For characterization of discontinuities using a 3-D laser scanner, a program for processing point clouds data from the laser scanner, for sampling from these point clouds data, and finally analyzing the discontinuity is needed. However, existing programs rarely have sufficient functions to properly analyze the discontinuities. In this study, a program was developed, which can automatically extract discontinuities from the point clouds data measured in a rock slope and tunnel wall using the laser scanner, and which can also undertake statistical analysis of the discontinuities. This developed program was verified by the application of discontinuity surveys in a rock slope and a tunnel. By undertaking the discontinuity survey using the laser scanner and comparing with the results of direct survey, the feasibility and rapidity of such surveys is expected to improve in areas out of man's reach in geotechnical surveys.
The technology of using laser to detect object shapes at a remote location and reconstructing them in another location based on the acquired data has already entered its practical phase. Application programs are actively being developed and used in various industries. Object shapes acquired by a remote measuring device are stored as point clouds data, and the technology for recreating the shapes by reconstructing polygons and curvatures based on the point clouds data is referred to as reverse engineering or reverse analytical engineering. Programs that reconstruct object shapes by applying the reverse analytical engineering technology include RapidForm, Geomagic Studio and Paraform. However, these application programs were designed to measure general three-dimensional objects such as factories, steel towers, vehicles and the human body, and their software structures are too complex to apply to a specific field such as rock slope surface surveying. Split Engineering recently invented Split-FX program for extracting discontinuities from remote data acquired using laser scanner. However, it is difficult to assert that the software offers sufficient functionality for surveying discontinuities because the length and spacing of discontinuity cannot be obtained directly from point clouds data. Accordingly, this study developed a program to facilitate discontinuity surveys of areas that are significantly extensive or inaccessible by investigators . In order to reduce the time and cost required for operating multiple programs simultaneously, the developed program integrates into a single automated process a series of tasks including extracting discontinuities from point clouds data acquired by a 3-D laser scanner and performing statistical analyses. The effectiveness and the applicability of the program were validated by surveying discontinuities in rock slope surfaces and tunnel walls with a 3-D laser scanner, analyzing discontinuity distribution characteristics with the program and comparing with the results of direct discontinuity surveys.
2. THEORIES APPLIED IN PROGRAM DEVELOPMENT
2.1. Point clouding data processing
Information acquired with a 3-D laser scanner is stored as tens or hundreds of thousands of point coordinates of 3-D space, and is referred to as point cloud data because its shape resembles clouds. In order to restore the shapes f surveyed rock surfaces from the point cloud data, polygon models must be created by accurately linking the space coordinates, and basic pre-processing such as filtering, smoothing and triangulation must be performed prior to creating polygon models.