Practical considerations for ray casting shear layer corrections

Aircraft noise reduction technology development has been aided by the use of acoustic phased arrays to identify component-level locations of noise sources. Acoustic phased arrays are commonly used in both closed-wall and open-jet wind tunnels, thus requiring accurate acoustic propagation models to focus the array. In particular, open-jet wind tunnels have complex flow fields including a free shear layer that the acoustic waves must propagate through. A method using ray tracing is reviewed and an enhancement proposed to reduce the computational time for cases requiring a large number of rays. The proposed reduced ray casting method uses ray tracing to the extreme edges of the region of interest and limits all casted acoustic rays to within that region. The results showed that a hemispherical spiral discretization had lower error in the estimated acoustic propagation time than uniform angular discretization. The proposed reduced ray casting method showed similar accuracy as the original ray casting method but with improvement in the computational times when the number of cast rays was greater than 3200 as needed for modeling acoustic propagation in larger industrial sized open-jet wind tunnels.

Using Virtual Scanning to Find Optimal Configuration of a 3D Scanner Turntable for Scanning of Mechanical Parts

The article describes a method of simulated 3D scanning of triangle meshes based on ray casting which is used to find the optimal configuration of a real 3D scanner turntable. The configuration include the number of scanners, their elevation above the rotary table and the number of required rotation steps. The evaluation is based on the percentage of the part surface covered by the resulting point cloud, which determines the ability to capture all details of the shape. Principal component analysis is used as a secondary criterion to also evaluate the ability to capture the overall general proportions of the model.

Research on Improved Ray Casting Algorithm and Its Application in Three-Dimensional Reconstruction

Spinal pathology treatment has become an urgent issue to be solved. How to effectively prevent and treat spinal pathology has become a research hotspot in the field of surgery. Aiming at the problem of too long volume rendering time caused by the trilinear interpolation sampling method in the reconstruction and visualization of the vertebra 3D model, an improved ray projection algorithm is proposed to quickly reconstruct a 3D vertebra model from medical CT vertebra images. This method first classifies CT data, assigns corresponding color values and opacity transfer functions to different types of data, and then uses inverse distance-weighted interpolation (IDWI) sampling to replace the trilinear interpolation sampling method for the voxel where the sampling point is located to accelerate the interpolation operation. The color value and opacity of the sampling points are obtained, and finally, the attributes of all the sampling points are synthesized and calculated to obtain the final rendering effect, and the reconstruction of the three-dimensional vertebra model is completed. Experimental results show that the proposed method not only can obtain higher quality rendered images but also has a certain improvement in rendering speed compared with traditional algorithms.

Researches on the Fast Determination of Cell Type of Cartesian Grid

The relationship between the spatial cell and the object is unknown for the Cartesian grid using the immersed boundary method. For the researches about complex geometry or multi-body relative motion, grid generation is a very time-consuming work, and the consumption is mainly concentrated in the position determination of the Cartesian cells, which we called the cell type determination. In this study, based on the axis-aligned bounding box method and the ray casting method, we employed the dot product method and the painting algorithm to investigate the acceleration method for Cartesian grid generation. The octree structure is used to store the Cartesian cells, and the k-dimensional tree is used to store the object surface. These data management strategy can minimize the CPU’s resource while have a small memory usage. The grid generation results show that the strategy we proposed has a high efficiency and well robustness, and the time consume can reduce more than 50% compare with the original method. When dealing with a enough complex problem, the time consume can even reaches several orders of magnitude difference compared with the original method.

Automatic sizing functions for unstructured mesh generation revisited

PurposeSizing functions are crucial inputs for unstructured mesh generation since they determine the element distributions of resulting meshes to a large extent. Meanwhile, automating the procedure of creating a sizing function is a prerequisite to set up a fully automatic mesh generation pipeline. In this paper, an automatic algorithm is proposed to create a high-quality sizing function for an unstructured surface and volume mesh generation by using a triangular mesh as the background mesh.Design/methodology/approachA practically efficient and effective solution is developed by using local operators carefully to re-mesh the tessellation of the input Computer Aided Design (CAD) models. A nonlinear programming (NLP) problem has been formulated to limit the gradient of the sizing function, while in this study, the object function of this NLP is replaced by an analytical equation that predicts the number of elements. For the query of the sizing value, an improved algorithm is developed by using the axis-aligned bounding box (AABB) tree structure.FindingsThe local operations of re-meshing could effectively and efficiently resolve the banding issue caused by using the default tessellation of the model to define a sizing function. Experiments show that the solution of the revised NLP, in most cases, could provide a better solution at the lower cost of computational time. With the help of the AABB tree, the sizing function defined at a surface background mesh can be also used as the input of volume mesh generation.Originality/valueTheoretical analysis reveals that the construction of the initial sizing function could be reduced to the solution of an optimization problem. The definitions of the banding elements and surface proximity are also given. Under the guidance of this theoretical analysis, re-meshing and ray-casting technologies are well-designed to initial the sizing function. Smoothing with the revised NLP and querying by the AABB tree, the paper provides an automatic method to get a high-quality sizing function for both surface and volume mesh generation.

Efficient and Accurate Object 3D Selection With Eye Tracking-Based Progressive Refinement

Selection by progressive refinement allows the accurate acquisition of targets with small visual sizes while keeping the required precision of the task low. Using the eyes as a means to perform 3D selections is naturally hindered by the low accuracy of eye movements. To account for this low accuracy, we propose to use the concept of progressive refinement to allow accurate 3D selection. We designed a novel eye tracking selection technique with progressive refinement–Eye-controlled Sphere-casting refined by QUAD-menu (EyeSQUAD). We propose an approximation method to stabilize the calculated point-of-regard and a space partitioning method to improve computation. We evaluated the performance of EyeSQUAD in comparison to two previous selection techniques–ray-casting and SQUAD–under different target size and distractor density conditions. Results show that EyeSQUAD outperforms previous eye tracking-based selection techniques, is more accurate and can achieve similar selection speed as ray-casting, and is less accurate and slower than SQUAD. We discuss implications of designing eye tracking-based progressive refinement interaction techniques and provide a potential solution for multimodal user interfaces with eye tracking.