Camera Path Research Articles

A PFM-based Global Convergence Visual Servo Path Planner

As a classical local path planning method,potential field method (PFM) is used widely in the robotics field because of its simplicity and elegance.However,a main drawback of this method is the existence of local minima when generating a path for a robot to follow.In this paper,we present a path planning approach for visual servo by using PFM method to keep the features within the camera field of view (FOV).A rigorous analysis is then presented to prove the global stability of the constructed path planning method.Moreover,the problem of how to obtain a better three-dimensional (3D) camera path is also studied extensively. Simulation results are provided to verify the performance of the proposed path planner.

Visual Servoing Path Planning via Homogeneous Forms and LMI Optimizations

Path planning is a useful technique for visual servoing as it allows one to take into account system constraints and achieve desired performances during the camera motion. In this paper, we propose a new framework for path planning based on the use of homogeneous forms and linear matrix inequalities (LMIs). Specifically, we introduce a general parametrization of the trajectories from the initial to the desired location based on homogeneous forms and a parameter-dependent version of the Rodrigues formula. This allows us to impose typical constraints (field of view, workspace, joint, avoidance of collision, and occlusion) via positivity conditions on suitable homogeneous forms. Then, we reformulate the problem of finding a trajectory in the 3-D space satisfying all these constraints as an LMI optimization that can handle the maximization of typical performances (e.g., visibility margin, similarity to a straight line). The planned camera path is tracked by using an image-based controller. The proposed approach is illustrated and validated through simulations and experiments.

Tangential Distance Fields for Mesh Silhouette Problems

Aabstract We consider a tangent-space representation of surfaces that maps each point on a surface to the tangent plane of the surface at that point. Such representations are known to facilitate the solution of several visibility problems, in particular, those involving silhouette analysis. In this paper, we introduce a novel class of distance fields for a given surface defined by its tangent planes. At each point in space, we assign a scalar value which is a weighted sum of distances to these tangent planes. We call the resulting scalar field a ‘tangential distance field’ (TDF). When applied to triangle mesh models, the tangent planes become supporting planes of the mesh triangles. The weighting scheme used to construct a TDF for a given mesh and the way the TDF is utilized can be closely tailored to a specific application. At the same time, the TDFs are continuous, lending themselves to standard optimization techniques such as greedy local search, thus leading to efficient algorithms. In this paper, we use four applications to illustrate the benefit of using TDFs: multi-origin silhouette extraction in Hough space, silhouette-based view point selection, camera path planning and light source placement.

Efficient unfolding of virtual endoscopy using linear ray interpolation

Unfold rendering enables us to understand the internal structure of organs more precisely. The most commonly used unfolding method is to cast rays radially along a pre-computed camera path. However, this may produce images of false pathological structures. Details on the organ surface may be lost when the organ’s curvature is relatively large due to adjacent ray planes crossing. Several methods are presented to avoid the penetration of ray planes. These methods result in severe computational overhead. We propose an efficient method of penetration-free ray casting for unfolding. It computes ray planes that do not intersect neighboring planes, using the noble intersection avoidance method. It determines the direction of all the rays fired from intermediate sampling points, by linearly interpolating the direction of the rays on two of the original ray planes. Experimental results show that it does not produce erroneous images since it exploits simple linear interpolation.

Re-cinematography

This article presents an approach to postprocessing casually captured videos to improve apparent camera movement. Re-cinematography transforms each frame of a video such that the video better follows cinematic conventions. The approach breaks a video into shorter segments. Segments of the source video where there is no intentional camera movement are made to appear as if the camera is completely static. For segments with camera motions, camera paths are keyframed automatically and interpolated with matrix logarithms to give velocity-profiled movements that appear intentional and directed. Closeups are inserted to provide compositional variety in otherwise uniform segments. The approach automatically balances the tradeoff between motion smoothness and distortion to the original imagery. Results from our prototype show improvements to poor quality home videos.

A PFM-based Global Convergence Visual Servo Path Planner

As a classical local path planning method, potential field method (PFM) is used widely in the robotics field because of its simplicity and elegance. However, a main drawback of this method is the existence of local minima when generating a path for a robot to follow. In this paper, we present a path planning approach for visual servo by using PFM method to keep the features within the camera field of view (FOV). A rigorous analysis is then presented to prove the global stability of the constructed path planning method. Moreover, the problem of how to obtain a better three-dimensional (3D) camera path is also studied extensively. Simulation results are provided to verify the performance of the proposed path planner.

