The impact of fill sinks algorithms in dijital elevationmodels and their influence on hill shading method

In this study, different methods used in the representation of the earth were examined and the most up-to-date shading method was emphasized. The shading method has been researched and studied in detail. The data used in the shading method, the geometric calculations used in determining the lighting value, and the factors affecting the shading are emphasized. Shading, which is one of the methods used in the representation of the earth, provides three-dimensional animation of the earth's topography. This allows a quick understanding of the surface. In the shading method, it is assumed that the earth is illuminated by a light source. According to the amount of illumination, places that are thought to receive light are expressed in light color, while places that do not receive light are expressed in dark color. During the production of digital elevation models, faulty areas occur for various reasons. Such areas are areas where water collects and cannot move, and they lead to negative results in hydrographic analysis. Therefore, it is necessary to clean the damaged areas and make them suitable for hydrological analysis. Otherwise, a meaningful river network cannot be created, basins cannot be defined and erroneous results are obtained. By using different pit filling algorithms used in the hydrological analysis, changes in digital elevation models for ASTER and SRTM data belonging to 4 different regions were examined. While determining the changes, the difference between the processed data obtained after the pit filling process and the original data was taken and a difference map was obtained. Statistical values of the differences obtained are presented with the help of tables by making a raster analysis. Afterward, the effects of the improvement on the shading method were examined and interpreted. According to the results obtained, it was determined that 3 different pit filling algorithms used had different effects on the data. Therefore, it was observed that there was a difference in the shadings obtained. Fill Sinks xxl, which made the maximum improvement on the data, became r.fill.dir, which made the minimum improvement. The best results were obtained with Fill Sinks (wang&liu). In addition, it was concluded that if the pit filling process is to be applied before shading, the amount of smoothing applied by the algorithm to be used for the pit filling process and the presence of natural or artificial objects in the area where the smoothing is applied should be considered.