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Orthogonal projection of points in CAD/CAM applications: an overview
Ko, Kwanghee,Sakkalis, Takis Society for Computational Design and Engineering 2014 Journal of computational design and engineering Vol.1 No.2
This paper aims to review methods for computing orthogonal projection of points onto curves and surfaces, which are given in implicit or parametric form or as point clouds. Special emphasis is place on orthogonal projection onto conics along with reviews on orthogonal projection of points onto curves and surfaces in implicit and parametric form. Except for conics, computation methods are classified into two groups based on the core approaches: iterative and subdivision based. An extension of orthogonal projection of points to orthogonal projection of curves onto surfaces is briefly explored. Next, the discussion continues toward orthogonal projection of points onto point clouds, which spawns a different branch of algorithms in the context of orthogonal projection. The paper concludes with comments on guidance for an appropriate choice of methods for various applications.
( Kwanghee Ko ),( Chunyoung Oh ) 호남수학회 2021 호남수학학술지 Vol.43 No.4
We used blood data to predict obesity by complementing the BMI risk, because some blood factors are significantly associated with obesity. For the sampling method, a two-step stratified colony sampling method was used based on sixteen blood factors collected by the Korea National Health and Nutrition Examination Survey(KNHANES). We identify the number of effective blood data of obesity in the final model as 6 ∼ 8 factors that differ somewhat depending on age and gender. Also, the coefficient of determination that represents the predictive power of obesity in the regression model is the highest for both men and women of aged 19 and in their 20s and 30s, and the predictive power decreases with increasing age.
고광희(Kwanghee Ko) (사)한국CDE학회 2010 한국CDE학회 논문집 Vol.15 No.3
This paper addresses the problem of determining if two surfaces intersect tangentially or transversally in a mathematically consistent manner and approximating an intersection curve. When floating point arithmetic is used in the computation, due to the limited precision, it often happens that the decision for tangential and transversal intersection is not clear cut. To handle this problem, in this paper, interval arithmetic is proposed to use, which provides a mathematically consistent way for such decision. After the decision, the intersection is traced using the validated ODE solver, which runs in interval arithmetic. Then an iterative method is used for computing the accurate intersection point at a given arc-length of the intersection curve. The computed intersection points are then approximated by using a B-spline curve, which is provided as one instance of intersection curve for further geometric processing. Examples are provided to demonstrate the proposed method.
Camera localization with Siamese neural networks using iterative relative pose estimation
김대운,Ko Kwanghee 한국CDE학회 2022 Journal of computational design and engineering Vol.9 No.4
This paper presents a novel deep learning-based camera localization method using iterative relative pose estimation to improve the accuracy of pose estimation from a single RGB image. Although most existing deep learning-based camera localization methods are more robust for textureless cases, illumination changes, and occlusions, they are less accurate than other non-deep learning-based methods. The proposed method improved the localization accuracy by using the relative poses between the input image and the training dataset images. It simultaneously trained the network for the absolute poses of the input images and their relative poses using Siamese networks. In the inference stage, it estimated the absolute pose of a query image and iteratively updated the pose using relative pose information. Real world examples with widely used camera localization datasets and our dataset were utilized to validate the performance of the proposed method, which exhibited higher localization accuracy than the state-of-the-art deep learning-based camera localization methods. In the end, the application of the proposed method to augmented reality was presented.
A method for image-based shadow interaction with virtual objects
Ha, Hyunwoo,Ko, Kwanghee Society for Computational Design and Engineering 2015 Journal of computational design and engineering Vol.2 No.1
A lot of researchers have been investigating interactive portable projection systems such as a mini-projector. In addition, in exhibition halls and museums, there is a trend toward using interactive projection systems to make viewing more exciting and impressive. They can also be applied in the field of art, for example, in creating shadow plays. The key idea of the interactive portable projection systems is to recognize the user's gesture in real-time. In this paper, a vision-based shadow gesture recognition method is proposed for interactive projection systems. The gesture recognition method is based on the screen image obtained by a single web camera. The method separates only the shadow area by combining the binary image with an input image using a learning algorithm that isolates the background from the input image. The region of interest is recognized with labeling the shadow of separated regions, and then hand shadows are isolated using the defect, convex hull, and moment of each region. To distinguish hand gestures, Hu's invariant moment method is used. An optical flow algorithm is used for tracking the fingertip. Using this method, a few interactive applications are developed, which are presented in this paper.
A point projection approach for improving the accuracy of the multilevel B-spline approximation
Moon, Seonghyeon,Ko, Kwanghee Society for Computational Design and Engineering 2018 Journal of computational design and engineering Vol.5 No.2
In this study, we present a method for improving the accuracy of the multilevel B-spline approximation (MBA) method. We combine a point projection method with the MBA method for reducing the approximation error by directly adjusting the control points in the local area. An initial surface is generated by the MBA method, and grid points are produced on the surface. These grid points are projected onto the scattered point set, and the distances between the grid points and the projected points are computed. The control points are then modified based on the distances. The proposed method shows better approximations even with the same number of control points and ensures $C^2$-continuity. The experimental results with examples verify the validity of the proposed method.