Exploring cultural heritage sites through space and time

Traveling through a single virtual environment only tells part of the story; a particularly interesting aspect is to illustrate how an area has developed over time. This article presents a unified approach to illustrating four-dimensional data concerning a cultural heritage site. The proposed framework provides a semi-automatic approach to both reconstructing the environment and bringing all the time-dependent models into an intuitive visualization package. For each time period considered for reconstruction, the system requires a set of building footprint maps depicting the layout of the environment plus a few statistics. The statistics govern the construction of three-dimensional building models, allowing each building's architectural style, typical building height, and roof style to be altered. This information is automatically processed and converted into a form that can be visualized. By integrating high quality landmark buildings from laser scanning or interactive modelling packages into the automatically generated scene, the cultural heritage site is realized both in a spatial and temporal context. The visualization is achieved via a 4D navigable movie which is presented using two concrete implementations written using Flash and OpenGL. The OpenGL-based implementation allows a collection of 3DS Max scenes to be automatically visualized requiring only a set of camera paths identified by the user.

Determination of camera parameters for character motions using motion area

We propose a method to determine camera parameters for character motion, which considers the motion by itself. The basic idea is to approximately compute the area swept by the motion of the character’s links that are orthogonally projected onto the image plane, which we call “motion area”. Using the motion area, we can determine good fixed camera parameters and camera paths for a given character motion in the off-line or real-time camera control. In our experimental results, we demonstrate that our camera path generation algorithms can compute a smooth moving camera path while the camera effectively displays the dynamic features of character motion. Our methods can be easily used in combination with the method for generating occlusion-free camera paths. We expect that our methods can also be utilized by the general camera planning method as one of heuristics for measuring the visual quality of the scenes that include dynamically moving characters.

Virtual world explorations by using topological and semantic knowledge

This paper is dedicated to virtual world exploration techniques. Automatic camera control is important in many fields as computational geometry, visual servoing, robot motion, graph drawing, etc. The paper introduces a high-level camera controlling approach in virtual environments. The proposed method is related to real-time 3D scene exploration and is made of two steps. In the first step, a set of good viewpoints is chosen to give the user a maximum knowledge of the scene. The second step uses the viewpoints to compute a camera path between them. Finally, we define a notion of semantic distance between objects of the scene to improve the approach.

Straight Line Path-Planning in Visual Servoing

This paper deals with visual servoing for 6-degree-of-freedom robot manipulators, and considers the problem of establishing whether and how it is possible to reach the desired location while keeping all features in the field of view and following a straight line in the Euclidean space. A path-planning technique based on a parametrization of the camera path through polynomials is proposed, which overcomes existing methods dealing with this problem. The generated image trajectory can be tracked by using an image-based visual servoing controller.

Computer‐aided virtual reconstruction of Italian ancient clocks

AbstractItaly has plenty of cultural heritages. The masterpieces are often placed in locations which are difficult to reach, moreover many artifacts, coming from man's creativity, have very complex functioning. The authors of this paper describe their experience in using the computer graphics capabilities in order to reproduce four ancient clocks functioning coming from different Italian regions. The study is based not only on the 3D‐shapes reconstruction but also on the simulation of their complex mechanisms in order to mimic their functioning. The realism of the reconstruction allows to use the graphical products in exhibits, museums and also for maintenance programs. The rendering techniques together with an accurate camera path, allow to get into the clock mechanisms and to appreciate all the features (and even secrets) that a simple glance cannot reveal. Copyright © 2006 John Wiley & Sons, Ltd.

Methods and data structures for virtual world exploration

This paper is dedicated to virtual world exploration techniques that help humans to understand a 3D scene. The paper presents a technique to calculate the quality of a viewpoint for a scene, and describes how this information can be used. A two-step method for an automatic real-time scene exploration is introduced. In the first step, a minimal set of “good” points of view is determined; in the second step, these viewpoints are used to compute a camera path around the scene. The proposed method enables one to get a good comprehension of a single virtual artifact or of the scene structure.

A new path planning algorithm for maximizing visibility in computed tomography colonography

In virtual colonoscopy, minimizing the blind areas is important for accurate diagnosis of colonic polyps. Although useful for describing the shape of an object, the centerline is not always the optimal camera path for observing the object. Hence, conventional methods in which the centerline is directly used as a path produce considerable blind areas, especially in areas of high curvature. Our proposed algorithm first approximates the surface of the object by estimating the overall shape and cross-sectional thicknesses. View positions and their corresponding view directions are then jointly determined to enable us to maximally observe the approximated surface. Moreover, by adopting bidirectional navigations, we may reduce the blind area blocked by haustral folds. For comfortable navigation, we carefully smoothen the obtained path and minimize the amount of rotation between consecutive rendered images. For the evaluation, we quantified the overall observable area on the basis of the temporal visibility that reflects the minimum interpretation time of a human observer. The experimental results show that our algorithm improves visibility coverage and also significantly reduces the number of blind areas that have a clinically meaningful size. A sequence of rendered images shows that our algorithm can provide a sequence of centered and comfortable views of colonography.

