Research On Technology Of Equal Waterline Information Extraction And Vertical Datum Transformation In Coastal Zone

Equal waterline information extraction and vertical datum transformation in coastal zone is a "bottleneck" restricting collaborative topography mapping and chart mapping development, It's also an important technical difficulty needed to be addressed in the coastal zone topographic mapping. Focused on coastal terrain mapping applications, and aimed to resolve the current labor-intensive and low efficiency practical problems in coastline measuring, in the thesis a systematic and deep research is made on theories and methods about precise and efficient access to the coastal land geographic information, charts mapping and the vertical datum transformation model. During the research aerospace remote sensing is utilized for its efficiency, flexibility, and other technical advantages and the coastal zone features are also considered. The main contributions and innovations in the thesis are listed as follows.1.The main differences and their causes between charts and topographic maps were analyzed. Some technical means were proposed to eliminate these differences, including unifying the chart types, spatial reference frame, mapping standards, data structure and formats.2 . A practical vertical datum transformation model was established for vertical transformation among topographic maps, coastal charts and coastal topographic maps. 5′×5′high accurate tidal harmonic constants model,5′×5′theoretical lowest tidal surface model and 2′×2′sea surface topography model of china offshore were built respectively.3.The coastal elevation / depth datum transformation model was applied to the coastal zone mapping project in the demonstration area to complete the accuracy access on conversion from the depth reference to"1985 National Height Datum". Studies showed that the conversion accuracy of general sea elements is better than 35cm, and that of lighthouses and other special elements is better than 5 cm.4.An in-depth analysis was made on the advantages and disadvantages of the GAC (geodesic active contour) model and edge detection algorithms in remote sensing image segmentation. A new waterline extraction method was proposed, which fused on the canny edge detection operator and the GAC model. Experimental results showed that the proposed method was reliable in extracting remote sensing images waterline, especially for waterline extraction of the weak edge or the edges of serious depression, with good smoothness and high precision5.The equal altitude constraint of the waterline was used in coastal stereos absolute orientation and block adjustment. And remote sensing external orientation and block adjustment method under the control equal altitude constraint was put forward. The precise tidal model was used to compute the instant elevation of the waterline at photography. The remote sensing image external orientation and block adjustment method assisted by the tidal modal was proposed. Using the above methods, it was well solved the problem of poor orientation accuracy in the coastal sea areas, reefs, shoals and other far area which were lack of control points, greatly improving the mapping accuracy.6.Investigation was made on the sea and land information fusion. Equal waterline information extraction method based on the tidal model was proposed. And through practical application on the aerial images and depth data of the Zhoushan islands, it was verified that this algorithm was feasible and efficient.