The hottest surface weight based on geomagicstudio

Surface reconstruction and case application based on Geomagic studio

Abstract: rapid surface reconstruction is an important development trend of reverse engineering software system. Through the process of generating CAD surface from point cloud, the design idea and application characteristics of Geomagic studio, a typical representative of rapid surface reconstruction system, are analyzed. Through examples, the shape of its surface stage and three different processing processes under the production module are analyzed, and the main characteristics of fast surface reconstruction based on Geomagic studio are summarized

key words: reverse engineering; Geomagic Studio； Fast surface reconstruction; Surface quality

1 introduction

Reverse Engineering (RE), also known as reverse engineering, is relatively traditional design. Traditional product realization usually starts from conceptual design to drawings, and then manufactures products. Reverse engineering of products starts with an existing part or prototype, first digitizes it, then constructs a CAD model, and finally manufactures products [1]

in reverse engineering, the reconstruction of 3D CAD surface model of physical object is the most critical and complex part of the whole reverse process [2]. According to the algorithm kernel of the reverse modeling system, there are mainly three surface reconstruction schemes: 1. Surface construction scheme based on quadrilateral B-spline or non-uniform rational B-spline surface; 2. Surface construction scheme based on triangular Bezier surface; 3. Surface object scheme described by polyhedron []. Further, according to the different reverse modeling strategies and implementation methods, the current surface reconstruction methods can be roughly divided into two kinds: traditional surface modeling methods and rapid surface modeling methods. The so-called traditional surface modeling method refers to the classical point line surface modeling method, which uses Bezier and NURBS surfaces to create surfaces directly from curves or measuring points; The fast surface modeling method refers to the creation of a surface through the opposite polygon lattice processing of the point cloud and the fitting of the lattice with Bezier or NURBS surfaces []

fast surface reconstruction system is Geomagic studio, and its complete process is as follows:

Step 1: reconstruct the triangular lattice surface from the point cloud

step 2 deals with trigonometric surface

step 3 model segmentation, parametric segmentation

step 4 rasterize and NURBS fit CAD model

this paper analyzes the whole process of Geomagic studio from point cloud to CAD model processing. This paper mainly analyzes three different reconstruction ideas and methods in the surface stage in step 3, and analyzes the differences and advantages of different methods with examples

2 point and polygon stage of rapid surface reconstruction

2.1 point stage of rapid surface reconstruction

point clouds in reverse engineering are mostly collected by three-dimensional scanning system, and are composed of a large number of points that can express the shape of the model. Due to the limitations of scanner scanning technology and the impact of scanning environment, it is inevitable to bring redundant point clouds or noise. You can manually select these point clouds to delete, or execute the command "isolated points outside the body" or select the upper limit of size in "non connected items" to delete redundant points. In many cases, the original point cloud data obtained from the scanner is very large, so the point cloud data can be sampled to improve efficiency. The software provides four sampling modes: curvature sampling, unified sampling, equidistant sampling and random sampling. Since more point representations are needed at the features of the model or in areas with large curvature changes, curvature sampling is selected in most cases. Select the percentage of samples to get the corresponding number of point clouds. Then wrap the point cloud and enter the polygon stage

2.2 polygon stage of fast surface reconstruction

the point cloud enters the polygon stage after triangulation. The model in the polygon stage is composed of a large number of triangles spliced between points. Because there are usually redundant, incorrect or inaccurate points, the triangles formed by these points also need to be deleted or otherwise processed. The "clear" and "eliminate nails" commands can make the surface of the model smoother; The simplify command reduces the number of triangles, and the refine command increases the number of triangles by 3 or 4 times; For holes with small curvature change, use the "fill hole" command to fill the curvature, so as to obtain a better complete surface, as shown in Figure 1

Figure 1 Effect Drawing of internal hole filling on the model surface

in the scanner system, the connection of two adjacent edges is often automatically processed into rounded corners. To process the rounded corners into right angles, you can select the edges that need to be sharpened and execute the "sharpening Wizard" command to sharpen them; For unwanted features, you can use the selection tool to select them, and then execute "eliminate features" to eliminate them; For irregular boundaries, you can execute the "boundary" command to reduce the number of control points to make the boundaries neat

when the polygon stage is satisfied with the model, carry out the last step of operation on the model: execute "repair the intersection area" to relax/eliminate the intersecting triangles; If no triangles intersect, the system prompts "no intersecting triangles". Even for different models, the operations in point stage and polygon stage are similar. The above commands are almost used in the processing of any model point cloud. In general, the quality of the final surface will be determined by the quality of the polygon stage, because the polygon stage is directly the next stage: the surface stage

