Photometric bundle adjustment (PBA) accurately estimates geometry from video. However, current PBA systems have a temporary map that cannot manage scene reobservations. We present, direct sparse mapping, a full monocular visual simultaneous localization and mapping (SLAM) based on PBA. Its persistent map handles reobservations, yielding the most accurate results up to date on EuRoC for a direct method.

This paper proposes a novel approach to registering deformations of 3D non-rigid objects for Augmented Reality applications. Our prototype is able to handle different types of objects in real-time regardless of their geometry and appearance (with and without texture) with the support of an RGB-D camera. During an automatic offline stage, the model is processed in order to extract the data that serves as input for a physics-based simulation. Using its output, the deformations of the model are estimated by considering the simulated behaviour as a constraint. Furthermore, our framework incorporates a tracking method based on templates in order to detect the object in the scene and continuously update the camera pose without any user intervention. Therefore, it is a complete solution that extends from tracking to deformation formulation for either textured or untextured objects regardless of their geometrical shape. Our proposal focuses on providing a correct visual with a low computational cost. Experiments with real and synthetic data demonstrate the visual accuracy and the performance of our approach.

Deformable models are widely used in many disciplines such as engineering and medicine. Real objects are usually scanned to create models in such applications. In many cases the shape of the object is extracted from volumetric data acquired during the scanning phase. At the same time, this volume can be used to define the model's appearance. In order to achieve a visualization that unifies the shape (physical model) and appearance (scanned volume) specially adapted volume rendering techniques are required. One of the most common volumetric visualization techniques is ray casting, which also enables the use of different corrections or improvements such as adaptive sampling or stochastic jittering. This paper presents an extensive study about a ray casting method for tetrahedral meshes with an underlying structured volume. This allows a direct visualization of the deformed model without losing the information contained in the volume. The aim of this study is to analyse and compare the different methods for ray traversal and illumination correction, resulting in a comprehensive relation of the different methods, their computational cost and visual performance.

A real-time Augmented Reality system that assists in maintenance is presented (Figure 1). The novelty of the proposed system relies on its ability of being a complete framework that is self supplied. All the data is extracted automatically during an offlne phase from a collection of 3D parts that are provided as untextured 3D triangle meshes. Our disassembly planning module computes the assembly/disassembly sequence finding collision-free trajectories [1]. Moreover, some basic geometric features, such as edges and junctions, are extracted to address the tracking problem. Additionally, these geometric features let us perform the 3D model recognition, which solves the first camera pose problem and performs the recovery in case of tracking failure [3]. During the online phase, these geometric features are used to build a markerless tracking that updates continuously the camera pose from a monocular image. This markerless tracking combines an edge tracker, a point based tracker and a 3D particle filter to offer a robust 3D tracking against undesirable conditions [2]. Once the camera pose has been computed, the system offers an augmented instruction, indicating how to assemble/disassemble the next part. Thus, the proposed AR system is a complete framework that runs in real-time and tries to facilitate the work of workers, replacing the paper-based documentation.

ABSTRACT We propose a novel mesh optimization approach that is useful for speeding up a simulation of finite elements‐based deformable objects. The approach is based on a quality metric derived from the critical simulation time step of explicit time integration schemes (i.e., the stability limit for the integration of dynamic equations). Our mesh smoothing approach consists of a set of small and independent spring systems. These are made up of a reference mesh node connected to a set of fixed endpoints, which represent the positions that maximize the time step of the elements adjacent to that node. The reference node is displaced to an equilibrium position through a few local iterations. Each spring's stiffness is weighted depending on the quality of its corresponding element. All spring systems can be computed in parallel. Global iterations update the mesh and spring systems. In addition, we combine our smoothing algorithm with topological transformations. With this approach, the simulation performance could be increased by more than 30% depending on the mesh. This approach is suitable for the generation of finite element method meshes, particularly those requiring interactive applications and haptic rendering. Copyright © 2012 John Wiley & Sons, Ltd.

We present a novel hybrid method to allow large time steps in explicit integrations for the simulation of deformable objects. In explicit integration schemes, the time step is typically limited by the size and the shape of the discretization elements as well as by the material parameters. We propose a two-step strategy to enable large time steps for meshes with elements potentially destabilizing the integration. First, the necessary time step for a stable computation is identified per element using modal analysis. This allows determining which elements have to be handled specially given a desired simulation time step. The identified critical elements are treated by a geometric deformation model, while the remaining ones are simulated with a standard deformation model (in our case, a corotational linear Finite Element Method). In order to achieve a valid deformation behavior, we propose a strategy to determine appropriate parameters for the geometric model. Our hybrid method allows taking much larger time steps than using an explicit Finite Element Method alone. The total computational costs per second are significantly lowered. The proposed scheme is especially useful for simulations requiring interactive mesh updates, such as for instance cutting in surgical simulations.

Mass-Spring Models (MSMs) are used to simulate the mechanical behavior of deformable bodies such as soft tissues in medical applications. Although they are fast to compute, they lack accuracy and their design remains still a great challenge. The major difficulties in building realistic MSMs lie on the spring stiffness estimation and the topology identification. In this work, the mechanical behavior of MSMs under tensile loads is analyzed before studying the spring stiffness estimation. In particular, the performed qualitative and quantitative analysis of the behavior of cubical MSMs shows that they have a nonlinear response similar to hyperelastic material models. According to this behavior, a new method for spring stiffness estimation valid for linear and nonlinear material models is proposed. This method adjusts the stress-strain and compressibility curves to a given reference behavior. The accuracy of the MSMs designed with this method is tested taking as reference some soft-tissue simulations based on nonlinear Finite Element Method (FEM). The obtained results show that MSMs can be designed to realistically model the behavior of hyperelastic materials such as soft tissues and can become an interesting alternative to other approaches such as nonlinear FEM.

This paper proposes a new real-time Augmented Reality based tool to help in disassembly for maintenance operations. This tool provides workers with augmented instructions to perform maintenance tasks more efficiently. Our prototype is a complete framework characterized by its capability to automatically generate all the necessary data from input based on untextured 3D triangle meshes, without requiring additional user intervention. An automatic offline stage extracts the basic geometric features. These are used during the online stage to compute the camera pose from a monocular image. Thus, we can handle the usual textureless 3D models used in industrial applications. A self-supplied and robust markerless tracking system that combines an edge tracker, a point based tracker and a 3D particle filter has also been designed to continuously update the camera pose. Our framework incorporates an automatic path-planning module. During the offline stage, the assembly/disassembly sequence is automatically deduced from the 3D model geometry. This information is used to generate the disassembly instructions for workers.

Maintenance operations have a great impact in the security and life expectancy of any product. Virtual Reality can help reducing costs and design time by moving testing from physical mock-ups to virtual ones. VR allows the application of additional tools not possible in a physical mock-up. The increase in power of current computers allows their use not only for visualization and interaction but also for geometrical analysis and reasoning. These capabilities provide designers with tools that can increase their productivity. This paper proposes methods for the generation of selective disassembly plans and the generation of collision free trajectories in the context of interactive simulation of maintenance operations. These methods provide a design team with additional tools to asses a design, prior to the construction of physical mock-ups and, therefore, reducing the cost of a project