André Kubagawa Sato

An algorithm for the strip packing problem using collision free region and exact fitting placement

The irregular shape packing problem is approached. The container has a fixed width and an open dimension to be minimized. The proposed algorithm constructively creates the solution using an ordered list of items and a placement heuristic. Simulated annealing is the adopted metaheuristic to solve the optimization problem. A two-level algorithm is used to minimize the open dimension of the container. To ensure feasible layouts, the concept of collision free region is used. A collision free region represents all possible translations for an item to be placed and may be degenerated. For a moving item, the proposed placement heuristic detects the presence of exact fits (when the item is fully constrained by its surroundings) and exact slides (when the item position is constrained in all but one direction). The relevance of these positions is analyzed and a new placement heuristic is proposed. Computational comparisons on benchmark problems show that the proposed algorithm generated highly competitive solutions. Moreover, our algorithm updated some best known results.

Registration of temporal sequences of coronal and sagittal MR images through respiratory patterns

Abstract This work discusses the determination of the breathing patterns in time sequence of images obtained from magnetic resonance (MR) and their use in the temporal registration of coronal and sagittal images. The registration is made without the use of any triggering information and any special gas to enhance the contrast. The temporal sequences of images are acquired in free breathing. The real movement of the lung has never been seen directly, as it is totally dependent on its surrounding muscles and collapses without them. The visualization of the lung in motion is an actual topic of research in medicine. The lung movement is not periodic and it is susceptible to variations in the degree of respiration. Compared to computerized tomography (CT), MR imaging involves longer acquisition times and it is preferable because it does not involve radiation. As coronal and sagittal sequences of images are orthogonal to each other, their intersection corresponds to a segment in the three-dimensional space. The registration is based on the analysis of this intersection segment. A time sequence of this intersection segment can be stacked, defining a two-dimension spatio-temporal (2DST) image. The algorithm proposed in this work can detect asynchronous movements of the internal lung structures and lung surrounding organs. It is assumed that the diaphragmatic movement is the principal movement and all the lung structures move almost synchronously. The synchronization is performed through a pattern named respiratory function. This pattern is obtained by processing a 2DST image. An interval Hough transform algorithm searches for synchronized movements with the respiratory function. A greedy active contour algorithm adjusts small discrepancies originated by asynchronous movements in the respiratory patterns. The output is a set of respiratory patterns. Finally, the composition of coronal and sagittal image pairs that are in the same breathing phase is realized by comparing of respiratory patterns originated from diaphragmatic and upper boundary surfaces. When available, the respiratory patterns associated to lung internal structures are also used. The results of the proposed method are compared with the pixel-by-pixel comparison method. The proposed method increases the number of registered pairs representing composed images and allows an easy check of the breathing phase.

Rotational Placement using Simulated Annealing and Collision Free Region

Abstract The packing problem, which considers how to arrange items on a container without overlaps, can increase the utility rate of the sheet stock. This paper investigates the irregular shape rotational packing problem. In this work the Simulated Annealing (SA) is combined with deterministic heuristics (larger first (LF), bottom left (BL) and translations only (Tr)). The problem is represented as an ordered list of items to be packed, and the items are placed touching already placed items or container. The items are placed on the vertices of the collision free region (CFR). The CRF is determined by a robust implementation of non manifold Boolean operations. Several results comparing the SA with deterministic heuristics are presented.

A Simulated Annealing Based Algorithm with Collision Free Region for the Irregular Shape Packing Problem

Abstract This paper investigates the irregular shape packing problem. The proposed algorithm constructively creates layouts from an ordered list of items and a placement heuristic. A moveable item is exclusively placed on a collision free region vertex. The container has a fixed width, while its length can change so that all items are placed on it. The objective is to find a layout of the set of items that minimizes the length of the container. The proposed algorithm has two hierarchical levels: core level with a simulated annealing algorithm, and the external level controlling the container length. The simulated annealing algorithm controls the ordered list of items and the placement of the items. If a feasible layout is found, the external level decreases the container length and applies the simulated annealing again. Otherwise, the container length is increased and the simulated annealing is applied again. Computational comparisons on benchmark problems show that the proposed algorithm generated highly competitive solutions. Moreover, our algorithm updated some best known results. Copyright

Temporal segmentation of lung region MR image sequences using hough transform

In this work, segmentation is an intermediate step in the registration and 3D reconstruction of the lung, where the diaphragmatic surface is automatically and robustly isolated. Usually, segmentation methods are interactive and use different strategies to combine the expertise of humans and computers. Segmentation of lung MR images is particularly difficult because of the large variation in image quality. The breathing is associated to a standard respiratory function, and through 2D image processing, edge detection and Hough transform, respiratory patterns are obtained and, consequently, the position of points in time are estimated. Temporal sequences of MR images are segmented by considering the coherence in time. This way, the lung silhouette can be determined in every frame, even on frames with obscure edges. The lung region is segmented in two steps: a mask containing the lung region is created, and the Hough transform is applied exclusively to mask pixels. The shape of the mask can have a large variation, and the modified Hough transform can handle such shape variation. The result was checked through temporal registration of coronal and sagittal images.

