Study On Technologies For Shoreline Abstraction Based On LiDAR

Shoreline, the boundary of land and sea, is the vital linear feature both on chart and topographic map, so it is important for topographic mapping, hydrographic survey, and coast zone survey and evolution study, to measure shoreline’s position, character, and variety fully, speedily, and accurately. LiDAR is the new technology and means for mapping and surveying coast zone, islands and reefs, and represent the new way, and it cans quickly acquire high density, and high precise 3D point clouds. Compared to field survey and remote sensing interpretation, the shoreline measurement under LiDAR is different both on theory and technology. At present, the correlative study is starting, applying the methods abroad to abstract shoreline from point clouds, the study on shoreline definition based tide datum, and how to calculate shoreline height in national tide, and the methods to abstract shoreline is little. So taking shoreline definition, abstracting method and module, the theory and technology system for shoreline abstraction based on LiDAR data is founded The main work and innovation are as follows:1. LiDAR and standard data format LAS are produced briefly, and take the airborne and boat-based data for example, data pretreatment that are noise elimination and filter are specified.2. Aimed at the ambiguous of national shoreline definition and position, the problems of definition are discussed based on the variable shoreline and its classification. Trace line is pointed out to be limit to mapping technology and means, and it is influenced by subjective factor, and it dissatisfied the main demand that features are represented in the only way of geometry and physics in Topography. By the history of shoreline mapping and surveying in abroad, it is found that definition based on visually discernible coastal feature must be to that based on specific tidal datum, and according to national tide, shoreline is the boundary of Mean High Water Surface and coast, that is Mean High Water Surface Line. It is unified to the definition based on tide datum under LiDAR3. Aimed at that MHWS is only in semidiurnal tide, in the view of tidal range change, the spring tide is spread including regression tide in diurnal tide from syzygy tide in semidiurnal tide, and then the concept of MHWS is perfect Statistical arithmetic based on factual water level data is designed, by simulation station near the complex tide, and the tide datum is demanded continuously and changing flatly in space, the mean higher high water surface of statistical arithmetic is determined.Then factual water level data of 50 coastal tidal stations are calculated, and it is tested that about 97% water level are under MHWS, and it is fit to the basic meaning-Shoreline is the boundary of halophile and freshwater circumstance biology.4. Aimed at that demands of point clouds filters is too high by both the contouring method and image segmentation method, and it can be easily effected by DEM error, improved image segmentation method is advanced. It is tested by example that by omitting constructing coastal DEMZDSM, and avoiding the effect of error, efficiency is improved, and the shoreline is more reliable, smoother, and the work is reduced by the improved method. Besides, by the four different examples, improved image segmentation method is proved to be current and universal.5. Aimed at that other proxy shorelines can’t be abstracted by features image segmentation method and the improved methods at the same time, point cloud rasterization method is put forward based on the thought of filter and point cloud processing directly. Firstly, point cloud is processed directly, then it is transformed to raster data by the procedure of point cloud rasterization, and shoreline is abstracted by tracking contour. It is tested the shoreline by rasterization is reasonable, reliable, and less work, and the shoreline’s precise is equal to that by improved image segmentation method. But in the way of abstracting other proxy shorelines, the new method is more efficiency. Besides, by four four different examples, point cloud rasterization method is proved to be current and universal.6. Aimed at that the current software of LiDAR point cloud is behind, and lack of abstracting shoreline function, shoreline abstracting module is designed based on ArcGIS Engine, combining the work of MHWS concept and arithmetic, the heights of MHWS is calculated by water level statistics, and shoreline can be abstracted by contouring, improved image segmentation method and point cloud rasterization method. The functions of reading and displaying LiDAR point cloud, data preprocessing, constructing DEM and raster data, and abstracting shoreline are realized.