Large Number Of Polygons Research Articles

Reconstruction of a 3D mesh with displacement vectors for medical images

2D medical images resolution from the current hardware becomes more important. The reconstruction of a 3D model from these images generates a large number of polygons, which leads to problems with the amount of information stored and also in terms of the complexity of calculations for display viewing in real-time. Our approach to 3D reconstruction of the human anatomy, from a sequence of 2D images is based on a low mesh resolution. This mesh is obtained by using the marching cubes algorithm of these medical images. Small reliefs lost in the base mesh are calculated from the information we have in 2D images. These reliefs are shown in the form of 2D vectors, which allows a very important optimisation of the 3D model storage. Details of each polygon mesh base are calculated in an independent manner, which facilitator the automatic generation of the displacement map for this mesh. The use of this card with the latest GPU accelerates the real-time calculations of visualisation.

An efficient algorithm for clipping operation based on trapezoidal meshes and sweep-line technique

This paper presents an efficient algorithm for clipping points, arcs and polygons, which is a common operation in geographic information system (GIS). By incorporating the sweep-line technique in the proposed algorithm, the involved polygons are decomposed into a collection of trapezoidal meshes. In this way, the clipping operation between the to-be-clipped point, arc, polygon features and the subject polygons is transformed into an operation between points, arcs and the decomposed trapezoidal meshes, which is much easier to implement. Experimental results demonstrate that the algorithm is computational efficient comparing to the existing methods, especially when the input data contain a large number of polygons. In addition, the amount of storage space required is moderate. Furthermore, this algorithm is very flexible and able to handle concave polygons and those with holes.

Reducing the Search Space for Pathfinding in Navigation Meshes by Using Visibility Tests

A navigation mesh (NavMesh) is a suitable tool for the representation of a three-dimensional game world. A NavMesh consists of convex polygons covering free space, so the path can be found reliably without detecting collision with obstacles. The main disadvantage of a NavMesh is the huge state space. When the <TEX>$A^*$</TEX> algorithm is applied to polygonal meshes for detailed terrain representation, the pathfinding can be inefficient due to the many states to be searched. In this paper, we propose a method to reduce the number of states searched by using visibility tests to achieve fast searching even on a detailed terrain with a large number of polygons. Our algorithm finds the visible vertices of the obstacles from the critical states and uses the heuristic function of <TEX>$A^*$</TEX>, defined as the distance to the goal through such visible vertices. The results show that the number of searched states can be substantially reduced compared to the <TEX>$A^*$</TEX> search with a straight-line distance heuristic.

Smooth force rendering on coarse polygonal meshes

AbstractPiecewise linear polygonal model has only G0 continuity, thus users can easily feel the edges when using haptic device to touch a solid represented by coarse polygonal meshes. To produce an appealing haptic sensation for smooth solids, a large number of polygons are needed in conventional approaches. This, however, slows down computation and consumes much more memory. In this paper, we present a method to generate smooth feedback force in haptic interaction with coarse polygonal meshes. Our method calculates the interaction force based on Gregory patches, which are locally constructed from n‐sided polygons and ensure G1 continuity across boundaries of patches. During the real time haptic interaction, the contact point is continuously tracked on the locally constructed Gregory patches and thus generates smooth haptic forces to be rendered. Our method is validated on various models with comparison to conventional force rendering techniques. Copyright © 2010 John Wiley &amp; Sons, Ltd.

Methods for rapidly processing angular masks of next-generation galaxy surveys

As galaxy surveys become larger and more complex, keeping track of the completeness, magnitude limit and other survey parameters as a function of direction on the sky becomes an increasingly challenging computational task. For example, typical angular masks of the Sloan Digital Sky Survey contain about N= 300 000 distinct spherical polygons. Managing masks with such large numbers of polygons becomes intractably slow, particularly for tasks that run in time with a naive algorithm, such as finding which polygons overlap each other. Here we present a ‘divide-and-conquer’ solution to this challenge: we first split the angular mask into pre-defined regions called ‘pixels’, such that each polygon is in only one pixel, and then perform further computations, such as checking for overlap, on the polygons within each pixel separately. This reduces tasks to ⁠, and also reduces the important task of determining in which polygon(s) a point on the sky lies from to ⁠, resulting in significant computational speedup. Additionally, we present a method to efficiently convert any angular mask to and from the popular healpix format. This method can be generically applied to convert to and from any desired spherical pixelization. We have implemented these techniques in a new version of the mangle software package, which is freely available at http://space.mit.edu/home/tegmark/mangle/, along with complete documentation and example applications. These new methods should prove quite useful to the astronomical community, and since mangle is a generic tool for managing angular masks on a sphere, it has the potential to benefit terrestrial mapmaking applications as well.

Legible Simplification of Textured Urban Models

Most of the algorithms used for research in mesh simplification and discrete levels of detail (LOD) work well for simplifying single objects with a large number of polygons. For a city-sized collection of simple buildings, using these traditional algorithms could mean the disappearance of an entire residential area in which the buildings tend to be smaller than those in commercial regions. To solve this problem, we developed a mesh-simplification algorithm that incorporates concepts from architecture and city planning. Specifically, we rely on the concept of urban legibility, which segments a city into paths, edges, districts, nodes, and landmarks. If we preserve these elements of legibility during the simplification process, we can maintain the city's image and create urban models that users can understand more effectively. To accomplish this goal, we divide our algorithm into five steps. During preprocessing, it performs hierarchical clustering, cluster merging, model simplification, and hierarchical texturing, at runtime, it employs LOD to select the appropriate models for rendering.

