Research On 3D Reconstruction Of The Ming And Qing Official-style Roof Based On A Decorative Components Template Library

The Ming and Qing official-style architectures is an important manifestation of the combination of traditional culture and art with science and technology,and is the unique "historical memory symbol" and "cultural development chain" of the Chinese capital.Due to long-term exposure to the outside world,most of the Ming and Qing official-style architectures are suffering from different degrees of damage due to social development,natural environment and human factors.If the information of the building ontology cannot be retained in stages,the historical and cultural information it carries will never exist again.Therefore,it is both complicated and urgent to carry out scientific and effective ontological protection and healthy development of the Ming and Qing official-style architectures.The roof volume of the Ming and Qing official-style architectures usually occupies more than half of the main body of the building.Its form and structure are exquisite and unique,and it is an important symbol of the Ming and Qing official-style architectures.Decorative component is the most special and complex part of roof structure,and it is difficult to accurately reconstruct its external features by traditional 3D modeling methods.Incomplete existing information and lack of access to original architectural drawings and other data make it impossible to accurately record the historical evolution and status quo of architectural structures.The fine three-dimensional reconstruction is conducive to the preservation of the status quo of the Ming and Qing official-style architectures,the formulation of relevant monitoring and restoration protection programs,and provides a reliable basis and scientific guidance for the information retention and daily management of the Ming and Qing official-style architectures.Based on the dense images matching point cloud and scanning point cloud data,this paper establishes a standardized and universal template library of the Ming and Qing official-style architecture roof’s decorative components,and then realizes the automatic fine three-dimensional reconstruction of the Ming and Qing official-style architecture roof’s decorative components.The main research results are as follows:(1)Established the template library for the decorative components of the Ming and Qing official-style architectures.A scientific recognizing of the roof structure of the Ming and Qing official-style architectures is an important prerequisite for establish a template library of roof decorative components,including the categories,forms,locations,functions,regulations and cultural connotations.In this template library,firstly,the rough 3D model reconstruction of components is realized based on the dense images matching point cloud or laser scanning point cloud data.Then the 3D modeling software was used to fine-tune the 3D model through human-computer interaction with reference to the design details recorded in architectural drawings and manuscripts.The components in the template library are stored according to the predefined three-step coding schema.(2)Form a Geo-Registration Mechanism for template library.After the template library is established,the next task is to perform a geo-registration of the corresponding model of the roof decorative components in the library with the point cloud collected for any Ming and Qing official-style architecture.The process first detects the decorative components on the collected digital images based on the You Only Look Once v3(YOLOv3)algorithm and determines the corresponding model in the template library according to the coding schema.Subsequently,the chosen 3D model in the template library is placed on the correct location of the roof using a point cloud matching algorithm like the SAMPLE Consensus Initial Alignment(SAC-IA)algorithm and the Scaling Iterative Closest Point(SICP)algorithm.(3)Verify the Geo-Registration Mechanism by typical roof decorative components.The results show that the Geo-Registration Mechanism proposed in this study performs well,and the overall accuracy of image recognition can reach 82.2%.Under the four levels of point cloud density,the root mean square error of the registration results is almost not more than0.02 m,of which 81.25% is less than 0.02 m and 25% is less than 0.01 m.In the implementation of the Geo-Registration Mechanism,the registration of various decorative components is completed within 5.5s.