Study On Disease Information Acquisition And Expression Of Point Cloud Data Of Ancient City Walls In China

China has a long history and many cultural relics.As one of the representatives of the inheritance and testimony of a long history,the city wall is also increasingly valued.The ancient city wall is a well-preserved defensive ancient structure made of brick and earth.After the changes of the world,although the scale is still magnificent and magnificent,the city wall itself is being eroded by various diseases.The ground three-dimensional laser scanning technology has become a popular method in the field of architectural heritage protection because of its high data quality and convenient data collection method.In this paper,the plane wall of an ancient city wall in a northern area is used as the research object.Through the on-site disease survey and the use of ground three-dimensional laser scanning technology to collect point cloud data,the focus is on the extraction method of the city wall crack disease and bulging disease and its visual expression is expanded.The main research contents and conclusions are as follows:(1)The ancient city wall diseases are divided into six categories by combining literature information and field investigation,and the causes of these six types of diseases are discussed in detail and the current measurement methods for different diseases are extracted.On-site investigation was conducted on the status quo of the ancient city wall and wall bricks in a place in the north,to investigate the disease of the city wall and to put forward reasonable suggestions for protection.The main diseases are: uneven settlement,bulging deformation,city wall cracks,weathering and exfoliation of city walls,destruction of natural creatures and artificial irrational utilization of existing diseases.Among them,the main causes are wall cracks,bulging and mortar loss.(2)Briefly explain the principle of three-dimensional laser scanning technology and classify the factors that affect the accuracy of ground three-dimensional laser scanning data acquisition: analyze in detail from three aspects of the instrument itself,the target object and the external environment,and provide data for the city wall industry Get practical advice.(3)Focus on the research of the method of extracting diseases of city wall cracks and city wall bulging,innovate and use a variety of mature algorithms,and expand the field of algorithm use.Including point cloud clustering,crack line extraction,point cloud slicing,point cloud plane fitting and other algorithms,the effect of different threshold settings on the extraction efficiency or accuracy in the algorithm was studied,and the typical wall diseases were successfully extracted through experiments,indicating that this method The effectiveness.(4)The typical city wall diseases are verified by examples,and the city wall cracks can be identified;the fitted city wall plane is compared with historical literature,the error is0.0756°,and the overall plane reliability is high,which ensures the reliability of subsequentbulging diseases.By visually processing the extracted data to generate heat maps and line drawings,it provides a more intuitive basis for the safety detection and evaluation of actual city walls.