Constructive Solid Geometry Objects Research Articles

Optimal Spatial Subdivision method for improving geometry navigation performance in Monte Carlo particle transport simulation

Geometry navigation is one of the key aspects of dominating Monte Carlo particle transport simulation performance for large-scale whole reactor models. In such cases, spatial subdivision is an easily-established and high-potential method to improve the run-time performance. In this study, a dedicated method, named Optimal Spatial Subdivision, is proposed for generating numerically optimal spatial grid models, which are demonstrated to be more efficient for geometry navigation than traditional Constructive Solid Geometry (CSG) models. The method uses a recursive subdivision algorithm to subdivide a CSG model into non-overlapping grids, which are labeled as totally or partially occupied, or not occupied at all, by CSG objects. The most important point is that, at each stage of subdivision, a conception of quality factor based on a cost estimation function is derived to evaluate the qualities of the subdivision schemes. Only the scheme with optimal quality factor will be chosen as the final subdivision strategy for generating the grid model. Eventually, the model built with the optimal quality factor will be efficient for Monte Carlo particle transport simulation. The method has been implemented and integrated into the Super Monte Carlo program SuperMC developed by FDS Team. Testing cases were used to highlight the performance gains that could be achieved. Results showed that Monte Carlo simulation runtime could be reduced significantly when using the new method, even as cases reached whole reactor core model sizes.

Path Planning for Lock Entering Maneuvers Using Nonlinear Programming

Abstract This paper presents a path planning method for lock entering maneuvers that is based on nonlinear programming. Fairway boundaries, lock walls and the input saturation of the thrust devices of the vessel are accounted for as inequality constraints in the optimization. The environmental constraints are modeled as polygons or constructive solid geometry objects. Each of the methods is used to compute a path for a typical inland vessel with a bow thruster and a rudder and propeller configuration.

Spatial bounding of complex CSG objects

Several computer graphics algorithms (such as ray-tracing) heavily relate their performances to the efficiency of the tests of intersection between the rays of a light source and the objects of a synthetic scene. Some solid modelling and robotics algorithms need also to test quickly the possible interferences of the different parts of a system such as the arms of different robots. To speed-up the test, the free shape objects to be tested are encapsulated into boxes and the test starts by performing a check on overlapping of the bounding boxes, thus producing a section of the space where an intersection can occur. Successively, if the boxes overlap, the test continues on the original free shape objects, but only in the portion of the 3D-space resulting from the first step. The authors present a simple, fast and efficient algorithm (called the 'bounding boxes group' method) to compute a tight bounding entity of a complex object modelled in the constructive solid geometry (CSG). If no upper limit is set to the number of elements of each bounding box group, the algorithm is shown to achieve the tightest possible solution. Algorithms are also presented which allow a reduction of the number of bounding elements but still provide a satisfactory and tight encapsulation.

Computing CSG-tree boundaries as algebraic expressions

Constructive solid geometry (CSG) defines objects as Boolean combinations of primitive solids, and usually stores them in binary trees. A bounding entity is an upper estimate of the extent of a CSG object. One of the problems in CSG is the search for the smallest bounding box of an object with the bounding boxes of the leaves as input. A method is presented that finds the smallest bounding box of the root; only prismatic boxes are considered. The method, called the canonical-form method, introduces an algebra of boxes which is shown to be a lattice. The lattice properties are then used to prove that the algorithm that computes the bounding boxes achieves a better approximation than the others. Some hints on implementation are then presented, and the efficiency of the method is compared with the S-bound method.

Near real-time CSG rendering using tree normalization and geometric pruning

A description is given of a set of algorithms for efficiently rendering an object defined by constructive solid geometry (CSG) directly onto a frame buffer without converting first to a boundary representation. This method requires only that the frame buffer contain sufficient memory to hold two color values, two depth values, and three one-bit flags. The algorithm first converts the CSG tree to a normalized form that is analogous to the sum-of-products form for Boolean switching functions. The following are developed: dynamic interleaving of Boolean tree normalization with bounding-box pruning, allowing efficient rendering for most CSG objects; a method for extending the technique to nonconvex primitives; and implementation of these ideas in an interactive CSG design system on the Pixel-planes 4 solid modeling system. In the design system the designer directly manipulates the CSG structure while continuously viewing the color rendering of the object being designed. >