Direct Segmentation of Algebraic Models for Reverse Engineering

In Reverse Engineering a physical object is digitally reconstructed from a set of boundary points. In the segmentation phase these points are grouped into subsets to facilitate consecutive steps as surface fitting. In this paper we present a segmentation method with subsequent classification of simple algebraic surfaces. Our method is direct in the sense that it operates directly on the point set in contrast to other approaches that are based on a triangulation of the data set. The segmentation process involves a fast algorithm for k-nearest neighbors search and an estimation of first and second order surface properties. The first order segmentation, that is based on normal vectors, provides an initial subdivision of the surface and detects sharp edges as well as flat or highly curved areas. One of the main features of our method is to proceed by alternating the steps of segmentation and normal vector estimation. The second order segmentation subdivides the surface according to principal curvatures and provides a sufficient foundation for the classification of simple algebraic surfaces. If the boundary of the original object contains such surfaces the segmentation is optimized based on the result of a surface fitting procedure.     

Combining inverse blending and Jacobian‐based inverse kinematics to improve accuracy in human motion generation

We present in the paper a hybrid method for motion editing combining motion blending and Jacobian‐based inverse kinematics (IK). When the original constraints are changed, a blending‐based IK solver is first employed to find an adequate joint configuration coarsely. Using linear motion blending, this search corresponds to a gradient‐based minimization in the weight space. The found solution is then improved by a Jacobian‐based IK solver by further minimizing the distance between the end effectors and constraints. To accelerate the searching in the weight space, we introduce a weight map, which pre‐computes the good starting positions for the gradient‐based minimization. The advantages of our approach are threefold: first, more realistic motions can be generated by utilizing motion blending techniques, compared with pure Jacobian‐based IK. The blended results also increase the rate of convergence of the Jacobian‐based IK solver. Second, the Jacobian‐based IK solver modifies poses in the pose configuration space and the computational cost does not scale with the number of examples. Third, it is possible to extrapolate the given example motions with a Jacobian‐based IK solver, while it is generally difficult with pure blending‐based techniques. Copyright © 2014 John Wiley & Sons, Ltd.     

Compressing dynamic meshes with geometric laplacians

This paper addresses the problem of representing dynamic 3D meshes in a compact way, so that they can be stored and transmitted efficiently. We focus on sequences of triangle meshes with shared connectivity, avoiding the necessity of having a skinning structure. Our method first computes an average mesh of the whole sequence in edge shape space. A discrete geometric Laplacian of this average surface is then used to encode the coefficients that describe the trajectories of the mesh vertices. Optionally, a novel spatio‐temporal predictor may be applied to the trajectories to further improve the compression rate. We demonstrate that our approach outperforms the current state of the art in terms of low data rate at a given perceived distortion, as measured by the STED and KG error metrics.     

Rate‐distortion optimized compression of motion capture data

Lossy compression of motion capture data can alleviate the problems of efficient storage and transmission by exploiting the redundancy and the superfluous precision of the data. When considering the acceptable amount of distortion, perceptual issues have to be taken into account. Current state of the art methods reduce the data rate required for high quality storage of motion capture data using various techniques. Most of them, however, do not use the common tools of general data compression, such as the method of Lagrange multipliers, and thus they obtain sub‐optimal results, making it difficult to do a fair comparison of their performance. In this paper, we present a general preprocessing step based on Lagrange multipliers, which allows to rigorously adjust the precision in each of the degrees of freedom of the input data according to the amount of influence the given degree of freedom has on the overall distortion. We then present a simple compression method based on Principal Component Analysis, which in combination with the proposed preprocessing achieves significantly better results than current state of the art methods. It allows optimization with respect to various distortion metrics, and we discuss the choice of the metric in two common but distinct scenarios, proposing a perceptually oriented comparison metric based on the relation of the problem at hand to the problem of compression of dynamic meshes.     

Multi-level hermite variational interpolation and quasi-interpolation

Based on the Hermite variational implicit surface reconstruction presented in Pan et al. (Science in China Series F: Information Sciences 52(2):308–315, 2009), we propose a multi-level interpolation method to overcome the problems resulted from using compactly supported radial basis functions (CSRBFs). In addition, we present a multi-level quasi-interpolation method which directly uses normal vectors to construct non-zero constraints and avoids solving any linear system, a common step of variational surface reconstruction, and leads to a fast and stable surface reconstruction from scattered points. With adaptive support size, our approach is robust and can successfully reconstruct surfaces on non-uniform and noisy point sets. Moreover, as the computation of quasi-interpolation is independent for each point, it can be easily parallelized on multi-core CPUs.     

Fast Force Field Approximation and its Application to Skeletonization of Discrete 3D Objects

In this paper we present a novel method to approximate the force field of a discrete 3d object with a time complexity that is linear in the number of voxels. We define a rule, similar to the distance transform, to propagate forces associated with boundary points into the interior of the object. The result of this propagation depends on the order in which the points of the object are processed. Therefore we analyze how to obtain an order‐invariant approximation formula. With the resulting formula it becomes possible to approximate the force field and to use its features for a fast and topology preserving skeletonization. We use a thinning strategy on the body‐centered cubic lattice to compute the skeleton and ensure that critical points of the force field are not removed. This leads to improved skeletons with respect to the properties of centeredness and rotational invariance.     

Real-time interaction with a humanoid avatar in an immersive table tennis simulation

In this paper, we report on the realization of an immersive table tennis simulation. After describing the hardware necessities of our system, we give insight into different aspects of the simulation. In particular, the developed methods for collision detection and physical simulation are presented. The design of the virtual opponent is of crucial importance to realize an enjoyable game. Therefore, we report on the implemented game strategy and the animation of the opponent. Since table tennis is one of the fastest sports, the synchronization of the human player's movements and the visual output on the projection wall is a very challenging problem to solve. To overcome the latencies in our system, we designed a prediction method that allows high speed interaction with our application     

V-Pong: an immersive table tennis simulation

Most applications for immersive virtual environments (VEs) allow slow-or medium-speed user interaction. Examples of this kind of interaction include changing an object's position, triggering an action, or setting a control parameter. To broaden the application range for VR systems, we need to integrate technologies that allow for faster VE-user movements. This raises the question, What response times can we achieve with VR systems built from standard recent hardware components? To answer this question, we created a table tennis simulation as this game involves fast user movements and has moderate space requirements. In this article we report on the realization of our immersive table tennis simulation, V-Pong.     

Geometric preprocessing of noisy point sets: an experimental study

Point based graphics avoids the generation of a polygonal approximation of sampled geometry and uses algorithms that directly work with the point set. Basic ingredients of point based methods are algorithms to compute nearest neighbors, to estimate surface properties as, e.g. normals and to smooth the point set. In this paper we report on the results of an experimental study that compared different methods for the mentioned subtasks.     

Fur Shading and Modification based on Cone Step Mapping

This paper presents an algorithm for the real time rendering of fur without adding fur‐specific geometry, such as shells, to the object. It is based on Cone Step Mapping and introduces a local distortion of the view vector to simulate a deformation of the heightfield‐bound hair geometry. While this distortion enables a more realistic fur rendering, some limitations emerge and have to be dealt with. A local light reflectance model including approximations of global light interactions with hair and skin is proposed. We furthermore show how material and geometric properties can locally be influenced through standard texture mapping. This includes most notably the local modification of growth and streak direction of the hairs.