoder.

Point processes for unsupervised line network extraction in remote sensing

Abstract: This paper addresses the problem of unsupervised extraction of line networks (for example, road or hydrographic networks) from remotely sensed images. We model the target line network by an object process, where the objects correspond to interacting line segments. The prior model, called "quality candy," is designed to exploit as fully as possible the topological properties of the network under consideration, while the radiometric properties of the network are modeled using a data term based on statistical tests. Two techniques are used to compute this term: one is more accurate, the other more efficient. A calibration technique is used to choose the model parameters. Optimization is done via simulated annealing using a reversible jump Markov chain Monte Carlo (RJMCMC) algorithm. We accelerate convergence of the algorithm by using appropriate proposal kernels. The results obtained on satellite and aerial images are quantitatively evaluated with respect to manual extractions. A comparison with the results obtained using a previous model, called the "candy" model, shows the interest of adding quality coefficients with respect to interactions in the prior density. The relevance of using an offline computation of the data potential is shown, in particular, when a proposal kernel based on this computation is added in the RJMCMC algorithm.

Monitor for CPAP/ventilator apparatus

Abstract: A monitor (200) includes a measurement line segment (202) adapted to be coupled between a patient interface and a positive airway pressure device. The measurement line segment defines a gas flow path. A sensor (208) includes two ports (210) in communication with the gas flow path through the measurement line segment, and a recording device (203) is adapted to record data collected by the sensor.

A new approach to line and line segment clipping in homogeneous coordinates

Abstract: The clipping operation is still the bottleneck of the graphics pipeline in spite of the latest developments in graphical hardware and a significant increase in performance. Algorithms for line and line segment clipping have been studied for a long time and many research papers have been published so far. This paper presents a new robust approach to line and line segment clipping using a rectangular window. A simple extension for the case of convex polygon clipping is presented as well.

Distortions of perceived length in the frontoparallel plane: Tests of perspective theories

Abstract: The perceived length of a line segment in a frontoparallel plane is sometimes affected by the presence of other line segments in the visual field. Perspective theories attribute such interactions to sizeconstancy scaling: The configuration of line segments present in the visual field includes depth cues that trigger size scaling of each line segment. In three experiments, we test this claim for a range of simple configurations composed of two line segments joined at a point. These configurations include the inverted T configuration of the bisection illusion, as well as the L configuration of the horizontal— vertical illusion. We conclude that the available depth cues, even when supplemented by known biases in perspective interpretations, do not account for observed distortions in judgments of relative length.

Orthogonal segment stabbing

Abstract: We study a class of geometric stabbing/covering problems for sets of line segments, rays and lines in the plane. While we demonstrate that the problems on sets of horizontal/vertical line segments are NP-complete, we show that versions involving (parallel) rays or lines are polynomially solvable.

Vision-based Approach to Obstacle Avoidance

Abstract: This paper describes a 3D obstacle modeling system which uses a 2D vision sensor. Prior work tracks feature points in a sequence of images and estimates their positions. However, in this paper we use obstacle edges instead. Using an image segmentation technique, edges are detected as line segments. Subsequently, these edges are modeled in a 3D space from the measured line segments using known camera motions. The z-test method is used for corresponding estimated line data with measurements. Line addition and deletion algorithms are also explained. Simulation results show that simple structures are accurately modeled by the suggested line-based estimator. Finally, this method is applied to a 3D terrain mapping problem. I. Introduction Unmanned aerial vehicles (UAVs) play an important role in military operations and have significant potential for commercial applications. UAVs are expected to operate in dangerous areas, such disaster site or enemy territory, and they can provide realtime information to the user. Various problems in UAV automation are still under investigation. One of these is obstacle detection and avoidance. If a vehicle operates in close proximity to unknown terrain or structures, its navigation system has to automatically detect obstacles and its guidance and control systems must avoid collisions with them. For obstacle detection, it is ideal to obtain 3D site mapping data of the terrain over which the UAV flies. Laser rangefinders can provide very accurate environmental data, 1 however, they are too large and heavy to install on small UAVs. Moreover, they are very expensive. Thus, a single 2D camera is chosen as a sensor for obstacle detection. It is reasonable to use a camera because they are low cost and meet the size and weight constraints of most small UAVs. Furthermore, a camera can be used to obtain sufficient information of the vehicles unknown operational environment in realtime. This paper considers the design of a 3D site modeling system using a single 2D camera. In some studies, vision-based terrain modeling is achieved by tracking many feature points in a sequence of images and updating estimates of their actual 3D positions 2 . 3 Unlike these studies, this paper describes the estimator design based on line information, instead of points. In general, edges of obstacles may appear as curved lines of finite length in an image. In particular, most artificial structures such as buildings have straight edges which appear as a set of straight line segments in an image. Therefore, our objective is to estimate actual obstacle edge lines from the line segments which are detected in an image through an image segmentation technique, and to create a 3D model of the obstacles. It is notable that the line-based estimator uses more structural information (points and their connectivity) than the point-based estimator to create an obstacle model. First, every line segment in a given measurement set is matched with estimated line data. The statistical z-test value is introduced to perform this correspondence. 4 The z-test value is taken for a certain error index. Then the z-test value is inversely related to the likelihood of an event that a given measurement corresponds to the line data chosen. When using the z-test, both estimation error and measurement error covariances are taken in account. For each measurement, the z-test value is calculated and a line which attains the least value is chosen. After a line is assigned, an extended Kalman filter (EKF) is applied to update the two endpoint positions for each line from the residuals of the two endpoints of the measured line segment