3 surface stage of rapid surface reconstruction

the method of surface stage is optional, and there are two modules to enter the surface stage: shape module and production module. There are two methods for shape module: one is to execute the command "detect contour"; The other starts with the command "detect curvature". The production module enters the fashion module of Geomagic Studio software. The following will analyze and summarize the two modules through specific examples

3.1 shape module

the example used here is the turbine blade, which is composed of a partial base and a complete blade, as shown in Figure 2. First, the first method under the shape module is used for processing

Figure 2 turbine blade figure

after entering the shape module, execute the "detect contour" command to detect the contour of the model surface to obtain the contour of the model. Firstly, the area with large curvature change of the model is detected (as shown in Figure 3a), and the contour line is obtained by extracting the center line of the area (as shown in Figure 3B). At the same time, the contour line divides the model surface into multiple panels; Execute the "contour line", and then the contour line automatically detected by the software. According to the characteristics of the model itself, use the commands of drawing, relaxation, contraction, etc. to accurately position the contour line and maintain the smoothness of the contour line. Execute the "subdivide/extend contour line" command, and the extension line is generated according to the contour line. The area occupied by the extension line on the model surface is the transition area between surfaces, so that the faces divided by the contour line are connected with each other to form a complete surface shape, and the black grid as shown in Figure 3C is the extension line

Figure 3 turbine model group diagram

the contour line divides the whole model into different areas, and each area is a panel. Execute the "construct patches" command to lay patches on each panel. The number of patches can be estimated automatically by the software or specified. Then execute the "move panel" command to define all panels, that is, specify all panel types. When defining the panel, grids, bars, circles, ellipses, collars and automatic detection are optional. In order to express the surface more accurately, try to make the definition of the panel within the first five definitions when constructing the surface slice. Finally, a uniform lattice model of surface patches can be obtained, as shown in Figure 4a. After all panels are gridded, execute the "construct grid" command to griddle all surfaces and fit NURBS surfaces. The final CAD model is shown in Figure 4B

Figure 4 NURBS surface of turbine blade

the contour of turbine blade is obvious, so you can use software to detect the contour line, but for the

model with less obvious contour line, such as handicrafts, the above method cannot be used. For the model with unclear contour, another modeling method is used, that is, the method starting from "detecting curvature". The example used in this method is the head statue of Venus, as shown in Figure 5

Figure 5 Venus head statue

compared with other mechanical part models, Venus model has the characteristics of complex surface and rich detail features. Especially for facial features, the contour line of their surface cannot be detected by using the above methods. After entering the shape module, first execute the "detect curvature" command. The results are shown in Figure 6 a. the black grid line is the detected curvature line, and the orange line is the contour line. Since the contour line automatically generated by the software is not exactly the contour line we need, we can upgrade the curvature line to the contour line by executing the "upgrade/constraint" command; Or degrade the contour line to curvature line, so as to obtain the ideal contour line. The facial part of Venus is the most important part of this model, so it is necessary to divide the facial contour carefully to achieve a more perfect effect

execute the "construct surface patch" command, construct the surface patch lattice within the contour line, and then execute the "move panel" command to make the surface patch lattice uniform and tidy. The operation steps are the same as the previous method, and the result is as shown in Figure 6B after the end of each experiment. Since most of the surfaces of handicrafts are irregular surfaces, automatic detection is generally selected when defining the panel. Finally, execute the "construct grid" command and the "fit NURBS" surface command, and the resulting CAD model is shown in Figure 6C

Figure 6 CAD model of Venus statue

through the comparison of two methods of shape module, it can be seen that the first method is more efficient and accurate for mechanical part models with regular shape, while for models with complex and irregular shape or that cannot be processed by the first method, such as handicraft models, it is suitable to choose the second method for processing

3.2 making module

the model used in this stage is also turbine blade. Through this model, the design idea of making module can be analyzed, and it can be compared with the process of making CAD model with no higher than gear 3 through the shape module when adjusting the collet position by pressing the up and down keys

first enter the production module. Execute the "detect contour" command to detect the contour of the model surface, or modify it manually based on the automatic detection of the software; Execute the "contour line" command to modify the extracted contour line so that the contour line can accurately express the surface contour. The contour line generation is the same as the operation of the shape module; Execute the "extend contour - adaptive" command. Adaptive extension extends according to the generated contour and the curvature change of the surface surface, so a better surface connection effect can be obtained [7]. However, here we not only provide you with a high-quality experimental machine, but also execute the command "create trimmed surface", which is divided into five steps. First, the first step of the command is "classification", and the command of "automatic detection" is executed to make the software classify the surface blocks. As shown in Figure 7a, root