A pairwise exact placement algorithm for the irregular nesting problem

The irregular nesting problem, a subset of cutting and packing problems, aims to minimise waste or unoccupied space inside a container and is found in wood, glass, shipbuilding and textile industries. The problem consists in finding the most compact arrangement of two-dimensional items inside a rectangular container without overlap. The length of the container is variable and up to four different orientations are allowed for each item. Overlap is avoided by using a constructive placement heuristic which places items one at a time, without colliding with other items. The proposed algorithm in this work uses a pairwise placement strategy in which one item is always positioned in exact fitting or sliding placements, which are positions where the item movement is restricted. A simulated annealing algorithm controls the placement sequence and guides the search over the solution space. Several placement heuristics were proposed and tests were conducted with benchmark instances. Results show improvement in efficiency and speed over previous works in some cases.

Placement Heuristics for Irregular Packing to Create Layouts with Exact Placements for Two Moveable Items

This paper discusses cutting and packing problems, which aim to minimize wasted material and can be found in industries such as textile, shipbuilding, wood or glass. The irregular strip packing problem is a variation of such problems in which the container has variable length and fixed width. Solution proposed uses the collision free region concept and its capability to detect exactly fitting and exactly sliding placements. These types of placements represent constrained positions for the item, and it usually constitutes a local optimum placement. The adopted algorithm uses pairwise placement such that one item is always placed in a exact fitting or exact sliding position. However, several possibilities exist, and it is necessary to pick one of them. Due to its different approach for item placement, three new placement heuristics were proposed for this implementation. Each was tested with an instance taken from literature, and compared with best result from the literature. A simulated annealing algorithm controls the sequence of item placement, and the placement position is deterministically determined. This work is a first tentative to determine the best placement position among all the local optimum placements.

3D Reconstruction Using Low Precision Scanner

The objective of this work is to use low precision laser sensor and create reasonably precise 3D reconstructions. The 3D reconstruction is executed by combining several point clouds obtained from different viewpoints. The proposed method was developed with three main steps: point cloud registration, error compensation and surface reconstruction. The ICP algorithm is improved to execute the point cloud registration: dynamic distance threshold, weighted distance, rigid body restriction and color information. It is shown that using this improved ICP, the number of point correspondences to evaluate the quadratic error converges to a value. The quadratic error can be determined independently of scene complexity. The point cloud errors are compensated using the consensus surface algorithm with signed distance. The surface is reconstructed using the marching cubes algorithm. Several results are shown to demonstrate the reliability of the proposed method.

Irregular packing overlap minimization using discrete Voronoi mountain

Abstract Cutting and packing problems are of great importance in a myriad of industries such as: wood, textile, glass and shipbuilding. The irregular strip packing problem considers a container with infinite length where irregular items must be inserted into. A group of solutions in the literature solves the problem by allowing overlap between items and then applying a method which minimizes the total overlap value of the layout. The best results in the literature were obtained using overlap minimization techniques and it is the strategy adopted in this work. Fast overlap evaluation is obtained by the employment of the Voronoi mountain concept. It is used to pre-evaluate the overlap value for two items by adopting a raster representation, which is stored prior to the execution of the algorithm. Tests performed using a benchmark case showed that, even with reduced precision, competitive layouts can be obtained using the proposed approach.

Matrix-vector multiplication and triangular linear solver using GPGPU for symmetric positive definite matrices derived from elliptic equations

The modern GPUs are well suited for intensive computational tasks and massive parallel computation. Sparse matrix multiplication and linear triangular solver are the most important and heavily used kernels in scientific computation, and several challenges in developing a high performance kernel with the two modules is investigated. The main interest it to solve linear systems derived from the elliptic equations with triangular elements. The resulting linear system has a symmetric positive definite matrix. The sparse matrix is stored in the compressed sparse row (CSR) format. It is proposed a CUDA algorithm to execute the matrix vector multiplication using directly the CSR format. A dependence tree algorithm is used to determine which variables the linear triangular solver can determine in parallel. To increase the number of the parallel threads, a coloring graph algorithm is implemented to reorder the mesh numbering in a pre-processing phase. The proposed method is compared with parallel and serial available libraries. The results show that the proposed method improves the computation cost of the matrix vector multiplication. The pre-processing associated with the triangular solver needs to be executed just once in the proposed method. The conjugate gradient method was implemented and showed similar convergence rate for all the compared methods. The proposed method showed significant smaller execution time.