Transversals to Line Segments in Three-Dimensional Space

Abstract: We completely describe the structure of the connected components of transversals to a collection of n line segments in ℝ3. Generically, the set of transversals to four segments consists of zero or two lines. We catalog the non-generic cases and show that n≥ 3 arbitrary line segments in ℝ3 admit at most n connected components of line transversals, and that this bound can be achieved in certain configurations when the segments are coplanar, or they all lie on a hyperboloid of one sheet. This implies a tight upper bound of n on the number of geometric permutations of line segments in ℝ3.

Word line arrangement having segmented word lines

Abstract: A three-dimensional (3D) passive element memory cell array provides short word lines while still maintaining a small support circuit area for efficiency. Short, low resistance word line segments on two or more word line layers are connected together in parallel to form a given word line without use of segment switch devices between the word line segments. A shared vertical connection preferably connects the word line segments together and connects to a word line driver circuit disposed generally below the array near the word line. Each word line driver circuit preferably couples its word line either to an associated one of a plurality of selected bias lines or to an unselected bias line associated with the driver circuit, which selected bias lines are themselves decoded to provide for an efficient multi-headed word line decoder.

Vision-Based Indoor Scene Analysis for Natural Landmark Detection

Abstract: In this paper a vision-based landmark extractor for goal-oriented navigation of a mobile robot is proposed. An indoor space scene analysis allows to detect natural structures relevant for navigation like doors or the floor in monocular images of the environment. The detection is based on a priori knowledge of the shape and functionality of searched structures. This algorithm works in real-time and is stable against variation of illumination. The approach is applicable for indoor environments which have clear line structures and large homogenous colour surfaces. The core of this method combines region based as well as edge based elements. The segmentation begins with an orientation selective Hough-Transform (OHT) including line segment detection and generates a reticule of convex polygons. Homogeneous colour similar polygons are segmented and merged by an region growing process. Finally a feature extraction and identification is performed to assign regions to known objects.

Method and system for optimizing the number of word line segments in a segmented MRAM array

Abstract: A method and system for programming and reading a magnetic memory is disclosed. The magnetic memory includes a plurality of selectable word line segments and a plurality of magnetic storage cells corresponding to each word line segment. The method and system include reading the magnetic storage cells corresponding to a word line segment to determine a state of each magnetic storage cell. In one aspect, the method and system also include utilizing at least one storage for storing a state of each of the magnetic storage cells determined during a read operation made during a write operation. The method and system also include writing data to a portion of the magnetic cells corresponding to the word line segment after the reading. The method and system also include rewriting the state to each of a remaining portion of the magnetic storage cells corresponding to the word line segment at substantially the same time as the portion of the magnetic cells are written.

Data acceptance for automated leukocyte tracking through segmentation of spatiotemporal images

Abstract: A crucial task in inflammation research and inflammatory drug validation is leukocyte velocity data collection from microscopic video imagery. Since manual methods are bias-prone and extremely time consuming, automated tracking methods are required to compute cell velocities. However, an automated tracking method is of little practical use unless it is accompanied by a mechanism to validate the tracker output. In this paper, we propose a validation technique that accepts or rejects the output of automated tracking methods. The proposed method first generates a spatiotemporal image from the cell locations given by a tracking method; then, it segments the spatiotemporal image to detect the presence or absence of a leukocyte. For segmenting the spatiotemporal images, we employ an edge-direction sensitive nonlinear filter followed by an active contour based technique. The proposed nonlinear filter, the maximum absolute average directional derivative (MAADD), first computes the magnitude of the mean directional derivative over an oriented line segment and then chooses the maximum of all such values within a range of orientations of the line segment. The proposed active contour segmentation is obtained via growing contours controlled by a two-dimensional force field, which is constructed by imposing a Dirichlet boundary condition on the gradient vector flow (GVF) field equations. The performance of the proposed validation method is reported here for the outputs of three different tracking techniques: the method was successful in 97% of the trials using manual tracking, in 94% using correlation tracking and in 93% using active contour tracking.

