Cave feature extraction and classification from rockery point clouds acquired with handheld laser scanners

Abstract

Rockeries are unique elements of Chinese classical gardens with historical, cultural, artistic, and scientific value. One of the essential characteristics of garden rockery is the cave features since cave morphological features determine the degree of “Tou” (riddled through) and “Lou” (hollowed out well) features as the defined by rockery appreciation theory, which is important for rockery heritage conservation, assessment, and management. However, in heritage studies, accurately identifying and evaluating rockery caves is a difficult task because of a cave's irregular shape. This paper proposes a methodology to extract and classify cave features by point clouds obtained from data using a handheld laser scanner with a camera. Without completing surface reconstruction, the rockery point cloud is first sliced into chips, then cave chips were extracted from these approximately two-dimensional chips and next merged to obtain three-dimensional cave point clouds. Finally, the cave boundary points are extracted from the cave and fitted by an ellipse for classification. To extract and classify cave features, a methodology to improve rockery digitalization quality is also proposed. The raw point cloud data were preprocessed by pose adjustment, noise removal, and hole repair. The experimental results for the two rockeries in Tongji University and Qiuxiapu Garden indicate that the improved digitization scheme generates complete and closed rockery point clouds, all types of caves were effectively extracted and classified by our proposed method. Additionally, the extracted caves are still represented by point clouds, which suggest the possibility for other research in the future.

A quantitative analysis method on the scale, shape and quantity of rockeries in Chinese classical gardens - Taking Wanfang Anhe Rockery in the Old Summer Palace as an example

“…In recent years, benefiting from the development of digital technology and the abundance of information means, the research on Chinese classical gardens has developed rapidly in terms of digital surveying and mapping, database construction, virtual scene restoration, archiving monitoring, management display, etc. For example, the Zhang Bo team firstly proposes to adopt 3D technology to carry out 3D surveying and mapping of rockery elements in classical gardens [35]; the Guo Daixi team digitally restored some scenic spots in the Old Summer Palace [36]; Wang Shiwei, Hu Jie et al used 3D digital technology to carry out digital mapping and model construction of Qianlong Garden in the Imperial Palace [37]; the Zhang Qingping team collected and integrated data about rockeries and arranged stones at Jiangnan private gardens like Zhan Garden, Ou Garden and Huanxiu Villa [38][39]; based on the "hole" characteristics of rockeries, Yang Chen proposed a method to extract and classify point-cloud cave characteristics [40]; as well as the Qin Ke team carried out long-term research on digitalization of Chinese classical gardens, especially rockery digitalization and quantitative analysis; for example, Wen Ning adopted spatial syntax to analyze the accessibility and connectivity of rockery space in Jingyi Garden [41], Chen Wanyu adopted finite element analysis to statically analyze and simulate the typical cases of rockeries and their skills [42], and Liao Yi, Jia Shizhen et al put forward the information classification of elements of ancient Chinese royal gardens; by taking Jianxinzhai Garden as an example, they classified the involved elements and put forward the path and method for constructing the 3D digital information database against ancient Chinese royal gardens [43][44].…”

A multi-criteria decision-making approach to assessing the health risk of rockeries in Chinese classical gardens

“…Rockeries are one of the most essential elements that distinguish Chinese classical gardens from other great gardens of the world [1][2][3]. They are an integral part of the Chinese heritage and an irreplaceable expression of Chinese traditional culture.…”