36225192
L-System Description of Subdivision Curves
In recent years, subdivision has emerged as a major geometric modeling technique. Algorithms for generating subdivision curves are often specified in terms of iterated matrix multiplication. Each multiplication maps a globally indexed sequence of points that represents a coarser approximation of the curve onto a longer sequence that represents a finer approximation. Unfortunately, this use of matrices and indices obscure the local and stationary character of typical subdivision rules. We introduce parametric context-sensitive L-systems with affine geometry interpretation as an alternative technique for specifying and generating subdivision curves. This technique is illustrated using Chaikin, cubic B-spline, and Dyn-Levin-Gregory (4-point) subdivision schemes as examples. L-systems formalize subdivision algorithms in an intuitive, concise, index-free manner, reflecting the parallel and local character of these algorithms. Furthermore, L-system specification of subdivision algorithms directly leads to their computer implementation.
17908956
Local Specification of Surface Subdivision Algorithms
Many polygon mesh algorithms operate in a local manner, yet are formally specified using global indexing schemes. This obscures the essence of these algorithms and makes their specification unnecessarily complex, especially if the mesh topology is modified dynamically. We address these problems by defining a set of local operations on polygon meshes represented by graph rotation systems. We also introduce the vv programming language, which makes it possible to express these operations in a machine-readable form. The usefulness of the vv language is illustrated by the application examples, in which we concentrate on subdivision algorithms for the geometric modeling of surfaces. The algorithms are specified as short, intuitive vv programs, directly executable by the corresponding modeling software.
2626294
Computation of shape through controlled active exploration
Accurate knowledge of depth continues to be of critical importance in robotic systems. Without accurate depth knowledge, tasks such as inspection, tracking, grasping, and collision-free motion planning prove to be difficult and often unattainable. Traditional visual depth recovery has relied upon techniques that require the solution of the correspondence problem or require known lighting conditions and Lambertian surfaces. In this paper, we present a technique for the derivation of depth from feature points on a target's surface using the controlled active vision framework. We use a single visual sensor mounted on the end-effector of a robotic manipulator to automatically select feature points and to derive depth estimates for those features using adaptive control techniques. Movements of the manipulator produce displacements that are measured using a sum-of-squared difference (SSD) optical flow. The measured displacements are fed into the controller to alter the path of the manipulator and to refine the depth estimate.<<ETX>>
6961424
Designing High-Performance Distributed Applications Using Software Performance Engineering: A Tutorial
Summary This paper reviewed the purpose of SPE, the steps forapplying the SPE methods throughout the life cycle ofnew systems, the data requirements and illustrated aperformance walkthrough approach for gathering thedata. The software and system execution models forassessing the performance of alternatives weredescribed and their use throughout the life cycle wasreviewed.SPE is becoming increasingly popular for large,strategic systems to systematically manage theperformance. The models are relatively easy toconstruct and evaluate with the performance modelingtools available today. SPE’s current problems are notthe technical problems of constructing and evaluatingthe performance models. The chief barriers aremaking developers and managers aware of SPE’spotential, and persuading them to incorporate themethods into their development life cycle. References [HEID93] Ruth V. Heidel and George W. Dodson,(Editor), Special Issue on Client/Server Computing ,CMG Transactions, no. 82, 1993.[SMIT88a] Connie U. Smith, "Applying SynthesisPrinciples to Create Responsive Software Systems,"
6910866
Performance Engineering Evaluation of Object Oriented Systems With SPE-ED
Although object-oriented methods have been shown to help construct software systems that are easy to understand and modify, have a high potential for reuse, and are relatively quick and easy to implement, concern over performance of object-oriented systems represents a significant barrier to its adoption. Our experience has shown that it is possible to design object-oriented systems that have adequate performance and exhibit the other qualities, such as reusability, maintainability, and modifiability, that have made OOD so successful. However, doing this requires careful attention to performance goals throughout the life cycle. This paper describes the use of SPE·ED, a performance modeling tool that supports the SPE process, for early life cycle performance evaluation of object-oriented systems. The use of SPE·ED for performance engineering of object-oriented software is illustrated with a simple example.
4403848
A Critical Appraisal of the Box Counting Method to Assess the Fractal Dimension of Tree Crowns
In this paper, we study the application of the box counting method (BCM) to estimate the fractal dimension of 3D plant foliage. We use artificial crowns with known theoretical fractal dimension to characterize the accuracy of the BCM and we extend the approach to 3D digitized plants. In particular, errors are experimentally characterized for the estimated values of the fractal dimension. Results show that, with careful protocols, the estimated values are quite accurate. Several limits of the BCM are also analyzed in this context. This analysis is used to introduce a new estimator, derived from the BCM estimator, whose behavior is characterized.
27891040
The Evolution of Software Performance Engineering: A Survey