Digital straight lines in the khalimsky plane

Abstract: We consider the digital plane of integer points equipped with the Khalimsky topology We suggest a digitization of straight lines such that the digitized image is homeomorphic to the Khalimsky line and a digitized line segment is a Khalimsky arc It is demonstrated that a Khalimsky arc is the digitization of a straight line segment if and only if it satisfies a generalized version of the chord property introduced by Rosenfeld

Online segmentation of freehand stroke by dynamic programming

Abstract: In this paper, a dynamic programming (DP) based approach is proposed to split a freehand stroke into the optimal number of line segments and elliptical arcs. Different from existing DP approaches, which often require a predefined fixed number and/or the templates of the result segments, our approach is actually a generic parameterized framework, which can be configured to some existing methods by fixing some of the parameters. Our key contributions is to avoid presetting of the number or templates of the segments and achieve the best tradeoff between the segment number and approximate error by using a suitable penalty function. Experiments show that our approach achieves high segmentation accuracy and can response to user's stroke input in real-time.

A Probabilistic Analysis of Trie-Based Sorting of Large Collections of Line Segments in Spatial Databases

Abstract: The size of five trie-based methods of sorting large collections of line segments in a spatial database is investigated analytically using a random lines image model and geometric probability techniques. The methods are based on sorting the line segments with respect to the space that they occupy. Since the space is two-dimensional, the trie is formed by interleaving the bits corresponding to the binary representation of the x and y coordinates of the underlying space and then testing two bits at each iteration. The result of this formulation yields a class of representations that are referred to as quadtrie variants, although they have been traditionally referred to as quadtree variants. The analysis differs from prior work in that it uses a detailed explicit model of the image instead of relying on modeling the branching process represented by the tree and leaving the underlying image unspecified. The analysis provides analytic expressions and bounds on the expected size of these quadtree variants. This enables the prediction of storage required by the representations and of the associated performance of algorithms that rely on them. The results are useful in the following two ways: They reveal the properties of the various representations and permit their comparison using analytic, nonexperimental criteria. Some of the results confirm previous analyses (e.g., that the storage requirement of the MX quadtree is proportional to the total lengths of the line segments). An important new result is that for a PMR and Bucket PMR quadtree with sufficiently high values of the splitting threshold (i.e., $\geq 4$) the number of nodes is proportional to the number of line segments and is independent of the maximum depth of the tree. This provides a theoretical justification for the good behavior and use of the PMR quadtree, which so far has been only of an empirical nature. The random lines model was found to be general enough to approximate real data in the sense that the properties of the trie representations, when used to store real data (e.g., maps), are similar to their properties when storing random lines data. Therefore, by specifying an equivalent random lines model for a real map, the proposed analytical expressions can be applied to predict the storage required for real data. Specifying the equivalent random lines model requires only an estimate of the effective number of random lines in it. Several such estimates are derived for real images, and the accuracy of the implied predictions is demonstrated on a real collection of maps. The agreement between the predictions and real data suggests that they could serve as the basis of a cost model that can be used by a query optimizer to generate an appropriate query evaluation plan.

Line detection based on chain code detection

Abstract: A new method for line detection based on chain code detection is proposed. First of all, chain codes are tracked in an edge image. After the curvature estimated, the corners in chain codes can be detected, and chain codes are separated at the corners. Chain codes of line segments are recognized, and only the chain codes, which represent line segments, are kept. Parameters of line segments are estimated according to the chain codes, and the piecewise line segments are linked based on the linking criterions. Experiments with images show that the method is effective for line detection.

Using line segments as structuring elements for sampling-invariant measurements

Abstract: When performing measurements in digitized images, the pixel pitch does not necessarily limit the attainable accuracy. Proper sampling of a bandlimited continuous-domain image preserves all information present in the image prior to digitization. It is therefore (theoretically) possible to obtain measurements from the digitized image that are identical to measurements made in the continuous domain. Such measurements are sampling invariant, since they are independent of the chosen sampling grid. It is impossible to attain strict sampling invariance for filters in mathematical morphology due to their nonlinearity, but it is possible to approximate sampling invariance with arbitrary accuracy at the expense of additional computational cost. In this paper, we study morphological filters with line segments as structuring elements. We present a comparison of three known and three new methods to implement these filters. The method that yields a good compromise between accuracy and computational cost employs a (subpixel) skew to the image, followed by filtering along the grid axes using a discrete line segment, followed by an inverse skew. The staircase approximations to line segments under random orientations can be modeled by skewing a horizontal or vertical line segment. Rather than skewing the binary line segment we skew the image data, which substantially reduces quantization error. We proceed to determine the optimal number of orientations to use when measuring the length of line segments with unknown orientation.

