In this paper, a symmetry detection algorithm for three-dimensional point cloud model based on weighted principal component analysis (PCA) is proposed. The proposed algorithm works as follows: first, using the point element’s area as the initial weight, a weighted PCA is performed and a plane is selected as the initial symmetry plane; and then an iterative method is used to adjust the approximate symmetry plane step by step to make it tend to perfect symmetry plane (dominant symmetry plane). In each iteration, we first update the weight of each point based on a distance metric and then use the new weights to perform a weighted PCA to determine a new symmetry plane. If the current plane of symmetry is close enough to the plane of symmetry in the previous iteration or if the number of iterations exceeds a given threshold, the iteration terminates. After the iteration is terminated, the plane of symmetry in the last iteration is taken as the dominant symmetry plane of the model. As shown in experimental results, the proposed algorithm can find the dominant symmetry plane for symmetric models and it also works well for nonperfectly symmetric models.

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Due to environmental changes and other reasons, the types of skin diseases continue to increase, the incidence rate and mortality rate are also rising, and the number of patients is increasing. In addition, people's care for the skin has increased, and the requirements for skin diagnosis and treatment have increased. There are few doctors and many patients, so it is difficult and troublesome to see a doctor. The diagnosis and treatment of skin diseases presents unprecedented challenges. In this paper, the WeChat applet of mobile terminals such as mobile phones is used as the front end to realize the collection, upload and display of information. The server end uses artificial intelligence technology such as convolutional neural network to realize the recognition of skin diseases, build an intelligent diagnosis and treatment system for skin diseases, and realize the diagnosis and scientific treatment suggestions for the patients.