Scalable and Efficient Video Coding Using 3-D Modeling

In this paper, we present a three-dimensional (3D) model-based video coding scheme for streaming static scene video in a compact way but also enabling time and spatial scalability according to network or terminal capability and providing 3D functionalities. The proposed format is based on encoding the sequence of reconstructed models using second-generation wavelets, and efficiently multiplexing the resulting geometric, topological, texture, and camera motion binary representations. The wavelets decomposition can be adaptive in order to fit to images and scene contents. To ensure time scalability, this representation is based on a common connectivity for all 3D models, which also allows straightforward morphing between successive models ensuring visual continuity at no additional cost. The method proves to be better than previous methods for video encoding of static scenes, even better than state-of-the-art video coders such as H264 (also known as MPEG AVC). Another application of our approach are smoothing camera path for suppression of jitter from hand-held acquisition and the fast transmission and real-time visualization of virtual environments obtained by video capture, for virtual or augmented reality and interactive walk-through in photo-realistic 3D environments around the original camera path

Way‐Finder: guided tours through complex walkthrough models

Abstract The exploration of complex walkthrough models is often a difficult task due to the presence of densely occluded regions which pose a serious challenge to online navigation. In this paper we address the problem of algorithmic generation of exploration paths for complex walkthrough models. We present a characterization of suitable properties for camera paths and we discuss an efficient algorithm for computing them with little or no user intervention. Our approach is based on identifying the free‐space structure of the scene (represented by a cell and portal graph) and an entropy‐based measure of the relevance of a view‐point. This metric is key for deciding which cells have to be visited and for computing critical way‐points inside each cell. Several results on different model categories are presented and discussed.

A model for smooth viewing and navigation of large 2D information spaces

Large 2D information spaces, such as maps, images, or abstract visualizations, require views at various level of detail: close ups to inspect details, overviews to maintain (literally) an overview. Users often change their view during a session. Smooth animations enable the user to maintain an overview during interactive viewing and to understand the context of separate views. We present a generic model to handle smooth image viewing. The core of the model is a metric on the effect of simultaneous zooming and panning, based on an estimate of the perceived velocity. Using this metric, solutions for various problems are derived, such as the optimal animation between two views, automatic zooming, and the parametrization of arbitrary camera paths. Optimal is defined here as smooth and efficient. Solutions are based on the shortest paths of a virtual camera, given the metric. The model has two free parameters: animation speed and zoom/pan trade off. A user experiment to find good values for these is described. Finally, it is shown how the model can be extended to deal also with rotation and nonuniform scaling.

Omnidirectional video

Omnidirectional video enables direct surround immersive viewing of a scene by warping the original image into the correct perspective given a viewing direction. However, novel views from viewpoints off the camera path can only be obtained if we solve the three-dimensional motion and calibration problem. In this paper we address the case of a parabolic catadioptric camera --- a paraboloidal mirror in front of an orthographic lens --- and we introduce a new representation, called the circle space, for points and lines in such images. In this circle space, we formulate an epipolar constraint involving a 4×4 fundamental matrix. We prove that the intrinsic parameters can be inferred in closed form from the two-dimensional subspace of the new fundamental matrix from two views if they are constant or from three views if they vary. Three-dimensional motion and structure can then be estimated from the decomposition of the fundamental matrix.

Optimal Camera Trajectory with Image-Based Control

Image-based servo is a local control solution. Thanks to the feedback loop closed in the image space, local convergence and stability in the presence of modeling errors and noise perturbations are ensured when the error is small. The principal deficiency of this approach is that the induced (3D) trajectories are not optimal and sometimes, especially when the displacement to realize is large, these trajectories are not physically valid leading to the failure of the servoing process. In this paper we address the problem of finding realistic image-space trajectories that correspond to optimal 3D trajectories. The camera calibration and the model of the observed scene are assumed unknown. First, a smooth closed-form collineation path between given start and end points is obtained. This path is generated in order to correspond to an optimal camera path. The trajectories of the image features are then derived and efficiently tracked using a purely image-based control. A second path planning scheme, based on the potential field method is briefly presented. It allows us to introduce constraints in the desired trajectory to be realized. Such constraints are, for instance, to ensure that the object of interest remains in the camera field of view and to avoid the robot joints limits. Experimental results obtained on a six-degrees-of-freedom eye-in-hand robotic system are presented and confirm the validity of the proposed approach.