Line textured target detection and tracking with applications to "Basket-run" detection

Abstract: A method of video surveillance may include pre-processing video data to obtain foreground edge information for at least one frame of said video data. The method may perform line segment detection on said foreground edge information to obtain one or more line segments. The line segment detection may be performed by means of an algorithm in which edge pixels are searched and line segments found are checked for validity. It may detect and track one or more targets based on said one or more line segments and may determine if at least one predetermined event is present in said at least one frame of said video data based on the detecting and tracking of said one or more targets.

Method and system for determining a singularity free momentum path

Abstract: A method for avoiding singularities in the movement of CMGs in an array of CMGs in a spacecraft includes a first step where a maneuver command to rotate a spacecraft orientation is received. Then, the torque needed to rotate the spacecraft's orientation is determined. Then, the torque is integrated to determine a momentum path. The momentum path is decomposed into a sequence of straight line segments. For each line segment, a unit vector along the straight line segments is determined. Then, it is determined if there is a continuous path connecting a start point and an end point of the line segment in a plane perpendicular to the unit vector. For each point along the path in the plane perpendicular to the unit vector, a set of gimbal angles is determined.

Geometric robot mapping

Abstract: The purpose of this paper is to present a technique to create a global map of a robot's surrounding by converting the raw data acquired from a scanning sensor to a compact map composed of just a few generalized polylines (polygonal curves). To merge a new scan with a previously computed map of the surrounding we use an approach that is composed of a local geometric process of merging similar line segments (termed Discrete Segment Evolution) of map and scan with a global statistical control process. The merging process is applied to a dataset gained from a real robot to show its ability to incrementally build a map showing the environment the robot has traveled through.

Fast 3D Line Segment–Triangle Intersection Test

Abstract: I present a clean algorithm for determining if a line segment intersects a triangle in three dimensions. The algorithm performs a few binary tests that check if a point of intersection of the line segment and triangle plane is inside the triangle. Then I present some essential optimizations for this algorithm that reduce overall computation complexity. The algorithm does not compute an intersection point. The algorithm is comparable with others, but I believe it is the fastest one when additional memory storage is available.

Exact and efficient cone-beam reconstruction algorithm for a short-scan circle combined with various lines

Abstract: X-ray 3D rotational angiography based on C-arm systems has become a versatile and established tomographic imaging modality for high contrast objects in interventional environment. Improvements in data acquisition, e.g. by use of flat panel detectors, will enable C-arm systems to resolve even low-contrast details. However, further progress will be limited by the incompleteness of data acquisition on the conventional short-scan circular source trajectories. Cone artifacts, which result from that incompleteness, significantly degrade image quality by severe smearing and shading. To assure data completeness a combination of a partial circle with one or several line segments is investigated. A new and efficient reconstruction algorithm is deduced from a general inversion formula based on 3D Radon theory. The method is theoretically exact, possesses shift-invariant filtered backprojection (FBP) structure, and solves the long object problem. The algorithm is flexible in dealing with various circle and line configurations. The reconstruction method requires nothing more than the theoretically minimum length of scan trajectory. It consists of a conventional short-scan circle and a line segment approximately twice as long as the height of the region-of-interest. Geometrical deviations from the ideal source trajectory are considered in the implementation in order to handle data of real C-arm systems. Reconstruction results show excellent image quality free of cone artifacts. The proposed scan trajectory and reconstruction algorithm assure excellent image quality and allow low-contrast tomographic imaging with C-arm based cone-beam systems. The method can be implemented without any hardware modifications on systems commercially available today.

Pointed and colored binary encompassing trees

Abstract: For n disjoint line segments in the plane we construct in optimal O(n log n) time an encompassing tree of maximum degree three such that at every vertex all incident edges lie in a halfplane defined by the incident input segment. In particular, this implies that each vertex is pointed. Furthermore, we show that any set of colored disjoint line segments (for each segment one endpoint is colored red and the other endpoint is colored blue) has an encompassing tree of maximum degree three in which no edge is monochromatic.

Geometric Reformulation of 3-Fingered Force-Closure Condition

Abstract: This paper addresses the problem of testing whether three contact points form a 3-fingered force-closure grasp in two dimensions. In particular, assuming frictional point contacts, we present a new necessary and sufficient condition for three fingers to form a force-closure grasp. The proposed condition is based on a technique for representing a friction cone as a line segment in a dual plane. This representation allows force-closure test to be formulated as the problem of intersection detection between a line segment and a convex polygon. The resulting geometric condition is presented along with an efficient algorithm for using the condition in force-closure test.