Triangle Facets Research Articles

Data Processing of Laser Metal Deposition Shaping Technology: Part I. Layered Algorithm Research

Based on the characteristics of Laser Metal Deposition Shaping (LMDS) technology, the related data processing algorithm was investigated in detail. This paper provides a kind of layered processing algorithm for STL file based on the limited topological information. At first, the triangle facets intersected with certain layered plane in the STL file were found out in disordered state, and then were read into the memory; secondly, the topological information was built to the found triangle facets; next, the intersecting lines between the layered plane and the triangle facets were figured out, so the contour lines on the layered plane were generated according to the founded topological sorting. Over and over, this process was finished until all layered contours were worked out. This algorithm could process the large STL files, save the memory expense, and improve the computing speed.

Implement and Application of Feature-Based Visibility Analysis on UG Flat

A new algorithm, named feature-based visibility analysis is proposed. This algorithm can be used widely in manufacture and process of parts or models. Compared with conventional triangle facet algorithm, the proposed feature-based algorithm can get global visibility more efficiency and accurately. The main visibility analysis consists of two steps: 1) Local visibility analysis. All features are classified into two types-features with local visibility and without local visibility. 2) Global visibility analysis. All features with local visibility should be analyzed further to detect whether the local visibility feature is sheltered by the other part of the model. In this paper, related principle and implement process (on UG flat) are introduced detailly. At last, the case study demonstrated the validity of the proposed method.

A computing method for accurate slice contours based on an STL model

The STL model has become a standard in rapid prototyping (RP) technology, but slice errors are high because of tessellation. To improve the precision of slice contours, a novel slicing method is presented to compute accurate contour curves based on an STL model. First, the normal vector of a triangle facet to be sliced is calculated. An interpolation curve between two vertices is constructed in a normal section to approximate the original curve in the normal section in terms of the position of the two vertices and the tangent vector at the two vertices. The exact points of the slice contour are obtained by calculating the intersection points between the interpolation curve and the slice plane. Finally, accurate smooth contours are achieved by fitting the intersection points with a cubic B-spline curve. The experimental results indicate that the presented slicing method improves the precision of cross contours.

Fast Shadowing Technique for Electrically Large Targets Using Z-Buffer

An improved fast shadowing technique fit for the calculation of electromagnetic field is proposed in this paper based on the shadowing technique of z-buffer in computer graphics. The traditional shadowing algorithm consumes too much time, for it is necessary to judge the shadowing relationship of every two facets. The proposed algorithm combining z-buffer with traditional algorithm falls into the shadowing processing using triangle facet modeling. The problem of great time consumption in shadowing judgment for electrically large targets is well solved through proper subdivision of buffer and localization of judgment within facets in the surrounding buffer elements. The proposed arithmetic has great advantages over the traditional one, especially in its high running speed. This improved technique is tested to be valid in that it remarkably increases the computation speed on the premise of satisfying the precision requirement.

Generation and optimization of slice profile data in rapid prototyping and manufacturing

STL-based slicing is the commonly used method in processing the problem of layered manufacturing. A slicing algorithm based on the model geometrical continuity is presented. In the strategy, the grouping matrix and the active triangle table were established by sorting for the triangular facets according to the minimum and maximum z -axis value of the triangular facets. By generating new intersecting facets table of each slicing plane and extracting only topology information of the current slicing plane, inner memory is remarkably saved, while the extracting time is also saved to some extent. The inefficient judgment about the location relations of triangle facets and slicing plane has been avoided, thus advanced the slicing efficiency. Aiming at the inherence error in slicing operation brought by the approximation of the standard STL model, such as the non-closed cross-section contour and so on, an effective filtering and optimization algorithm based on feature analysis for the slicing profile has been put forward. A case study is also presented to illustrate the feasibility and efficiency for the developed algorithms and the proposed strategy.

Analysis of Antenna Around NURBS Surface With Hybrid MoM-PO Technique

The hybrid method of moments and physical-optics (MoM-PO) approach is used to calculate the radiation pattern of antenna around arbitrarily shaped structure. The structure is modeled with Non-uniform rational B-spline (NURBS) surfaces. The hybrid MoM-PO approach is implemented by modifying the impedance matrix of the MoM region with PO. Formula for the scattered PO field is deduced for cases of antenna located around NURBS surface. The stationary phase method (SPM) is applied for the integral of the induced current in the PO region. Results obtained from this method and from MoM-PO approach based on triangle facet model agree well while the former is more efficient in execution time

AUTO CONVERSION FROM 3D SOLID MODEL TO A PLATE AND SHELL MODEL USED IN FEM ANALYSIS

In order to meet the need of FEM analysis for plate and shell structure, a 3D solid model is output by STL file. The model's topology relationship is reconstructed and its surfaces are re-triangulated. On this basis elements and surfaces are classified, and valid triangle facets are chosen, and their thickness and mid-plane position are calculated. These triangle facets are carried to their middle position so that the mid-plane model of a plane and shell structure which is suited for FEM analysis is formed. This method is used to the solid models of some thin-wall structure in practice so that their mid-plane models are extracted successfully, which shows that work and analysis time for FEM models of a plate and shell structure can be reduced greatly.

