• Proceedings of the Korea Multimedia Society Conference
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• 2002.05d
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• pp.901-906
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• 2002

This paper is a research about method, that is used in Rapid Prototyping system, that inserts and extracts watermark in STL(standard transform language) that has a 3D geometrical model. The proposed algorithm inserts watermark in the vertex domain of STL facet without the distortion of 3D model. If we make use of a established algorithm for watermarking of STL, a watermark inserted to 3D model can be removed by simple attack that change order of facet. The proposed algorithm has robustness about these attack. Experiment results verify that the proposed algorithm, to encode and decode watermark in STL 3D geometrical model, doesn't distort a 3D model at all. And it shows that the proposed algorithm is available.

• Journal of the Korean Society for Precision Engineering
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• v.13 no.10
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• pp.46-55
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• 1996

As industrial standard data, the STL format which approximates three dimensional CAD model to triangular facets, is used for RP(Rapid Prototyping) system in recent days. Because most RP system take the only form of two dimensional line segments as an input stream inspite of its imperfectness while converting into STL format, a CAD model is converted into a standard industrial format which is composed of many triangular facets. The error verifying process is composed of four main steps, and these are 1) Remove facets with two or more vertices equal to each other. 2) Fix overlapping error such as more than three facets adjacent to anedge. 3) Fill holes in the mesh by using Delaunay triangulation method. 4) Correct the wrong direction and normal vectors. This paper is concerned with serching the mentioned errors in advance and modifying them.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.17 no.3
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• pp.78-86
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• 2018

The 3D mesh model is used in various fields, such as virtual reality, shape-based searching, 3D simulation, reverse engineering, 3D printing, and laser scanning. There are various formats for the 3D mesh model, but STL and OBJ are the most typical. Since application systems support different 3D mesh formats, developing technology for converting 3D mesh models from one format into another is necessary to ensure data interoperability among systems. In this paper, we propose a method to convert a 3D mesh model in STL format into the OBJ format. We performed the basic design of the conversion system and developed a prototype, then verified the proposed method by experimentally converting an STL file into an OBJ file for test cases using this prototype.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.6 no.1
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• pp.51-58
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• 1997

The verification of the STL file is essential to build the confident parts using a RP machine, because the STL file obtained from the CAD software has many errors-the orientation of triangle does not coincide with adjacent triangles or some triangles are omitted, overlpped and so forth. Especially, the STL file translated from the surface model has more errors than those translated from the solid model. In this study, all possible errors were classified with the most general from and the causes of errors were analyzed to verify and correct errors. Using the triangle based non-manifold geometric modeling, these errors were corrected. Especially, this study took the notice of the problem about the intersected triangles and non-manifold properties overlooked in the previous studies. But this study has a penalty on computing time of $O(n^2)$.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2007.11a
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• pp.347-348
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• 2007

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1995.10a
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• pp.889-893
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• 1995

This paper verified error of STL file and presented a new application of reformed division method for reducing to appeared error by using Delaunay triangulation method that used to modify error of verified data. First, it is analyzed each vertices in hole error and classified follow case that is 1. case of plan or slope, 2. case of edge, 3. case of apex and 4. case of rapid curve, and reduced volume tolerance between original model and converted model after convert STL file.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1996.04a
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• pp.597-601
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• 1996

Nowadays, the STL format, industrial standard data, which approximates three dimensional CAD model to triangular facets, is used for RP(Rapid Prototyping) system. Because most RP machine is accpted to only two dimensional line segments, but some STL translators are sometimes poorly implemented. The error verifying process is as follows. 1) Remove facets with two or more vertices equal to each other. 2) Fix overlapping error such as more than three facets adjacent to an edge. 3) Fill holes in the mesh by using Delaunay triangulation method. 4) Repair wrong direction and value of normal vectors. This paper is concerned with searching the mentioned errors in advance and modifying them.

• Journal of the Korean Society for Precision Engineering
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• v.14 no.2
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• pp.136-144
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• 1997

Usually triangular patches are used to transfer geometric shape in Rapid Prototyping CAM system. STL, a list of triangles, is de facto standard in RP industry. Because STL does not have topological infoma- tion, it can cause errornous results. So STL should be verified before using. After adding support structures to anchor the part to the platform and to prevent sagging or distortion, slicing and layer by layer manufactur- ing process are done. But triangular patch is surface model and cannot provide sufficient information on geometry in the above processes. So, geometric modeling is necessary in verifying STL, adding support structures and slicing. It is natural that triangle based modeling is the best when tringular patches are used as input. Considering support structures, solid and faces coexist in RP process. Therefore non-manifold modeler is required. In this study, triangle based non-manifold geometric modeling is proposed for RP sys- tem consistent with STL input.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2002.10a
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• pp.595-598
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• 2002

Laser scanners are getting used more and more in reverse engineering and inspection. For CNC-driven laser scanners, it is important to automate the scanning operations to improve the accuracy of capture point data and to reduce scanning time in industry. However, there are few research works on laser scan planning system. In addition, it is difficult to directly analyze multi-patched freeform models. In this paper, we propose an STL (Stereolithography) mesh based laser scan planning system for complex freeform surfaces. The scan planning system consists of three steps and it is assumed that the CAD model of the part exists. Firstly, the surface model is approximated into STL meshes. From the mesh model, normal vector of each node point is estimated. Second, scan directions and regions are determined through the region growing method. Also, scan paths are generated by calculating the minimum-bounding rectangle of points that can be scanned in each scan direction. Finally, the generated scan directions and paths are validated by checking optical constraints and the collision between the laser probe and the part to be scanned.

• International Journal of CAD/CAM
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• v.2 no.1
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• pp.55-67
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• 2002

In many areas of industry, it is desirable to have fast and reliable systems in order to quickly obtain suitable solid models for computer- aided analyses. Nevertheless it is well known that the data exchange process between CAD modelers and CAE packages can require significative efforts. This paper presents an approach for geometrical data exchange through triangulated boundary models. The proposed framework is founded on the use of STL file specification as neutral format file. This work is principally focused on data exchange among CAD modelers and FEA packages via STL. The proposed approach involves the definition of a topological structure suitable for the STL representation and the development of algorithms for topology and geometry data processing in order to get a solid model suitable for finite element analysis or other computer aided engineering purposes. Different algorithms for model processing are considered and their pros and cons are discussed. As a case study, a prototype modeler which supports an exporting filter for a commercial CAE package has been implemented.