A Clustering Framework for Real-time Rendering of Tree Foliage

Real-time rendering of vegetation is currently a problem in need of a solution. The lack of plants and trees reduces the realism of outdoor scenes. The large number of polygons that form this kind of objects implies that current hardware cannot achieve interactive rendering of outdoor scenes. This paper deals with this problem and it presents a multiresolution scheme that allows us to represent the whole geometry of the trees and forests using both uniform and variable levels of detail. The method presented here models the trees using two multiresolution approaches, due to the different characteristics of the geometry that forms them. The trunk is modelled with a solution oriented towards representing continuous meshes, and the foliage is modelled with the multiresolution model Level of Detail Foliage, presented in a previous work. Both of them have been designed to take advantage of the graphics hardware by adapting the data structures and the rendering algorithms to make the visualisation time efficient. The main characteristic of Level of Detail Foliage is the fact that it classifies the leaves that form the foliage in independent clusters in order to improve the visualisation time. In this paper, it has been efficiently implemented and extended to allow us to change the level of detail in a variable manner, by adapting the resolution of the crown of the tree to certain criteria determined by the application.

Image-Based Modeling of Urban Buildings Using Aerial Photographs and Digital Maps

A VR (virtual reality) simulator which is used for helicopter simulations requires a virtual environment of real world urban areas. However, real urban environments are continuously changing. It is necessary to develop a modeling method that makes direct use of GIS (geographical information system) data which is updated periodically. A flight simulation needs to visualize not only buildings in the near distance but also a large number of buildings in the far distance. We propose a method for modeling urban environments from aerial images and digital maps with relatively little manual work. An image-based method is applied to the urban modeling that considers the characteristics of Korean cities. Buildings in the distance can be presented without creating a large number of polygons. The proposed method consists of a pre-processing stage that prepares the model from the GIS data and a modeling stage that creates the virtual urban environment. The virtual urban environment utilizes the height map of buildings.

New colonoscopy simulator with improved haptic fidelity

Colonoscopy is a safe and effective procedure to diagnose and treat the large bowel with the help of the flexible endoscope. This paper presents a new colonoscopy training simulator to help trainees practice and acquire the necessary skills and experiences with no risk to the patients and possibly less cost. The simulator includes a specialized haptic interface to transfer force feedback through a long and flexible tube, and graphics algorithms to display the virtual colon realistically while managing the large number of polygons. A new 2-d.o.f. haptic device with folding guides is developed to transmit large decoupled forces of the colonoscopy simulation to the user. The physicians apply a jiggling motion to the colonoscopy tube to advance the scope. This jiggling is an important skill of colonoscopy and is incorporated for the first time by using the new sensor mechanism. A colonoscope handle that shares the look, feel and functions with an actual colonoscope is developed with the necessary electronics inside. The simulator contains controllers to compensate for the inertia and friction effects, and is evaluated by physicians. New graphics algorithms including polygon reduction, navigation and collision detection are developed to compute the deformation and the corresponding reflective force in real-time.

A desktop VR prototype for industrial training applications

The recent advances in computer graphics has spurred interest from both academics and industries in virtual reality (VR) enabled training applications. This paper presents a desktop VR prototype for industrial training applications. It is designed and implemented as a general shell by providing the data interface to import both the virtual environment models and specific domain knowledge. The geometric models of the virtual environment are constructed using feature-based modelling and assembly function by external CAD tools, and then transferred into the prototype through a conversion module. A hierarchical structure is proposed to partition and organise these imported virtual environment models. Based on this structure, a visibility culling approach is developed for fast rendering and user interaction. The case study has demonstrated the functionality of the proposed prototype system by applying it to a maintenance training application for a refinery bump system, which, in general, has a large number of polygons and a certain depth complexity. Significant speedup in both context rendering and response to user manipulations has been achieved to provide the user with a fast system response within the desktop virtual environment. Compared with the immersive VR system, the proposed system has offered an affordable and portable training media for industrial applications.

An analytic visible surface algorithm for independent pixel processing

An algorithm is presented that solves the visible surface problem at each pixel independently. This allows motion blur and depth of field blurring to be integrated into the algorithm. It also allows parallel processing. The algorithm works on large numbers of polygons. An analytic Gaussian filter is used. The filter can be elongated or scaled differently for each polygon to adjust for its speed or distance from the focal plane. This is achieved by shrinking or scaling the polygon prior to solving the hidden surface problem so that blurring is correctly presented when objects obscure each other.

Circumscribing a convex polygon by a polygon of fewer sides with minimal area addition

An approach and an algorithm are introduced for circumscribing a given n-sided convex polygon P n by an m-sided polygon P m , ( m < n), so that the added area is minimal. This algorithm constitutes one building block in an algorithm for efficient nesting of arbitrary geometric shapes in a given rectangular board. Flame cutting of steel sheets and laser cutting of textiles are two industrial situations where this problem is of great importance. The approach follows a top-down stepwise refinement and reduction of the original problem into simpler subproblems, the solutions of all of which permit the solution of the original problem. It is first shown that the optimal circumscription of P n by P m may be obtained by ( n − m) iterative single side reductions. The solution of the single side reduction problem is then characterized, and an algorithm which is based on the triangle rotating side problem is proposed. This last problem is concerned with passing the third side of a triangle through a given point that lies within the area bounded by the two other given sides so that the triangle area is minimized. On the way to proving the optimality of the algorithms for the original problem and its subproblems, new concepts and theorems are introduced. The algorithm was tested on a very large number of polygons with varying numbers of sides and shapes, which were circumscribed by hexagons. The average efficiency—defined as the ratio of the area of P n to that of P m —was 96%. As n increases, efficiency reduces and approaches asymptotically the maximum achievable efficiency for circumscribing a circle (“infinite” sided polygon) by a regular hexagon: 90.69%. With n = 50 the average efficiency was 91.8%.