The Ancient Great Wall Site Monitoringof Zhenbeitai And Its Periphery

The ancient Great Wall is the treasure of the Chinese nation, which across the Chinese mainland. Due to the natural factors and human activities, the ancient Great Wall is suffering from damage. It is urgent to preserve such cultural heritage of mankind. In order to effectively protect the Great Wall, China has launched a national project to establish an IntelliSense system to monitor the status of the ancient Great Wall. This thesis is an important part of the project and its mission is to build the three-dimensional digital model of the Great Wall. Establishing 3D digital model of the Great Wall can provide a modern technology support for the protection of the Great Wall.In order to monitor the status of the large-scale Great Wall, a small unmanned helicopter with digital camera and Light Detection and Ranging(LiDAR) system which contains a laser rangefinder, an inertial measurement unit and global positioning systems is applied. In this paper, a 2D laser scanner with light weight and small size is combined with a servo to simulate a 3D laser scanner which is costly, bulky and heavy. Besides, a hover-scan-fly method is implemented in this paper to acquire the surface point clouds of the target due to the unconstructed ancient Great Wall.After acquire the original data, it is time to implement the data processing. 3D point clouds acquisition is introduced firstly. Then, the point clouds registration algorithm is applied to each neighboring two point clouds automatically. However, the pose uncertainties of the small unmanned helicopter could always cause the mismatching among point clouds acquired by each hovering scan. This problem would become more severe as the mapping area becomes larger scale and more unconstructed. And the result always appears either not closed or layered. To solve those problems, this paper applied the Graph optimization theory. Also, this article describes two common points cloud processing algorithm such as downsampling and denoising and smoothing. With better quality of data, it is easy to using Geomagic Studio to establish 3D digital model.This thesis had taken lots of experiments for the ancient Great Wall in Yulin City of Shanxi Province, which verify the correctness and practicability of the above reconstruction methods.