Analysis of Antenna Around Nurbs Surface With Iterative Mom-Po Technique

The iterative MoM-PO approach is utilized to calculate the radiation pattern of antenna around arbitrarily shaped structure. The structure is composed of Non-uniform rational B-spline (NURBS) surfaces. The hybrid MoM-PO approach is implemented by iterating the voltage matrix of the MoM region. A more rigorous formula for the scattered field of the PO region is presented in case that the antenna is located close to the structure. The stationary phase method (SPM) is applied for the integral of the induced current in the PO region. Results obtained from this method and from iterative MoM-PO approach based on triangle facet model agree well.

A three-dimensional deformable model for segmentation of human prostate from ultrasound images.

Segmentation of human prostate from ultrasound (US) images is a crucial step in radiation therapy, especially in real-time planning for US image-guided prostate seed implant. This step is critical to determine the radioactive seed placement and to ensure the adequate dose coverage of prostate. However, due to the low contrast of prostate and very low signal-to-noise ratio in US images, this task remains as an obstacle. The manual segmentation of this object is time consuming and highly subjective. In this work, we have proposed a three-dimensional (3D) deformable surface model for automatic segmentation of prostate. The model has a discrete structure made from a set of vertices in the 3D space that form triangle facets. The model converges from an initial shape to its equilibrium iteratively, by a weighted sum of the internal and external forces. Internal forces are based on the local curvature of the surface and external forces are extracted from the volumetric image data by applying an appropriate edge filter. We have also developed a method for initialization of the model from a few initial contours that are drawn on different slices. During the deformation, a resampling procedure is used to maintain the resolution of the model. The entire model is applied in a multiscale scheme, which increases the robustness and speed, and guarantees a better convergence. The model is tested on real clinical data and initial results are very promising.

The cut cone III: On the role of triangle facets

The cut polytopeP n is the convex hull of the incidence vectors of the cuts (i.e. complete bipartite subgraphs) of the complete graph onn nodes. A well known class of facets ofP n arises from the triangle inequalities:x ij +x ik +x jk ≤ 2 andx ij -x ik -x jk ≤ 0 for 1 ≤i,j, k ≤n. Hence, the metric polytope Mn, defined as the solution set of the triangle inequalities, is a relaxation ofP n . We consider several properties of geometric type for Pn, in particular, concerning its position withinM n . Strengthening the known fact ([3]) thatP n has diameter 1, we show that any set ofk cuts,k ≤ log2 n, satisfying some additional assumption, determines a simplicial face ofM n and thus, also, ofP n . In particular, the collection of low dimension faces ofP n is contained in that ofM n . Among a large subclass of the facets ofP n , the triangle facets are the closest ones to the barycentrum of Pn and we conjecture that this result holds in general. The lattice generated by all even cuts (corresponding to bipartitions of the nodes into sets of even cardinality) is characterized and some additional questions on the links between general facets ofP n and its triangle facets are mentioned.

Periodic lateral structure of Al content modulations in AlGaAs grown on vicinal (111)A GaAs by molecular beam epitaxy

The photoluminescence spectra of single quantum well (SQW) structures grown on (111)A GaAs misoriented 3° towards the [100] direction are red shifted and broadened. These spectra also have extra peaks on the high-energy side, and the surface of the SQWs show giant steps towards [110] and [101] direction. Cross-sectional transmission electron microscopy of the SQWs on the 3°-misoriented (111)A surface clearly shows that the Al content is lower in the AlGaAs regions parallel to the (221)A or (331)A orientation and that the widths of GaAs wells increases at the risers of the giant steps towards [110] and [101]. On the exactly (111)A surfaces, the peak cathodoluminescence wavelength shows that the Al content on the AlGaAs triangle facets consisting of (221)A or (331)A planes is lower than on the flat surfaces. The AlGaAs layers grown on (111)A GaAs misoriented toward [011] have photoluminescence spectra whose intensity is stronger, and whose line width is narrower than the spectra from the AlGaAs layers grown on (111)A GaAs misoriented toward [100]. These phenomena are especially active for the AlGaAs grown on (111)A GaAs misoriented toward [110]. These novel lateral structures are most likely caused by the different sticking coefficients of Ga adatoms between on (111)A surfaces and (110) surfaces.

The cut cone III: On the role of triangle facets

The cut cone III: On the role of triangle facets